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Cid Jacobs
Theoretical Meteorologist
Join date: 18 Jul 2004
Posts: 4,304
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10-30-2006 15:06
Linden Lab,
I was wondering if it is possible to disclose, or give some behind the scenes in any form, in the way wind in Second Life is calculated, in specific to the speed and direction. Is the current speed and direction directly related to the next updated speed or wind, is it completely random? How often is it updated? Any information on this and any other weather systems in Sl now or in the future would be appreciated. Thank you for your time.
Sincerely,
Cid Jacobs
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Torley Linden
Enlightenment!
Join date: 15 Sep 2004
Posts: 16,530
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11-02-2006 14:45
Cid! I got your notecard inworld... do you still want an answer to this? With the curious questions about weather you've asked over time, it sounds like there should be a FAQ in the future so all Second Life meterologists can benefit. In any case, I'll ask Andrew, who's helped provide answers for related questions before.  |
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Andrew Linden
Linden staff
Join date: 18 Nov 2002
Posts: 692
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11-21-2006 09:50
I know I answered this before, but I couldn't find the link. It's lost!
The wind is based on the 2D stable fluid method described in Jos Stam's article in the Siggraph 1999 proceedings. Each region is its own incompressible simulation but it trades boundary conditions with its neighbors so it is possible for one region to affect another. The consequence of this is that the largest coherent vortex that the wind can form is on the scale of a single region, however wind flowing out of one region will push that in the other so some wind structures are larger than a single sim.
It has some pseudo stable chaos magic injected that keeps it boiling, and the chaos is scaled by the sun position so that the ambient activity varies on a daily schedule. I think there is a small offset that causes the global wind average to point away from the sun around sunrise and sunset, however it has been a long time since I've looked at that code.
There used to be a way to interact with the wind (push it around) but one of the other developers quietly disabled that feature sometime after launch in June 2003, and I've never got around to putting it back in.
Originally we were very concerned about how many CPU cycles the wind would use so it is dialed down to a fairly low resolution (16x16) simulation with only a few steps a second. Someday it would be nice to revisit the wind simulation code and enhance it, however looking at my busy schedule it would be a year or two away at least.
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