Viewshed operation.

[andrewbt]

I think this is a duplicate of #24 ?

[lossyrob]

thanks, closed #24

[lossyrob]

Notes on Viewshed from @rcheetham :

• Esri docs - will provide parameters and general information on inputs and outputs - http://resources.arcgis.com/en/help/main/10.1/index.html#//009z000000v8000000 And this one adds some info on curvature and refraction corrections: http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=How%20Viewshed%20works
• GRASS docs - some general information on parameters and a basic algorithm - http://grass.osgeo.org/grass70/manuals/r.viewshed.html
• Sextant has a viewshed opp and source code is at: https://code.google.com/p/sextante/
• SAGA has a viewshed opp and source codes is at: http://sourceforge.net/projects/saga-gis/

• This is the kind of problem that gets academics excited - here are a few articles:

  -> ftp://ftp.disi.unige.it/person/MagilloP/PDF/visib02.pdf - a survey of algorithms -> http://www.asprs.org/a/publications/pers/2003journal/july/2003_jul_767-774.pdf - includes a comparison of different approaches -> Kim, Y., Rana, S., & Wise, S. (2004). Exploring Multiple Viewshed Analysis Using Terrain Features and Optimisation Techniques. Computers and Geosciences, 30(9), 1019. http://www.cs.rpi.edu/~cutler/publications/andrade_geoinformatica.pdf -> http://www.asprs.org/a/publications/pers/96journal/october/1996_oct_1157-1164.pdf -> http://www.researchgate.net/publication/220913363_An_Efficient_Algorithm_to_Compute_the_Viewshed_on_DEM_Terrains_Stored_in_the_External_Memory

• Hey, what's that - http://www.heywhatsthat.com/ - could be used for testing to confirm results match another app

A related task would be to generate a profile for a given path across an elevation.

[lossyrob]

Fixed by #783