Constraint Points Constraint Linear Features

23 Copyright © 2016 Open Geospatial Consortium Note that the rendering outcome into the Elevation dataset may vary depending on the rendering order of overlapping points, lines or polygons polygons. In order to achieve deterministic outcome by all types of client-devices, client-devices are required to sort features by their layer priority number LPN before using them to constrain the terrain elevation dataset. The rendering of a point, a linear or polygon polygon features into the Uniformly Sampled Terrain Elevation dataset is performed into the same LOD as the LOD in which the vector feature appeared.

6.6.1 Constraint Points

This section describes the required client-device behavior for PointZ and MultiPointZ features used as terrain elevation constraint points AHGT is true into a uniformly sampled terrain elevation dataset. The application of a constraint point P is very much like drawing an anti-aliased rectangle centered on P into the uniform terrain elevation grid. The rectangle shape is defined by feature attributes BBL, BBH and AO1. Consider a terrain grid element A in the immediate vicinity of a constraint point P. After applying the constraint P to terrain grid element A, the new elevation � is: � = � ∗ ��� + � ∗ ���� where… � is elevation of grid element A � is elevation of constraint point P ��� is the percentage overlap of constraint point P onto grid element A ���� = 1 − ��� 24 Copyright © 2016 Open Geospatial Consortium Figure 6-7: Application of Constraint Point - Uniformly-Sampled Terrain

6.6.2 Constraint Linear Features

This section describes the required client-device behavior for PolyLineZ features used as terrain elevation constraint linear feature AHGT is true into a uniformly sampled terrain elevation dataset. First, the PolyLineZ feature is broken into a series of constraint lines. The application of each constraint line L is very much like drawing an anti-aliased line centered on L into the uniform terrain elevation grid. The width of the line is defined by feature attribute WGP. Consider a terrain grid element A in the immediate vicinity of a constraint line L, defined by vertices V1 and V2. After applying the constraint line L to terrain grid element A, the new elevation � is: � = � ∗ ��� + � ∗ ���� where… � is elevation of grid element A � is interpolated elevation of constraint line L at grid element A A B C D Ain A BB BB P 25 Copyright © 2016 Open Geospatial Consortium ��� is the percentage overlap of constraint line L onto grid element A ���� = 1 − ��� Figure 6-8: Application of Constraint Line - Uniformly-Sampled Terrain

6.6.3 Constraint Polygons