PDM-UG: Portions of the Part Shape
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This page belongs to the PDM Usage Guide.
The PDM Schema supports the requirement to identify explicitly a portion of shape that may be associated with other information – including dedicated geometric models. Property information can be linked to shape aspects via property definitions. A prominent special case is the assignment of dedicated shape_representations as shown in the diagram below. The shape_representation can either represent the part shape completely or just partial geometry.
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The Instance Model: EXPRESS entities and attributes
The EXPRESS entities and attributes used to support the requirements of independent property identification are illustrated in Diagram 9.
Shape aspect
An instance of shape_aspect is used to identify a portion of a part shape. To this portion of the part shape properties can be associated with the portion. Typically the geometric elements that establish the shape_aspect are collected in a shape_representation which is related to the shape_aspect via instances of property_definition and shape_definition_representation. In cases in which a shape_representation deliberately represents only portions of an overall part shape it is recommended to relate this shape_representation to the part shape via the usage of shape_aspect.
Attributes
- The name is the organizational name of the shape_aspect.
- The description attribute provides an optional textual description of the shape_aspect.
- The of_shape attribute references the product_definition_shape of which the shape_aspect is a portion.
- The product_definitional attribute indicates whether the portion of shape lies on the physical boundary of the part shape.
| ENTITY shape_aspect | Attribute Population | Remarks |
| name | type: label = STRING | |
| description | type: text = STRING | OPTIONAL |
| of_shape | type: entity = product_definition_shape | |
| product_definitional | type: LOGICAL | If a value of TRUE is given, then it is asserted that the shape_aspect is on the physical boundary of the product_definition_shape. |
===Preprocessor Recommendations=== None specified.
===Postprocessor Recommendations=== None specified.
===Related Entities=== None specified.
The Instance Model: STEP exchange file format (ISO10303 Part 21 syntax)
#700 = PRODUCT_DEFINITION_SHAPE('shape_p',$,#260);
#710 = SHAPE_ASPECT('aspect1',$,#700,.T.);
/* Entities #730 to #790 define the geometry related to */
/* shape_aspect #710 */
#730 = PROPERTY_DEFINITION('shape for aspect1',$,#710);
#740 = SHAPE_DEFINITION_REPRESENTATION(#730,#750);
#750 = SHAPE_REPRESENTATION('sa1',(#795),#760);
