[postgis-users] ST_Translate

[Bob Pawley]

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
>>>
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>
> -- 
> Martin Davis
> Senior Technical Architect
> Refractions Research, Inc.
> (250) 383-3022
>
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