[postgis-users] Question on GEOMETRY type

[Charles Galpin]

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:

http://postgis.refractions.net/docs/ST_MakePoint.html

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. 

http://postgis.refractions.net/docs/AddGeometryColumn.html

hth
charles

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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