[postgis-users] Question on GEOMETRY type

Charles Galpin cgalpin at lhsw.com
Wed May 19 05:55:11 PDT 2010

I'm no expert but the third dimension appears to be supported by most types and the docs are pretty good about showing this. Take a point for example:


You can add a third argument to add the z coordinate.  Use ST_Y(point) to access the third dimension.

Oh, and when you add your geometry column, be sure to specify a dimension of 3. 



On May 19, 2010, at 6:27 AM, 孙琦 wrote:

> Hi experts,
> Do we have a way to resolve the third dimensionality of GEOMETRY data? As known, those single types(POINT, LINESTRING, POLYGON....) all have the corresponding XYM versions with suffix M. Thus, if we have three-dimensionality feature, we can discriminate its third dimensionality as Z or M by the returned geometry type. However, if the mixed-typed (GEOMETRY) is used, it seems that it's hard to resolve the 3rd dimensionality. By the Postgis 1.5.1 manual, no GEOMETRYM type is provided to fix the issue. So can someone tell me if there is another way to do the work?
> Thanks,
> Cheney
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