Changes between Initial Version and Version 1 of UserWikiBufferMeters

Timestamp:

Apr 14, 2020, 3:14:16 PM (4 years ago)

Author:

mdavis

Comment:

—

UserWikiBufferMeters

@@ +1 @@
+= Buffer geodetic geometry using meters =
+
+Constructs a buffer of a geodetic (lat/long) geometry using a distance in meters.
+Uses a transformation to a suitable UTM zone, so only works for geometries with extent less than a few degrees of longitude. 
+
+Note: not sure if this is better than simply casting to `geography`?
+
+Sources: 
+* https://blog.datapolitan.com/2013/11/22/st_buffer_meters/
+* [https://gist.github.com/datapolitan/9ef9489eac5686ca3b34 st_buffer_meters.sql]
+* [https://gist.github.com/datapolitan/ffdeb086b3c4531d9f4e utmzone.sql]
+
+{{{
+/* Function: ST_Buffer_Meters(geometry, double precision)
+DROP FUNCTION ST_Buffer_Meters(geometry, double precision);
+Usage: SELECT ST_Buffer_Meters(the_geom, num_meters) FROM sometable; */
+ 
+ 
+CREATE OR REPLACE FUNCTION ST_Buffer_Meters(geometry, double precision)
+RETURNS geometry AS
+$BODY$
+DECLARE
+orig_srid int;
+utm_srid int;
+ 
+BEGIN
+orig_srid:= ST_SRID($1);
+utm_srid:= utmzone(ST_Centroid($1));
+ 
+RETURN ST_transform(ST_Buffer(ST_transform($1, utm_srid), $2), orig_srid);
+END;
+$BODY$ LANGUAGE 'plpgsql' IMMUTABLE
+COST 100;
+
+/* Function: utmzone(geometry)
+DROP FUNCTION utmzone(geometry);
+Usage: SELECT ST_Transform(the_geom, utmzone(ST_Centroid(the_geom))) FROM sometable; */
+ 
+CREATE OR REPLACE FUNCTION utmzone(geometry)
+RETURNS integer AS
+$BODY$
+DECLARE
+geomgeog geometry;
+zone int;
+pref int;
+ 
+BEGIN
+geomgeog:= ST_Transform($1,4326);
+ 
+IF (ST_Y(geomgeog))>0 THEN
+pref:=32600;
+ELSE
+pref:=32700;
+END IF;
+ 
+zone:=floor((ST_X(geomgeog)+180)/6)+1;
+ 
+RETURN zone+pref;
+END;
+$BODY$ LANGUAGE 'plpgsql' IMMUTABLE
+COST 100;
+}}}
+