ISO/TS 21957

Road vehicles — Visibility — Specifications and test procedures for head-up displays (HUD)

This document provides a common framework of definitions and measurement methods for the design, and ergonomics testing of automotive head-up displays (HUDs) independent of technologies except where noted. Applications in both passenger cars (including sport utility vehicles and light trucks) and commercial vehicles (including heavy trucks and buses) are covered. This document does not include helmet-mounted HUDs or other head carried gear such as glasses. Areas covered in this document include: — guidance on how to establish reference points and representative viewing conditions based on vehicle coordinates and ranges of driver's/passenger's eye points; — descriptions of the HUD image geometry and optical properties measurements; — definitions of the HUD virtual image and driver vision measurements; — static and dynamic laboratory tests, and dynamic field operational assessments that include suggested vehicle setup procedures in order to measure HUD image attributes.

Véhicules routiers — Visibilité — Spécifications et procédures d'essai pour les affichages tête haute (HUD)

General Information

• Status: Not Published
• ICS: 43.040.15 - Car informatics. On board computer systems
• Technical Committee: ISO/TC 22/SC 35 - Lighting and visibility
• Drafting Committee: ISO/TC 22/SC 35/WG 3 - Visibility
• Current Stage: 6000 - International Standard under publication
• Completion Date: 03-May-2023

Standards Content (Sample)

ISO/DTS 21957-#:2022:2023(E)
Date: 2023-02
ISO TC 22/SC 35/WG 3
Secretariat: UNI

Road vehicles — Visibility — Specifications and test procedures for Headhead-up displays

(HUD)
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© ISO /PDTS 21957-#:2022(E)2020 – All rights reserved
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ISO/DTS 21957:2023(E)
© ISO 20XX

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this

publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical,

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iv © ISO 2023 – All rights reserved
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ISO/DTS 21957:2023(E)
Contents

Foreword ............................................................................................................................................................. 7

Introduction ....................................................................................................................................................... 8

1 Scope ....................................................................................................................................................... 1

2 Normative references ....................................................................................................................... 1

3 Terms and definitions ....................................................................................................................... 2

3.1 Terms related to vehicules .............................................................................................................. 2

3.2 Terms related to the eyellipse and eyebox ................................................................................ 4

3.3 Terms related to an HUD system ................................................................................................... 7

4 Abbreviated terms .......................................................................................................................... 14

5 Specification, verification, and reference point definition for HUD image evaluation

............................................................................................................................................................... 14

5.1 General ................................................................................................................................................ 14

5.2 Eyellipse and the eye centroid location.................................................................................... 15

5.3 Eyebox location ................................................................................................................................ 16

6 Evaluation, test and measurement ............................................................................................ 18

6.1 General ................................................................................................................................................ 18

6.1.1 Measurement setup ........................................................................................................................ 18

6.2 Characterization of the HUD spatial and orientational aspects ....................................... 31

6.2.1 Optical accommodation distance ............................................................................................... 31

6.2.2 Look down angle (LDA), look over angle (LOA) and image orientation coordinates 35

6.2.3 Display field of view (DFoV) ......................................................................................................... 41

6.3 Luminance/brightness and contrast ......................................................................................... 42

6.3.1 Luminance and luminance non-uniformity measurement ................................................ 42

6.3.2 Chromaticity measurement ......................................................................................................... 44

6.3.3 Contrast ratio .................................................................................................................................... 45

6.4 Spatial characteristics .................................................................................................................... 46

6.4.1 Resolution .......................................................................................................................................... 46

6.4.2 Ghost image ....................................................................................................................................... 50

6.4.3 Distortion and rotation.................................................................................................................. 54

6.4.4 Deviation ratio of aspect ratio ..................................................................................................... 60

6.5 Others .................................................................................................................................................. 60

6.5.1 General ................................................................................................................................................ 60

6.5.2 Care and considerations ................................................................................................................ 60

6.5.3 Capability of geometric adjustability to the driver head position ................................... 61

6.5.4 Display visual performance adjustability ................................................................................ 61

6.5.5 Automatic adjustment accuracy and latency .......................................................................... 62

7 Laboratory assessment on vehicle setup and eyellipse location (procedure for

measurement of HUD virtual image) ........................................................................................ 63

7.1 General ................................................................................................................................................ 63

7.2 Vehicle setup ..................................................................................................................................... 63

7.3 Mannequin/visual reference eye point installation ............................................................ 63

7.4 External environmental condition ............................................................................................. 64

7.4.1 External light environment .......................................................................................................... 64

