maya.public

Parameters

Name	Type	Mode
param_inputgeom	USER-DEFINED	IN

Definition

DECLARE     
	vexhull GEOMETRY;
	var_resultgeom geometry;
	var_inputgeom geometry;
	vexring GEOMETRY;
	cavering GEOMETRY;
	cavept geometry[];
	seglength double precision;
	var_tempgeom geometry;
	scale_factor integer := 1;
	i integer;
	
	BEGIN

-- First compute the ConvexHull of the geometry
		vexhull := ST_ConvexHull(param_inputgeom);
		var_inputgeom := param_inputgeom;
		--A point really has no concave hull
		IF ST_GeometryType(vexhull) = 'ST_Point' OR ST_GeometryType(vexHull) = 'ST_LineString' THEN
			RETURN vexhull;
		END IF;

-- convert the hull perimeter to a linestring so we can manipulate individual points
		vexring := CASE WHEN ST_GeometryType(vexhull) = 'ST_LineString' THEN vexhull ELSE ST_ExteriorRing(vexhull) END;
		IF abs(ST_X(ST_PointN(vexring,1))) < 1 THEN --scale the geometry to prevent stupid precision errors - not sure it works so make low for now
			scale_factor := 100;
			vexring := ST_Scale(vexring, scale_factor,scale_factor);
			var_inputgeom := ST_Scale(var_inputgeom, scale_factor, scale_factor);
			--RAISE NOTICE 'Scaling';
		END IF;
		seglength := ST_Length(vexring)/least(ST_NPoints(vexring)*2,1000) ;

vexring := ST_Segmentize(vexring, seglength);
		-- find the point on the original geom that is closest to each point of the convex hull and make a new linestring out of it.
		cavering := ST_Collect(
			ARRAY(

SELECT 
					ST_ClosestPoint(var_inputgeom, pt ) As the_geom
					FROM (
						SELECT  ST_PointN(vexring, n ) As pt, n
							FROM 
							generate_series(1, ST_NPoints(vexring) ) As n
						) As pt
				
				)
			)
		;

var_resultgeom := ST_MakeLine(geom) 
			FROM ST_Dump(cavering) As foo;

IF ST_IsSimple(var_resultgeom) THEN
			var_resultgeom := ST_MakePolygon(var_resultgeom);
			--RAISE NOTICE 'is Simple: %', var_resultgeom;
		ELSE 
			--RAISE NOTICE 'is not Simple: %', var_resultgeom;
			var_resultgeom := ST_ConvexHull(var_resultgeom);
		END IF;
		
		IF scale_factor > 1 THEN -- scale the result back
			var_resultgeom := ST_Scale(var_resultgeom, 1/scale_factor, 1/scale_factor);
		END IF;
		RETURN var_resultgeom;
	
	END;

_st_concavehull(geometry)

Parameters

Definition