[R-sig-Geo] Adding smoothing factor to terrain function in raster

[Alex Zvoleff]

Dear list (and Robert Hijmans in particular),

I am using  the terrain function in the raster package to calculate
slope and aspect prior to performing topographic correction. The
landsat package supports applying a smoothing factor during the slope
calculation, to avoid over-correction of reflectance in high slope
areas with low illumination (as suggested by Riaño, Salas, and Aguado
2003). However I have been using the terrain function in the raster
package to calculate slope and aspect since it can handle large
rasters and is coded in C.

Attached is a patch to allow applying a smoothing factor when
calculating slope using the terrain function in raster. Is there a
chance of including the attached changes (based on r2994) in the next
release of raster?

Thanks,
Alex

Ref: Riaño D., Chuvieco E., Salas J., and Aguado I., 2003. Assessment
of different topographic corrections in Landsat-TM data for mapping
vegetation types. IEEE Transactions on Geoscience and Remote Sensing
41: 1056-1061.

-- 
Alex Zvoleff
Postdoctoral Associate
Tropical Ecology Assessment and Monitoring (TEAM) Network
Conservation International
2011 Crystal Dr. Suite 500, Arlington, Virginia 22202, USA
Tel: +1-703-341-2749, Fax: +1-703-979-0953, Skype: azvoleff
http://www.teamnetwork.org | http://www.conservation.org
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