[postgis-users] ST_intersection converting st_linestring to st_multilinestring

Hugues François hugues.francois at irstea.fr
Wed Apr 12 12:29:55 PDT 2017


I think this is consistent to have a homogeneous geometry type since a linestring could intersect numerous polygons of a multipolygon. Did you tried the st_dump function on the resulting st_multilinestring ? 

(st_dump(multilinestring)).geom will return the different linestrings which compose the multi ones. 



De: "Hemant Bist" <hemantbist at gmail.com> 
À: "PostGIS Users Discussion" <postgis-users at lists.osgeo.org> 
Envoyé: Mercredi 12 Avril 2017 21:14:07 
Objet: [postgis-users] ST_intersection converting st_linestring to st_multilinestring 

I am trying to figure out if this is expected behavior, or I am running into some bug / misinterpreting results. 

I am doing st_intersection(st_linestring, st_multipolygon). This is latlon geometry(EPSG:4326). The multiploygon is actually a polygon (with only one polygon in multipolygon) 

When I view the results as KML the intersection look correct, but the problem I see is that the resulting linestrings are unnecessarily getting split in mulilinestring. 

1) Every linestring is converted to multilinestring resulting in large nubmer of st_numgeomtries for each multilinestring. (even when the linestring is contained in polygon) 
2) ST_LineMerge on the resulting multilinestring does help but its far from "perfect" e.g. if the linestring is contained in polygon I expected the result to be one linesting, but the result of st_numgeometries() is more than 50. 

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