EN ISO 25178-71:2026

• Abstract:

  This document specifies Type S1 software measurement standards, reference data, and Type S2 software measurement standards, reference software, for verifying the software of measuring instruments. It also specifies the surface data file (SDF) format of Type S1 software measurement standards for the calibration of instruments for the measurement of surface texture by the profile and areal method as defined in the profile and areal surface texture chain of standards, the chain links F and G.; The SDF format applies to profile and areal topography measurement data extracted with an orthogonal grid (see ISO 14406:2010, 5.2) and equidistant sampling intervals, regardless of the measurement principle.; NOTE Throughout this document, the terms “reference data” and “reference software” are used as substitutes for software measurement standards of Type S1 and Type S2, respectively. In practice, “reference data” is sometimes referred to as “software gauge” or “softgauge”.

• Status: Published
• Publication Date: 01-Sep-2026
• ICS: 17.040.20 - Properties of surfaces
• ICS: 17.040.40 - Geometrical Product Specification (GPS)
• Technical Committee: CEN/TC 290 - Dimensional and geometrical product specification and verification
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 02-Sep-2026
• Completion Date: 02-Sep-2026
• Ref Project: SIST EN ISO 25178-71:2026 - Geometrical product specifications (GPS) - Surface texture: Areal - Part 71: SDF file format (ISO 25178-71:2026)

• Replaces: EN ISO 25178-71:2017 - Geometrical product specifications (GPS) - Surface texture: Areal - Part 71: Software measurement standards (ISO 25178-1:2017)
• Effective Date: 17-Jan-2024
• Consolidated By: ISO 25178-71:2026 - Geometrical product specifications (GPS) — Surface texture: Areal — Part 71: SDF file format
• Effective Date: 12-Feb-2026

EN ISO 25178-71:2026 is the CEN adoption of ISO 25178-71:2026 for geometrical product specifications (GPS) - surface texture, areal, Part 71. It specifies Type S1 software measurement standards, called reference data, and Type S2 software measurement standards, called reference software, for verifying measuring-instrument software. It also defines the surface data file (SDF) format used for calibration data in profile and areal surface texture measurement.

What does EN ISO 25178-71:2026 specify?

EN ISO 25178-71:2026 specifies both the software reference material and the file format used to store it. In practice, it gives a common way to package surface topography data so that software in measuring instruments can be checked and calibrated consistently.

The document applies to profile and areal topography measurement data extracted with an orthogonal grid and equidistant sampling intervals, regardless of the measurement principle. That makes it useful across different instrument types, as long as the data are laid out in the SDF structure.

Part of the document	What it covers
Clause 1	Scope
Clause 2	Normative references
Clause 3	Terms and definitions
Clause 4	Types of software measurement standards
Clause 5	File format for Type S1 reference data
Clause 6	Software measurement standard certificate
Annex A	ASCII and binary representation of the SDF format
Annex B	Relationship to the GPS matrix model

What are the key requirements of EN ISO 25178-71:2026?

Type S1 and Type S2 software measurement standards

Clause 4 distinguishes two kinds of software measurement standards. Type S1 is reference data - a computer data file with a digital representation of a measured or mathematically generated surface - and Type S2 is reference software - traceable computer software used as a comparison reference.

For users, this means the standard covers both the data fed into software under test and the reference program used to check results. The point is to verify things like form removal, filter algorithms, and parameter calculation against known results.

SDF file structure

Clause 5.1 says the file extension is .sdf and the SDF format is divided into three records: header, data area, and trailer. Annex A gives the ASCII and binary representation rules.

That structure matters because it tells software developers how to parse the file and where to look for metadata, measurement values, and any extra historical information.

Header content and versioning

Clause 5.2 defines the header fields, including version number, manufacturer identifier, creation and modification timestamps, matrix size, scale factors, Z-resolution, compression type, data type, and checksum type. The document specifies version 1.0 and version 2.0 of the format.

Version 2.0 adds a new version number scheme and changes the size of the matrix dimensions from 2-byte to 4-byte unsigned integers. It also adds int8 and binary32 as supported data types. In practice, that tells implementers what file variants they need to read or write.