7.4.2 Road surface ahead ......................................................................................................................... 65

8 Environmental test ......................................................................................................................... 66

© ISO 2020 – All rights reserved © ISO 2023 – All rights v
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ISO/DTS 21957:2023(E)

8.1 General ................................................................................................................................................ 66

8.1.1 Measurement setup ........................................................................................................................ 66

8.1.2 Measurement procedure ............................................................................................................... 67

8.1.3 Protection of HUD unit against foreign objects, liquids ...................................................... 67

9 Consideration when using HUD .................................................................................................. 68

Annex A (informative) Eyellipse versus eyebox ................................................................................. 69

Annex B (informative) Subjective evaluation for a 3D HUD ........................................................... 73

Annex C (informative) Environmental test of the HUD engine ...................................................... 92

Annex D (informative) Environmental interfering factors in HUD performance for

windscreen ........................................................................................................................................ 97

Annex E (informative) Consideration on additional factor affecting the HUD

performance/visibility .................................................................................................................. 98

Annex F (informative) HUD using alternative image generation technologies ..................... 100

Bibliography ................................................................................................................................................. 103

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ISO/DTS 21957:2023(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

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organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO

collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any

patent rights identified during the development of the document will be in the Introduction and/or on

the ISO list of patent declarations received (see www.iso.org/patents).

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www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee [or Project Committee] ISO/TC [or ISO/PC] 22, Road

Vehicles, Subcommittee SC 35, Lighting and visibility].

This second/third/… edition cancels and replaces the first/second/… edition (ISO #####:####), which

has been technically revised.
The main changes compared to the previous edition are as follows:
— xxx xxxxxxx xxx xxxx
A list of all parts in the ISO ##### series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

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ISO/DTS 21957:2023(E)
Introduction

This document outlines Ergonomicergonomic specifications, evaluations and test methods for the design

and laboratory assessment measurement of Headhead-up Displaydisplay (HUD) displayed image

qualities like virtual image distance (X), aspect ratio (Y& and Z), luminance, contrast, and image height

adjustment ranges. This document also outlines procedures for measuring HUD images for the purpose

of laboratory assessments, as measured from observation areas defined by an Eyeboxeyebox, and

provides the definition of the Eyeboxeyebox from the locating the driver’s Eyellipse (Seeeyellipse (see

ISO 4513:2022).

This document also provides a standard measurement practice of HUD virtual images for HUD bench

testing, static and dynamic laboratory test, as well as methods for documenting HUD virtual image

attributes such as size, luminance, contrast, field of view, image location adjustment ranges, and HUD

Eyeboxeyebox attributes using image readability standards from SAE 1757J1757-1, SAE 1757J1757-2,

ISO 15008 or other applicable standards where required.

Identification of patent holders: the following text shall be included if patent rights have been identified.

The International Organization for Standardization (ISO) [and/or] International Electrotechnical

Commission (IEC) draw[s] attention to the fact that it is claimed that compliance with this document may

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Information may be obtained from the patent database available at .

Attention is drawn to the possibility that some of the elements of this document may be the subject of

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identifying any or all such patent rights.
© ISO 2020 – All rights reserved
viii © ISO 2023 – All rights reserved
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TECHNICAL SPECIFICATION ISO/DTS 21957:2023(E)
Road vehicles — Visibility — Specifications and test procedures
for Headhead-up displays (HUD)
1 Scope

This document provides a common framework of definitions and measurement methods for the design,

and ergonomics testing of automotive head-up displays (HUDs) independent of technologies except

where noted. Applications in both passenger cars (including sport utility vehicles and light trucks) and

commercial vehicles (including heavy trucks and buses) are covered. This document does not include

helmet-mounted HUDs or other head carried gear such as glasses.
Areas covered in this standarddocument include:

- — guidance on how to establish reference points and representative viewing conditions based on

vehicle coordinates and ranges of driver / passengerdriver's/passenger's eye points;

- — descriptions of the HUD image geometry and optical properties measurements;
- — definitions of the HUD virtual image and driver vision measurements;

- — static and dynamic laboratory tests, and dynamic field operational assessments that include

suggested vehicle setup procedures in order to measure HUD image attributes.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 4130, Road vehicles— — Three-dimensional reference system and fiducial marks— — Definitions

ISO 4513, Road vehicles— — Visibility— — Method for establishment of Eyellipseeyellipses for driver's eye

location
ISO 6549 16750-2:— , Road vehicles—Procedure for H- and R-point determination

ISO 16750-2, 3, 4, and 5 , Road vehicles -- — Environmental conditions and testing for electrical and

electronic equipment — Part 2: Electrical loads

UnderFifth edition under preparation. Stage at the time of publication: ISO/DIS 6549FDIS 16750-

2:2023.

