Before two days i had problem with conversion of MultiLineString to
LineString
http://postgis.17.x6.nabble.com/st-union-and-st-linemerge-returns-multilinestring-td5007358.html
<http://postgis.17.x6.nabble.com/st-union-and-st-linemerge-returns-multilinestring-td5007358.html>
. Later I found out that this problem appears with more spatial functions.
For eg. result I get from ST_LineMerge with geometry from database is
different then result of ST_LineMerge with geometry read as ST_GeomFromText
(they have same points, and are in same reference system).
Also I made small script that test geometries:
DO $$
DECLARE
v_boundaryUnion geometry;
v_unitBoundary geometry;
BEGIN
SELECT ST_Union(b."Geometry")
INTO v_boundaryUnion
FROM myschema."Boundary" a
INNER JOIN myschema."BoundaryGeom" b
ON b."BoundaryId" = a."BoundaryId"
WHERE a."UnitId" = 1;
RAISE NOTICE 'BOUNDARY UNION: %', ST_AsText(v_boundaryUnion);
SELECT ST_Boundary("Geometry")
INTO v_unitBoundary
FROM myschema."UnitGeom"
WHERE "UnitId" = 1;
RAISE NOTICE 'UNION BOUNDARY: %', ST_AsText(v_unitBoundary);
IF ST_Equals(v_boundaryUnion, v_unitBoundary) THEN
RAISE NOTICE 'EQUALS';
ELSE
RAISE NOTICE 'DIFFERENCE';
END IF;
v_boundaryUnion := ST_GeomFromWKB(ST_AsBinary(v_boundaryUnion), 3765);
RAISE NOTICE 'UNION FROM WKB: %', ST_AsText(v_boundaryUnion);
IF ST_Equals(v_boundaryUnion, v_unitBoundary) THEN
RAISE NOTICE 'EQUALS';
ELSE
RAISE NOTICE 'DIFFERENCE';
END IF;
v_boundaryUnion := ST_GeomFromText(ST_AsText(v_boundaryUnion), 3765);
RAISE NOTICE 'UNION FROM WKT: %', ST_AsText(v_boundaryUnion);
IF ST_Equals(v_boundaryUnion, v_unitBoundary) THEN
RAISE NOTICE 'EQUALS';
ELSE
RAISE NOTICE 'DIFFERENCE';
END IF;
END $$;
result of this script is:
EQUALS
EQUALS
DIFFERENCE
Later on if I make operations with geometry from wkt i get expected results
(eq. ST_Difference), same as in JTS, and with original geometry I have some
really strange behaviour.
I don't have any idea why this thing happens. Metadata seems to be OK also:
f_table_name, f_geometry_column, coord_dimension, srid, type
"UnitGeom";"Geometry";2;3765;"GEOMETRY"
"BoundaryGeom";"Geometry";2;3765;"LINESTRING"
Any idea what could be wrong?
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