Name
CG_GenerateSkillionRoof — Generate a skillion (single-slope) roof from a footprint polygon.
Synopsis
geometry CG_GenerateSkillionRoof(geometry geom, float8 height, float8 slope_angle, integer primary_edge_index);
Description
Generate a skillion (single-slope, shed-style) roof as a 3D
PolyhedralSurface Z from a 2D footprint polygon.
The entire roof surface slopes in one direction.
height sets the maximum ridge height (default 3.0),
slope_angle sets the pitch in degrees (default
30.0), and primary_edge_index selects which
polygon edge defines the high side (0-based, default 0).
When the combination of height and
slope_angle would cause a side wall to vanish
(the slope reaches the far edge before the full height is achieved),
that face is omitted from the result. This means the number of
output patches can vary depending on the parameters — a lower
height relative to the footprint depth produces more faces than
a taller, steeper configuration.
Availability: 3.7.0 - requires SFCGAL >= 2.3.0.
This method needs SFCGAL backend.
This function supports Polyhedral surfaces.
Examples
Height 2.0 produces 6 faces (all walls present); height 4.0 produces 5 faces (one side wall is filtered out because the slope reaches the far edge before the full height).
-- height 2.0 → 6 patches
SELECT ST_NumPatches(
CG_GenerateSkillionRoof(
'POLYGON((0 0,5 0,5 4,0 4,0 0))',
2.0));
-- 6
-- height 4.0 → 5 patches (one face filtered)
SELECT ST_NumPatches(
CG_GenerateSkillionRoof(
'POLYGON((0 0,5 0,5 4,0 4,0 0))',
4.0));
-- 5
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