3

I am not able to st_split a line with a point on it.

I have a linestring and a point in epsg:3857 coordinate system. Their distance is 0:

select st_distance(
    st_geomfromtext('LineString (2121053.78109818324446678 6023680.98843276314437389, 2121127.97553879721090198 6023651.31408391986042261)',3857),
    st_geomfromtext('Point (2121091.12965324986726046 6023666.05073604825884104)',3857)
);
 st_distance
-------------
           0
(1 row)

The split returns the original line:

select st_astext(st_split(
    st_geomfromtext('LineString (2121053.78109818324446678 6023680.98843276314437389, 2121127.97553879721090198 6023651.31408391986042261)',3857),
    st_geomfromtext('Point (2121091.12965324986726046 6023666.05073604825884104)',3857)
    ));
                                             st_astext                            
----------------------------------------------------------------------------------------------------
 GEOMETRYCOLLECTION(LINESTRING(2121053.78109818 6023680.98843276,2121127.9755388 6023651.31408392))
(1 row)

The same result if I try to snap the point on the line with st_closestpoint:

select st_Astext(st_split(
    st_geomfromtext('LineString (2121053.78109818324446678 6023680.98843276314437389, 2121127.97553879721090198 6023651.31408391986042261)',3857),
    st_closestpoint(
        st_geomfromtext('LineString (2121053.78109818324446678 6023680.98843276314437389, 2121127.97553879721090198 6023651.31408391986042261)',3857),
        st_geomfromtext('Point (2121091.12965324986726046 6023666.05073604825884104)',3857)
    )));

                                         st_astext                            
----------------------------------------------------------------------------------------------------
 GEOMETRYCOLLECTION(LINESTRING(2121053.78109818 6023680.98843276,2121127.9755388 6023651.31408392))
(1 row)

Postgis version:

    postgis_full_version
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 POSTGIS="2.3.2 r15302" GEOS="3.5.0-CAPI-1.9.0 r4084" PROJ="Rel. 4.9.2, 08 September 2015" GDAL="GDAL 1.11.3, released 2015/09/16" LIBXML="2.9.3" LIBJSON="0.11.99" RASTER
(1 row)

I'm on Debian 16.04 xenial and postgresql-9.6-postgis-2.3 from pgdg repository.

This might be related (this is why I upgraded from postgis 2.2.1):

http://trac.osgeo.org/postgis/ticket/3422

Improve this question
2
  • 17 places of precision with a unit of meters brings you to a distance of hundredths of femtometers (roughy one twentieth of proton radius). I doubt your data is that precise.
    – Vince
    Mar 21, 2017 at 23:37
  • Yes, my data is not that precise. However the points I try to split the line with are calculated by postgis using st_intersection. Anyhow the rounding to any precision should solve this and seemingly it does not.
    – csandor
    Mar 22, 2017 at 14:04

1 Answer 1

Reset to default
2

The ST_Split http://postgis.net/docs/ST_Split.html document page suggest to use ST_Snap http://www.postgis.org/docs/ST_Snap.html for better robustness. It seems to be a good suggestion:

select st_astext(st_split(
    st_snap(
    st_geomfromtext('LineString (2121053.78109818324446678 6023680.98843276314437389, 2121127.97553879721090198 6023651.31408391986042261)',3857),
    st_geomfromtext('Point (2121091.12965324986726046 6023666.05073604825884104)',3857),0.001),
    st_geomfromtext('Point (2121091.12965324986726046 6023666.05073604825884104)',3857)
    ));



"GEOMETRYCOLLECTION(LINESTRING(2121053.78109818
6023680.98843276,2121091.12965325 6023666.05073605),LINESTRING(2121091.12965325 6023666.05073605,2121127.9755388 6023651.31408392))"
Improve this answer
1
  • Thanks for this. I actually have tried st_snap before. Your example snaps the line to the point then splits it. What I tried is to st_snap the point to the line which does not work as it tried to snap to a line vertex (with great tolerance given) instead of snapping to the interior line points. This latter is needed of course. That is why I stick with st_closestpoint.
    – csandor
    Mar 22, 2017 at 7:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.