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changeset 2956:974122125a76

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Let it be an error if closest points of DISMARs on axis are equal This might be the case e.g. if both distance marks are very far away from the available axis geometries. Instead of returning a point in such a case, which would likely be an unexpected result, raise an exception by means of STRICT.
author Tom Gottfried <tom@intevation.de>
date Mon, 08 Apr 2019 14:53:09 +0200
parents e9ff3e8d3c46
children b74ebeb2bdc8
files schema/isrs_functions.sql
diffstat 1 files changed, 8 insertions(+), 3 deletions(-) [+]
line wrap: on
line diff
--- a/schema/isrs_functions.sql	Mon Apr 08 11:58:00 2019 +0200
+++ b/schema/isrs_functions.sql	Mon Apr 08 14:53:09 2019 +0200
@@ -65,13 +65,18 @@
                 FROM waterway.waterway_axis, utm_zone),
         -- In order to guarantee the following ST_Covers to work,
         -- snap distance mark coordinates to axis
-        points AS (
+        points0 AS (
             SELECT ST_ClosestPoint(
                     wtwaxs,
                     ST_Transform(geom, z)) AS geom
                 FROM ST_Dump(ISRSrange_points(stretch)), utm_zone, (
                     SELECT ST_Collect(wtwaxs) AS wtwaxs
                         FROM axis) AS ax),
+        -- Ensure two distinct points on axis have been found
+        points AS (
+            SELECT geom
+                FROM points0
+                WHERE 2 = (SELECT count(DISTINCT geom) FROM points0)),
         axis_snapped AS (
             -- Iteratively connect non-contiguous axis chunks
             -- to find the contiguous axis on which given distance marks lie
@@ -119,8 +124,8 @@
         -- end of the resulting linestring, that significantly differ from
         -- the direction of the input linestring due to finite precision
         -- of the calculation. The generated small segment of the
-        -- resulting line leads to unexpected results of the buffer with
-        -- endcap=flat in the CTE below.
+        -- resulting line would lead e.g. to unexpected results in an area
+        -- generated by ISRSrange_area().
         SELECT ST_SimplifyPreserveTopology(ST_LineSubstring(
                     axis_segment.line, min(fractions.f), max(fractions.f)),
                 0.0001) AS line