Windlight - The Sun, Azimuth and Altitude

You'll have to excuse me if this topic has been brought up before but while testing the latest WindLight client I just relised what has been bugging me about the noon lighting for so long.

It's not the lack of shadows or the ambient light or gamma or anything that has been previously mentioned in the more recent blog entries.

The sun appears to be pointing straight down!

Now I know the common belief is that this is what defines Noon but that's only true at very specific locations in the world. Depending where you are the sun will peak higher in the sky. Where I am in the UK the sun doesn't climb very high (only to around 60 degrees above the horizon) at noon. In fact if you look at this page: http://aa.usno.navy.mil/data/docs/AltAz.php

You can look up where you live (This page is invaluable for photographers doing landscapes as you can find out exactly when the sun has set). Heck even in LA in July the sun only gets to about 80 degrees above the horizon.

I'd hope that WindLight can be adjusted to support calculations like these so you might enter a longitude and latitude and have it simulate the arc of the sun in the sky more accurately. This would put an end to all those sims getting flat shaded during noon thanks to a sun casting perfectly down and stop avatars from getting some terrible shadowing under their nose, eyes and cheeks.

I've pasted the data from LA on July 22nd 2007 so you can all look and see how far off the sun in Windlight actually is. As way of explanation: Altitude of 0 degreees means the horizon. 90 degrees is aimed straight down. a negative value means the sun is below the horizon. The Azimuth is the position in the sky relative to north (0 degrees).

Astronomical Applications Dept.
U.S. Naval Observatory
Washington, DC 20392-5420

LOS ANGELES, CALIFORNIA
o , o ,
W118 22, N34 05

Altitude and Azimuth of the Sun
Jul 22, 2007
Pacific Standard Time

Altitude Azimuth
(E of N)

h m o o
04:00 -11.2 55.9
04:10 -9.5 57.5
04:20 -7.7 59.1
04:30 -5.9 60.6
04:40 -4.1 62.1
04:50 -2.2 63.6
05:00 0.2 65.0
05:10 1.8 66.4
05:20 3.6 67.7
05:30 5.5 69.1
05:40 7.4 70.4
05:50 9.3 71.7
06:00 11.3 73.0
06:10 13.3 74.3
06:20 15.3 75.5
06:30 17.3 76.8
06:40 19.3 78.0
06:50 21.3 79.3
07:00 23.3 80.6
07:10 25.4 81.8
07:20 27.4 83.1
07:30 29.5 84.4
07:40 31.5 85.7
07:50 33.6 87.0
08:00 35.7 88.3
08:10 37.7 89.7
08:20 39.8 91.1
08:30 41.9 92.6
08:40 43.9 94.1
08:50 46.0 95.7
09:00 48.0 97.3
09:10 50.1 99.1
09:20 52.1 100.9
09:30 54.2 102.9
09:40 56.2 105.0
09:50 58.2 107.3
10:00 60.1 109.8
10:10 62.0 112.6
10:20 63.9 115.6
10:30 65.8 119.0
10:40 67.5 122.9
10:50 69.2 127.3
11:00 70.8 132.4
11:10 72.3 138.2
11:20 73.6 144.9
11:30 74.6 152.5
11:40 75.5 161.0
11:50 76.0 170.3
12:00 76.2 180.1
12:10 76.0 189.8
12:20 75.5 199.0
12:30 74.6 207.6
12:40 73.6 215.2
12:50 72.3 221.8
13:00 70.8 227.6
13:10 69.2 232.7
13:20 67.5 237.1
13:30 65.7 241.0
13:40 63.9 244.4
13:50 62.0 247.4
14:00 60.1 250.2
14:10 58.1 252.7
14:20 56.1 255.0
14:30 54.1 257.1
14:40 52.1 259.1
14:50 50.1 260.9
15:00 48.0 262.6
15:10 45.9 264.3
15:20 43.9 265.9
15:30 41.8 267.4
15:40 39.7 268.8
15:50 37.7 270.2
16:00 35.6 271.6
16:10 33.5 273.0
16:20 31.5 274.3
16:30 29.4 275.6
16:40 27.4 276.9
16:50 25.3 278.1
17:00 23.3 279.4
17:10 21.2 280.6
17:20 19.2 281.9
17:30 17.2 283.1
17:40 15.2 284.4
17:50 13.2 285.7
18:00 11.2 286.9
18:10 9.3 288.2
18:20 7.3 289.5
18:30 5.4 290.8
18:40 3.5 292.2
18:50 1.7 293.6
19:00 0.1 294.9
19:10 -2.3 296.4
19:20 -4.2 297.8
19:30 -6.0 299.3
19:40 -7.8 300.8
19:50 -9.6 302.4
20:00 -11.3 304.0

Unfortuantely there is no direct lattitude adjustment in windlight wich is too bad. However there is an "east angle" feature whic in combination with the "time of day" slider when setting up control points in the day editor will allow you to make the sun traverse the sky at a lower angle.

And when Windlight falls under sim control you can set it for your sim for all visitors.

I am PRAYING that all the windlight functions will be exposed to LSL in which case you can then mimic winter and summer anywhere in the world and have random "weather" as well

But it would be easier if they specified an additional feature that allowed you to specify the lattitude from +90 to -90 and the sun would automatially travel acrross the sky at the proper angle.

The world is flat though and supported by a giant turtle everyone knows that!

You forgot about the elephans! Think of the elephans man, the elephants!

Maybe if someone could script the Giant Turtles to tilt in a lattitude/longditudle way, we can perhaps all be happy, although then I forsee the sea spilling off the map .

In several VR enviroment programmes I have used, it was a function to put in your actual lattitude/longditude settings, and link that to the OS time and date, whereby you could have actual daylight/nightitme effects for your small corner of the globe. You could override the time and adjust the sun/moon angles etc.
I'd like to see this function, coupled with the ability to ray trace the scene before taking a still shot, or.... making a movie (that would be wild).

Actually, the SL sun doesn't go straight overhead either, and the path it follows seems to vary over time.