Calculating Aspect from the Raster Calculator

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04-20-2014 01:07 PM
JerryHolton
New Contributor
Hi,

Does anybody know how to calculate aspect with the Raster Calculator?  I have a 10 meter, GRID, floating point DEM that I downloaded from the USGS. I can easily calculate using the Aspect Geoprocessing tool, but this will not work well for true quantitative analysis. I would like to to be able to generalize aspect by categorizing the aspects into 4 categories, N, S, E, and W.

I would like to convert aspects from 315.1?? to 45?? = N, 45.1?? to 135?? = E, 135.1?? to 225?? = S, 225.1?? to 135 = W. I am pretty certain there is an expression that allows you to perform this transformation but have not been able to find anything on line and am not completely familiar with the raster calculator expressions.

If anybody has experience with this or suggestions on how to go about doing this, I would be extremely grateful.  Thank you so much.

Sincerely,

Tom Holton
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4 Replies
JimCousins
MVP Regular Contributor
Tom,
What about running the aspect tool, and then performing a simple reclassification to get your quadrants from the aspect results?
Regards,
Jim
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JerryHolton
New Contributor
Hi Jim,

I have tried that many times. It never really appears to work correctly. I've tried all the classification methods for this and it doesn't really work.

If you know how to do it using the reclassification tool, I would love to hear how it can be done because I have exhausted myself trying to get it to work.  Thanks so much.

Any thoughts would be greatly appreciated.

Tom
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JimCousins
MVP Regular Contributor
I am not quite clear on what you mean by "it doesn't work".
I ran aspect on a raster dataset, and used the image attached for inputs for Reclassify tool. Seems to function correctly. Note: I did not include a class for flat. (I used the Classify tool within this dialog to create the old value classes).
Regards,
Jim
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JerryHolton
New Contributor
Hi Jim,

I believe that worked. That should work for my analysis. I appreciate the help.

Tom
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