Data area and missing points

Clause 5.3 stores the coded height information as a matrix in a right-handed coordinate system. The x-direction follows the columns, the y-direction follows the rows, and the scale factors define the coordinates in metres.

Non-measured or spurious points are marked by the minimum value of the chosen data type, or by BAD in ASCII files. That gives users a clear way to preserve and recognize invalid data during processing.

Trailer and certificate information

Clause 5.4 allows a variable-length trailer for historical information such as operator name, measurement conditions, sample specification, and processing steps like filtering or data inversion. For version 2.0, the trailer uses the same tagged format as the header.

Clause 6 says each calibrated software measurement standard shall be accompanied by certificate information such as the title, supplier identity, certificate identification, actual specification operator, calibrated value with uncertainty, calibration details, reference conditions, and whether the values are direct or synthetic. For Type S2, it also asks for identification of the hardware or operating systems used for development, checking, or verification.

What terms does EN ISO 25178-71:2026 define?

• software measurement standard - reference data or reference software intended to reproduce a measurand value with known specification uncertainty so software can be verified.
• ASCII - a 7-bit character encoding that is congruent with UTF-8 in the first 128 characters.
• uint8 - a 1-byte unsigned integer representation with values from 0 to 255.
• int8 - a 1-byte signed integer representation with values from -128 to 127.
• uint32 - a 4-byte unsigned integer representation with values from 0 to 4 294 967 295.
• binary32 - a 4-byte IEEE 754 single-precision floating-point representation.
• binary64 - an 8-byte IEEE 754 double-precision floating-point representation.
• datetime - a 12-character ASCII date-time string in the format DDMMYYYYhhmm.

Who uses EN ISO 25178-71:2026?

EN ISO 25178-71:2026 is used by people who develop, verify, calibrate, or supply software for surface texture measuring instruments. The introduction notes that the SDF format is already used in industry, especially by instrument manufacturers and academia.

It is also relevant to quality and calibration teams that need documented reference data, reference software, calibrated values, uncertainty information, and traceable records for surface texture software checks.

What changed in EN ISO 25178-71:2026 from the previous edition?

EN ISO 25178-71:2026 is the third edition and cancels and replaces EN ISO 25178-71:2017. The foreword says the document was technically revised.

The changes stated in the document are:

• version number 2.0 was added
• the number of columns and rows is represented as a 4-byte unsigned integer in version 2.0 instead of a 2-byte unsigned integer
• two additional data types were added for version 2.0: a 1-byte signed integer and a 4-byte floating point type

Which standards are used with EN ISO 25178-71:2026?

• ISO/IEC Guide 99 - provides the metrology vocabulary used in the normative references.
• ISO 14638 - places the document in the GPS matrix model.
• ISO 8015 - supplies the fundamental GPS rules that apply unless otherwise indicated.
• ISO 14253-1 - supplies the default decision rules for conformity and nonconformity.
• ISO 14406:2010 - is referenced for orthogonal grid extraction.
• ISO 17450-2 - is referenced for the actual specification operator used in the certificate.
• ISO/IEC Guide 98-3 - is referenced for uncertainty of measurement.
• ISO/IEC 10646 - supports the ASCII note in the definitions.
• ISO 80000-2 - supports the mathematical symbols used in the formulas.
• IEEE 754:2019 - supports the floating-point representations used for binary32 and binary64.

What does the EN ISO 25178-71:2026 document contain?

The document contains tables for the header fields and supported data types, plus the rules for how those fields are encoded in ASCII and binary form. It also contains a matrix definition for the data area and formulas that map the stored values to x, y, and z coordinates.

Annex A gives the file-layout rules for ASCII and binary SDF files, including line endings, field order, separators, and the end marker. It also includes an example file layout.

Annex B explains how the document fits into the GPS matrix model and shows its place in the profile and areal surface texture chain of standards. Figures in the document show the ASCII forms of binary32 and binary64 values and the coordinate layout of the data area.

