[GRASS5] [bug #3029] (grass) NTv2 grid file out-of-bounds errors

[Harmish Bowman via RT]

maybe a solution in this email from Frank on the GDAL mailing list, perhaps
the side effects (bad data, even with a warning) outweigh the benefits.

Hamish




From: Frank Warmerdam <fwarmerdam at gmail.com>
Subject: Re: [Gdal-dev] WGS84 to NAD27 failed to load NAD27-83 correction file
Date: Tue, 22 Mar 2005 18:49:16 -0500
To: "Sheykhet, Rostic" <rsheykhet at sanz.com>
Cc: gdal-dev at xserve.flids.com
Reply-To: warmerdam at pobox.com
Sender: gdal-dev-bounces at xserve.flids.com

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,
-- 
---------------------------------------+--------------------------------------
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    | Geospatial Programmer for Rent
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