[postgis-users] Question on GEOMETRY type

孙琦 qsundw at gmail.com
Wed May 19 19:19:23 PDT 2010

Thank you all for the reply. I found several of answers have been thrown
out, but I just see them from the summary of yesterday's topic, not get
those replies directly. Actually, I didn't get any mail from the list yet,
perhaps, it's due that I just joined the list yesterday. So if you reply in
this thread, please copy qsundw at gmail.com.

The provided methods (SE_IsMeasured() and SE_Is3D() zmflag()) do work on
getting the dimension of a given geometry value. Probably, I didn't express
myself well. What I really want to know is if there is some meta data to
judge the type of the geometry column, not from sampling the data. For
example, the POINTM can be used to know the column has 3dm points. But
unfortunately, the corresponding GEOMETRYM type isn't provided for the
mixed-type column in Postgis1.5.  Can you tell me if there is some method to
workaround the issue?


On Wed, May 19, 2010 at 10:23 PM, 孙琦 <qsundw at gmail.com> wrote:

> Can anyone throw some lights on the question?
> Thanks,
> Cheney
> On Wed, May 19, 2010 at 6:27 PM, 孙琦 <qsundw at gmail.com> 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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