[postgis-users] Weird behavior transforming from srid 4269 to 2163

[Frank Warmerdam]

Paragon Corporation wrote:
> Disregard this last question if its not a trivial one.  We just decided not
> to use this projection for this project since it renders differently under
> proj 4.5 than 4.6 and found one that seems to work for us that will render
> the same under both.
> 
> Our main concern was not so much that we keep data in 2163 projection, but
> that a lot of the tools we use are compiled with the older proj library and
> we didn't want to change that at this moment. So this little difference in
> behavior would cause potential problems when reprojecting non-postgis data.
> 
> Thanks,
> Regina 
> 
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paragon
> Corporation
> Sent: Tuesday, January 29, 2008 9:12 AM
> To: 'PostGIS Users Discussion'
> Subject: RE: [postgis-users] Weird behavior transforming from srid 4269 to
> 2163
> 
> Anyway to make the new bahave like the old? 

Regina,

The key to having PROJ 4.6 do an ellipsoid based datum shift is to attach
a +towgs84=0,0,0 parameter to the coordinate system(s) that lack any
datum information.  This could be added in the PROJ.4 string in the
spatial_ref_sys table for EPSG:2163 for instance.

But generally I think the old behavior is bad and folks should either stay
with the older PROJ if they need to avoid changes, and upgrade when they are
ready to deal with this issue.

I sympathize with the pain.

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org