SLOVENSKI STANDARD
01-november-2026
Specifikacija geometrijskih veličin izdelka (GPS) - Tekstura površine: Ravna - 71.
del: Format SDF datoteke (ISO 25178-71:2026)
Geometrical product specifications (GPS) - Surface texture: Areal - Part 71: SDF file
format (ISO 25178-71:2026)
Geometrische Produktspezifikation (GPS) - Oberflächenbeschaffenheit: Flächenhaft -
Teil 71: Software-Normale (ISO 25178-71:2026)
Spécification géométrique des produits (GPS) - État de surface: Surfacique - Partie 71:
Format de fichier SDF (ISO 25178-71:2026)
Ta slovenski standard je istoveten z: EN ISO 25178-71:2026
ICS:
17.040.20 Lastnosti površin Properties of surfaces
17.040.40 Specifikacija geometrijskih Geometrical Product
veličin izdelka (GPS) Specification (GPS)
35.080 Programska oprema Software
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 25178-71
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2026
EUROPÄISCHE NORM
ICS 17.040.20 Supersedes EN ISO 25178-71:2017
English Version
Geometrical product specifications (GPS) - Surface texture:
Areal - Part 71: SDF file format (ISO 25178-71:2026)
Spécification géométrique des produits (GPS) - État de Geometrische Produktspezifikation (GPS) -
surface: Surfacique - Partie 71: Format de fichier SDF Oberflächenbeschaffenheit: Flächenhaft - Teil 71:
(ISO 25178-71:2026) Software-Normale (ISO 25178-71:2026)
This European Standard was approved by CEN on 14 August 2026.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 25178-71:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 25178-71:2026) has been prepared by Technical Committee ISO/TC 213
"Dimensional and geometrical product specifications and verification" in collaboration with Technical
Committee CEN/TC 290 “Dimensional and geometrical product specification and verification” the
secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2027, and conflicting national standards shall
be withdrawn at the latest by March 2027.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 25178-71:2017.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 25178-71:2026 has been approved by CEN as EN ISO 25178-71:2026 without any
modification.
International
Standard
ISO 25178-71
Third edition
Geometrical product specifications
2026-08
(GPS) — Surface texture: Areal —
Part 71:
SDF file format
Spécification géométrique des produits (GPS) — État de surface:
Surfacique —
Partie 71: Format de fichier SDF
Reference number
ISO 25178-71:2026(en) © ISO 2026

ISO 25178-71:2026(en)
© ISO 2026
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, including photocopying, or posting on
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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 25178-71:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Types of software measurement standards . 4
4.1 General .4
4.2 Type S1, reference data .4
4.3 Type S2, reference software .4
5 File format for Type S1, reference data . 4
5.1 General .4
5.2 Record 1 — Header .5
5.2.1 General .5
5.2.2 Version number .5
5.2.3 Measurement instrument manufacturer's identifier .5
5.2.4 Original creation date and time .5
5.2.5 Last modification date and time.5
5.2.6 Number of columns in the data matrix, M .5
5.2.7 Number of rows in the data matrix, N .5
5.2.8 X-scale factor .5
5.2.9 Y-scale factor .6
5.2.10 Z-scale factor . .6
5.2.11 Z-resolution .6
5.2.12 Compression type .6
5.2.13 Data type .6
5.2.14 Checksum type . .6
5.2.15 Header description .6
5.3 Record 2 — Data area .7
5.3.1 General .7
5.3.2 Handling of non-measured or spurious points . .8
5.4 Record 3 — Trailer .9
6 Software measurement standard certificate . 9
Annex A (normative) ASCII and binary representation of the SDF format .10
Annex B (informative) Relationship to the GPS matrix model .12
Bibliography .13

