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#1
Martin Gamache

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I'm having a real hard time using a GTOPO30 Antartica tile from
here

Manifold will not display this file correctly and I cannot import it to a ESRI grid using arctoolbox. Natural Scene Designer also chokes on it.
Projection is described here.
It sounds like a basic polar stereographic projection but for some reason nothing will read it in as such.


I know I figured out how to use this data a couple years ago, but I either don't have the right tools anymore or I'm using a different dataset.

Anyone have any suggestions?

mg

#2
mike

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I'm having a real hard time using a GTOPO30 Antartica tile from
here

Manifold will not display this file correctly and I cannot import it to a ESRI grid using arctoolbox. Natural Scene Designer also chokes on it.
Projection is described here.
It sounds like a basic polar stereographic projection but for some reason nothing will read it in as such.


I know I figured out how to use this data a couple years ago, but I either don't have the right tools anymore or I'm using a different dataset.

Anyone have any suggestions?

mg

<{POST_SNAPBACK}>


I found a how-to here: http://rockyweb.cr.u...ch/gtopo30.html

Try this (slightly tweaked):

1) Use WinZIP or other extracting software. If you are using WinZip to uncompress this file, please turn off (uncheck) the TAR File Smart conversion found under Options / Configuration (then under Misc. if using Winzip 8.0). See: http://LPDAAC.usgs.g...faq_gtopo30.asp for more information.

2) Rename your resulting .DEM to .BIL in Windows Explorer.

3) Using ESRI's ArcToolbox: Access Image to grid and convert your BIL to a ESRI Grid. (in ArcGIS 9.x it would be the "Raster to Other Format (multiple)" tool).

4) Open ESRI's ArcMap. Add the Spatial Analyst extension and toolbar. Click on Add data, and add your GRID.

5) The grid needs further processing, though, because some of the values are incorrect. According to the documentation, IMAGEGRID does not support conversion of signed image data, therefore the negative 16-bit DEM values will not be interpreted correctly. After running IMAGEGRID, an easy fix can be accomplished using the following formula in Grid:

out_grid = con(in_grid >= 32768, in_grid - 65536, in_grid)

this is what i entered to make it work: out_grid = con([antarcps] >= 32768, [antarcps] - 65536, [antarcps])

You can calculate the above formula using the Raster Calculator in the Spatial Analyst extension in ArcMap. The ocean on the screen shot is elevation value -9999 and the land elevations are in meters.

The converted grid will then have the negative values properly represented, and the statistics of the grid should match those listed in the .STX file. If desired, the -9999 ocean mask values in the grid could then be set to NODATA with the SETNULL function.

You can also check "Display Background" and enter in "-9999" in the box and set the color to NoColor. This will give you the invisible background.

#3
mdsumner

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This worked for me in Manifold (might be out by 1 pixel in the Y):

Attached Files



#4
Martin Gamache

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Mike and MDSUMMER,

Thanks for the solutions. It turns out the winzip settings were to blame. I recently installed it on my new machine and the Smart TAR settings were stil checked.

This solved the problem and Manifold read the DEM in correctly with the GTOPO import.

mg

#5
mike

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Great, glad to see it worked.

#6
mdsumner

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What's the project BTW? You might also be interested in these data for Antarctica:

http://www.antarctic...uk/aedc/bedmap/

http://www.add.scar.org/add_main.html




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