[postgis-users] Bug dropping the Z coordinate?

Tue Jan 12 09:23:32 PST 2010

Thank you all for the great help as always.  Regina, that's certainly
an option, but, yes, I need to package this information into an
ArcObjects IEnvelope object.  What I did in the past was use my WKB
parser to hydrate an ArcObjects polygon (implements IEnvelope)
directly.  Now, since this is no longer possible, I will have to build
it by hand and Paul's method will suit this task the best.

Again, thank you for all the help.
-Abe

On Tue, Jan 12, 2010 at 3:13 AM, Paragon Corporation <lr at pcorp.us> wrote:
> Abe,
>
> Nothing to apologize for.  Your etiquette was fine I just wasn't clear if
> you needed it represented or not.
>
> You oould go with Paul's approach of doing the ST_ASbinary and the
> ZXMax,...separately.
>
> But do you absolutely need it as one geometry?  If you do then I was
> thinking return a 3D line.  It wouldn't represent right but will encode all
> the information in a geometry that you can then safely apply
> ST_AsEWKB/ST_AsGeomFromWKB
>
> So write an SQL function that takes an ST_Box3D and returns a 3D line
>
>
> CREATE OR REPLACE FUNCTION zig_extentline(ext box3d)
>  RETURNS geometry AS
> $$
> SELECT ST_MakeLine(ST_MakePoint(ST_Xmin($1), ST_YMin($1),
> ST_Zmin($1)),ST_MakePoint(ST_XMAx($1), ST_YMax($1), ST_ZMax($1)) ) ;
> $$
>  LANGUAGE 'sql' IMMUTABLE
>  COST 10;
>
>
> --testing with this
> SELECT ST_ZMax(ST_GeomFromEWKB(ST_AsEWKB(zig_extentline('BOX3D(0 0 0,0 0
> 1)'::box3d))));
>
> Gives
> 1
>
> 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: Monday, January 11, 2010 12:46 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] Bug dropping the Z coordinate?
>
> I need to report back to ArcGIS what the bounds of the data is.  The way
> zigGIS works is it parses all geometry data returned from PostGIS as WKB.
> We're extending zigGIS to handle ZM coordinates.  I'll be happy to put in a
> special case for the extents query where if I have to parse things manually
> I will.  But I'm not even sure how to get a ST_Extent3d query into a from
> that I can consume (note that going through Npgsql has its own challenges
> with working with non-standard types).  I'd parse binary if ST_AsEWKB
> worked, I'd parse text if ST_AsEWKT worked.
>
> Regina, I'm a bit confused how you started your last response.  If I broke
> list etiquette then I apologize.  I did the work to boil down my initial
> question into an easily reproducible test case which I thought was
> exercising a bug.  My apologies for not getting to the point immediately.
>
> Thanks.
>
> On Mon, Jan 11, 2010 at 12:14 PM, Paragon Corporation <lr at pcorp.us> wrote:
>> Abe,
>> One thought that comes to mind is store it as a multipolygon with each
>> polygon being a different edge of the box, but I'm not sure that would
>> be terribly useful for your use-case.
>>
>> Leo
>>
>> -----Original Message-----
>> From: postgis-users-bounces at postgis.refractions.net
>> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
>> Abram Gillespie
>> Sent: Monday, January 11, 2010 11:38 AM
>> To: PostGIS Users Discussion
>> Subject: Re: [postgis-users] Bug dropping the Z coordinate?
>>
>> 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_Typ
>>> e
>>> Functi
>>> 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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