I think that no comparison can be made between different programs results without knowing the value of DeltatT that has been used. Ephemeris tables usually declare the value of DeltaT that was used. It is also worthy to note that for gnomonic applications all these results are more than correct :-) Regards. Gian
----Messaggio originale---- Da: [email protected] Data: 03/03/2010 20.51 A: "John Goodman"<[email protected]> Cc: "Sundial List"<[email protected]> Ogg: Re: Solar position calculator Hi I got following results from the link http://www.roman-britain.org/astronomy/astro.htm# which I believe is trustworthy azimuth=200.7233 (20.7233 if south is the zeropoint) altitude= 39.1827 I also tested the results with my own semi-accurate PcAllakka with following results azimuth=200.715 and altitude=39.188 Anyone interested can load the program from http://pc-calculator.110mb.com/allakka/ or perhaps some of you is curious enough to visit my solar tracking sundial pages at http://pc-calculator.110mb.com/tracker/solartracker.html Greetings Aimo Niemi 2010/3/3 John Goodman <[email protected]> If anyone needs to make precise solar position calculations, the following software may be useful. There are a few caveats. The software is not a stand-alone application, it's a software library. The software library needs to be used from the command line and it runs using the Python programming language. I'm a Mac user and this is one of those rare occasions when an arcane set of requirements actually favors the Mac. While Macintosh users tend to be allergic to the command line, it has existed in the OS for the past 10 years. Python is there too, lurking under the surface. I don't know enough about the PC, but clearly the command line is there and Python is available too. ( http://www.python.org/download/windows/ ) With all that preface, here's what the code can do. Once the necessary files are installed, you can type the following commands and see the following results: >>> import datetime, solar >>> d = datetime.datetime(2010, 3, 3, 18, 0, 0) >>> lat = 42.0 >>> long = -71 >>> solar.GetAltitude(lat, long, d) 39.203509044804704 >>> solar.GetAzimuth(lat, long, d) -20.717667802423591 >>> Someone with an ephemeris can check these results. The format for datetime is "yyyy, mm, dd, hh, mm, ss", optionally followed by a number of microseconds. The time value entered is for UTC. There are other functions for calculations that I haven't explored. You can read more about the software tools at http://pysolar.org/ Example uses are shown at http://wiki.github.com/pingswept/pysolar/examples The software itself is at http://github.com/pingswept/pysolar/downloads All of this software is the work of Brandon Stafford, who has generously offered his code free of charge to anyone who may find it useful. I have little experience with this software but, as much as I can, I'll be happy to help anyone trying to use it. If there are any questions, I can pass them on to Brandon. I hope this is helpful to some. --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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