[postgis-users] ST_Translate

[Burgholzer,Robert]

Bob,
What Marin said was that since you chose to base the offset calculations
for each shape on the centroid of that particular shape relative to your
reference shape, all shapes would be moved to center on your reference
shape. 

If you wish to preserve their positions relative to one another, you
would have to use the centroid of the group of "process"es being moved
as the basis for your offset calculations, i.e.:

insert into entity (the_geom, position)
select
st_translate (public.process.the_geom,
st_x (st_centroid(spatial_ref.the_geom)) -
st_x (st_centroid (old_ref.the_geom)),
st_y (st_centroid(spatial_ref.the_geom))-
st_y (st_centroid (old_ref.the_geom))), ('i')
from  spatial_ref,  process, 
   (select extent(the_geom) as the_geom from process) as old_ref
where spatial_ref.position_ = '1' ;

HTH

Robert W. Burgholzer
Surface Water Modeler
Office of Water Supply and Planning
Virginia Department of Environmental Quality
rwburgholzer at deq.virginia.gov
804-698-4405
Open Source Modeling Tools:
http://sourceforge.net/projects/npsource/

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob
Pawley
Sent: Wednesday, July 09, 2008 12:39 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] ST_Translate

I  thought that the centrioid of each of the six geometries that make up
the 
whole would have been translated to its appropriate spot relative to
where 
it began.

This is obviously not the case.

Where is my thinking wrong??

Might it have soemthing to do with centroids of individual geometries as

compared to the centroid of the shape as a whole??

Bob

----- Original Message ----- 
From: "Martin Davis" <mbdavis at refractions.net>
To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
Sent: Wednesday, July 09, 2008 9:07 AM
Subject: Re: [postgis-users] ST_Translate


> Looks to me like you're translating each geometry by a different
amount. 
> Using the SQL below, the centroid of each individual geom will be
moved to 
> be coincident with the centroid of spatial_ref.the_geom.
>
> You need to determine a single delta x,y to translate them all by, if
you 
> want them to be in the same position relative to each other.
>
> Bob Pawley wrote:
>> Hi Regina
>>
>> Following is the query I am using.
>>
>> The shapefile is also attached if any one wants to try it.
>>
>> The shape was converted from a DXF file with the default SRID.
>>
>> Bob
>> insert into entity (the_geom, position)
>> select
>> st_translate (public.process.the_geom,
>> st_x (st_centroid(spatial_ref.the_geom)) -
>> st_x (st_centroid (public.process.the_geom)),
>> st_y (st_centroid(spatial_ref.the_geom))-
>> st_y (st_centroid (public.process.the_geom))), ('i')
>> from  spatial_ref,  process
>> where spatial_ref.position_ = '1' ;
>>
>>
>>
>>
>>
>> ----- Original Message ----- From: "Paragon Corporation"
<lr at pcorp.us>
>> To: "'PostGIS Users Discussion'"
<postgis-users at postgis.refractions.net>
>> Sent: Wednesday, July 09, 2008 12:11 AM
>> Subject: RE: [postgis-users] ST_Translate
>>
>>
>>> Bob,
>>>
>>> Doesn't quite make sense to me why translating before ST_Union would

>>> cause
>>> distortion if you are translating all the same amount.
>>>
>>> What is the SRID of the data you are translating and what does your
>>> translate query and union query look like?
>>>
>>> Thanks,
>>> Regina
>>>
>>> -----Original Message-----
>>> From: postgis-users-bounces at postgis.refractions.net
>>> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Bob
>>> Pawley
>>> Sent: Tuesday, July 08, 2008 5:30 PM
>>> To: PostGIS Users Discussion
>>> Subject: [postgis-users] ST_Translate
>>>
>>> I've imported a shapefile that requires six rows in the table.
>>>
>>> When I translate that shape, of six rows, to another location the
shape
>>> becomes distorted.
>>>
>>> When I collect the six rows by using ST_Union, then translate the
single 
>>> row
>>> to the new position, there is no distortion.
>>>
>>> Is there a method of using ST_Translate, without also using
ST_Union, 
>>> and
>>> still avoid the distortion of the shape??
>>>
>>> I need the  geometries of the shape separate to be able to identify
the
>>> parts of the shape I need. I seem to lose this informaion when I
employ
>>> ST_Union.
>>>
>>> Bob
>>>
>>> _______________________________________________
>>> postgis-users mailing list
>>> postgis-users at postgis.refractions.net
>>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>>
>>>
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>>
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>>
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>
> -- 
> Martin Davis
> Senior Technical Architect
> Refractions Research, Inc.
> (250) 383-3022
>
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