|
|
@@ -43,14 +43,15 @@ model accounts for sky obstruction by local relief features. Several solar
|
|
|
parameters are saved in the resultant maps' history files, which may be viewed
|
|
|
with the <a href="r.info.html">r.info</a> command.
|
|
|
|
|
|
-<p>The solar incidence angle raster map <i>incidout</i> is computed specifying
|
|
|
-elevation raster map <i>elevin</i>, aspect raster map <i>aspin</i>, slope
|
|
|
-steepness raster map <i>slopin,</i> given the day <i>day</i> and local time
|
|
|
+<p>
|
|
|
+The solar incidence angle raster map <i>incidout</i> is computed specifying
|
|
|
+elevation raster map <i>elev_in</i>, aspect raster map <i>asp_in</i>, slope
|
|
|
+steepness raster map <i>slope_in,</i> given the day <i>day</i> and local time
|
|
|
<i>time</i>. There is no need to define latitude for locations with known
|
|
|
and defined projection/coordinate system (check it with the <a href="g.proj.html">
|
|
|
g.proj</a>
|
|
|
command). If you have undefined projection, (x,y) system, etc. then the latitude
|
|
|
-can be defined explicitly for large areas by input raster map <i>latin</i>
|
|
|
+can be defined explicitly for large areas by input raster map <i>lat_in</i>
|
|
|
with interpolated latitude values. All input raster maps must
|
|
|
be floating point (FCELL) raster maps. Null data in maps are excluded from
|
|
|
the computation (and also speeding-up the computation), so each output raster
|
|
|
@@ -61,23 +62,28 @@ The specified day <i>day</i> is the number of the day of the general year
|
|
|
where January 1 is day no.1 and December 31 is 365. Time <i>time</i> must
|
|
|
be a local (solar) time (i.e. NOT a zone time, e.g. GMT, CET) in decimal system,
|
|
|
e.g. 7.5 (= 7h 30m A.M.), 16.1 = 4h 6m P.M..
|
|
|
-<p>Setting the solar declination <i>declin</i> by user is an option to override
|
|
|
+
|
|
|
+<p>
|
|
|
+The solar <i>declination</i> parameter is an option to override
|
|
|
the value computed by the internal routine for the day of the year. The value
|
|
|
of geographical latitude can be set as a constant for the whole computed
|
|
|
region or, as an option, a grid representing spatially distributed values
|
|
|
over a large region. The geographical latitude must be also in decimal system
|
|
|
with positive values for northern hemisphere and negative for southern one.
|
|
|
-In similar principle the Linke turbidity factor (<i>linkein</i>, <i>lin</i>
|
|
|
+In similar principle the Linke turbidity factor (<i>linke_in</i>, <i>lin</i>
|
|
|
) and ground albedo (<i>albedo</i>, <i>alb</i>) can be set.
|
|
|
<p>Besides clear-sky radiations, the user can compute a real-sky radiation (beam,
|
|
|
-diffuse) using <i>coefbh</i> and <i>coefdh </i>input raster maps defining
|
|
|
+diffuse) using <i>coef_bh</i> and <i>coef_dh</i> input raster maps defining
|
|
|
the fraction of the respective clear-sky radiations reduced by atmospheric
|
|
|
factors (e.g. cloudiness). The value is between 0-1. Usually these
|
|
|
coefficients can be obtained from a long-terms meteorological measurements
|
|
|
provided as raster maps with spatial distribution of these coefficients separately
|
|
|
-for beam and diffuse radiation (see Suri and Hofierka, 2004, section 3.2).<p>The solar irradiation or irradiance raster maps <i>beam_rad</i>, <i>diff_rad</i>,
|
|
|
-<i>refl_rad</i> are computed for a given day <i>day,</i> latitude <i>latin</i>,
|
|
|
-elevation <i>elevin</i>, slope <i>slopein</i> and aspect <i>aspin</i> raster maps.
|
|
|
+for beam and diffuse radiation (see Suri and Hofierka, 2004, section 3.2).
|
|
|
+
|
|
|
+<p>
|
|
|
+The solar irradiation or irradiance raster maps <i>beam_rad</i>, <i>diff_rad</i>,
|
|
|
+<i>refl_rad</i> are computed for a given day <i>day,</i> latitude <i>lat_in</i>,
|
|
|
+elevation <i>elev_in</i>, slope <i>slope_in</i> and aspect <i>asp_in</i> raster maps.
|
|
|
For convenience, the output raster given as <i>glob_rad</i>
|
|
|
will output the sum of the three radiation components. The program uses
|
|
|
the Linke atmosphere turbidity factor and ground albedo coefficient.
