[Gdal-dev] WGS84 to NAD27 failed to load NAD27-83 correction file

[Frank Warmerdam]

On Tue, 22 Mar 2005 16:40:43 -0700, Sheykhet, Rostic <rsheykhet at sanz.com> wrote:
>  
> 
> Hi all, 
> 
> I am trying to convert a WGS84 query envelope to NAD27.  It works fine for
> smaller areas, but on an envelope larger than continental US, I get a
> "failed to load NAD27-83 correction file" error.  What am I doing wrong?  

Rostic, 

The problem is that there is no datum shift file for most parts of the
world, so some of the points cannot be datum shifted when you go
outside valid areas. 

If you don't mind hacking the code a bit, you could modify 
proj/src/pj_datums.c so that the definition of nad27 is

"nadgrids=@conus, at alaska, at ntv2_0.gsb, at ntv1_can.dat, at null"

This basically means if none of the grids are match the point
to shift, apply the "null" grid which does nothing. 

> Perhaps on a related note, is there a way to get an envelope/bounding box of
> a coordinate reference system? 

No, I'm afraid not. 

Best regards,
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