gtopo30 DEM for Imagine
by: George Hilley and Stephen Holloway
Login to tejon.la.asu.edu
The full gtopo30 dataset is available.
For other unix machines, download from
http://edcdaac.usgs.gov/gtopo30/gtopo30.htmlGo to the website and enter in lat/lon coordinates for area of interest.
Note the corresponding plate numbers.
gtopo30 is already available in grid format.
mkdir workspace
cd workspace
Launch arc/info.
arc: cw .
arc: copy /usr/local/data/gtopo30/plate# /plate#
This must be copied within arc to maintain proper grid format.
arc: display 9999
arc: grid
grid: filename = merge(plate#, plate#, ...)
grid: mape filename
grid: image filename
This merged file will likely be larger than the area you need so you will need to section out.
grid: quit
arc: ae
arcedit: mape filename
arcedit: image filename
arcedit: draw
Define your area and note the lat/lon units for your boundaries.
arcedit: quit
arc: grid
grid: setwindow minx miny maxx maxy
grid: filenamecrop = filename
grid: mape filenamecrop
grid: image filenamecrop
In order to remove the bathymetry and coastline errors, use the following command.
grid: tmp = setnull(filenamecrop <= 0 , filename)
grid: image tmp
grid: kill filenamecrop all
grid: rename tmp filenamecrop
grid: quit
arc: ae
arcedit: mape filenamecrop
arcedit: image filenamecrop
arcedit: draw
To create another cropped image, find lat/lon boundaries again.
arcedit: quit
grid: setwindow minx miny maxx maxy
grid: filenamezoom = filenamecrop
grid: mape filenamezoom
grid: image filenamezoom
If you need to redo the extents, repeat the above starting with arc: ae.
If everything is ok then use the following command.
grid: quit
arc: quit
To export this grid file is a more readily usable format use ERDAS Imagine.
cd workspace
% imagine &
Import grid file into Imagine grid format
Main Button Bar->Import->Type: grid->Media: file->filename
Open file.
Viewer->File->Open->Raster Layer
File Type: GRID->Filename: filename->Raster Options->Display as: Pseudo Color->OK
Reproject into the appropriate projection, typically transverse mercator.
Viewer-> Raster->Geometric Correction->Reproject->Transverse Mercator, scale factor 1
Latitude and longitude are the center of the image for projection purposes.
To adjust the assigned topography colors.
Raster->Attributes->Edit->Column Properties->Editable.
Use color ramps to assign colors.
File->Save->All Layers
This *.img file can be used for image draping or exported as a *.tif for use in figures.
For nice shaded relief DEM figures, in Imagine use the following commands:
Image Interpreter->Topographic Analysis->Shaded Relief
Use file as DEM.
Use file as overlay (specify pseudo color).
Set the z factor and sun position accordingly.