prEN ISO 25178-3

• Abstract:

  This part of ISO 25178 specifies the complete specification operator for surface texture (scale limited surfaces); by areal methods.

• Status: Not Published
• Publication Date: 12-Mar-2028
• ICS: 17.040.40 - Geometrical Product Specification (GPS)
• Technical Committee: CEN/TC 290 - Dimensional and geometrical product specification and verification
• Current Stage: 4020 - Submission to enquiry - Enquiry
• Start Date: 24-Sep-2026
• Completion Date: 24-Sep-2026
• Ref Project: oSIST prEN ISO 25178-3:2026 - Geometrical product specifications (GPS) - Surface texture: Areal - Part 3: Specification operators (ISO/DIS 25178-3:2026)

• Revises: EN ISO 25178-3:2012 - Geometrical product specifications (GPS) - Surface texture: Areal - Part 3: Specification operators (ISO 25178-3:2012)
• Effective Date: 04-Jun-2025

Overview

prEN ISO 25178-3 is a draft Geometrical Product Specifications (GPS) standard for surface texture: areal methods, published under the CEN and ISO parallel process. It focuses on the complete specification operator for scale-limited surfaces, helping users define surface texture requirements in a clear and unambiguous way.

This draft standard is relevant to engineers, metrologists, and designers working with areal surface texture measurement, surface roughness, and GPS drawing indications. It supports consistent specification of surface parameters and helps align design intent with verification practice.

As part of the ISO 25178 series, this document plays an important role in the broader GPS matrix model and follows the fundamental rules of ISO GPS standards.

Key Topics

The standard addresses practical rules for building a complete specification operator for areal surface texture. Key areas include:

• Default specification operators for different surface types
• S-F surfaces with small scales nesting index Nis
• S-F surfaces with large scales nesting index Nic
• S-L surfaces for roughness-like evaluation
• Evaluation area considerations
• Nesting indices and how they support scale limitation in surface texture analysis

It also provides default settings for items such as:

• Extraction
• Tolerance type
• Tolerance acceptance rule
• Areal Gaussian filter
• Association method
• Default units and attribute values for parameters from ISO 25178-2

A notable feature of this revision is that it removes some defaults that are too important to remain implicit, especially where they affect the intended function or verification outcome. This makes surface texture specification more transparent and better suited to modern areal metrology.

Applications

prEN ISO 25178-3 is especially useful in industries where surface condition influences function, performance, or quality control. Typical applications include:

• Mechanical engineering
• Precision manufacturing
• Optical and non-contact surface measurement
• Calibration and verification procedures
• Drawing-based surface texture specification
• Functional design of engineered surfaces

The standard is valuable when selecting the correct surface texture parameters and when ensuring that the specification is compatible with the intended surface function, measuring instrument, and verification method.

It also offers guidance for cases where the measured electromagnetic surface may differ from the expected mechanical surface, which is important in modern non-contact metrology.

Related Standards

prEN ISO 25178-3 is closely linked to several GPS and surface texture standards, including:

• ISO 25178-2 - surface texture parameters
• ISO 25178-1 - surface texture terminology and concepts
• ISO 17450-2 - specification operators
• ISO 14638 - GPS matrix model
• ISO 8015 - fundamental GPS rules
• ISO 14253-1 - default decision rules for verification
• ISO 16610-61, ISO 16610-71, ISO 16610-85 - filtering and segmentation methods

For organizations using GPS standards for surface texture, this document supports better specification control, improved interoperability, and more reliable metrological interpretation.

