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The SEDRIS Data Representation Model
APPENDIX A - Classes Face Direction |
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An instance of this DRM class specifies, for the associated relationship, whether the front or back of the target face is associated with the surface being described.
Consider an <Areal Feature> instance representing a grass-covered region, consisting of a single <Feature Face> instance. The <Face Direction> link object on the relationship between them is set to SE_TRUE, indicating that the front (that is, the top) side of the face corresponds to the <Areal Feature> instance.
Consider a <Polyhedron> instance specifying a room within a building and a <Geometry Volume> instance representing the topological connectivity of the boundary of the room. The <Polygon> instance representing a wall of the room that is an interior wall of the building has a <Geometry Face> instance associated to the <Polyhedron> instance through a <Face Direction> link object with front field = SE_FALSE.
A second <Polyhedron> instance representing a room on the other side of the same wall has a <Geometry Volume> instance associated to the same <Polygon> instance, but through a <Face Direction> link object with front = SE_TRUE.
In such a case the <Feature Face> instance appears twice in the collection of <Feature Face> components of the <Areal Feature> instance, once with the front field of the corresponding <Face Direction> link object set to SE_TRUE, and once with the front field of the corresponding <Face Direction> link object set to SE_FALSE.
In such a case the <Feature Face> instance appears once in the collection of <Feature Face> components of each of the two <Areal Feature> instances. For the <Areal Feature> instance corresponding to the front side of the face, the corresponding <Face Direction> link object has front set to SE_TRUE, while for the <Areal Feature> instance corresponding to the back side of the <Feature Face> instance, the <Face Direction> link object has front set to SE_FALSE.
If the value of the front field is SE_TRUE, the front face is associated with the given DRM object. Otherwise, it is the back face that is associated.
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