Part 2 and Part 3 under preparation. (Stage at the time of publication, ISO/DIS 16750-2, -3)

© ISO 2023 – All rights reserved 1
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ISO/DTS 21957:2023(E)

ISO 16750-3:— , Road vehicles — Environmental conditions and testing for electrical and electronic

equipment — Part 3: Mechanical loads

ISO 16750-4:— , Road vehicles — Environmental conditions and testing for electrical and electronic

equipment — Part 4: Climatic loads

ISO 16750-5:— , Road vehicles — Environmental conditions and testing for electrical and electronic

equipment — Part 5: Chemical loads
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1 Vehicular-Terms related terms to vehicules
3.1.1
vehicular coordinate system

three-dimensional reference coordinate system showing the supporting surface of the vehicle as the zero

Z plane (horizontal zero plane), the zero Y plane (vertical longitudinal zero plane), and the zero X plane

(vertical transverse zero plane) at non-operational conditions

Note 1 to entry: It is defined on a right-handed coordinate system having the x-axis positive pointing opposite of the

forward movement direction, z-axis positive being orthogonal to the ground plane and pointing upwards, and the

y-axis positive pointing to the right seen in forward movement direction. (See also (3.1.2) for reference grid under

operational condition).)
3.1.2
three-dimensional reference grid

longitudinal plane X-Z, a horizontal plane X-Y and a vertical transverse plane Y-Z which isare used to

determine the dimensional relationships between the positions of design points on drawings and their

positions on the actual vehicle when the vehicle coordinates is in operational condition

Note 1 to entry: There can be national regulation applicable which specifies the vehicle operation condition affecting

the three-dimensional reference grid which is used in the evaluation procedure of this document. For example, in

countries adopting the UN Regulation No. 125, the operation condition determining the three-dimension reference

grid is given in the UN Regulation No. 125, 2.3 (See also (3.1.1)). ).
3.1.3
V point

vision point positions in the passenger compartment determined as a function of vertical longitudinal

planes passing through the centres of the outermost designated seating positions on the front seat and in

Fourth edition under preparation. Stage at the time of publication: ISO/FDIS 16750-3:2023.

Fourth edition under preparation. Stage at the time of publication: ISO/FDIS 16750-4:2023.

Third edition under preparation. Stage at the time of publication: ISO/FDIS 16750-5:2023.

2 © ISO 2023 – All rights reserved
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ISO/DTS 21957:2023(E)

relation to the "R" point and the design angle of the seat-back, and are used for verifying compliance with

driver's fields of view requirements
3.1.4
H point

pivot centre of the torso and thigh of the 3-D H machine installed in the vehicle seat, and located in the

centre of the centre line of the device which is between the ‘H’ point sight buttons on either side of the 3-

D H machine

Note 1 to entry: The H point is detailed in ISO 6549 and it is used to determine the location of the eyellipse. (3.2.1).

The "H point" corresponds theoretically to the "R" point.
3.1.5
SgRP
seating reference point
R point

design point defined by the vehicle manufacturer for each seating position and established with respect

to the three-dimensional reference system

Note 1 to entry: The R point is detailed in ISO 6549 and it is used to determine the location of the eyellipse. (3.2.1).

3.1.6
windscreen datum point

point situated at the intersection with the windscreen (3.3.13) of lines radiating forward from the V points

(3.1.3) to the outer surface of the windscreen
3.1.7
P point

point about which the driver's head rotates when driver views objects on a horizontal plane at eye level

Note 1 to entry: HUDHead-up display (HUD) (3.3.1) images are presented to the driver intended to be observed with

the head oriented in a forward direction (for P3 and P4, see Figure 7). Nevertheless, small head rotation may occur

while accessing device for indirect vision with some minor residual head turn around this point (for P1 and P2, see

Figure 7).
3.1.8
E point

point representing the centre of the driver's eyes and used to assess the extent to which "A" pillars

obscure the field of vision

Note 1 to entry: The E points arepoints' definition is adopted infrom UN Regulation 125 when observing the

direction of "A" pillar while the driver's ocular reference point (ORP) defined in 3.16 are3.17 is the centercentre at

forward-facing driver head orientation. See Figure 1 for the correlation of E point to with P point. (3.1.7).

