[postgis-users] Re: Projection...

[Wacek]

On Thu, Sep 22, 2005 at 04:36:22PM +0200, Nicolas Ribot wrote:

>>> > Hi,
>>> >
>>> > I have some data from USA in 'NAD83 Nevada East' fromat (EPSG:32107 -
>>> > ?). I want to change it to WGS84 (EPSG:4326) using PostGIS. When I use:
>>> >
>>> > "select updategeometrysrid('table', 'the_geom', 4326);" resulting values
>>> > are'nt correct. What am I doing wrong?
>>> >
>>> > Thanks in advance for your replies.
>>> >
>>> > Best regards
>>> > Wacek
>>> >
>>    
>>
>> 
>> Hi Wacek,
>> 
>> calling updategeometrysrid only changes the internal geometries SRID.
>> It does not reproject them.
>> You have to explicitly transform the geometries from the source
>> coordinates system to the target one, using the tranform() function.
>> 
>> select transform(the_geom, 4326) from table;
>> 
>> You can either create a new table containing the transformed
>> geometries, or drop SRID constraint on your table, transform the
>> geometries and re-add the SRID constraint adapted to the new
>> geometries' SRID
>  
>

Or:
	SELECT updateGeometrySRID('mytable', 'the_geom', 4326);
	UPDATE mytable set the_geom =
		transform(SetSRID(the_geom, 32107), 4326);

--strk;

----------------------------------

Hi, again.

This works but values after reprojection aren't quite correct (every point has the same coordinates). I have checked reprojecting my own points between these two SRIDs and it is correct. I am wondering if the source data SRID is really 32107 ('NAD83 Nevada East'). Vendor does not provide such information. To check this I use UDIG ('User-friendly Desktop Internet GIS') and his layer information feature. After adding a layer from file the visualisation is OK, but after exporting it to DB and trying to visualize it from there no features are rendered. That's why I am asking about reprojecting this data to SRID:4326. I am using source file http://gisgate.co.clark.nv.us/gismo/downloads/scl_l.zip containing streets in Clark County in USA. How can I check what SRID is my source data? Maybe someone can try reprojecting source data I have mentioned to 4326 and tell me about the results. 

Thanks a lot for your previous posts and looking forward for some new :)

Wacek



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