[GRASS-dev] [GRASS GIS] #2606: Bugs in r.sun

[GRASS GIS]

#2606: Bugs in r.sun
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 Reporter:  ojni0001  |       Owner:  grass-dev@…              
     Type:  defect    |      Status:  new                      
 Priority:  normal    |   Milestone:                           
Component:  Default   |     Version:  unspecified              
 Keywords:            |    Platform:  MSWindows 7              
      Cpu:  x86-64    |  
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 I am new to this, so some things I write here may not be how it should be.
 My environment:
 Win7 x64
 GRASS Version (7beta and RC1) and hence 32 bit binary
 (although I mentioned GRASS7, but it may be present in GRASS 6, and
 earlier versions)

 I have 2 issues, probably needs 2 tickets but I am mentioning here both.

 I used a virtual landscape with elevation = constant (i.e. flat)

 Issue 1.

 I found that if I am using the aspect raster, zero degree is East and 270
 is South (as mentioned in the help).
 But if I am using a single value for aspect, zero or 360 degrees is North
 and 180 degree is
 South. I don't know if 90 degree is East or West. So, either help document
 has to be changed or the algorithm.

 Issue 2.

 When the slope is more than 60 degrees (probably from 45 degrees) facing
 North (northwards from east or west and North), the global radiation
 values are increasing

 i.e. the radiation value for slope of 70 degrees is more than when the
 slope is 60 degrees
    the radiation value for slope of 90 degrees is more than when the slope
 is 80 degrees

 Here, is a small table for demonstration (aspect of 0 or 360 is North, as
 mentioned in issue 1 above)
 Jan->17 (day=17), Feb->16 (day=47), Mar->16 (day=75) April->15 (day=105),
 May->15 (day=135)

 slope    aspect    Jan    Feb    Mar    Apr    May

 10    345    1.61    2.45    3.59    5.24    6.52

 20    345    0.93    1.73    2.93    4.70    6.18

 30    345    0.36    1.04    2.21    4.03    5.67

 40    345    0.13    0.46    1.49    3.26    5.01

 50    345    0.12    0.15    0.85    2.42    4.22

 60    345    0.11    0.16    0.85    2.38    4.17

 70    345    0.10    '''0.59    1.63    3.38    5.12'''

 80    345    '''0.54    1.29    2.47    4.30    5.94'''

 90    345    '''1.20    2.05    3.28    5.11    6.62'''

 10    360    1.59    2.42    3.57    5.23    6.52

 20    360    0.87    1.66    2.87    4.67    6.17

 30    360    0.27    0.91    2.11    3.99    5.66

 40    360    0.13    0.26    1.30    3.21    5.00

 50    360    0.12    0.14    0.47    2.36    4.21

 60    360    0.11    0.13    0.56    2.48    4.35

 70    360    '''0.10    0.35    1.51    3.49    5.32
 '''

 80    360    '''0.38    1.12    2.42    4.41    6.15
 '''

 90    360    '''1.08    1.97    3.28    5.22    6.81'''

 For testing I have attached a zipped file (simulation for slope 0 to 90,
 step 10 degrees and for aspect 0 to 360, step 15 degrees) with the script
 and sample elevation (flat landscape) file. The table may look a bit
 different but the pattern will be similar.

 Thank you.

 Nirmal

-- 
Ticket URL: <http://trac.osgeo.org/grass/ticket/2606>
GRASS GIS <http://grass.osgeo.org>