Discharge Map

[mzwarg]

Hello,

New here so apologize in advance but I have searched the forum and watched as many tutorials as I can find to not ask a redundant question...

I am simulating a fire growing from a fuel tank on a vehicle that encompasses the entire vehicle. I am working with a fire expert so the results need to be as physically accurate as possible. Working with the expert I have created a series of maps in Mudbox to define the area of discharge over time on the geometry. I then tried animating mix maps in 3dsMax. That yielded a sharp 'pop' in the transition despite the transitions animated over several seconds? So I thought it was maybe a mix map 3dsMax issue and then took the maps into After Effects and animated the transitions and rendered out an image stream. I got the same results of very sharp transitions.

I am suspecting that Phoenix discharge map only works on pure white and black values and my maps may need to change to not have any gray values?

Thank you for any help you can offer.

[Ivaylo Katev]

no, the discharge is not pure on/off, it accepts gray scale. can we see some render results, in the most cases one picture worth a thousand of words

[mzwarg]

I have been doing some testing and have found that to paint where fire will emit on the geometry the discharge map transitions work out better sharp edged, black to white with very little or no feathering of gray-scale. I was using black and white maps to contrast but stumbled upon another problem. With pure white defining where the fire emits it was coming out like a flame thrower. Am I correct, does the grayscale value effect the velocity of the discharge? What does pure white or black equate to when the discharge is set to 1 and the discharge map is used? I've been dialing in my settings and found that my output at 0.001 with a black and white map now yields wind rather than a flame thrower velocity. Is there a better way than what I'm doing?


Password: Phoenix

[Ivaylo Katev]

i played a bit with the discharge map, to check that everything is ok. well, i think i found the reason for the confusion, the discharge map is working, but it's hard to make difference between the gray and white zones. actually the discharge affects only the velocity of the outgoing fire, it's hard to create fire zones with different height by it, because the flames are mixing quickly and the result is homogenous fire.
can you give some reference, real or cg, what you are trying to do? i'm sure we can find the correct way.

[mzwarg]

I've been referencing this video:

Currently I need to slow down the velocity of the outgoing fire so the smoke doesn't carry as much of the inertia. I've got the fire to a near believable height and the flames and smoke emitting more realistically, but it still has the look of a gust of wind pushing the inertia of the smoke. Should I be increasing the cooling factor? Increasing the smoke buoyancy? Or lowering the discharge map's output further?

I have to use an animated map to animate the growth of the fire based upon a fire experts input of the event. The map grows over time and is very specific to the other sources of fire that get composited.

[Ivaylo Katev]

well, if you need to decrease the outgoing velocity, just decrease the global discharge. the source uses both the map and the discharge parameter, the local discharge is the product of the map brightness and the discharge value. the result is set as velocity, the direction is the geometry normal. to understand this better, you can export the velocity channel and visualize the velocity in the viewport. playing with the lower limit of the visualization, you can measure the content of each cell, and you will see that the surface velocities are exactly the product of the map and the discharge.

[mzwarg]

That's what I've been finding in testing, reducing the map output and the global discharge. I had to increase the decimal precision in 3ds Max just to be able to get the values reduced enough to get acceptable results. I'm working in feet units.

[Ivaylo Katev]

this sounds strange, feet unit is pretty good, is not miles or kilometers to need so small value of the discharge. the discharge value means speed, a normal fire has speed about few feets per second so this must be the proper value.