[GRASSLIST:2853] RE: Need instuctions?
Kidd, James P.
james.kidd at Covance.Com
Fri Jan 4 07:11:03 EST 2002
Thanks for the advice, I'll try it later this week. Incidentally, I checked
the ESRI website and found that the raster calculator in Spatial Analyst
(arcview 8.1) can merge grids together using a map algebra function: merge.
It works great where the edges meet.
SAS Liaison Programmer
Covance Central Laboratory Services
8211 SciCor Dr
Indianapolis, Indiana 46214
james.kidd at covance.com
From: John Dougherty [mailto:jwd at softcom.net]
Sent: Friday, January 04, 2002 12:56 AM
To: Kidd, James P.
Subject: Re: [GRASSLIST:2844] Need instuctions?
On Thursday 03 January 2002 05:28 am, you wrote:
> I have been a reader of the grass list for a few weeks. I need some
> instructions on how to read in some dem files that I converted from sdts
> format. I am trying to build a county database using a number of
> file formats, but have run into some difficulty with the dems.
The best approach is to read in the SDTS format rather than convert to dem
form. You should expand the sdts into a directory with all the associated
files, and then I believe you call r.in.gdal using the CATD? file. Once the
file has been read in, it has to be processed to identify the elevation
and areas with 0 values.
When I was asking the same questions earlier, Rich Shepard sent me the
below which illustrates the necessary steps in bring in an SDTS dem. Each
step can be carried out independently from the command line. I have
Dr. Shepard's comments.
# Edit the invocations of r.in.gdal and r.null to reflect your data files as
# Call r.in.gdal
r.in.gdal -o input=<filename> output=<newfilename[.dem]>
# Imports a DEM file using r.in.gdal. You call the stdts ****CATD.DDF file
# as the option input=<filenameCATD.DDF>. Leave out the <, and >. Simply
# replace the <filename> with the name (and path) of the CATD file from the
# SDTS files. Then you should give a new file name for the output file,
# which in the case of a dem STDS file will be a dem. You will not require
# "dem" suffix, but it may be of aid in remembering what the file is.
# Example invocation:
# r.in.gdal -o input=1418CATD.DDF output=oreana
# Call r.null
r.null -f map=<dem file name> setnull=-32766
# After successfully running r.in.gdal, you will need to r.null to process
# the new file. When you invoke r.null the data in your dem may be either
# of floating point or integer numeric type. You need to change the '-f' to
# an '-i' if the file is interger meters in elevation. The '-map=' option
# should give the name of the new dem file that was produced by r.in.gdal,
# with the path if necessary. The 'setnull=' option replaces SDTS null with
# GRASS null.
# Example invocation:
# r.null -f map=oreana setnull=-32766
After this has been done for each of the dem files you want to tile
you need to call these files into a display terminal with d.rast. I believe
you use the -o option to cause the zero values to be treated as transparent.
Provided that the dems have common edges, they will then be displayed tiled
Before they can be displayed successfully, you also NEED to have read these
files into a Grass LOCATION that has appropriate projection and
geo-coordinate boundaries that will enclose the necessary. Trying to learn
this process has been deleterious to the density of my hair, but I am given
to understand that after a while it becomes second nature.
> I guess my first question is: Is this the right list to submit help
> I normally use ArcView 8.1 on the NT side of life and find that while I
> read in the dems into it, I can not merge them. I don't have access to
> ArcInfo so I am looking to GRASS for the solution.
If you have access to the ESRI Spatial Analyst you should be able to do this
in AV 8.1. You could in the earlier version.
> Does anyone know how to do this? I kinda need step by step instructions
> since the help files seem to say it can be done, but don't really spell
> how to do it.
> Could someone point me in the right direction on this?
> Thanks in advance.
John W. Dougherty
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