sql

lib/sql/scripts-available/CDB_XYZ.sql

@@ -0,0 +1,62 @@
+-- {
+-- Return pixel resolution at the given zoom level
+-- }{
+CREATE OR REPLACE FUNCTION @extschema@.CDB_XYZ_Resolution(z INTEGER)
+RETURNS FLOAT8
+AS $$
+  -- circumference divided by 256 is z0 resolution, then divide by 2^z
+  SELECT 6378137.0*2.0*pi() / 256.0 / power(2.0, z);
+$$ LANGUAGE SQL IMMUTABLE PARALLEL SAFE STRICT;
+-- }
+
+-- {
+-- Returns a polygon representing the bounding box of a given XYZ tile
+--
+-- SRID of the returned polygon is forceably 3857
+--
+-- }{
+CREATE OR REPLACE FUNCTION @extschema@.CDB_XYZ_Extent(x INTEGER, y INTEGER, z INTEGER)
+RETURNS GEOMETRY
+AS $$
+DECLARE
+  origin_shift FLOAT8;
+  initial_resolution FLOAT8;
+  tile_geo_size FLOAT8;
+  pixres FLOAT8;
+  xmin FLOAT8;
+  ymin FLOAT8;
+  xmax FLOAT8;
+  ymax FLOAT8;
+  earth_circumference FLOAT8;
+  tile_size INTEGER;
+BEGIN
+
+  -- Size of each tile in pixels (1:1 aspect ratio)
+  tile_size := 256;
+
+  initial_resolution := @extschema@.CDB_XYZ_Resolution(0);
+  --RAISE DEBUG 'Initial resolution: %', initial_resolution;
+
+  origin_shift := (initial_resolution * tile_size) / 2.0;
+  -- RAISE DEBUG 'Origin shift  (after): %', origin_shift;
+
+  pixres := initial_resolution / (power(2,z));
+  --RAISE DEBUG 'Pixel resolution: %', pixres;
+
+  tile_geo_size = tile_size * pixres;
+  --RAISE DEBUG 'Tile_geo_size: %', tile_geo_size;
+
+  xmin := -origin_shift + x*tile_geo_size;
+  xmax := -origin_shift + (x+1)*tile_geo_size;
+  --RAISE DEBUG 'xmin: %', xmin;
+  --RAISE DEBUG 'xmax: %', xmax;
+
+  ymin := origin_shift - y*tile_geo_size;
+  ymax := origin_shift - (y+1)*tile_geo_size;
+  --RAISE DEBUG 'ymin: %', ymin;
+  --RAISE DEBUG 'ymax: %', ymax;
+  
+  RETURN @postgisschema@.ST_MakeEnvelope(xmin, ymin, xmax, ymax, 3857);
+END
+$$ LANGUAGE 'plpgsql' IMMUTABLE STRICT PARALLEL SAFE;
+-- }