I want to extrude a polygon shape in postgis to create a pseudo 3D effect. To this end I have written a crude function to achieve it. This is very much test code and it creates a new Y vertice for each point on the polygon and then closes it by returning to the original point:-
CREATE OR REPLACE FUNCTION public.extrude_polygon(wkb_geometry_param geometry, height integer, simplify boolean DEFAULT false) RETURNS geometry AS $BODY$DECLAREf int;ret_geom geometry;wkb_geometry geometry;BEGIN--convert polygon to linestringIF ST_GeometryType(wkb_geometry_param) != 'ST_Polygon' THEN RETURN NULL;END IF;IF simplify THEN wkb_geometry = ST_Simplify(ST_Transform(ST_Exteriorring(wkb_geometry_param), 27700), 0.5);ELSEwkb_geometry = ST_Transform(ST_Exteriorring(wkb_geometry_param), 27700);END IF;--initialise output geometryret_geom =ST_MakeLine(ST_PointN(wkb_geometry,1),ST_PointN(wkb_geometry,1));--Move first point to upSELECT ST_AddPoint(ret_geom, ST_MakePoint(ST_X(ST_PointN(wkb_geometry, 1)), ST_Y(ST_PointN(wkb_geometry, 1)) + height)) into ret_geom;FOR f IN 1..ST_NPoints(wkb_geometry) LOOP IF f < ST_NPoints(wkb_geometry) THEN --across to next high point SELECT ST_AddPoint(ret_geom, ST_MakePoint(ST_X(ST_PointN(wkb_geometry, f + 1)), ST_Y(ST_PointN(wkb_geometry, f + 1)) + height) ) into ret_geom; --down to next point SELECT ST_AddPoint(ret_geom, ST_PointN(wkb_geometry,f + 1)) into ret_geom; --back to last point SELECT ST_AddPoint(ret_geom, ST_PointN(wkb_geometry,f)) into ret_geom; --back then up again SELECT ST_AddPoint(ret_geom, ST_PointN(wkb_geometry,f + 1)) into ret_geom; SELECT ST_AddPoint(ret_geom, ST_MakePoint(ST_X(ST_PointN(wkb_geometry, f + 1)), ST_Y(ST_PointN(wkb_geometry, f + 1)) + height) ) into ret_geom;ELSE --across to first high point SELECT ST_AddPoint(ret_geom, ST_MakePoint(ST_X(ST_PointN(wkb_geometry, 1)), ST_Y(ST_PointN(wkb_geometry, 1)) + height) ) into ret_geom; SELECT ST_AddPoint(ret_geom, ST_PointN(wkb_geometry,1)) into ret_geom;END IF;END LOOP;RETURN ST_Buffer(ST_Buffer(ST_MakePolygon(ret_geom),10), -10);END;$BODY$ LANGUAGE plpgsqlIt works with simple polygons but has problems with interior rings, but the main issue is that it is really slow. I need to output the resultant shape as a polygon that can be shaded and rendered in mapserver. Hence the buffer operations at the end which is the only way I know of reducing the shape to it's outline.
The end result will be an extruded shape representing the original polygon. I can then offset the original polygon by the same extrusion distance and place it on top to make the roof.
I considered using the ST_Extrude function in postgis-2.1.1 BUT this creates a ST_PolyhedralSurface type and I am not able to render it in mapserver. As far as I can tell there is no way to create an outline of this either as ST_Buffer does not work with ST_polyhedralsurfaces.
So, my question is, can my function be improved? Or is there a better approach. The output needs to look as per the diagram which I created by placing the offset polygon onto my extruded shape.
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CREATE OR REPLACE FUNCTION public.extrude_polygon(wkb_geometry_param geometry, height integer, simplify boolean DEFAULT false) RETURNS geometry AS $BODY$DECLAREf int;ret_geom geometry;wkb_geometry geometry;BEGIN--convert polygon to linestringIF ST_GeometryType(wkb_geometry_param) != 'ST_Polygon' THEN RETURN NULL;END IF;IF simplify THEN wkb_geometry = ST_Simplify(ST_Transform(ST_Exteriorring(wkb_geometry_param), 27700), 0.5);ELSEwkb_geometry = ST_Transform(ST_Exteriorring(wkb_geometry_param), 27700);END IF;--initialise output geometryret_geom =ST_MakeLine(ST_PointN(wkb_geometry,1),ST_PointN(wkb_geometry,1));--Move first point to upSELECT ST_AddPoint(ret_geom, ST_MakePoint(ST_X(ST_PointN(wkb_geometry, 1)), ST_Y(ST_PointN(wkb_geometry, 1)) + height)) into ret_geom;FOR f IN 1..ST_NPoints(wkb_geometry) LOOP IF f < ST_NPoints(wkb_geometry) THEN --across to next high point SELECT ST_AddPoint(ret_geom, ST_MakePoint(ST_X(ST_PointN(wkb_geometry, f + 1)), ST_Y(ST_PointN(wkb_geometry, f + 1)) + height) ) into ret_geom; --down to next point SELECT ST_AddPoint(ret_geom, ST_PointN(wkb_geometry,f + 1)) into ret_geom; --back to last point SELECT ST_AddPoint(ret_geom, ST_PointN(wkb_geometry,f)) into ret_geom; --back then up again SELECT ST_AddPoint(ret_geom, ST_PointN(wkb_geometry,f + 1)) into ret_geom; SELECT ST_AddPoint(ret_geom, ST_MakePoint(ST_X(ST_PointN(wkb_geometry, f + 1)), ST_Y(ST_PointN(wkb_geometry, f + 1)) + height) ) into ret_geom;ELSE --across to first high point SELECT ST_AddPoint(ret_geom, ST_MakePoint(ST_X(ST_PointN(wkb_geometry, 1)), ST_Y(ST_PointN(wkb_geometry, 1)) + height) ) into ret_geom; SELECT ST_AddPoint(ret_geom, ST_PointN(wkb_geometry,1)) into ret_geom;END IF;END LOOP;RETURN ST_Buffer(ST_Buffer(ST_MakePolygon(ret_geom),10), -10);END;$BODY$ LANGUAGE plpgsqlIt works with simple polygons but has problems with interior rings, but the main issue is that it is really slow. I need to output the resultant shape as a polygon that can be shaded and rendered in mapserver. Hence the buffer operations at the end which is the only way I know of reducing the shape to it's outline.
The end result will be an extruded shape representing the original polygon. I can then offset the original polygon by the same extrusion distance and place it on top to make the roof.
I considered using the ST_Extrude function in postgis-2.1.1 BUT this creates a ST_PolyhedralSurface type and I am not able to render it in mapserver. As far as I can tell there is no way to create an outline of this either as ST_Buffer does not work with ST_polyhedralsurfaces.
So, my question is, can my function be improved? Or is there a better approach. The output needs to look as per the diagram which I created by placing the offset polygon onto my extruded shape.
أكثر...