The horizontal coordinate system of Radiance and the calculation method of Solar altitude and azimuth

radiance-general
1

Hi everyone,

When I use the month day hour as input of gensky or gendaylit, it will output Solar altitude and azimuth (like 28.4 -10.8). Based on the result I found that the horizontal coordinate system of Radiance is different from the general one. For example, for the horizontal coordinate system of packages (pysolar and pvlib) in Python, it is clockwise and the azimuth values for different directions are as follows.
Cardinal point Azimuth

North 0°
East 90°
South 180°
West 270

But for Radaince, I found the azimuth values for different directions is as shown below. Am I right?

Cardinal point Azimuth
North ±180°
East -90°
South 0°
West 90

Best regards,
Hao

2

Looks like this never got answered. Yes, your table is correct. There is a single line in the gensky man page that verifies it:

The altitude is measured in degrees above the horizon, and the azimuth is measured in degrees west of South.

Cheers,
-Greg

1 Like
3

Hi Greg, thank you very much for your reply.

Cheers,
Hao