[GRASSLIST:10510] Re: importing projection info with v.in.ogr

[Tom Russo]

On Tue, Feb 21, 2006 at 09:19:15PM -0500, we recorded a bogon-computron collision of the <fonnesbeck at gmail.com> flavor, containing:
> On 2/21/06, Tom Russo <russo at bogodyn.org> wrote:
> > On Tue, Feb 21, 2006 at 06:42:57PM -0500, we recorded a bogon-computron collision of the <fonnesbeck at gmail.com> flavor, containing:
> > >
> > > However, when I try to import layers from another location (with a
> > > different projection) using v.proj, I get an error:
> > >
> > > Input Projection Parameters: +proj=latlong +a=6378137
> > > +rf=298.257222101 +no_defs
> > > +nadgrids=/Applications/Grass/grass61cvs.app/Contents/Resources/grass-6.1.cvs/etc/nad/FL
> > >
> > > Output Projection Parameters: +proj=aea +lat_1=24 +lat_2=31.5
> > > +lat_0=24 +lon_0=-84 +x_0=400000 +y_0=0 +no_defs +a=6378137
> > > +rf=298.2572221010002
> > > pj_transform() failed
> > > cause: failed to load NAD27-83 correction file
> > > Error in pj_do_transform
> >
> > Every time I've seen this error it has been because of a mistaken attempt
> > to datum shift values that lie outside the range in which NAD27 datum shift
> > grids apply.  For example, attempting to transform the coastline of all
> > of North America (including Alaska) using the CONUS grid (which is only defined
> > over the lower 48).  You're apparently using a Florida grid --- are your
> > vectors absolutely, positively within the bounds of that grid?
> >
> > AFAICT, the FL grid is only valid from -88deg longitude to -80deg longitude and
> > from 24deg latitude to 32deg latitude.  If your vectors have any points that
> > lie outside this region the proj.4 library will puke trying to datum shift.
> 
> Well, I was importing a FL shoreline vector layer, which you would
> think would be within the FL grid, but I could be wrong.

I took a quick look at what that lat/lon region contained, and it looks like
there are some islands that are probably part of Florida that are outside
the region in which the grid is valid.  That could be the issue if your
coastline layer contains those islands.

What are the bounding coordinates of your vector layer?  That is, in the lat/lon
location where your vector layer lives, what does v.info say?  If it 
shows the extents of the layer not being completely inside the [-88,24]/[-80,32]
bounding rectangle of the FL datum-shift grid, then attempting to project 
it to a layer that isn't in exactly the same datum will cause it to give
the sort of error above.

There are, of course, other reasons for that error, but in each case in my
experience it has always been due to me attempting something like what
I mentioned before.

-- 
Tom Russo    KM5VY     SAR502  DM64ux         http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 
"And, isn't sanity really just a one-trick pony anyway? I mean all you get is
 one trick, rational thinking, but when you're good and crazy, oooh, oooh,
 oooh, the sky is the limit."  --- The Tick