Changes between Version 3 and Version 4 of UserWikiVariableBuffer

Timestamp:

Nov 25, 2019, 11:06:17 AM (4 years ago)

Author:

mdavis

Comment:

—

UserWikiVariableBuffer

@@ -4 +4 @@
 
 The function below generates variable-distance buffers.
+
 It operates by creating the union of a series of segment buffers .
 Each segment buffer is the convex hull of the buffers of the segment start and end points, 
 with the buffer distance computed proportionally to the fractional distance along the line.
 
-**Note: currently only the end distance can be given.  The start distance is fixed to be (approximately) 0.**
-
 === Example ===
 {{{
-SELECT ST_VariableBufferFromLine( 'LINESTRING( 0 0, 100 0)' , 10 );
+SELECT ST_VariableBufferFromLine( 'LINESTRING( 0 0, 100 0)' , 1, 10 );
 }}}
 
@@ -19 +18 @@
 CREATE OR REPLACE FUNCTION ST_VariableBufferFromLine(
     geom GEOMETRY, 
+    start_dist NUMERIC,
     end_dist NUMERIC
 )
@@ -31 +31 @@
         (SELECT (dump).path[1], 
             ST_Buffer( (dump).geom, 
-                GREATEST(end_dist * ST_LineLocatePoint(geom, (dump).geom), 0.001)) AS geom 
+                start_dist + (end_dist - start_dist) * ST_LineLocatePoint(geom, (dump).geom) 
+                ) AS geom 
         FROM step1),
     step3 AS