= 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;
}}}