|
|
|
@@ -86,6 +92,7 @@ is near the annual average for rural-city areas. The Linke
|
|
|
factor for an absolutely clear atmosphere is <i>lin</i>=1.0. See notes below
|
|
|
to learn more about this factor. The incidence solar angle is the angle between
|
|
|
horizon and solar beam vector.
|
|
|
+
|
|
|
<p>
|
|
|
The solar radiation maps for a given day are computed by integrating the
|
|
|
relevant irradiance between sunrise and sunset times for that day. The
|
|
|
@@ -100,30 +107,34 @@ sun placed for every degree of movement in the sky you should set the
|
|
|
to every 3 minutes. Of course setting the time step to be very fine
|
|
|
proportionally increases the module's running time.
|
|
|
<p>The output units are in Wh per squared meter per given
|
|
|
-day [Wh/(m*m)/day]. The incidence angle and irradiance/irradiation maps can
|
|
|
-be computed without shadowing influence of relief by default or they can
|
|
|
-be computed with this influence using the flag <i>-s</i>. In mountainous areas
|
|
|
-this can lead to very different results! The user should be aware that taken
|
|
|
-into account the shadowing effect of relief can slow
|
|
|
-down the speed of computing especially when the sun altitude is low.
|
|
|
- When considering shadowing effect (flag <i>-s</i>) speed and precision computing
|
|
|
-can be controlled by a parameter <i>dist</i> which defines the sampling density
|
|
|
+day [Wh/(m*m)/day]. The incidence angle and irradiance/irradiation maps are
|
|
|
+computed with the shadowing influence of relief by default. It is also possible
|
|
|
+for them to be computed without this influence using the planar flag (<i>-p</i>).
|
|
|
+In mountainous areas this can lead to very different results! The user should be
|
|
|
+aware that taking into account the shadowing effect of relief can slow
|
|
|
+down the speed of computation, especially when the sun altitude is low.
|
|
|
+
|
|
|
+<p>
|
|
|
+When considering the shadowing effect, speed and precision of computation
|
|
|
+can be controlled by the <i>distance_step</i> parameter, which defines the sampling density
|
|
|
at which the visibility of a grid cell is computed in the direction of a
|
|
|
path of the solar flow. It also defines the method by which the obstacle's
|
|
|
-altitude is computed. When choosing <i>dist</i> less than 1.0 (i.e. sampling
|
|
|
-points will be computed at <i>dist</i> * cellsize distance), r.sun takes
|
|
|
-altitude from the nearest grid point. Values above 1.0 will use the maximum
|
|
|
+altitude is computed. When choosing a <i>distance_step</i> less than 1.0 (i.e. sampling
|
|
|
+points will be computed at <i>distance_step</i> * cellsize distance), <em>r.sun</em> takes
|
|
|
+the altitude from the nearest grid point. Values above 1.0 will use the maximum
|
|
|
altitude value found in the nearest 4 surrounding grid points. The default
|
|
|
-value <i>dist</i>=1.0 should give reasonable results for most cases (e.g.
|
|
|
-on DEM). <i>Dist</i> value defines a multiplying coefficient for sampling
|
|
|
+value <i>distance_step</i>=1.0 should give reasonable results for most cases (e.g.
|
|
|
+on DEM). The <i>distance_step</i> value defines a multiplying coefficient for sampling
|
|
|
distance. This basic sampling distance equals to the arithmetic average of
|
|
|
both cell sizes. The reasonable values are in the range 0.5-1.5. The values
|
|
|
below 0.5 will decrease and values above 1.0 will increase the computing
|
|
|
speed. Values greater than 2.0 may produce estimates with lower accuracy
|
|
|
in highly dissected relief. The fully shadowed areas are written to the output
|
|
|
maps as zero values. Areas with NULL data are considered as no barrier with
|
|
|
-shadowing effect .
|
|
|
-<p>The maps' history files are generated containing the following listed
|
|
|
+shadowing effect.
|
|
|
+
|
|
|
+<p>
|
|
|
+The maps' history files are generated containing the following listed
|
|
|
parameters used in the computation: <br>
|
|
|
- Solar constant 1367 W.m-2 <br>
|
|
|
- Extraterrestrial irradiance on a plane perpendicular to the solar beam [W.m-2] <br>
|
|
|
@@ -194,13 +205,13 @@ differences of up to an hour, in some cases (like Western Spain) even more.
|
|
|
On top of this, the offset varies during the year according to the Equation
|
|
|
of Time.
|
|
|
<p>
|
|
|
-To overcome this problem, the user can use the option <em>civiltime=<timezone_offset></em>
|
|
|
+To overcome this problem, the user can use the option <em>civil_time=<timezone_offset></em>
|
|
|
in r.sun to make it use real-world (wall clock) time. For example, for Central
|
|
|
Europe the timezone offset is +1, +2 when daylight saving time is in effect.
