[GRASSLIST:2715] Re: stitching geotiffs

[Glynn Clements]

Martin du Saire wrote:

> >>Outstanding!  Thank you Richard and  Glynn.  I think I may eventually 
> >>have to r.patch the individual maps.  I was playing around with two maps 
> >>within a single zone, and the r.stats -a -n map1,map2 output did not 
> >>reflect what I expected to be the composite of the two (Actually, the 
> >>numbers made no sense at all).  One last question:
> >>Without having specific datum in my adjacent zones (14, 16), is there 
> >>some way to make upper-bound estimates on the amount of distortion 
> >>resulting from the r.proj method=nearest (the maps are land-use/cover)?
> >>Thanks again.
> >>Martin
> >
> >That's a hard question that I will not try to answer directly. Map 
> >distortion can involve linear, directional, and/or area distortion. So 
> >first you
> 
> 
> Thanks again.
> 
> Having a little trouble with r.proj though:
> 
> ERROR> Input map is outside current region
> 
> I read the thread that involved some problem with southern hemisphere 
> projection data from U of Maryland...I am working in the NE USA...geotiffs 
> from the USGS site (for what that is worth).
> 
> Region/projection info for the location I am attempting to project the map 
> into are:
> 
> g.region -p
> 
> projection: 1 (UTM)
> zone:       19
> datum:      nad83
> ellipsoid:  grs80
> north:      2734830
> south:      1944930
> west:       1721790
> east:       2041380

That's way off. Valid eastings for UTM are within 350km of the false
500km false easting, i.e. ~166000-834000. That's at the equator; the
valid range decreases with increasing latitude. So, your region is off
by a couple of zones.

Zone 18 is 72-78 degrees West, while zone 19 is 66-72 degrees West.

Also, that particular region appears way South (somewhere to the East
of Guadeloupe); The North value of 2734830 is about right for the
southern tip of Florida (but that would be zone 17).

-- 
Glynn Clements <glynn.clements at virgin.net>