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

[Edward Bridges]

Hmmm.

Ok so when I added the column, the paramters I passed where:
SELECT AddGeometryColumn('', 'point', 'coordinate', 600613, 'POINT', 0);

where 0 was the result of st_dimension, so should it be:
SELECT AddGeometryColumn('', 'point', 'coordinate', 600613, 'POINT', 2);

for a point?

Should it also be 2 for polygons -- given that these are the dimensions 
of the same coordinate space?

Thanks!
Ed

pcreso at pcreso.com wrote:
> The number of dimensions in this case is teh number of coordinates, if your point has 2 (X & Y) then it is 2, not 0. If it is an XYZ point, then ndim = 3.
>
> ndim does not reere to points @ 0, lines @ 1 & polygons @ 2, but the dimensions of the coordinate space.
>
> Cheers,
>
>   Brent Wood
>
>
> --- On Mon, 7/28/08, Edward Bridges <postgis at eqbridges.com> wrote:
>
>   
>> From: Edward Bridges <postgis at eqbridges.com>
>> Subject: [postgis-users] ndim vs. st_dimension and enforce_dims_coordinate constraint
>> To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
>> Date: Monday, July 28, 2008, 7:30 AM
>> Hello,
>>
>> 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)'));
>>  st_dimension
>> --------------
>>             0
>> (1 row)
>>
>> rover=# select * from ndims( ST_GeomFromText('POINT(1
>> 1)'));
>>  ndims
>> -------
>>      2
>> (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?
>>
>> Thanks,
>> Ed
>>
>>
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