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From Thomas.Huld jrc.it Thu Jul 26 11:01:44 2007
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To: Markus Neteler <neteler itc.it>
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CC: Jaro Hofierka <hofierka geomodel.sk>, "marcel.suri jrc.it"
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<marcel.suri jrc.it>, Tomas Cebecauer <tomas.cebecauer jrc.it>
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Date: Thu, 26 Jul 2007 11:01:44 +0200
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Subject: Re: r.horizon source code
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I'm sending the r.sun sources to you here, even though the description is not
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yet up to date. I think it works OK now, though I haven't tried all possible
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combinations of options. For instance, I haven't ever used the incidence
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angle or insolation time outputs. There's no reason why they should have
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stopped working but there are always changes that break something unexpected.
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- possibility to read in horizon rasters to use with the shadow calculation.
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- Calculation of the shadowing effect should now also work in lat/lon
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- There was a bug in r.sun whereby the shadowing effect was calculated wrong
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when the left-right and up-down directions in the projection are different
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from east-west and north-south, as is the case in the projection we use
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(Lambert Azimuthal) when moving away from the point of origin. This has been
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fixed now though only checked with Lambert Azimuthal.
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- I'm not sure if this went in already in a previous version, but the
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algorithm now also takes into account the curvature of the earth when
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- new output possibility: glob_rad, which is the sum of the three radiation
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- new input parameter: <i>civiltime</i>. When this parameter is given, the
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single time calculation will calculate the irradiance at the *same* time for
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the entire raster instead of using the local solar time. The value of
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<i>civiltime</i> is the timezone, relative to GMT. (+1 for central Europe)
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- new input parameter <i>numpartitions</i> No change in the calculation
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methods, but the program will read the input rasters and do the calculations
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in a number of chunks, instead of reading in everything at the start. Output
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is still only at the very end. This is only to save memory. It will not work
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if you try to calculate shadows without the horizon information, and the
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program will tell you so.
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- I reorganized the source code quite a lot. In particular, I spun off several
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functions into a separate source file called rsunlib.c. I also organized many
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of the global variables into <i>struct</i>'s for an easier overview. I did
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this because we work here with several derivatives of r.sun:
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* r.sunyear which calculates the optimum inclination angle for maximum
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* r.pv which calculates the PV output taking into account also temperature
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* r.sun.2axis which is r.sun for a moving plane, whose normal always points
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to the sun (two-axis tracking solar energy systems).
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Splitting the source code made it easier to reuse bits for these r.sun
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derivatives. I haven't updated the Makefile to account for these changes yet.
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Look at the little script "compdebug" in the source directory.
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There may be other changes that I've forgotten about but nothing dramatic.
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Joint Research Centre of the European Commission
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e-mail: Thomas.Huld@jrc.it
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