SLOVENSKI STANDARD
01-november-2026
Specifikacija geometrijskih veličin izdelka (GPS) - Tekstura površine: ploskovna -
3. del: Operatorji specifikacij (ISO/DIS 25178-3:2026)
Geometrical product specifications (GPS) - Surface texture: Areal - Part 3: Specification
operators (ISO/DIS 25178-3:2026)
Geometrische Produktspezifikation (GPS) - Oberflächenbeschaffenheit: Flächenhaft -
Teil 3: Spezifikationsoperatoren (ISO/DIS 25178-3:2026)
Spécification géométrique des produits (GPS) - État de surface: Surfacique - Partie 3:
Opérateurs de spécification (ISO/DIS 25178-3:2026)
Ta slovenski standard je istoveten z: prEN ISO 25178-3
ICS:
17.040.20 Lastnosti površin Properties of surfaces
17.040.40 Specifikacija geometrijskih Geometrical Product
veličin izdelka (GPS) Specification (GPS)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 25178-3
ISO/TC 213
Geometrical product specifications
Secretariat: BSI
(GPS) — Surface texture: Areal —
Voting begins on:
Part 3: 2026-09-23
Specification operators
Voting terminates on:
2026-12-16
Spécification géométrique des produits (GPS) — État de surface:
Surfacique —
Partie 3: Opérateurs de spécification
ICS: 17.040.40; 17.040.20
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
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 SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 25178-3:2026(en)
DRAFT
ISO/DIS 25178-3:2026(en)
International
Standard
ISO/DIS 25178-3
ISO/TC 213
Geometrical product specifications
Secretariat: BSI
(GPS) — Surface texture: Areal —
Voting begins on:
Part 3:
Specification operators
Voting terminates on:
Spécification géométrique des produits (GPS) — État de surface:
Surfacique —
Partie 3: Opérateurs de spécification
ICS: 17.040.40; 17.040.20
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document has not been edited by the ISO Central Secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2026
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 25178-3:2026(en)
ii
ISO/DIS 25178-3:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Complete specification operator . 1
4.1 General .1
4.2 Default specification operators .2
4.2.1 General default specification operators .2
4.2.2 Default specification operators for S-F surfaces (Nis nesting index) .2
4.2.3 Default specification operators for S-F surfaces (Nic nesting index) .3
4.2.4 Default specification operators for S-L surfaces .3
4.3 Other specification operators .4
4.3.1 Evaluation area .4
4.3.2 Nesting indices .4
5 General information . 4
Annex A (informative) Complete specification operator . 5
Annex B (normative) Default attribute values for parameters from ISO 25178-2 . 6
Annex C (normative) Default units for parameters from ISO 25178-2 . 8
Annex D (informative) Changes made to 2012 edition of this document .12
Annex E (informative) Considerations on how to adapt specification operators to verification .13
Annex F (informative) Relation with the GPS matrix . 17
Bibliography .18

iii
ISO/DIS 25178-3:2026(en)
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 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 213, Dimensional and geometrical product
specifications and verification.
This second edition cancels and replaces the first edition (ISO 25178-3:2012), which has been technically
revised.
The main changes are summarized in Annex D.
A list of all parts in the ISO 25178 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
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO/DIS 25178-3:2026(en)
Introduction
This document is a geometrical product specifications (GPS) standard and is to be regarded as a general GPS
standard (see ISO 14638). It influences chain link C of the chains of standards on areal surface texture.
The ISO GPS matrix model given in ISO 14638 gives an overview of the ISO GPS system of which this document
is a part. The fundamental rules of ISO GPS given in ISO 8015 apply to this document and the default decision
rules given in ISO 14253-1 apply to the specifications made in accordance with this document, unless
otherwise indicated.
For more detailed information on the relation of this document to the other standards and the GPS matrix
model, see Annex F.
This document specifies the specification operators according to ISO 17450-2.

v
DRAFT International Standard ISO/DIS 25178-3:2026(en)
Geometrical product specifications (GPS) — Surface texture:
Areal —
Part 3:
Specification operators
1 Scope
This document specifies the complete specification operator for surface texture (scale-limited surfaces) by
areal methods.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the terms and definitions given ISO 14406, ISO 17450-1, ISO 17450-2, and
ISO 25178-2 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/
4 Complete specification operator
4.1 General
The complete specification operation (see ISO 17450-2) consists of all the operators required for an
unambiguous specification. It consists of an ordered full set of unambiguous specification operations,
explicit or default, in an unambiguous order.
The advantage of the default specification operators given in 4.2 to 4.3 is to simplify the drawing indications
by allowing some notations to be omitted, but yet to be defined. However, this simplification shall not
degrade the intention of the designer to control a mechanical function through tolerances on surface texture
parameters.
Default specifications should only be adopted when they are compatible with the intended specification.
Designers shall always ensure that all specification operators, default or not, are adapted to the application,
to the surface function, to the surface features and to the metrological characteristics of the instruments
used in verification.
Compared to the first edition of this document, the new version removes defaults that are too important to
be hidden as defaults (such as the main nesting index). Annex D provides a list of modifications between the
former edition and this one.
Differences induced by choices made in verification are summarized in the associated uncertainty.

