ISO 10303-21:2016(E)
The following example shows how to define the basic units of a typical STEP file as EXPRESS constants.
CONSTANT plane_angle_radian : si_unit := named_unit (?) || plane_angle_unit () || si_unit (?, radian); solid_angle_steradian : si_unit := named_unit (?) || solid_angle_unit () || si_unit (?, steradian); length_millimeter : si_unit := named_unit (?) || length_unit () || si_unit (milli, metre); END_CONSTANT; CONSTANT seven_dimensions_a : dimensional_exponents := dimensional_exponents (0., 0., 0., 0., 0., 0., 0.); degree_to_radian : measure_with_unit := measure_with_unit (plane_angle_measure (0.01745329252), radian)); plane_angle_degree : conversion_based_unit := conversion_based_unit ('degree', degree_to_radian)) || named_unit (seven_dimensions_a) || plane_angle_unit (); END_CONSTANT; CONSTANT seven_dimensions_b : dimensional_exponents := dimensional_exponents (1., 0., 0., 0., 0., 0., 0.); inch_to_millimeter : measure_with_unit := measure_with_unit (length_measure (25.4), inch)); imperial_length_inch : conversion_based_unit := conversion_based_unit ('inch', inch_to_millimetre)) || named_unit (seven_dimensions_b) || length_unit (); END_CONSTANT;
NOTE These examples are for illustration only.
The following example uses the previously defined EXPRESS constants to define a geometric context for a STEP file.
ISO-10303-21; HEADER; FILE_DESCRIPTION( /* description */ ('example of how to reference EXPRESS constants that define units'), /* implementation_level */ '4;3'); FILE_NAME( /* name */ 'example.stp', /* time_stamp */ '2013-02-09T12:37:49-05:00', /* author */ (''), /* organization */ (''), /* preprocessor_version */ '', /* originating_system */ '', /* authorisation */ ''); FILE_SCHEMA(('AP242_MANAGED_MODEL_BASED_3D_ENGINEERING_MIM_LF')); /* AP242 Schema */ ENDSEC; DATA; #10 = ( GEOMETRIC_REPRESENTATION_CONTEXT(3) GLOBAL_UNIT_ASSIGNED_CONTEXT((#IMPERIAL_LENGTH_INCH, #PLANE_ANGLE_RADIAN, #SOLID_ANGLE_STERADIAN) REPRESENTATION_CONTEXT('','3D') ); .... ENDSEC; END-ISO-10303-21;
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