Hi,
New to GIS, and new to GRASS. Trying to learn using GRASS 6.0.1/GDAL under ubuntu dapper
On importing a .jpg, .tif, etc. that is not georeferenced the tutorial explains using i.group i.target, i.point, i.rectify, which I can do. But I'm wondering if it is possible to avoid the mouse by specifing both sets of points textually.
For instance if I'm trying to georeferece a global image of a known pixel resolution and projection like NASA's blue marble: http://visibleearth.nasa.gov/view_rec.php?id=2430
Then I'd prefer some way to say:
x,y = lat, long
0,0 = -180,90
0,1024 = -180,-90
or some such thing - without having to duke it out with the mouse. Is there some way to do this?
A related question is: if I do use the mouse how concerned with the mouse coordinate accuracy do I need to be? It is unimagineable that I will actually hit the precise pixel values with mouse interface as it is.
Best,
david
David Ottina wrote:
New to GIS, and new to GRASS. Trying to learn using GRASS 6.0.1/GDAL
under ubuntu dapper
On importing a .jpg, .tif, etc. that is not georeferenced the tutorial
explains using i.group i.target, i.point, i.rectify, which I can do.
But I'm wondering if it is possible to avoid the mouse by specifing
both sets of points textually.
For instance if I'm trying to georeferece a global image of a known
pixel resolution and projection like NASA's blue marble:
http://visibleearth.nasa.gov/view_rec.php?id=2430
If the projection is known, it's simpler to create a new location with
the correct projection, import the image there, then set the map's
corners with r.region.
If you want to use the map in a location with a different projection,
you can use r.proj to create a re-projected copy of the map.
Then I'd prefer some way to say:
x,y = lat, long
0,0 = -180,90
0,1024 = -180,-90
If the image is a whole-earth lat/lon map, import it into a lat/lon
location then use "r.region n=90 s=-90 e=180 w=-180".
However, some import modules have problems importing into lat/lon
locations as the default bounds result in a north value greater than
90. In that case, switch the location to x/y by editing the WIND file
before importing, then change it back afterwards.
--
Glynn Clements <glynn@gclements.plus.com>
Thanks very much for the help Glynn.
Here is some additional information on the WIND work around for whomever
may be interested...
However, some import modules have problems importing into lat/lon
locations as the default bounds result in a north value greater than
90. In that case, switch the location to x/y by editing the WIND file
before importing, then change it back afterwards
Yep, this gets around the "Illegal latitude for South" error!
To be able to display the map go to the map's header file in:
mylocation/mymapset/cellhd/
and change 'proj = 0' to 'proj = 3'. I believe 0 is for x,y and 3 is
for lat/lon. In my case I had to do this for three files, one for each
color band.
best,
david