[postgis-users] ndim vs. st_dimension and enforce_dims_coordinate constraint

Edward Bridges postgis at eqbridges.com
Sun Jul 27 12:30:36 PDT 2008


I have a table with a geometry column which the AddGeometryColumn stored 
procedure has created a check constraint like so:
Check constraints:
    "enforce_dims_coordinate" CHECK (ndims(coordinate) = 0)

So, this uses the internal function "ndims" to check the dimensionality 
of the input coordinate.

However, I'm getting a discrepancy when inserting a point into this 
column since ndims and st_dimensions are returning conflicting 
(apparently) values:

rover=# select * from st_dimension( ST_GeomFromText('POINT(1 1)'));
(1 row)

rover=# select * from ndims( ST_GeomFromText('POINT(1 1)'));
(1 row)

It seems that the ndims function returns only 2, 3, or 4; can someone 
please explain why the differing values and how to insert data into a 
point-type geometry column (seems to work fine with polygon) without 
crossing the check constraint?


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