I'm confused.
I want to set up a new project and use UTM wgs 84.
But, some of my data is drg(base USGS topo map), which are lat/long, and the field data I want to use is x,y( I have UTM coords which I can georeference to).
So when I set up the project, which coord should I use?
When I went to use UTM, I did not understand how to get the north, south, east, west info. Grass did not like the tiff, and associated tfw for the base map.
using Ubuntu, Grass 6.3
Thanks,
Tom
hi
So when I set up the project, which coord should I use?
You must create two location: the first one UTM WGS84 and the second one
long/lat WGS84
you import your long/lat data into the proper location and then you can
use v.proj or r.proj to reproject them into the UTM WGS84 location
another solution is to use gdalwarp or ogr2ogr.... but could be hard if
you are just starting to learn foss4g softwares..
When I went to use UTM, I did not understand how to get the north,
south, east, west info. Grass did not like the tiff, and associated
tfw for the base map.
grass imports tiff files...
you must use the --o option (override projection) to import data with
r.in.gdall
using Ubuntu, Grass 6.3
hope this helps...
Thanks,
Tom
Ivan
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On 21/07/08 05:28, mtnbiketrail@zzz.com wrote:
When I went to use UTM, I did not understand how to get the north, south, east, west info. Grass did not like the tiff, and associated
tfw for the base map.
Could you elaborate on what you mean by "Grass did not like the tiff",
i.e. exact command used and error message received ?
Many geotiffs are georeferenced (hence the tfw file), but do not contain
any information about the projection system they are in.
But you can create the location with an extension of 1 in both directions and then use the r.in.gdal '-e' flag to extend the default location extension to the extension of your file.
On 21/07/08 12:52, ivan marchesini wrote:
grass imports tiff files... you must use the --o option (override
projection) to import data with r.in.gdal
I've seen too much abuse of this option to let a general statement like this pass: only if you are sure that the file is in the same projection system as your location, but, for example, it does not contain any information about its system, then use '-o'. In any other case don't, but rather investigate about the (possible) differences in projection systems...
Moritz
On Sun, Jul 20, 2008 at 08:28:54PM -0700, we recorded a bogon-computron collision of the <mtnbiketrail@zzz.com> flavor, containing:
I'm confused.
I want to set up a new project and use UTM wgs 84.
But, some of my data is drg(base USGS topo map), which are lat/long,
Most USGS DRG topo maps are georeferenced in UTM (only those that have been
monkeyed with by other agencies are not). Some state and local GIS departments
reprocess them with software that removes the TIFF tags that GDAL would use
to figure out what to do with them, even when they don't change the projection.
Any USGS topo for California will have been reprojected to an equal-area
projection, and any USGS topo covering territory under the authority of the
Tennesee Valley Authority will be in UTM but with no geotiff tags necessary
for GDAL to recognize them. But real USGS topos for any other part of the
US should be in UTM and have GeoTIFF tags identifying the coordinate system.
What does the following command output?
gdalinfo file.tif
That'll tell you for sure. If you see the line
Coordinate System is `'
then you have a file that has all the geotiff tags missing. If it says
anything else, then the file contains information that tells you what
coordinate system it uses.
If the tags are missing, but you have .tfw files and other metadata that tell
you for sure what the coordinate system of the file really is, then you can
often re-insert the appropriate tags with a gdal_translate command.
I second Mortiz' comment about the misuse of "-o" to r.in.gdal. It is better
to understand exactly what the coordinate system of your image file is and
get it imported in a location where -o is not necessary than to just force
r.in.gdal to ignore projection problems.
and the field data I want to use is x,y( I have UTM coords which I can
georeference to).
So when I set up the project, which coord should I use?When I went to use UTM, I did not understand how to get the north,
south, east, west info. Grass did not like the tiff, and associated
tfw for the base map.
If the file is a real USGS DRG file from USGS (and not reprocessed by someone
else) then it should be possible to create a new location from the .tif file
by doing
r.in.gdal input=file.tif location=newlocation output=somename
The new location will have the right coordinate system IF the tif file had
the correct GeoTIFF tags that USGS puts in. If the files were reprocessed
by some other agency, all bets could be off and you'd have to do more work
to get it done right.
--
Tom Russo KM5VY SAR502 DM64ux http://www.swcp.com/~russo/
Tijeras, NM QRPL#1592 K2#398 SOC#236 AHTB#1 http://kevan.org/brain.cgi?DDTNM
"Argue for your limitations and sure enough, they're yours." -- R. Bach
Okay. some details.
I am working in California maps. I had trouble creating a new project/mapset, but it is working now. I used r.in.gdal to bring in the Geotiff and Grass sees it as NAD83 Albers Conical. I tried to use the command gdalinfo and Grass could not file the file. Even though it is showing in the Map Display.
Whatever.
here is the g.region -p, I have no idea if it is correct. I don’t understand the negative west, east numbers yet.
projection: 99 (Albers Equal Area)
zone: 0
datum: nad83
ellipsoid: grs80
north: 405480.97282175
south: 391273.11966856
west: -271733.88910031
east: -260832.03532599
nsres: 1.52772615
ewres: 1.52772615
rows: 9300
cols: 7136
cells: 66364800
My next question is: I need this base Geotiff in UTM WGS84. From what the other email said, I have to create a new location. Does the area covered have to be the same? I am still having a hard time with the project region syntax.
I also have GPS waypoints(in UTM, WGS84) I want to bring into the mapset. From what I read points should be treated as vectors? Is there a way to mass import points into the database?
I ordered the Neteler book, I hope it has real examples.
Thanks,
Tom
Tom Russo wrote: