[postgis-users] datum shifting in postgis?

[Paul Ramsey]

PostGIS uses proj4 for transforms, so its datum support is only as good 
as your proj4 installation. Proj4 can do simple grid shifts, but you 
MUST INCLUDE THE GRID SHIFT FILES when you compile it.

ftp://ftp.remotesensing.org/pub/proj/proj-nad27-1.2.tar.gz

Untar that into the nad directory of the proj4 source BEFORE running 
./configure in your proj4 build.

Yes, this is tricky. But it does work!

Paul

Howard Foster wrote:

> Hello all,
> 
> Does postgis have a datum shift function?  My transformed data (e.g., 
> select transform(the_geom, 26910) from roads;) displays the classic 
> offset error of unshifted data (PostGIS version 0.8.2, Postgres v 8., 
> NAD27, NAD83).  A naive call of  proj4 (which is how I understand the 
> transform function works) won't do datum shifting even though various 
> srids have datum parameters.
> 
> Any help?
> 
> Thanks a bunch,
> -Howard (Research Specialist, GISC, UC Berkeley)
> 
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