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Begin forwarded message:
From: Amanda Wintcher <[EMAIL PROTECTED]>
Date: February 9, 2007 6:19:36 AM AKST
To: [EMAIL PROTECTED]
Subject: New and inexperienced--how to make NASA SRTM work properly?
Reply-To: [EMAIL PROTECTED]
Apologies if this is too basic (or long) for this list.
I have downloaded some SRTM tiles (version 2 from
ftp://e0srp01u.ecs.nasa.gov/srtm/), and I am particularly
interested in
N038W002 (Murcia, southeastern Spain). I have some problems that I
don't know how to solve, and the User Guide doesn't give enough detail
to figure them out.
How do I make the SRTM data appear as 3-D digital elevation models? I
had some help from another person who was able to make it work with an
older version of ArcGIS, but I don't know how to reproduce it with
qGIS.
This is what I have tried:
Opened the .hgt file in 3 DEM, making sure to select the NASA SRTM
option. Change projection to UTM has four ellipsoid options: WG84,
WGS72, NAD83, and NAD27. I have tried all four in order to see
what UTM
coordinates I get for the "corners" of the tile.
To check myself, I then opened up the GEOTRANS 2.3 program in order to
convert the lat/lon coordinates to UTMs. However, I don't know which
ellipsoid to pick for this part--what is the appropriate choice for
the
SRTM data? None of the options gives the same UTM coordinate for the
southwest corner of the tile in both programs.
I saved the SRTM file as a GeoTiff DEM in any case, using the WG84
datum, as I have a set of shape files with an outline of the region
and
topo lines that someone else has given me and that is the system they
use according to the metadata in qGIS.
I then changed the projection to the following:
QGIS SRSID: 1248
PostGIS SRID: 23030
+proj=utm +zone=30 +ellps=intl +units=m +no_defs
which is described as "ED50 UTM Zone 30N", which should be what I want
so far as I can tell, based on the info on the paper maps I am
using to
navigate on the ground.
So far, I have managed to get all of the layers in the same place and
they look to be in the right spot. But how do I now make the 3-D
information visible beyond a greyscale background? What is this
kind of
operation actually called?
I have no experience in GIS but I am trying to use qGIS for my PhD
project. I have a set of archaeological sites and I want to look at
their geographic context (e.g. landforms, visibility, etc.) in an
attempt to assess how different kinds of sites are related to each
other.
Thanks for any help. A pointer to a more comprehensive manual (other
than the user guide), preferably something that I can download or
otherwise consult offline, would be great, too.
By the way, I am using qGIS 0.8.0 (Titan). According to the "about"
page, it has PostgreSQL support and is compiled/running against Qt
4.2.2, if that means anything. It's on Windows XP, and I have
previously installed the experimental native windows GRASS version
6.3.cvs. That seems to work okay as the GRASS tools in qGIS seem
to be
fine. I don't know anything about coding or writing scripts, but I'm
not afraid to learn how!
Amanda
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