<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>GRASS GIS: r.sunmask</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link rel="stylesheet" href="grassdocs.css" type="text/css"> </head> <body bgcolor="white"> <img src="grass_logo.png" alt="GRASS logo"><hr align=center size=6 noshade> <h2>NAME</h2> <em><b>r.sunmask</b></em> - Calculates cast shadow areas from sun position and DEM. Either A: exact sun position is specified, or B: date/time to calculate the sun position by r.sunmask itself. <h2>KEYWORDS</h2> raster <h2>SYNOPSIS</h2> <b>r.sunmask</b><br> <b>r.sunmask help</b><br> <b>r.sunmask</b> [-<b>zvsg</b>] <b>elev</b>=<em>string</em> <b>output</b>=<em>string</em> [<b>altitude</b>=<em>float</em>] [<b>azimuth</b>=<em>float</em>] [<b>year</b>=<em>integer</em>] [<b>month</b>=<em>integer</em>] [<b>day</b>=<em>integer</em>] [<b>hour</b>=<em>integer</em>] [<b>minute</b>=<em>integer</em>] [<b>second</b>=<em>integer</em>] [<b>timezone</b>=<em>integer</em>] [<b>east</b>=<em>value</em>] [<b>north</b>=<em>value</em>] [--<b>overwrite</b>] [--<b>verbose</b>] [--<b>quiet</b>] <h3>Flags:</h3> <DL> <DT><b>-z</b></DT> <DD>Zero is a real elevation</DD> <DT><b>-v</b></DT> <DD>verbose output (also print out sun position etc.)</DD> <DT><b>-s</b></DT> <DD>calculate sun position only and exit</DD> <DT><b>-g</b></DT> <DD>Print the sun position output in shell script style</DD> <DT><b>--overwrite</b></DT> <DD>Allow output files to overwrite existing files</DD> <DT><b>--verbose</b></DT> <DD>Verbose module output</DD> <DT><b>--quiet</b></DT> <DD>Quiet module output</DD> </DL> <h3>Parameters:</h3> <DL> <DT><b>elev</b>=<em>string</em></DT> <DD>Name of elevation raster map</DD> <DT><b>output</b>=<em>string</em></DT> <DD>Output raster map having shadows</DD> <DT><b>altitude</b>=<em>float</em></DT> <DD>A: altitude of the sun above horizon, degrees</DD> <DD>Options: <em>0-89.999</em></DD> <DT><b>azimuth</b>=<em>float</em></DT> <DD>A: azimuth of the sun from the north, degrees</DD> <DD>Options: <em>0-360</em></DD> <DT><b>year</b>=<em>integer</em></DT> <DD>B: year (1950..2050)</DD> <DT><b>month</b>=<em>integer</em></DT> <DD>B: month (0..12)</DD> <DT><b>day</b>=<em>integer</em></DT> <DD>B: day (0..31)</DD> <DT><b>hour</b>=<em>integer</em></DT> <DD>B: hour (0..24)</DD> <DT><b>minute</b>=<em>integer</em></DT> <DD>B: minutes (0..60)</DD> <DT><b>second</b>=<em>integer</em></DT> <DD>B: seconds (0..60)</DD> <DT><b>timezone</b>=<em>integer</em></DT> <DD>B: timezone (east positive, offset from GMT, also use to adjust daylight savings)</DD> <DT><b>east</b>=<em>value</em></DT> <DD>east coordinate (point of interest, default: map center)</DD> <DT><b>north</b>=<em>value</em></DT> <DD>north coordinate (point of interest, default: map center)</DD> </DL> <H2>DESCRIPTION</H2> <em>r.sunmask</em> 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 <a href=http://rredc.nrel.gov/>NREL</a> 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. <P> 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. <h2>Notes</h2> 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). <p> 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 <em>g.region -l</em> displays the map center's coordinates. <P> Note for module usage with <em>-g</em> flag and calculations close to sunset/sunrise: <pre> [...] sunangleabovehorizont=0.434240 sunrise=07:59:19 sunset=16:25:17 Time (07:59:02) is before sunrise (07:59:19)! WARNING: Nothing to calculate. Please verify settings. No map calculation requested. Finished. </pre> In above calculation appears to be a mistake as the program indicates that we are before sunrise while the <i>sun angle above horizon</i> is already positive. The reason is that <i>sun angle above horizon</i> is calculated with correction for atmosphere refraction while <i>sunrise</i> and <i>sunset</i> are calculated <b>without</b> correction for atmosphere refraction. The output without <em>-g</em> flag contains related indications. <h2>Acknowledgements</h2> Acknowledgements: National Renewable Energy Laboratory for their <a href=http://rredc.nrel.gov/solar/codes_algs/solpos/>SOLPOS 2.0</a> sun position algorithm. <H2>SEE ALSO</H2> <EM> <a href="g.region.html">g.region</a>, <a href="r.sun.html">r.sun</a>, <a href="r.slope.aspect.html">r.slope.aspect</a> </EM> <H2>AUTHOR</H2> Janne Soimasuo, Finland 1994<br> update to FP by Huidae Cho 2001<br> added solpos algorithm feature by Markus Neteler 2001 <p><i>Last changed: $Date: 2004-12-07 17:12:41 +0100 (Tue, 07 Dec 2004) $</i> <HR> <P><a href="index.html">Main index</a> - <a href="raster.html">raster index</a> - <a href="full_index.html">Full index</a></P> <P>© 2003-2008 <a href="http://grass.osgeo.org">GRASS Development Team</a></p> </body> </html>
