DESCRIPTION
r.sunmask creates an output map layer based on an input elevation
raster map layer and the sun position. The output map layer contains the
cast shadow areas arising from sun shine and elevations. The user can define
the sun position either directly or the module calculates it from given
location and date/time parameters using the
NREL sun position algorithm. So either
"A:"-parameters to specify the exact known sun position or "B:-parameters"
to specify date/time for sun position calculation by r.sunmask itself have
to be used.
The module performs sunset/sunrise checks and refraction correction for sun
position calculation. Local coordinate systems are internally transformed to
latitude/longitude for the SOLPOS algorithm. The elevation is not considered
in the sunset/sunrise calculations.
Notes
r.sunmask and daylight savings: Rather than convert time to GMT, the solpos
algorithm uses what is called Local Standard Time, which is generally
defined politically as an offset from GMT. So the key is the offset from
GMT, which the solpos Time Zone parameter. If the user specifies clock time
(different for winter and summer), he/she would have to change the Time Zone
parameter seasonally in r.sunmask (timezone parameter).
Note: In latitude/longitude locations the position coordinates pair
(east/west) has to be specified in decimal degree (not D:M:S). If
not specified, the map center's coordinates will be used.
Also g.region -l displays the map center's coordinates.
Acknowledgements
Acknowledgements: National Renewable Energy Laboratory for their SOLPOS 2.0 sun position
algorithm.
SEE ALSO
g.region,
r.sun,
r.slope.aspect
AUTHOR
Janne Soimasuo, Finland 1994
update to FP by Huidae Cho 2001
added solpos algorithm feature by Markus Neteler 2001
Last changed: $Date: 2003/05/06 15:35:18 $