iii
ISO 25178-71:2026(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 document 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, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 290, Dimensional and geometrical product specification and verification, in
accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 25178-71:2017), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the version number 2.0 has been added, which incorporates a number of new functionalities (see 5.2.2);
— in version number 2.0, the number of columns and the number of rows of the data matrix is represented
as a 4-byte unsigned integer instead of a 2-byte unsigned integer (see 5.2.6 and 5.2.7);
— in version number 2.0, two additional data types are available for data storage: a 1-byte signed integer
and a 4-byte floating point (see 5.2.13).
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 25178-71:2026(en)
Introduction
This document is a geometrical product specification (GPS) standard and is to be regarded as a general GPS
standard (see ISO 14638). It influences the chain links F and G of the chains of standards on profile and 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 of the relation of this document to other standards and the GPS matrix model,
see Annex B.
This document is concerned with Type S1 software measurement standards (reference data), and Type S2
software measurement standards (reference software). It also defines the surface data file (SDF) format for
reference data.
The SDF format is already used by the industry, in particular, by instrument manufacturers and academia.
The basic concept of the SDF format was originally developed for tactile measuring instruments as part of
[6]
the European Surfstand project and EUR 15178.

v
International Standard ISO 25178-71:2026(en)
Geometrical product specifications (GPS) — Surface texture:
Areal —
Part 71:
SDF file format
1 Scope
This document specifies Type S1 software measurement standards, reference data, and Type S2 software
measurement standards, reference software, for verifying the software of measuring instruments. It also
specifies the surface data file (SDF) format of Type S1 software measurement standards for the calibration
of instruments for the measurement of surface texture by the profile and areal method as defined in the
profile and areal surface texture chain of standards, the chain links F and G.
The SDF format applies to profile and areal topography measurement data extracted with an orthogonal
grid (see ISO 14406:2010, 5.2) and equidistant sampling intervals, regardless of the measurement principle.
NOTE Throughout this document, the terms “reference data” and “reference software” are used as substitutes
for software measurement standards of Type S1 and Type S2, respectively. In practice, “reference data” is sometimes
referred to as “software gauge” or “softgauge”.
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/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated terms
(VIM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC Guide 99 and the following
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
software measurement standard
reference data or reference software intended to reproduce the value of a measurand with known
specification uncertainty, in order to verify the software used to calculate the value of a measurand
3.2
American Standard Code for Information Interchange
ASCII
7-bit character encoding which is congruent with UTF-8 encoding in the first 128 characters
Note 1 to entry: See ISO/IEC 10646.

ISO 25178-71:2026(en)
3.3
uint8
1-byte (8-bit) representation of an unsigned integer
Note 1 to entry: The value range of “uint8” is from 0 to 255.
Note 2 to entry: In version number 1.0 of the SDF format, the term BYTE was used instead of uint8.
3.4
int8
1-byte (8-bit) representation of a signed integer
Note 1 to entry: The value range of “int8” is from −128 to 127.
3.5
uint16
2-byte representation of an unsigned integer
Note 1 to entry: The value range of “uint16” is from 0 to 65 535.
Note 2 to entry: The least significant byte shall be stored first in the lowest memory address, which is known as the
[7]
“little endian” concept.
3.6
int16
2-byte representation of a signed integer
Note 1 to entry: The value range of “int16” is from −32 768 to 32 767.
Note 2 to entry: The least significant byte shall be stored first in the lowest memory address, which is known as the
[7]
“little endian” concept.
3.7
uint32
4-byte representation of an unsigned integer
Note 1 to entry: The value range of “uint32” is from 0 to 4 294 967 295.
Note 2 to entry: The least significant byte shall be stored first in the lowest memory address, which is known as the
[7]
“little endian” concept.
3.8
int32
4-byte representation of a signed integer
Note 1 to entry: The value range of “int32” is from −2 147 483 648 to 2 147 483 647.
Note 2 to entry: The least significant byte shall be stored first in the lowest memory address, which is known as the
[7]
“little endian” concept.
3.9
binary32
4-byte single precision representation of a normalized floating point number according to IEEE 754
38 38
Note 1 to entry: The value range of “binary32” is from 3,402823466 10 to 3,402823466×10 .
Note 2 to entry: The least significant byte shall be stored first in the lowest memory address, which is known as the
[7]
“little endian” concept.
Note 3 to entry: Many programming languages support the 4-byte single precision representation in accordance with
IEEE 754. However, alternative terms are often used instead of “binary32”. For example, “float” in C and C++.

ISO 25178-71:2026(en)
Note 4 to entry: The ASCII representation
...