[GRASSLIST:3046] r.los - question

[Izak Thomas Henry Deyzel]

Good day,

Does anyone know if r.los takes the curvature of the earth in effect
during its calculation?

ALSO:

"DESCRIPTION
 r.los generates a raster map output in which the cells that are visible
from a user-specified observer location are marked with integer values
that represent the vertical angle (in degrees) required to see those
cells (viewshed)."

The vertical angle as in: ?
    180 deg                  
   |
   |
    ----- 90 (91 - 1 degree above horizontal?)
   |
   |
     0
OR ?
    0
   |
   |
    ----- 90 (89 - 1 degree above horizontal?)
   |
   |
    180

Please help. 

Does any references exist to literature for the method of r.los?

Thanks.

Izz

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