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

Overview

EN ISO 25178-71:2026 (Geometrical Product Specifications - GPS - Surface Texture: Areal - Part 71: SDF File Format) is an international standard developed by CEN under the ISO 25178 series. This document specifies the requirements for software measurement standards (Type S1 and Type S2) used to verify the software of measuring instruments, focusing on the specification and application of the Surface Data File (SDF) format for surface texture measurements. The standard is crucial for ensuring data interoperability, traceable calibration, and software verification in profile and areal surface texture metrology.

Key Topics

• Surface Data File (SDF) Format
  EN ISO 25178-71:2026 defines the SDF file format, designed for digitally representing surface measurement data in both profile and areal modes. The format supports orthogonal grids and equidistant sampling intervals, ensuring data consistency across different measuring principles.

• Type S1 and S2 Software Measurement Standards

  • Type S1 (“reference data”/“softgauge”): Digital files representing measured or mathematically generated surfaces, used for direct software testing and calibration.
  • Type S2 (“reference software”): Traceable reference software that can be used to test and compare the results of measurement instrument software.

• Data file structure
  SDF files are divided into header, data, and trailer sections, supporting both ASCII and binary representations. The structure includes identifiers for manufacturer, creation/modification dates, matrix dimensions, scale factors, and data types.

• Traceability and Calibration
  Provides protocols for calibration certificates, including required fields such as uncertainty estimates, reference conditions, and identification data.

• Conformance and Interoperability
  The adoption of a standardized data format promotes interoperability between instruments and analytical software, supporting robust quality assurance processes.

Applications

EN ISO 25178-71:2026 is applied in several key industrial and research contexts:

• Instrument Calibration and Verification
  Facilitates the verification and calibration of areal surface texture measuring instruments by using standardized SDF files and reference data.

• Software Quality Assurance
  Enables developers and users to test surface texture analysis software systematically against certified reference data and reference software, ensuring compliance and comparability of results.

• Data Exchange and Archiving
  The standardized SDF format simplifies the sharing, long-term storage, and analysis of surface topography data between different stakeholders, including manufacturers, researchers, and regulatory bodies.

• Research and Academic Use
  Academic institutions use the SDF format for simulations, algorithm testing, and method development, reinforcing reproducibility in surface metrology studies.

• Industrial Quality Control
  Manufacturers implement the standard in production environments to certify measuring systems, uphold product quality, and meet contractual and regulatory requirements.

Related Standards

Adherence to EN ISO 25178-71:2026 is reinforced by alignment with related standards in the field of geometrical product specification and measurement:

• EN ISO 25178 Series: Comprehensive family for areal surface texture measurement and analysis.
• ISO 8015: Fundamental rules of GPS, providing a universal framework for interpretation and implementation.
• ISO 14253-1: Decision rules for verification of conformity with specifications.
• ISO 14406:2010: Details orthogonal grid sampling applicable in SDF specification.
• ISO/IEC Guide 99: International vocabulary of metrology.
• ISO 14638: GPS matrix model reference, aiding in understanding standard interrelationships.

Practical Value

By defining the SDF format and associated software measurement standards, EN ISO 25178-71:2026 enables:

• Reliable and traceable instrument and software performance
• Enhanced comparability and repeatability in surface texture measurements
• Efficient quality control and compliance with international best practices
• Streamlined data exchange and long-term usability of measurement data

Keywords: surface texture, areal measurement, SDF file format, GPS standard, metrology software verification, reference data, reference software, calibration, surface metrology, data interoperability, quality control, ISO 25178-71

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
...