llCloud

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Revision as of 17:22, 3 February 2010 by Pete Olihenge (talk | contribs) (Corrected reference in notes to range of values returned)
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Summary

Function: float llCloud( vector offset );
0.0 Forced Delay
10.0 Energy

Returns a float that is the cloud density at the object position + offset

• vector offset

Examples

<lsl> default {

   touch_start(integer num)
   {
       llSay(0,"Cloud density:" + (string)llCloud(ZERO_VECTOR));
   }

}

</lsl>

Notes

How clouds work:

  • SL features a cellular automata-based weather system.
  • There are 16x16 square cloud "cells" per sim (which means each is 16x16m in size).
  • The cloud density data is sent from the server to the client once every time the agent connects to a simulator via logging in or teleporting into a simulator.
  • The client attempts to render clouds from the cloud algorithm results sent from the server, which is why different clients can see different cloud formations and de-synchronizes cloud view from the server over time.
  • The Z value in the vector is irrelevant (clouds are always between about 180-200m absolute height).
  • It returns a value between 0.0 and 2.0, with 0.0 being no clouds, and 1.0 very dense clouds. Values returned in the range 1.0 - 2.0 indicate rainfall, but the option for rain is not currently implemented.
  • Clouds and wind are related.


The cloud seed/growth/dissipation algorithm uses a solenoidal vector field, which is a vector field with zero-divergence: ∇ · v = 0

This condition is satisfied whenever v has a vector potential A, because if v = ∇ ⨯ A then ∇ · v = ∇ · (∇ ⨯ A) = 0

See Also

Functions

•  llWind
•  llGetSunDirection

Deep Notes

Signature

function float llCloud( vector offset );