Changes between Initial Version and Version 1 of UserWikiVariableBuffer

Timestamp:

Nov 25, 2019, 10:04:50 AM (4 years ago)

Author:

mdavis

Comment:

—

UserWikiVariableBuffer

@@ +1 @@
+= Variable-Distance Buffer =
+
+Source: [https://gis.stackexchange.com/questions/340968/varying-size-buffer-along-a-line-with-postgis GIS StackExchange: Varying size buffer along a line with PostGIS] 
+
+Using the function given below, variable-distance buffers can be generated.
+
+=== Example ===
+{{{
+SELECT gid, ST_VariableBufferFromLine(geom,10.0) AS geom FROM mylines
+}}}
+
+=== Code ===
+{{{
+CREATE OR REPLACE FUNCTION ST_VariableBufferFromLine(
+    geom GEOMETRY, 
+    Length_BufferSize_Ratio NUMERIC
+)
+
+RETURNS GEOMETRY AS
+
+$BODY$
+
+WITH 
+    step1 AS 
+        (SELECT ST_DumpPoints(geom) AS dump, 
+        ST_Length(geom) AS len, 
+        geom),
+    step2 AS
+        (SELECT (dump).path[1], 
+        ST_Buffer((dump).geom, GREATEST(ST_LineLocatePoint(geom, (dump).geom)*len/Length_BufferSize_Ratio,0.001)) AS geom 
+         FROM step1),
+    step3 AS
+        (SELECT 
+        ST_ConvexHull(ST_Union(geom, LEAD(geom) OVER(ORDER BY path))) AS geom 
+        FROM step2)
+SELECT ST_Union(geom) AS geom FROM step3
+
+$BODY$
+
+LANGUAGE SQL;
+}}}