[postgis-users] Bug dropping the Z coordinate?

[Paul Ramsey]

Just spitballing, since you have to work with what's there, perhaps do
a st_extent to get x/y then do a second pass getting zmin and zmax?

P

On Mon, Jan 11, 2010 at 8:38 AM, Abram Gillespie
<abe.gillespie.lists at gmail.com> wrote:
> OK, I'll ask this then.  What's the best way to get this:
>
> select ST_Extent3d(geometry_column) from my_table;
>
> Into EWKB w/o losing the Z (or M) coordinate?
>
> Doing:
>
> select ST_AsEWKB(ST_Extent3D(geometry_column)) from my_table;
>
> unfortunately falls prey to the issue we're discussing.
>
> Thanks.
> -Abe
>
> On Sun, Jan 10, 2010 at 10:53 PM, Paragon Corporation <lr at pcorp.us> wrote:
>> As a side note.  ST_Zmax doesn't exist for geometries.  It works because
>> geometries can be autocast to boxes.
>>
>> See matrix
>> http://www.postgis.org/documentation/manual-svn/ch08.html#PostGIS_TypeFuncti
>> onMatrix
>>
>> -----Original Message-----
>> From: postgis-users-bounces at postgis.refractions.net
>> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paragon
>> Corporation
>> Sent: Sunday, January 10, 2010 10:50 PM
>> To: 'PostGIS Users Discussion'
>> Subject: Re: [postgis-users] Bug dropping the Z coordinate?
>>
>> Abe,
>>
>> It seems we are flattening the box3d geometry in to a 2D polygon always
>> instead of as a 3D/2.5D polygon.
>> I'm not sure it's a bug though, because I think a box3d is an invalid 2.5/3D
>> polygon if you were to construct it.
>>
>> Can you envision it?
>>
>> Paul, Mark or Kevin might have a better clue, but I think it's at best an
>> ambiguous 3D polygon and that is the problem. A box3d isn't really a 3D box,
>> its more just a coordinate bounding thing.
>>
>> Hope that helps,
>> Regina
>>
>> -----Original Message-----
>> From: postgis-users-bounces at postgis.refractions.net
>> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Abram
>> Gillespie
>> Sent: Sunday, January 10, 2010 4:31 PM
>> To: PostGIS Users Discussion
>> Subject: [postgis-users] Bug dropping the Z coordinate?
>>
>> Is this a bug?
>>
>> select ST_ZMax('BOX3D(0 0 0,0 0 1)'::box3d);
>>
>> versus
>>
>> select ST_ZMax(ST_GeomFromEWKB(ST_AsEWKB('BOX3D(0 0 0,0 0 1)'::box3d)));
>>
>> The first query returns "1" as expected but the second returns "0" as
>> unexpected.
>>
>> I'm trying to add Z/M support to zigGIS and this is show-stopping me.
>> Any work-arounds if this is a bug?  Also, I'll be happy to report the bug if
>> so.
>>
>> Thanks.
>> -Abe
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