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Bump Map Toolbox: Output Issue

July 27 2011 | 4 comments
Categories: ArcGIS Methods, Data Modeling, Map Data

I've recently added the bump map toolbox and ran the scripts without issue several times as I fine tuned the settings to better represent the vegetation I was working with. I'm not sure what happened, as I did not change or alter the tools, but all the output files now look like the attached image (top part of the image is zoomed out, bottom is zoomed in). I tried removing the toolbox and adding it again, emptying the directories, adding the toolbox from a different directory...but no luck.


Mapping Center Answer:

If you take a look at the Bump Map presentation we gave at NACIS in 2009 (see the Mapping Center Other Resources - Presentations page and scroll down to the "ArcGIS Bump Map Model" presentation), you will see that this is a function of resolution. In essence, the problem relates to the resolution of the DEM being larger than the resolution of the bumps so it has to be resampled. Our bump map tools should take care of this problem as we use the correct resampling method in the tools (bilinear interpolation rather than the default method of nearest neighbor). Hopefully you are not getting these results when using our tools!

If you did, try this:  First calculate the resolution at which the tool will NOT resample the DEM.  Use this formula:

(radius * 2)/11

to find the smallest radius you can use without causing the DEM to resample. Set your radii to that value or larger and see what happens. Let us know so that we will can determine if we have to review the tools for errors!  Thanks!


Mapping Center Followup Questions.... posted by scott berard on Jul 28 2011 9:57AM
If I read your response correctly, the tools should deal w/ this issue and resample the DEM. Seeing as the tools are currently not doing this in my case, your suggestion is that I recreate the DEM at a lower resolution. Is that a correct statement?

Also, can you explain the process of utilizing the formula: (radius * 2)/11. Basically I need you to dumb down the process into steps so I can follow along.

Two suggestions - actually three... posted by Aileen Buckley on Jul 28 2011 10:27AM
You could try one of these two solutions just to see if you can get a result that is not striped, and if you can, then we can see about getting the result you really want:
1. Change the resolution of your DEM, or
2) Use a radius that is larger and does not cause resampling.
If you still get the same result, then I would like to suggest that you send us a bit of your data so we can try this ourselves and see what is happening. You would also need to send us the parameters you are using to create the various bumps.

The reason we are using this formula (as noted in the PPT) is that we determined that the smoothest looking bumps we could generate at the coarsest resolution required 11 cells. So the model creates bumps that are 11 cells in diameter for the smallest bumps. Does that make sense?
My Parameters posted by scott berard on Aug 2 2011 9:05AM
As I've still not been able to produce an output w/out stripes, I cleaned out the countless files I've created and started clean. A test using your data and parameters produces a result near identical to your own. As your map was produced for a 1:63600 scale, could the scales I'm looking at be affecting the outcome? The maps I plan on using this technique on range from 1:2400 to 1:7200. My current dem has a cell size of 1,1 while the veg mask is 4,4 (but I've tried lower resolutions) and the parameters that seem to best reflect the veg is 10, 30, 300.

Do you see any red flags based on the above info?

Should work posted by Aileen Buckley on Aug 2 2011 1:25PM
Since the parameters you are using should produce results with no stripes, I would like to ask if you could send me a bit of your data to experiment with to see if I can find the problem from this end.

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