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| Subject: | Re: [gislist] DEM slope & aspect |
| Date: |
08/16/2006 07:35:00 PM |
| From: |
Quantitative Decisions |
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At 10:00 AM 8/17/2006 +1000, Tony.Davidson@rpdc.tas.gov.au wrote:
>I'm looking for information regarding the bivariate linear interpolation
>method for determining slope and aspect for gridded DEMs. To my knowledge
>the method isn't widely used with DEM grids and so far my literature
>searches haven't found any reference to it.
>Does anyone out there know where I might find information about the
>method's application and limitations?
Horn's 1981 survey in the IEEE proceedings is a widely cited reference for
slope, aspect, and hillshade methods. You can obtain a scanned copy on the
Web at
http://www.cs.bgu.ac.il/~ben-shahar/Teaching/Computational-Vision/Readings/1981:Horn:Hill_Shading_and_the_Reflectance_Map.pdf
.
I am not familiar with any bivariate linear interpolation method for
determining slope and aspect of DEMs. If it is the same as described at
http://www.quantdec.com/SYSEN597/GTKAV/section9/map_algebra.htm , then one
obvious problem is that both the slope and aspect may fail to be continuous
along any segment connecting two adjacent grid cell centers. It will also
be biased, as Horn points out. To eliminate both these problems one could
modify bilinear interpolation so it applies to the elevations at the NE,
SE, SW, and NW corner cells, and then do some smoothing, but that would be
more complicated than and probably inferior to the standard method (least
squares fit of a plane to the 3 x 3 neighborhood).
Cheers,
Bill Huber
Quantitative Decisions
Rosemont, PA
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