NewEdgesSplit does not snap to edge

[tomass]

ST_NewEdgesSplit is unable to split an edge with an error "SQL/MM Spatial exception - point not on edge".

Script to reproduce an error is attached. It drops and then creates a new topology to make sure we have a clean environment. Inserts new edge. Then a call to ST_Distance shows that a distance to the node which will be used as a split point for an edge is "9.946529457016767e-10" away. Then a call to ST_NewEdgesSplit fails with an error:

ERROR:  SQL/MM Spatial exception - point not on edge

NOTE: If I do a workaround and modify an edge adding a new point to the edges geometry - then call to ST_NewEdgesSplit is successful.

Tested on Centos8.1, PostgreSQL 12.1, Postgis3.0.1 (topology 3.0.1), GEOS3.7.2.

[strk]

What you describe is not a bug but expected behavior. ST_NewEdgeSplit and ST_ModEdgeSplit and all other ISO-SQLMM defined topology functions (those starting with ST_) do not consider the topology "precision" (no such concept in ISO-SQLMM).

I think there's an enhancement ticket in this trac instance about adding support for "tolerance" in these functions.

[tomass]

Thank you. Do I understand correctly, that in PostGIS/Topology 3.0.1 you can only split an existing edge at the vertex which already exists in edges geometry?

I am using a workaround of calling ST_ChangeEdgeGeom and adding a new vertex at the point where I want to split an edge prior to calling ST_NewEdgeSplit/ST_ModEdgeSplit. Is this the correct way to split an edge at any point, at least for now?

[strk]

Yes, that's a possible way. The topology population functions do this, if the splitting point is not found on the edge by ST_Contains