Overview
EN ISO 25178-72:2017/A1:2020 is an amendment to the ISO 25178-72 standard that defines the x3p XML file format for exchanging areal (3D) surface texture data. Published by CEN in September 2020, this amendment clarifies coordinate systems, axis types, scaling and increments, matrix dimensions, binary validity storage and vendor-specific extensions to ensure robust, interoperable storage and transfer of surface metrology data.
Key topics and technical requirements
- File format & XML schema
- The amendment updates the XML schema (x3p/ISO5436_2 namespace) and example elements used to store measurement metadata and data matrices.
- Coordinate systems
- Defines global coordinate system (3D, right-handed for original point cloud) and view coordinate system (3D, right-handed for stored point coordinates). Conversion may require rotation and translation.
- Axis types
- AxisType must be either
"I" (incremental) or "A" (absolute). The x and y axes may be incremental or absolute; z coordinates shall be absolute.
- Absolute vs incremental storage
- Absolute axis: explicit storage of x, y, z as dimensionless values; multiply by a scaling factor (calibration factor) to get metres.
- Increment element: positive length in metres used as either increment for incremental axes or scaling factor for absolute axes (named I_x, I_y, I_z).
- Coordinate transformation
- Global coordinates (X,Y,Z in metres) are computed from dimensionless view coordinates (x,y,z) via a rotation matrix, increments/scaling and offsets (I_x, I_y, I_z; O_x, O_y, O_z).
- Matrix dimensions
- MatrixDimension contains SizeX, SizeY, SizeZ to describe the stored data matrix (u,v,w), which may not directly map 1:1 to x,y,z when incremental axes are used.
- Validity and binary storage
- Binary validity files are written as a packed array of bits; byte and bit indices are specified for decoding.
- Vendor-specific extensions
- VendorSpecificID is a URI identifying vendor extension files placed inside the x3p ZIP container (domain name mapped to folder path). Unknown VendorSpecificID elements may be ignored safely.
- Revision string
- The Revision record is specified to contain the string “ISO25178 -72: 2017/ DAM1” per the amendment.
Applications and who uses it
- Surface metrology & quality control: interchange of areal surface measurements between instruments and analysis software.
- Instrument manufacturers & software developers: implementers of data export/import (x3p) to ensure compatibility.
- Metrology labs & QA engineers: archiving, traceability and exchange of 3D surface texture datasets.
- Researchers & standards bodies: consistent representation of measurement metadata and coordinate transforms.
Related standards
- ISO 25178 series (areal surface texture standards)
- ISO 5436-2 (referenced XML implementation/schema in the amendment)
Keywords: ISO 25178-72, x3p, surface texture, areal, XML file format, GPS, geometrical product specifications, surface metrology, coordinate transformation, vendor specific extensions.