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

Sheykhet, Rostic rsheykhet at sanz.com
Wed Mar 23 11:13:35 EST 2005


Thanks for your response.  I have recompiled proj4 (and gdal 1.2.6 just
in case) with the change.  I am still getting exact same error,
though...  Any pointers are appreciated.



-----Original Message-----
From: Frank Warmerdam [mailto:fwarmerdam at gmail.com] 
Sent: Tuesday, March 22, 2005 4:49 PM
To: Sheykhet, Rostic
Cc: gdal-dev at xserve.flids.com
Subject: Re: [Gdal-dev] WGS84 to NAD27 failed to load NAD27-83
correction file

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?


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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