Extract gtopo30 data for any area

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.html

Go 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.