Particle System parameters and texture for fog and clouds

I am experimenting with particle system (PS) and I obtained a lot of interesting effects by changing the parameters and textures to show as particles. However I was not yet able to create two effects I need: a realistic fog that stays permanently on ground and covers just avatar's forelegs, and a white nembus in sky. I know that SL is NOT using PS to make clouds, so I do not expect to obtain a result comparable to SL one, but at least as close as possible.

Any help appreciated. I already know the PS basics and understand most parameters, even if I still cannot predict a priori an effect without seeing it ... not so expert.

Thank you in advance.

The key ingredients to realistic cloud/fog effects are

1) Relatively low (say, 0.4 to 0.6) PSYS_PART_START_ALPHA petering out to zero for PSYS_PART_END_ALPHA

2) Low PSYS_SRC_BURST_SPEED_MIN & PSYS_SRC_BURST_SPEED_MAX values, albeit enough to make the particle move away from the prim; 0.08 and 0.15 respectively are good starting points

3) Set PSYS_SRC_PATTERN to PSYS_SRC_PATTERN_ANGLE or PSYS_SRC_PATTERN_ANGLE_CONE , set PSYS_SRC_ANGLE_BEGIN and PSYS_SRC_ANGLE_END appropriately. (say, about 1.3 and 1.57 respectively)

4) PSYS_PART_START_SCALE & PSYS_PART_END_SCALE set to produce a long, wide flat shape. (say, <0.2,0.05,0.0> & <4.2,1.3,0.0> respectively)

5) PSYS_PART_START_COLOR set to about <0.816,0.816,0.816> (light gray) but suit to taste

6) PSYS_PART_END_COLOR set to a darker shade of grey (try <0.216,0.216,0.216> but, again. adjust to suit

7) PSYS_PART_BOUNCE_MASK = ON ('0x004' value in PSYS_PART_FLAGS)

Suitable light, opaque texture UUID for PSYS_SRC_TEXTURE

9) Adjust PSYS_SRC_BURST_PART_COUNT and PSYS_SRC_BURST_RATE to change density. The higher _COUNT and lower _RATE is the more dense the cloud/fog formation

This will give you a decent starting template from which to kick-off...

BTW: I also use llFrand for the size and colour vectors to introduce a wider variety of individual cloud/fog emissions

oooo Debbie, really great info there. Thanks for posting!

Realistic fog requires LOTS of superposed particles with very low alpha (mostly transparent), and should be set as emissive (during the day at least) so your fog doesn't weirdly changes lightness when you turn your head.

Also, note that maximum particle size is 4m in each direction, anything higher is capped. That's why I've switched to using huge prims instead of big clutters of thousands of particles for clouds. Maximum life of a particle is, AFAIK, 30 seconds only.

If you want to spread your particles faster than in 30 seconds you can, instead of using a low burst speed, use a null burst speed with varying burst radius and a timer function. This way you can spread your particles in a few calls of the timer.