ISO/DIS 25178-3:2026(en)
Annex E provides considerations and concepts related to verification, and in particular about the relationship
between mechanical and electromagnetic surfaces.
4.2 Default specification operators
4.2.1 General default specification operators
Unless otherwise specified, the general defaults given in Table 1 shall apply.
Table 1 — General default specification operators
Criterion Default settings
a
Extraction Mechanical surface.
Orientation of the evaluation area There is no default for the orientation of the evaluation area with regard to the
surface lay. If the lay orientation is specified, the X-axis of the evaluation area
b
shall be oriented orthogonal to the lay.
Surface imperfection When specifying surface texture, the surface is the toleranced feature. Surface
imperfections shall be included in the specified surface, unless imperfections
are specified separately.
When specifying surface texture for material measures, in the context of calibra-
tion procedures, surface imperfections are excluded from the specified surface.
c
Tolerance type Upper specification limit.
d
Tolerance acceptance rule Maximum tolerance acceptance rule.
a
In verification, when using non-contact instruments, see Annex E for advice and recommendations.
b
If there is no texture direction, the orientation does not matter and can be free.
c
The “U” symbol can be omitted.
d
The “Tmax” symbol can be omitted (see ISO 25178-1)
See Annex E for considerations about stylus tip radius, sampling distance and evaluation area.
4.2.2 Default specification operators for S-F surfaces (Nis nesting index)
An S-F surface, which is equivalent to a primary profile in profile surface texture, is obtained by application
of an S-Filter with a small scales nesting index, Nis, and an F-operation, from the mechanical, electromagnetic
or auxiliary surface (see ISO 25178-2:2021, Annex G).
Unless otherwise specified, the defaults given in Table 2 shall be applied for S-F surfaces with an S-Filter
nesting index Nis.
Table 2 — Default specification operators for S-F surfaces (Nis nesting index)
Criterion Default settings
Areal S-Filter type Areal Gaussian filter according to ISO 16610-61.
Areal S-Filter nesting index, Nis 0,002 5 mm.
F-operator association method Association by least squares (LS) deviation from the nominal
geometrical shape (see NOTE 1 and NOTE 2 below).
Sphere radius Shall be equal or smaller than 80 % of Nis. a
Sampling distance Shall be equal or smaller than 20 % of Nis.
a
The sphere radius is specified to allow the realization of the mechanical surface.
NOTE 1 By default, all variables are part of the LS optimization. In case one of the variables is fixed (e.g. the radius)
it needs to be written explicitly in the specification.
NOTE 2 For surface texture analysis where slope or form is not significant, the ordinary least squares (OLS)
association method is sufficient. However, when there is a significant slope or form, the total least squares (TLS)
association method is preferred and therefore can be indicated as a non-default association method.

ISO/DIS 25178-3:2026(en)
4.2.3 Default specification operators for S-F surfaces (Nic nesting index)
An S-F surface, equivalent to a waviness profile in profile surface texture, is obtained by application of an
S-Filter with a large scales nesting index Nic, from the S-F surface defined in 4.2.2 (see also Annex G in
ISO 25178-2:2021).
Unless otherwise specified, the defaults given in Table 3 shall be applied for S-F surfaces with an S-Filter
nesting index Nic.
Table 3 — Default specification operators for S-F surfaces (Nic nesting index)
Criterion Default settings
Areal S-Filter type Areal Gaussian filter according to ISO 16610-61.
Areal S-Filter nesting index, Nic There is no default value for the large scales nesting index Nic. Therefore, Nic
shall be specified in the specification.
A surface texture specification for an S-F surface without an explicit nesting
index Nic is incomplete.
In the presence of large intended geometrical or periodical surface features, or in the case of structured or
[24]
stratified surfaces, designers should specify either:
— a non-default Chebyshev association (Minimum Zone); see ISO 4351 and Reference [27]; or
— a non-default areal robust Gaussian filter according to ISO 16610-71; or
— a non-default segmentation method according to ISO 16610-85.
See also Reference [29].
4.2.4 Default specification operators for S-L surfaces
This S-L surface is obtained by application of an L-Filter with large scales nesting index, Nic, from the S-F
surface defined in 4.2.2 (see also Annex G in ISO 25178-2:2021)
Unless otherwise specified, the defaults given in Table 4 shall apply for S-L surfaces.
Table 4 — Default specification operators for S-L surfaces
Criterion Default settings
Areal L-Filter type Areal Gaussian filter according to ISO 16610-61.
Areal L-Filter nesting index Nic There is no default value for Nic. The large scales nesting index, Nic, shall be
specified in the specification symbol.
A surface texture specification for an S-L surface without an explicit nesting
index Nic is incomplete.
NOTE The S-L surface is obtained from an S-F surface with a small S-Filter nesting index Nis. See ISO 25178-2:2021, Annex G.
See Tables 2 and 3 for the default specifications of the F-operator and the S-Filter.
In the presence of large intended geometrical or periodical surface features, or in the case of structured or
[25]
stratified surfaces, designers may specify either:
— a non-default Chebyshev association (Minimum Zone); see ISO 4351 and Reference [27]; or
— a non-default areal robust Gaussian filter according to ISO 16610-71; or
— a non-default segmentation method according to ISO 16610-85.
See also Reference [29].
ISO/DIS 25178-3:2026(en)
4.3 Other specification operators
4.3.1 Evaluation area
There is no default value for the evaluation area.
Specifications are given for an identified feature on the drawing, not on a specific evaluation area, unless
a restricted portion of the feature is indicated in the specification. The tolerance should be fulfilled in any
evaluation area within the specified surface.
See Clause D.5 for considerations about evaluation area in verification.
4.3.2 Nesting indices
Designers need to ensure that the specified nesting index corresponds to the proper scale limitation, as
obtained from a correlation to the surface function of interest. There is no restriction in the value of the
nesting index, as long as it is meaningful for the application.
NOTE The first version of this document mentioned a logarithmic series (based on 0,1; 0,2; 0,25; 0,5; 0,8 numbers),
but designers can select any value outside this series as long as it makes sense for the application (e.g. values of 0,4 or
0,85 are possible).
See Clauses D.3 and D.4 for considerations about nesting indices in verification.
5 General information
A decision tree for the complete specification operator is given in Annex A.
The default attribute values for the parameters defined in ISO 25178-2 shall be in accordance with Annex B.
The default units for parameters defined in ISO 25178-2 shall be in accordance with Annex C.
Annex D provides a summary of modifications made since the first edition.
Considerations regarding the relationship between mechanical surface and electromagnetic surface in
verification are given in Annex E.
The relation to the GPS matrix model is given in Annex F.