Dimensions in millimetres
© ISO 2023 – All rights reserved 3
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ISO/DTS 21957:2023(E)
a) Plan view b) Side view
Key
left eye
R right eye
P neck pivot point
1 driver head centre line
line, viewed end on, between E and E
2 L R
Figure 1 — Neck pivot point and associated eye points
3.1.9
seat-back angle

angle measured between a vertical line through the H point (3.1.4) and the torso line using the back-angle

quadrant on the 3-D H machine
3.1.1410
A pillar

roof support forward of the vertical transverse plane located 68 mm in front of the V points (3.1.3) and

includes non-transparent items such as windscreen (3.3.13) mouldings and door frames, attached or

contiguous to such a support
3.33.2 3.2 Eyellipse and EyeboxTerms related termsto the eyellipse and
definitionseyebox
3.2.1
Eyellipse
eyellipse
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ISO/DTS 21957:2023(E)

statistical distribution of eye locations in three-dimensional space located relative to defined vehicle

interior reference points

[SOURCE: ISO 4513:2022,, 3.1, modified — explanation on "contraction of the words “eye” and “ellipse”

used to describe" is deleted, and Note 1 to entry is not included here]

Note 1 to entry: Eyellipse is a term derived as a contraction of the words “eye” and “ellipse” and it is defined in ISO

4513. Unless otherwise specified, the eyellipse space in this document refers to the specific eyellipse representing

the distribution of the 95 % percentile of driver population as seated in the drive seat. Figure 2 shows an eyellipse

model which would be located as shown in Figure 3.
Key
X, ellipse axes
Deleted Cells
Deleted Cells
Deleted Cells
Deleted Cells
Figure 2 — Eyellipse
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ISO/DTS 21957:2023(E)
Key
A19 seat track rise TL23 seat track travel
AHP accelerator heel point W y-coordinate of the SgRP

BOFRP ball of foot reference point X x-coordinate of the eyellipse centroid location

H8 z-coordinate of the AHP Ycycl mid-eye y-coordinate

H z distance of the SgRP (3.1.5) from the AHP Z z-coordinate of the eyellipse centroid location

30 c
L1 x-coordinate of the BOFRP β side view angle
L x distance from the steering wheel centre to BOFRP 1 zero X grid
L x-coordinate of the SgRP 2 zero Y grid
SgRP seating reference point 3 zero Z grid
TH21 H-point vertical adjustment 4 H-point travel path

Figure 3 — Location of the Eyellipseeyellipse relative to Driver Packaging Dimensionsdriver

packaging dimensions

Note to entry: Eyellipse is a term derived as a contraction of the words “eye” and “ellipse” and it is defined

under ISO 4513. Unless otherwise specified, the eyellipse space in this document refer to the specific

eyellipse representing the distribution of the 95 % percentile of driver population as seated in the drive

seat. Figure 2 show an eyellipse model which would be located as shown in Figure 3.

3[SOURCE: ISO 4513:2022, 3.1, modified — Explanation on "contraction of the words “eye” and “ellipse”

used to describe" has been deleted, Figure 3 was added and Note 1 to entry has been replaced.]

3.2.2.2
Eyebox
eyebox
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ISO/DTS 21957:2023(E)

simplified two-dimensional rectangular box model providing the representative distribution range of the

driverdriver's eye reference point for evaluation, encapsulation and having its frame line tangential to

the eyellipse (3.2.1)

Note 1 to entry: The Eyeboxeyebox is an area covering the entire range of driver with different physical

characteristics and a device under test (DUT) (3.3.25) may not necessarily be capable to conveyof conveying visual

information within the entire Eyeboxeyebox range without personal adjustment. See also "Adjustedadjusted

viewable HUD window". (3.2.3). It is rather a rectangular vertical plane defined at the centercentre of the eyellipse

and actually it is not a three-dimensional box.
3.2.3
adjusted viewable HUD window
observation eyebox window at adjusted condition

range designed to convey the visual information to the viewer at adjusted condition, within which the

image generated by the DUT shall satisfydevice under test (DUT) (3.3.25) satisfies the required image

quality condition

Note 1 to entry: The driverdriver's eye position is expected to come somewhere within the Eyellipseeyellipse (3.2.1)

range. A head-up display (HUD) (3.3.1) system is often composed withof a reflective device transferring image from

the imaging device towards the driverdriver's eye, and its visibility affectis affected by the observation point. To

satisfy needs of driverdrivers with different gendergenders or anthropometric characteristics, a system may

provide adjustability to satisfy those different needs. A DUT adjusted to a specific eye position shall provide

satisfactory image within aan expect range of driver head movement.