|
|
|
<p>
|
|
|
<!-- WE DON'T KNOW, check source code:
|
|
|
-If the user use the <em>civiltime</em> parameter, also the longitude needs to
|
|
|
-be supplied as a raster map with the <em>longin</em> parameter. Within a
|
|
|
+If the user use the <em>civil_time</em> parameter, also the longitude needs to
|
|
|
+be supplied as a raster map with the <em>long_in</em> parameter. Within a
|
|
|
latlon location, such a map can be easily made with:
|
|
|
|
|
|
<div class="code"><pre>
|
|
|
@@ -212,18 +223,18 @@ END OF WE DON'T KNOW
|
|
|
|
|
|
<h3>Shadow maps</h3>
|
|
|
A map of shadows can be extracted from the solar incidence angle map
|
|
|
-(incidout). Areas with zero values are shadowed. The <em>-s</em> flag
|
|
|
-has to be used.
|
|
|
+(incidout). Areas with zero values are shadowed. This will not work
|
|
|
+if the <em>-p</em> flag has been used.
|
|
|
|
|
|
<h3>Large maps and out of memory problems</h3>
|
|
|
|
|
|
With a large number or columns and rows, <b>r.sun</b> can consume
|
|
|
significant amount of memory. While output raster maps are not
|
|
|
-partitionable, the input raster maps are using the <em>numpartitions</em>
|
|
|
+partitionable, the input raster maps are using the <em>num_partitions</em>
|
|
|
parameter.
|
|
|
|
|
|
In case of out of memory error (<tt>ERROR: G_malloc: out of memory</tt>), the
|
|
|
-<em>numpartitions</em> parameter can be used to run a segmented calculation
|
|
|
+<em>num_partitions</em> parameter can be used to run a segmented calculation
|
|
|
which consumes less memory during the computations.
|
|
|
|
|
|
The amount of memory by <b>r.sun</b> is estimated as follows:
|
|
|
@@ -234,10 +245,10 @@ The amount of memory by <b>r.sun</b> is estimated as follows:
|
|
|
# rows,cols: rows and columns of current region (find out with g.region)
|
|
|
# IR: number of input raster maps without horizon maps
|
|
|
# OR: number of output raster maps
|
|
|
-memory_bytes = rows*cols*(IR*4 + horizonsteps + OR*4)
|
|
|
+memory_bytes = rows*cols*(IR*4 + horizon_steps + OR*4)
|
|
|
|
|
|
# with input raster map partitioning:
|
|
|
-memory_bytes = rows*cols*((IR*4+horizonsteps)/numpartitions + OR*4)
|
|
|
+memory_bytes = rows*cols*((IR*4+horizon_steps)/num_partitions + OR*4)
|
|
|
</pre></div>
|
|
|
|
|
|
<h2>EXAMPLES</h2>
|
|
|
@@ -248,14 +259,14 @@ g.region rast=elevation.dem -p
|
|
|
|
|
|
# calculate horizons
|
|
|
# (we put a bufferzone of 10% of maxdistance around the study area)
|
|
|
-r.horizon elevin=elevation.dem horizonstep=30 bufferzone=200 horizon=horangle dist=0.7 maxdistance=2000
|
|
|
+r.horizon elev_in=elevation.dem horizon_step=30 bufferzone=200 horizon=horangle distance_step=0.7 maxdistance=2000
|
|
|
|
|
|
# slope + aspect
|
|
|
r.slope.aspect elevation=elevation.dem aspect=aspect.dem slope=slope.dem
|
|
|
|
|
|
# calculate global radiation for day 180 at 14:00hs
|
|
|
-r.sun -s elevation.dem horizon=horangle horizonstep=30 aspin=aspect.dem \
|
|
|
- slopein=slope.dem glob_rad=global_rad day=180 time=14
|
|
|
+r.sun elevation.dem horizon=horangle horizon_step=30 asp_in=aspect.dem \
|
|
|
+ slope_in=slope.dem glob_rad=global_rad day=180 time=14
|
|
|
</pre></div>
|
|
|
|
|
|
<p>
|
|
|
@@ -267,8 +278,8 @@ in non-leap years):
|
|
|
<div class="code"><pre>
|
|
|
g.region rast=elev_ned_30m -p
|
|
|
|
|
|
-# considering cast shadows (-s)
|
|
|
-r.sun -s elev_ned_30m lin=2.5 alb=0.2 day=172 \
|
|
|
+# considering cast shadows
|
|
|
+r.sun elev_ned_30m lin=2.5 alb=0.2 day=172 \
|
|
|
beam_rad=b172 diff_rad=d172 \
|
|
|
refl_rad=r172 insol_time=it172
|
|
|
|
Hamish Bowman