ISO 25178-72:2017

Overview

ISO 25178-72:2017 defines the x3p XML file format for storage and exchange of areal surface texture, topography and profile data. Part of the ISO 25178 GPS (Geometrical Product Specifications) series, this standard specifies the container layout, mandatory files, data types and metadata required to reliably share 2½D topographies, point clouds and multilayer surface representations between instruments, software and laboratories.

Keywords: ISO 25178-72, x3p, XML file format, surface texture, areal, topography data, GPS.

Key Topics and Requirements

• File container: An x3p file is a zip-container with the filename extension .x3p (lowercase on case-sensitive systems).
• Minimum contents: The root of the zip must contain main.xml and md5checksum.hex.
• main.xml: Central XML record that holds header information, axis definitions, metadata, 3D point data references, and checksum info.
• Binary data support: Coordinates and validity masks may be stored in binary files (recommended paths: bindata/bindata.bin and bindata/valid.bin), with relative paths referenced from main.xml.
• Data types: The standard defines numeric representations used in x3p (e.g., int16, int32, float32, float64) and supports IEEE 754 NaN for invalid values.
• Units and offsets: All coordinates must be specified in metres (SI). A recommended offset centers the stored point cloud at the origin.
• Coordinate systems & matrices: Definitions include global and view coordinate systems, rotation matrix for orientation, and the data matrix concept for indexed point arrays.
• Vendor extensions: Custom files (images, extra metadata) are permitted provided they do not use the reserved filenames.
• Integrity: An MD5 checksum file (md5checksum.hex) is required to verify container integrity.

Applications and Users

ISO 25178-72 (x3p) is used by:

• Metrology laboratories and quality-control engineers for reliable exchange of surface texture measurements.
• Instrument manufacturers and software developers implementing areal-topography data import/export.
• Research institutions and academia sharing topography datasets.
• Production engineers and surface scientists integrating profilometry data across systems.

Benefits include interoperable data exchange, unambiguous metadata, and support for both ASCII/XML and efficient binary encodings.

Related Standards

• ISO 25178 series (surface texture - areal)
• ISO 25178-600 (metrological characteristics for areal-topography measuring methods)
• ISO 5436-2 (related topography data definitions)
• ISO 14638, ISO 8015, ISO 14253-1 (GPS framework and decision rules)
• openGPS (open-source x3p implementations)

Use ISO 25178-72:2017 when you need a standardized, machine-readable format (x3p) to store, validate and exchange areal surface texture and topography datasets across instruments and software tools.