ISO/DIS 25178-3:2026(en)
Annex A
(informative)
Complete specification operator
Figure A.1 gives the list of mandatory and default specifications for each of the three surface types.

Interpretation of examples:
a (above) The Sz parameter is calculated on the primary surface and its maximum value is 3 µm.
(below) The Smr parameter (material ratio) is calculated at a depth of 0,5 µm below the highest point, on the primary-
like S-F surface, with a Gaussian filter and a nesting index Nis of 0,002 5 mm, and its maximum value is 40 %.
b (above) The Ssw parameter (dominant wavelength) is calculated on the waviness-like S-F surface, with a Gaussian
filter and a nesting index Nic of 2 mm, and the maximum value for Ssw is 8 mm.
(below) The Smr parameter (material ratio) is calculated at a depth of 0,1 µm below the highest point, on the
waviness-like S-F surface, with a Gaussian filter and a nesting index Nic of 0,4 mm, and its maximum value is 30 %.
c (above) The Sq parameter is calculated on the roughness-like S-L surface, with a Gaussian filter and a nesting index
Nic of 0,8 mm, and its maximum value is 0,7 µm.
(below) The Sk parameter is calculated on the roughness-like S-L surface, with a Robust Gaussian filter (non-default)
and a nesting index Nic of 2,5 mm, and its maximum value is 3,5 µm.
NOTE The order of block in the root symbol above anticipates the forthcoming revision of ISO 25178-1.
Figure A.1 — Examples of minimal indications depending on the surface type

ISO/DIS 25178-3:2026(en)
Annex B
(normative)
Default attribute values for parameters from ISO 25178-2
B.1 General
Parameters not listed in Tables B.1 to B.3 do not have attributes.
B.2 Spatial parameters
Attributes for spatial parameters shall be in accordance with Table B.1.
Table B.1 — Default attribute values for spatial parameters
Subclause in Parameter Attribute Default value
ISO 25178-2:2021
4.3.2 Sal fastest decay to a specified value s, with 0 ≤ s < 1 s is 0,2
4.3.3 Str fastest and slowest decays to s, with 0 ≤ s < 1 s is 0,2
4.3.4 Std texture direction from reference direction θ θ is 0°
ref ref
B.3 Volume parameters
Attributes for volume parameters shall be in accordance with Table B.2.
Table B.2 — Default attribute values for volume parameters
Subclause in Parameter Attribute Default value
ISO 25178-2:2021
4.5.6.2 Vvv material ratio p p is 80 %
4.5.6.3 Vvc material ratios p and q p is 10 %
q is 80 %
4.5.7.2 Vmp material ratio p p is 10 %
4.5.7.3 Vmc material ratios p and q p is 10 %
q is 80 %
B.4 Multi-scale geometric
Attributes for multi-scale geometric parameters shall be in accordance with Table B.3.
Table B.3 — Default attribute values for multi-scale geometric parameters
Subclause in Parameter Attribu
...