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@@ -15,21 +15,24 @@ position calculation. Local coordinate systems are internally transformed to
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latitude/longitude for the SOLPOS algorithm. The elevation is not considered
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in the sunset/sunrise calculations.
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-<h2>Notes</h2>
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+<h2>NOTES</h2>
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r.sunmask and daylight savings: Rather than convert time to GMT, the solpos
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algorithm uses what is called Local Standard Time, which is generally
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defined politically as an offset from GMT. So the key is the offset from
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GMT, which the solpos Time Zone parameter. If the user specifies clock time
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(different for winter and summer), he/she would have to change the Time Zone
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-parameter seasonally in r.sunmask (timezone parameter).
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+parameter seasonally in r.sunmask (timezone parameter). See also
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+<a href="http://en.wikipedia.org/wiki/Daylight_saving_time_by_country">Daylight saving time by region and country</a>.
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+
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<p>
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Note: In latitude/longitude locations the position coordinates pair
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(east/west) has to be specified in decimal degree (not D:M:S). If
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not specified, the map center's coordinates will be used.
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Also <em>g.region -l</em> displays the map center's coordinates.
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-<p>Note for module usage with <em>-g</em> flag and calculations
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+<p>
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+Note for module usage with <em>-g</em> flag and calculations
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close to sunset/sunrise:
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<pre>
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@@ -51,6 +54,44 @@ calculated with correction for atmosphere refraction while
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correction for atmosphere refraction. The output without
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<em>-g</em> flag contains related indications.
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+<h2>EXAMPLE</H2>
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+
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+Example for North Carolina sample data set for the calculation
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+of sun position angles and more:
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+
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+<div class="code"><pre>
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+# set the region to a place near Raleigh (NC)
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+g.region rast=elev_lid792_1m -p
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+
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+# compute the sun position
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+r.sunmask -s --v elev_lid792_1m out=dummy year=2012 month=2 \
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+ day=22 hour=10 minute=30 sec=0 timezone=-5
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+Using map center coordinates: 638650.000000 220375.000000
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+Calculating sun position... (using solpos (V. 11 April 2001) from NREL)
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+2012/02/22, daynum: 53, time: 10:30:00 (decimal time: 10.500000)
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+long: -78.678856, lat: 35.736160, timezone: -5.000000
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+Solar position: sun azimuth: 143.006424, sun angle above horz. (refraction corrected): 36.233883
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+Sunrise time (without refraction): 06:58:11
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+Sunset time (without refraction): 17:58:47
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+
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+# with -g flag
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+r.sunmask -s -g --v elev_lid792_1m out=dummy year=2012 month=2 \
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+ day=22 hour=10 minute=30 sec=0 timezone=-5
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+Using map center coordinates: 638650.000000 220375.000000
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+Calculating sun position... (using solpos (V. 11 April 2001) from NREL)
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+date=2012/02/22
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+daynum=53
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+time=10:30:00
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+decimaltime=10.500000
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+longitudine=-78.678856
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+latitude=35.736160
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+timezone=-5.000000
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+sunazimuth=143.006424
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+sunangleabovehorizon=36.233883
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+sunrise=06:58:11
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+sunset=17:58:47
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+</pre></div>
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+
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<h2>Acknowledgements</h2>
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Acknowledgements: National Renewable Energy Laboratory for their
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Markus Neteler