Note 2 to entry: An HUD system capableis a system to provideexpected to be capable of providing a uniform image

quality to the entire eyellipse range without any deterioration of the image quality, and this implies to cover a

certain acceptable range of eye movement coverage doeswhile in operation that may not need to be cared.

Otherwise, the cause a drastical degradation on the perceived image quality by the driver normal head movements

within this specified window. The DUT shall be capable toof properly conveyconveying the visual information to at

least a defined range characterized according to this constrained window once adjusted by each driver. This

auxiliary observation Eyeboxeyebox (3.2.2) range is defined as complementary range for image quality evaluation.

Note 3 to entry: If the quality of the image conveyed to the viewer drastically varyvaries within this range, it may

induce discomfort. ButOn the other hand, if the quality of the image gradually degrades with the driver head

displacement going beyond this adjusted viewable HUD window position, the degradation of the image caused by

the displacement of head position will motivate the driver to return his head position to within this window,

therefore, to enable such design strategy which may motivate the driver to return his head position within the

adjusted viewable HUD window, but it does not prevent to cause degradation when the driver may move his/her

eyes beyond this range as a mean to motivate the driver to maintain their head to a certain limited range to be able

to access to the visual information conveyed by the HUD. the image quality beyond this range does not necessarily

need to fulfil the same image quality as required with driver eye at nominal position.

3.2.4
eye position tracker
equipment to localize the dynamic positioning of the driverdriver's eye

Note 1 to entry: The detected position of the eye serves to dynamically control and generate augmented reality

imageimages of intended information according to g
...

FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 21957
ISO/TC 22/SC 35
Road vehicles — Visibility —
Secretariat: UNI
Specifications and test procedures for
Voting begins on:
2023-03-07 head-up displays (HUD)
Voting terminates on:
Véhicules routiers — Visibilité — Spécifications et procédures d'essai
2023-05-02
pour les affichages tête haute (HUD)
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/DTS 21957:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023
---------------------- Page: 1 ----------------------
ISO/DTS 21957:2023(E)
FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 21957
ISO/TC 22/SC 35
Road vehicles — Visibility —
Secretariat: UNI
Specifications and test procedures for
Voting begins on:
head-up displays (HUD)
Voting terminates on:
Véhicules routiers — Visibilité — Spécifications et procédures d'essai
pour les affichages tête haute (HUD)
COPYRIGHT PROTECTED DOCUMENT
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All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
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DOCUMENTATION.
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IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: [e-mail]
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/DTS 21957:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
© ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023
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ISO/DTS 21957:2023(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction .............................................................................................................................................................................................................................. vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

3.1 Terms related to vehicules ........................................................................................................................................................... 2

3.2 Terms related to the eyellipse and eyebox .................................................................................................................... 4

3.3 Terms related to an HUD system .......................................................................................................................................... 6

4 Abbreviated terms ..........................................................................................................................................................................................12

5 Specification, verification, and reference point definition for HUD image evaluation .........12

5.1 General ........................................................................................................................................................................................................12

5.2 Eyellipse and the eye centroid location .........................................................................................................................12

5.3 Eyebox location ................................................................................................................................................................................... 13

6 Evaluation, test and measurement ................................................................................................................................................15

6.1 General ........................................................................................................................................................................................................ 15

6.1.1 Measurement setup ...................................................................................................................................................... 15

6.2 Characterization of the HUD spatial and orientational aspects .............................................................. 24

6.2.1 Optical accommodation distance ..................................................................................................................... 24

6.2.2 Look down angle (LDA), look over angle (LOA) and image orientation

coordinates ........................................................................................................................................................................... 27

6.2.3 Display field of view (DFoV) ..................................................................................................................................30

6.3 Luminance/brightness and contrast ............................................................................................................................... 31

6.3.1 Luminance and luminance non-uniformity measurement ........................................................ 31

6.3.2 Chromaticity measurement ................................................................................................................................... 33

6.3.3 Contrast ratio ..................................................................................................................................................................... 33

6.4 Spatial characteristics ..................................................................................................................................................................34

6.4.1 Resolution ..............................................................................................................................................................................34

6.4.2 Ghost image .......................................................................................................................................................................... 37

6.4.3 Distortion and rotation .............................................................................................................................................40

6.4.4 Deviation ratio of aspect ratio ............................................................................................................................ 43

6.5 Others .......................................................................................................................................................................................................... 43

6.5.1 General ..................................................................................................................................................................................... 43

6.5.2 Care and considerations ........................................................................................................................................... 43

