I believe this is correct, yes.
···
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Randolph
On 2011-08-11 09:14:49 -0700, Ji Zhang said:
Dear Radiance experts,
May I confirm with you that in Radiance there're several conventions regarding some of the locational information should be specified:
1. Longitude east of Greenwich is specified as NEGATIVE value: e.g Singapore's longtitude of 104E should be specified as -104.
2. A positive azimuth angle denotes an angle starting from due SOUTH and rotating clockwise.
3. Standard meridian of a city equals to the Greenwich Mean Time of the city multiplied by 15, and a NEGATIVE value indicates a timezone EAST of Greenwich (e.g. Singapore belongs to the EAST8 timezone, so it's meridian is -120=(8*15)*(-1) )Take London as an example, to know the solar altitude and azimuth at 9:00am 1st Jan at London (altitude 51.15N and longitude 0.18W), the gensky command is: "gensky 1 1 9:00GMT -a 51.15 -o 0.18 -m 0" or "gensky 1 1 9:00 -a 51.15 -o 0.18 -m 0"
and you'll get:
# gensky 1 1 9:00GMT -a 51.1500015259 -o 0.180000007153 -m 0
# Local solar time: 8.93
# Solar altitude and azimuth: 5.5 -41.8
# Ground ambient level: 6.0
......and in this case the solar azimuth thus obtained indicates an angle starting from due South and rotating clockwise for 41.8 degree.
Thanks!
Ji
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