[GRASS-dev] Re: [GRASS GIS] #498: r.sun2 commissioning trials

GRASS GIS trac at osgeo.org
Wed Jan 25 22:27:37 EST 2012

#498: r.sun2 commissioning trials
 Reporter:  hamish  |       Owner:  hamish          
     Type:  defect  |      Status:  assigned        
 Priority:  major   |   Milestone:  6.4.2           
Component:  Raster  |     Version:  svn-develbranch6
 Keywords:  r.sun   |    Platform:  All             
      Cpu:  All     |  

Comment(by hamish):

 Replying to [comment:19 dylan]:
 > The output looks correct when slope and aspect are specified.

 One thing I notice about sa_diff_rad.015.jpg is that the diffuse output
 there seems to incorporate the effects of direct shading, while
 diff_rad.015.jpg does not.

 I would ~ guess that the amount of diffuse light reaching a grid cell
 would be directly proportional to the visible sky. (stable throughout the
 day; should be independent of aspect (sa_diff.015.jpg is correlated with
 aspect); perhaps we should try a new r.surf.volcano surface and see how
 much diffuse light gets into a deep caldera or well, with the only visible
 sky a small amount directly above)

 Ultimately I think a formal verification of the model using (multiple)
 real light meters is going to be necessary, but to get the deployment
 design right we're going to have to become experts in the algorithm. (e.g.
 if a light meter is shaded by a reflective wall, its beam will be 0 but
 will it's diffuse be increased vs a black wall? how many bounces does
 reflected light follow? just one?)

 here's another pseudo-data test-case, I'll post results once it finishes.

 #spearfish (further north than NC so more defined shadows)
 g.region -d
 r.mapcalc "undulates = (2 + sin( row() * 2 ) + cos( col() * 2 )) * 500"
 r.colors undulates color=bcyr
 nviz undulates

 time r.sun -s elevin=undulates day=$DAY step=0.05 \
   beam_rad=rad_test.und.355.beam \
   diff_rad=rad_test.und.355.diff \


Ticket URL: <https://trac.osgeo.org/grass/ticket/498#comment:22>
GRASS GIS <http://grass.osgeo.org>

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