6.5.3 Capability of geometric adjustability to the driver head position ...................................... 43

6.5.4 Display visual performance adjustability .................................................................................................44

6.5.5 Automatic adjustment accuracy and latency .........................................................................................44

7 Laboratory assessment on vehicle setup and eyellipse location (procedure for

measurement of HUD virtual image) ..........................................................................................................................................45

7.1 General ........................................................................................................................................................................................................ 45

7.2 Vehicle setup .......................................................................................................................................................................................... 45

7.3 Mannequin/visual reference eye point installation ......... ..................................................................................46

7.4 External environmental condition ....................................................................................................................................46

7.4.1 External light environment ...................................................................................................................................46

7.4.2 Road surface ahead ....................................................................................................................................................... 47

8 Environmental test .........................................................................................................................................................................................48

8.1 General ........................................................................................................................................................................................................48

8.1.1 Measurement setup ......................................................................................................................................................48

8.1.2 Measurement procedure ..........................................................................................................................................49

8.1.3 Protection of HUD unit against foreign objects, liquids ...............................................................49

9 Consideration when using HUD ........................................................................................................................................................49

iii
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ISO/DTS 21957:2023(E)

Annex A (informative) Eyellipse versus eyebox ...................................................................................................................................50

Annex B (informative) Subjective evaluation for a 3D HUD .....................................................................................................53

Annex C (informative) Environmental test of the HUD engine .............................................................................................65

Annex D (informative) Environmental interfering factors in HUD performance for

windscreen ........................................................................................................................................... ...................................................................69

Annex E (informative) Consideration on additional factor affecting the HUD performance/

visibility .....................................................................................................................................................................................................................70

Annex F (informative) HUD using alternative image generation technologies ..................................................72

Bibliography .............................................................................................................................................................................................................................75

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ISO/DTS 21957:2023(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 22, Road Vehicles, Subcommittee SC 35,

Lighting and visibility.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/DTS 21957:2023(E)
Introduction

This document outlines ergonomic specifications, evaluations and test methods for the design and

laboratory assessment measurement of head-up display (HUD) displayed image qualities like virtual

image distance (X), aspect ratio (Y and Z), luminance, contrast and image height adjustment ranges.

This document also outlines procedures for measuring HUD images for the purpose of laboratory

assessments, as measured from observation areas defined by an eyebox, and provides the definition of

the eyebox from the locating the driver’s eyellipse (see ISO 4513).

This document also provides a standard measurement practice of HUD virtual images for HUD bench

testing, static and dynamic laboratory test, as well as methods for documenting HUD virtual image

attributes such as size, luminance, contrast, field of view, image location adjustment ranges and HUD

eyebox attributes using image readability standards from SAE J1757-1, SAE J1757-2, ISO 15008 or other

applicable standards where required.
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TECHNICAL SPECIFICATION ISO/DTS 21957:2023(E)
Road vehicles — Visibility — Specifications and test
procedures for head-up displays (HUD)
1 Scope

This document provides a common framework of definitions and measurement methods for the design,

and ergonomics testing of automotive head-up displays (HUDs) independent of technologies except

where noted. Applications in both passenger cars (including sport utility vehicles and light trucks) and

commercial vehicles (including heavy trucks and buses) are covered. This document does not include

helmet­mounted HUDs or other head carried gear such as glasses.
Areas covered in this document include:

— guidance on how to establish reference points and representative viewing conditions based on

vehicle coordinates and ranges of driver's/passenger's eye points;
— descriptions of the HUD image geometry and optical properties measurements;
— definitions of the HUD virtual image and driver vision measurements;

— static and dynamic laboratory tests, and dynamic field operational assessments that include

suggested vehicle setup procedures in order to measure HUD image attributes.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 4130, Road vehicles — Three-dimensional reference system and fiducial marks — Definitions

ISO 4513, Road vehicles — Visibility — Method for establishment of eyellipses for driver's eye location

ISO 16750­2:— , Road vehicles — Environmental conditions and testing for electrical and electronic

equipment — Part 2: Electrical loads

ISO 16750­3:— , Road vehicles — Environmental conditions and testing for electrical and electronic

equipment — Part 3: Mechanical loads

ISO 16750­4:— , Road vehicles — Environmental conditions and testing for electrical and electronic

equipment — Part 4: Climatic loads

ISO 16750­5:— , Road vehicles — Environmental conditions and testing for electrical and electronic

equipment — Part 5: Chemical loads
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

1) Fifth edition under preparation. Stage at the time of publication: ISO/FDIS 16750­2:2023.

