About Validation Properties

STEP exchange can be checked through validation properties. For each type of data, validation properties are specified through the recommended practices. Validation properties are:

• computed on the native data at export and are stored in the STEP file,
• computed on the imported data at import and compared with the validation properties found in the STEP file. A status of comparison is provided in the report file.

The following validation properties are available:

• Geometric Validation Properties (GVP) for geometric exchange (at part and assembly level),
• Assembly Validation Properties (AVP) for assembly structure exchange (at assembly level),
• Annotation validation properties for FTA exchange (at part level).

The following topics are discussed:

• Validation Properties at Part Level
• Validation Properties at Assembly Level
• Global Status of the Comparison of the Validation Properties at Import

Validation Properties at Part Level

Geometric Validation Properties (GVP)

The exported STEP file includes geometric validation properties for each solid, shell and a global GVP for the whole part.

For each solid or shell, the report file gives the computed geometric validation properties:

• Centroid: coordinates of the center of gravity (applies to solid and shell),
• Area: area of the entity (wetted area for solids) (applies to solid and shell),
• Volume: volume of the entity (for solids only) (applies to solid).

These properties are completed with the estimation of their computation errors for each solid and each shell:

• The estimation of the computation error on the area or the volume is provided as a relative value.
• The estimation of the computation error on the centre of gravity is provided as an absolute value for each coordinate and a bounding box of the entity.

Geometric Validation Properties (GVP) Check at Import

For each imported solid or shell, and for the imported part as a whole, the report file indicates the geometric validation properties computed on the imported data, the GVP read in the STEP file and the status of comparison between the two sets of GVP.

In addition, the report provides the following error information computed on each imported solid or shell:

• Centroid deviation error (distance measure) (applies to solid, shell, product or instance),
• Surface area difference value and error ratio (applies to solid, shell or product),
• Volume difference value and error ratio (applies to solid or product).

These properties are completed with the estimation of their computation errors for each solid and each shell:

• The estimation of the computation error on the area or the volume is provided as a relative value.
• The estimation of the computation error on the centre of gravity is provided as an absolute value for each coordinate and a bounding box of the entity.

The status of comparison for a given solid or shell is ok if:

• ratios (Volume difference and Surface area difference) are lower than 1%.
• and the centroid deviation is lower than 1 mm.

Example:

If all status are ok, the global status is ok too.

Example:

Clouds of Points (COPS)

When standard validation properties are not accurate enough, e.g. for aeronautic long term archiving, COPS ensure that the archived data are equivalent to the native data, within a given tolerance by comparing any face with any check point lying on it.

At export:

• The STEP file is enriched with COPS properties (i.e. a cloud of points) for each exported face.
• These points are computed inside the face, on the support of the face or on the boundary of the face.
• The syntax of the STEP file respects the Recommended Practices.
• See also SAG for COPS creation density.

At import:

• For each face, the COPS properties are read and the distance between each point of the cloud and the support surface of the face is computed.
• If the distance is greater than a user defined tolerance, there is an error message in the err file.
• See also Tolerance for COPS deviation.

Example of error file at import:

Example of report file at import: The global status includes the COPS check : if a COPS deviation is found during the translation, then the global status of the GVP is KO.
 

• The check at import is reported only in the report and error files.
• The repartition of the points in the face is automatic. A high curvature will generate many points.
• You cannot define an area to be controlled by COPS. The whole product exported is checked.
• The unit used for geometric validation properties is the STEP length user unit.

Annotation Validation Properties for FTA

Only annotations and tolerances at Part level (stored in a representation, not in a product) are taken into account.

At import, the Validation Properties status takes the validation properties for the FTA annotations into account:

• number of annotations,
• number of saved views (captures),
• total length of the polylines representing each annotation,
• centroid of the polylines representing each annotation.

Example:

Detailed properties are written in the report files at export and at import, in order to allow an automatic check of the exchange by comparison of the reports. This comparison is not done by the translator. The additional properties are the following:

• at export:
  • V5 Type and sub-type,
  • V5 User name,
  • Number of polylines of the wireframe graphical representation of the annotation,
  • Total length of the wireframe graphical representation of the annotation,
  • Centroid of the wireframe graphical representation of the annotation.
  • example of report:
    
• at import:
  • STEP type of the GD&T,
  • Number of polylines of the annotation,
  • Total length of the the annotation,
  • Centroid of the annotation.
  • example of report:
    

Validation Properties at Assembly Level

The assembly product structure can be checked either by Geometric Validation Properties (GVP) or by Assembly Validation Properties (AVP):

• The GVP are dependent on the geometry conversion and are KO when the geometry conversion is partial at any level.
• The AVP are defined independently from the geometry and allow to check assemblies conversion even when the geometry itself is not exchanged (ie nested assemblies use cases).

Geometric Validation Properties (Extended GVP)

Those described above apply also to product or instances. In addition:

• On the product, centroid, volume and area are defined,
• On the instance, a centroid is defined.

Example:

Assembly Validation Properties

For each product having instances, the number of instances and a notional centroid are stored in the STEP file as validation properties at export and checked at import.

At export, for each product, 2 properties are stored in the STEP file:

• Its number of instances,
• Its notional centroid (useful for checking the position of each instance of the product).

At import, the status for validation properties in the report file takes into account the validation properties check at assembly level, done according to the option.

• If product assembly properties are found, these properties are checked and Product/Instances geometric validation properties, if any, are ignored.
• When assembly properties are checked, the result of the comparison of the assembly properties appears in the report file for each product.

Example:

Global Status of the Comparison of the Validation Properties at Import

At import, a global status of the check of all the validation properties is provided.

This status also provides a sub-status for GVP, AVP and COPS. In addition, maximum errors are provided.

The maximum deviation found for each comparison (centroid, area and volume) is given in the report file with the corresponding entities (the maximum deviations found do not necessarily apply to a single object).

Example: