On 09/29/2010 06:12 PM, Mario Julio Barragan Arce wrote:
Hello. I need to learn how to use GIS and I have chosen to do it with
GRASS. My plan is to learn GIS/GRASS essentials during the next 12
months and start applying it for my
Welcome, and good decision.
research the 12 months after that. I have started reading the
documentation available and playing with the sample data set. However,
I would also like to start playing with a dataset for Puerto Rico (PR)
and I am having problems to import it. How would I go about importing
a new dataset?
In particular, there is a landcover raster image in Erdas "img" format
(prgap_landcover.img) that I would like to import from here:
ftp://ftp.gap.uidaho.edu/products/Puerto_Rico/GISdata/Landcover/1_Land_cover_grid/
(1) What do I do with this img file? Do I first copy and paste it to
my GIS Data Directory? If not, how do I go about telling GRASS where
this file is (if I want to import it)?
If the file is somewhere on your computer, then just enter the path to
it with the 'input=' parameter to r.in.gdal. Something like:
r.in.gdal in=/path/to/prgap_landcover.img out=prgap_landcover
(BTW, I think you can actually even import into GRASS straight from the
URL...)
(2) I read about the commands to import raster Erdas/IMG files to
GRASS (r.in.gdal -e in=<image.img> out=<image>). If I want to use this
command, should my img file be in the GIS Data Directory first as I
suggested in (1)? Where do I type this command? The GRASS Command Line
window seems to open for an existing Location.
(3) When do I create the location for my data? Do I do this before
anything else?
YES, before anything else. This step is crucial, and sometimes confuses
new users. You *must* have a correct LOCATION defined at the start such
that it matches the CRS of the original data. GRASS always insists that
all maps in a LOCATION are projected in exactly the same CRS.
From the metadata below it looks like this file is projected in the LCC
projection matching the EPSG code of 2866. That's NAD83(HARN) Puerto
Rico and Virgin Islands.
You might try to first use the wizard to create a new location based on
this EPSG code. That insures all the parameters get entered properly.
Then, after starting GRASS in this location (also create a MAPSET - the
GRASS way to keep maps filed in some directory which is logical for your
work), try the r.in.gdal command.
(4) When trying to create a location from the Location Wizard, I chose
as the method "Select coordinate system parameters from a list". I did
this because there is another file in the above mentioned ftp folder
with several parameters which seem to me the kind of information that
the wizard asks (see an excerpt below). From there I chose "lcc" as
the projection code. However, from here onwards I start having
problems. For instance, I don't know whether to choose "Datum with
associated ellipsoid" or "Ellipsoid only". Also, the wizard asks me
"Central Parallel", "First Standard Parallel", "Second Standard
Parallel", and I don't know how that relates to the two
"Standard_Parallel" parameters given below and where do I get the
other "Parallel" parameter from? I seem to be missing one. For the
geodetic datum I think I have to choose "nad83" and I think I will
choose "No transformation" at the end of the wizard.
Any suggestions will be very welcome. Thank you in advance. Saludos,
Julio.
Cheers. For future questions, let us know your OS and version of GRASS.
And posting the output of commands like g.region -p, v.info, r.info will
often help.
Regards,
Micha
Spatial_Reference_Information:
Horizontal_Coordinate_System_Definition:
Planar:
Map_Projection:
Map_Projection_Name: Lambert Conformal Conic
Lambert_Conformal_Conic:
Standard_Parallel: 18.033333
Standard_Parallel: 18.433333
Longitude_of_Central_Meridian: -66.433333
Latitude_of_Projection_Origin: 17.833333
False_Easting: 200000.000000
False_Northing: 200000.000000
Planar_Coordinate_Information:
Planar_Coordinate_Encoding_Method: row and column
Coordinate_Representation:
Abscissa_Resolution: 15
Ordinate_Resolution: 15
Planar_Distance_Units: meters
Geodetic_Model:
Horizontal_Datum_Name: North American Datum of 1983
Ellipsoid_Name: Geodetic Reference System 80
Semi-major_Axis: 6378137.000000
Denominator_of_Flattening_Ratio: 298.257222
This mail was received via Mail-SeCure System.
_______________________________________________
grass-user mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/grass-user
This mail was received via Mail-SeCure System.
--
Micha Silver
Arava Development Co. +972-52-3665918
http://surfaces.co.il
_______________________________________________
grass-user mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/grass-user