2) Fourth edition under preparation. Stage at the time of publication: ISO/FDIS 16750­3:2023.

3) Fourth edition under preparation. Stage at the time of publication: ISO/FDIS 16750­4:2023.

4) Third edition under preparation. Stage at the time of publication: ISO/FDIS 16750­5:2023.

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ISO/DTS 21957:2023(E)

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms related to vehicules
3.1.1
vehicular coordinate system

three-dimensional reference coordinate system showing the supporting surface of the vehicle as the

zero Z plane (horizontal zero plane), the zero Y plane (vertical longitudinal zero plane), and the zero X

plane (vertical transverse zero plane) at non­operational conditions

Note 1 to entry: It is defined on a right-handed coordinate system having the x-axis positive pointing opposite

of the forward movement direction, z-axis positive being orthogonal to the ground plane and pointing upwards,

and the y-axis positive pointing to the right seen in forward movement direction. (See also 3.1.2 for reference

grid under operational condition.)
3.1.2
three-dimensional reference grid

longitudinal plane X­Z, a horizontal plane X­Y and a vertical transverse plane Y­Z which are used to

determine the dimensional relationships between the positions of design points on drawings and their

positions on the actual vehicle when the vehicle coordinates is in operational condition

Note 1 to entry: There can be national regulation applicable which specifies the vehicle operation condition

affecting the three­dimensional reference grid which is used in the evaluation procedure of this document.

For example, in countries adopting the UN Regulation No. 125, the operation condition determining the three-

dimension reference grid is given in the UN Regulation No. 125, 2.3 (See also 3.1.1).

3.1.3
V point

vision point positions in the passenger compartment determined as a function of vertical longitudinal

planes passing through the centres of the outermost designated seating positions on the front seat and

in relation to the "R" point and the design angle of the seat-back, and are used for verifying compliance

with driver's fields of view requirements
3.1.4
H point

pivot centre of the torso and thigh of the 3­D H machine installed in the vehicle seat, and located in the

centre of the centre line of the device which is between the ‘H’ point sight buttons on either side of the

3­D H machine

Note 1 to entry: The H point is detailed in ISO 6549 and it is used to determine the location of the eyellipse (3.2.1).

The "H point" corresponds theoretically to the "R" point.
3.1.5
SgRP
seating reference point
R point

design point defined by the vehicle manufacturer for each seating position and established with respect

to the three-dimensional reference system

Note 1 to entry: The R point is detailed in ISO 6549 and it is used to determine the location of the eyellipse (3.2.1).

3.1.6
windscreen datum point

point situated at the intersection with the windscreen (3.3.13) of lines radiating forward from the V

points (3.1.3) to the outer surface of the windscreen
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ISO/DTS 21957:2023(E)
3.1.7
P point

point about which the driver's head rotates when driver views objects on a horizontal plane at eye level

Note 1 to entry: Head-up display (HUD) (3.3.1) images are presented to the driver intended to be observed with

the head oriented in a forward direction (for P3 and P4, see Figure 7). Nevertheless, small head rotation may

occur while accessing device for indirect vision with some minor residual head turn around this point (for P1 and

P2, see Figure 7).
3.1.8
E point

point representing the centre of the driver's eyes and used to assess the extent to which "A" pillars

obscure the field of vision

Note 1 to entry: The E points' definition is adopted from UN Regulation 125 when observing the direction of "A"

pillar while the driver's ocular reference point (ORP) defined in 3.3.17 is the centre at forward­facing driver head

orientation. See Figure 1 for the correlation of E point to with P point (3.1.7).

Dimensions in millimetres
a) Plan view b) Side view
Key
E left eye
E right eye
P neck pivot point
1 driver head centre line
2 line, viewed end on, between E and E
L R
Figure 1 — Neck pivot point and associated eye points
3.1.9
seat-back angle

angle measured between a vertical line through the H point (3.1.4) and the torso line using the back­

angle quadrant on the 3-D H machine
3.1.10
A pillar

roof support forward of the vertical transverse plane located 68 mm in front of the V points (3.1.3) and

includes non­transparent items such as windscreen (3.3.13) mouldings and door frames, attached or

contiguous to such a support
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ISO/DTS 21957:2023(E)
3.2 Terms related to the eyellipse and eyebox
3.2.1
eyellipse

statistical distribution of eye locations in three-dimensional space located relative to defined vehicle

interior reference points

Note 1 to entry: Eyellipse is a term derived as a contraction of the words “eye” and “ellipse” and it is defined

in ISO 4513. Unless otherwise specified, the eyellipse space in this document refers to the specific eyellipse

representing the distribution of the 95 % percentile of driver population as seated in the drive seat. Figure 2

shows an eyellipse model which would be located as shown in Figure 3.
Key
X, Y, Z ellipse axes
Figure 2 — Eyellipse
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ISO/DTS 21957:2023(E)
Key
A seat track rise TL seat track travel
19 23
AHP accelerator heel point W y-coordinate of the SgRP

BOFRP ball of foot reference point X x-coordinate of the eyellipse centroid location

H z­coordinate of the AHP Y mid-eye y-coordinate
8 cycl

H z distance of the SgRP (3.1.5) from the AHP Z z-coordinate of the eyellipse centroid location

30 c
L x-coordinate of the BOFRP β side view angle
L x distance from the steering wheel centre to 1 zero X grid
BOFRP
L x-coordinate of the SgRP 2 zero Y grid
SgRP seating reference point 3 zero Z grid
TH H-point vertical adjustment 4 H­point travel path
Figure 3 — Location of the eyellipse relative to driver packaging dimensions

[SOURCE: ISO 4513:2022, 3.1, modified — Explanation on "contraction of the words “eye” and “ellipse”

used to describe" has been deleted, Figure 3 was added and Note 1 to entry has been replaced.]

3.2.2
eyebox

simplified two-dimensional rectangular box model providing the representative distribution range of

the driver's eye reference point for evaluation, encapsulation and having its frame line tangential to the

eyellipse (3.2.1)

Note 1 to entry: The eyebox is an area covering the entire range of driver with different physical characteristics

and a device under test (DUT) (3.3.25) may not necessarily be capable of conveying visual information within the

entire eyebox range without personal adjustment. See also adjusted viewable HUD window (3.2.3). It is rather a

rectangular vertical plane defined at the centre of the eyellipse and actually it is not a three-dimensional box.

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ISO/DTS 21957:2023(E)
3.2.3
adjusted viewable HUD window
observation eyebox window at adjusted condition

range designed to convey the visual information to the viewer at adjusted condition, within which the

image generated by the device under test (DUT) (3.3.25) satisfies the required image quality condition

Note 1 to entry: The driver's eye position is expected to come somewhere within the eyellipse (3.2.1) range. A

head-up display (HUD) (3.3.1) system is often composed of a reflective device transferring image from the imaging

device towards the driver's eye, and its visibility is affected by the observation point. To satisfy needs of drivers

with different genders or anthropometric characteristics, a system may provide adjustability to satisfy those

different needs. A DUT adjusted to a specific eye position shall provide satisfactory image within an expect range

of driver head movement.

Note 2 to entry: An HUD system is a system expected to be capable of providing a uniform image quality to the

entire eyellipse range without deterioration of the image quality, and this implies to cover a certain acceptable

range of eye movement coverage while in operation that may not cause a drastical degradation on the perceived

image quality by the driver normal head movements within this specified window. The DUT shall be capable

of properly conveying the visual information to at least a defined range characterized according to this

constrained window once adjusted by each driver. This auxiliary observation eyebox (3.2.2) range is defined as

complementary range for image quality evaluation.

Note 3 to entry: If the quality of the image conveyed to the viewer drastically varies within this range, it may

induce discomfort. On the other hand, if the quality of the image gradually degrades with the driver head

displacement going beyond this adjusted viewable HUD window position, the degradation of the image caused

by the displacement of head position will motivate the driver to return his head position to within this window,

therefore, to enable such design strategy which may motivate the driver to return his head position within the

adjusted viewable HUD window, but it does not prevent to cause degradation when the driver may move his/

her eyes beyond this range as a mean to motivate the driver to maintain their head to a certain limited range to

be able to access to the visual information conveyed by the HUD. the image quality beyond this range does not

necessarily need to fulfil the same image quality as required with driver eye at nominal position.

3.2.4
eye position tracker
equipment to localize the dynamic positioning of the driver's eye

Note 1 to entry: The detected position of the eye serves to dynamically control and generate augmented reality

images of intended information according to geometrical positional configuration of the driver's eye point of

observation. Other adaptations or adjustments according to detected driver's eye position may apply.

3.3 Terms related to an HUD system
3.3.1
HUD
head-up display

information display system that enables the driver to access visual information within a driver's

direct field of view without requiring drivers to move their gaze orientation toward the traditional

information cluster panel display

Note 1 to entry: The nomenclature of head-up display (HUD) came from the use of this

...