why do not absorbtion/scattering ramps work

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why do not absorbtion/scattering ramps work

Postby coilbook » Tue Jan 17, 2017 4:17 pm

coilbook Tue Jan 17, 2017 4:17 pm
hi is there any way to have darker smoke coming out and dissipating to white? Ramps do nothing thank you
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Re: why do not absorbtion/scattering ramps work

Postby coilbook » Tue Jan 17, 2017 4:27 pm

coilbook Tue Jan 17, 2017 4:27 pm
looks like max grid value solved it. Does anyone know what is max grid value for? Thank you
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Re: why do not absorbtion/scattering ramps work

Postby haze » Tue Jan 17, 2017 7:07 pm

haze Tue Jan 17, 2017 7:07 pm
coilbook wrote:looks like max grid value solved it. Does anyone know what is max grid value for? Thank you


From https://docs.otoy.com/#standalone-v2-new-features-in-v3
There is an important consequence of volume animations specifically related to volume ramps: There is a “Max value” on the ramps, which you must set to a reasonable value. This value is used to scale grid values to between 0 and 1, so that the ramp can map these back to colours in the colour gradient. This is needed because maximum values in the grids sometimes differ greatly throughout VDB sequences. If you set a Max value too high or too low, this will still work, but you will only see a subset of the colours in the gradient that you specify. The maximum values for grids in the current VDB selected are now shown in the volume node’s inspector pane. A good rule of thumb is to choose a value near to these, but you are free to customise as you like. The max value should be set to the max value of the channel for all the volumes in a sequence. For an indication, please see the info provided by the volume node in the node stack.
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Re: why do not absorbtion/scattering ramps work

Postby Goldisart » Wed Jan 18, 2017 7:29 am

Goldisart Wed Jan 18, 2017 7:29 am
https://youtu.be/CWJN7Gfeht0

I ran it very convenient to set up really looking forward to support for Phoenix FD format * AUR
CAM_0010029.png

question !!!! when you plan to support the Phenix FX ????? or, again, will render using the VBD file anyway
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Re: why do not absorbtion/scattering ramps work

Postby coilbook » Sat Jul 29, 2017 2:08 pm

coilbook Sat Jul 29, 2017 2:08 pm
haze wrote:
coilbook wrote:looks like max grid value solved it. Does anyone know what is max grid value for? Thank you


From https://docs.otoy.com/#standalone-v2-new-features-in-v3
There is an important consequence of volume animations specifically related to volume ramps: There is a “Max value” on the ramps, which you must set to a reasonable value. This value is used to scale grid values to between 0 and 1, so that the ramp can map these back to colours in the colour gradient. This is needed because maximum values in the grids sometimes differ greatly throughout VDB sequences. If you set a Max value too high or too low, this will still work, but you will only see a subset of the colours in the gradient that you specify. The maximum values for grids in the current VDB selected are now shown in the volume node’s inspector pane. A good rule of thumb is to choose a value near to these, but you are free to customise as you like. The max value should be set to the max value of the channel for all the volumes in a sequence. For an indication, please see the info provided by the volume node in the node stack.



Hi Can you explain what it means "The max value should be set to the max value of the channel for all the volumes in a sequence. " Still not clear what to set it for in phoenix.
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Re: why do not absorbtion/scattering ramps work

Postby haze » Mon Jul 31, 2017 2:19 am

haze Mon Jul 31, 2017 2:19 am
Assume for the moment that you have no animation in your scene. Looking at the volume node in octane, the node inspector will give you some numbers such as "abs. scat. emis: 6.51/4.10/3.00" at the top. These numbers give you the max values of each channel of the volume that is currently loaded. For example, max value of absorption is 6.15.

If you have no animation in your scene, then you would always set the volume ramp "Max Value" to 6.51 for this volume, and the whole colour range of the ramp will be displayed.

Now assume you have 2 volumes in an animation, and the max value of absorption is 6.51 in one of them, and say 3 in the other. If you left the ramp's "Max Value" on 6.51 then the colours of the volumes will be consistent for the same densities in both. However, on the volume with max absorption value of 3, you wont see the whole colour range. Similarly, if you have another volume in the sequence that has max absorption value of 12, then you'll see the whole colour range, but much of it will just be the colour on the max end of the ramp.

What I suggest is to scrub through the timeline, and look at the max values of the volumes. Pick a value that's suitably close to the max value that you see, but one that still gives you a reasonable spread of colours (ie, it really comes down to how you want to setup your ramp)
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Re: why do not absorbtion/scattering ramps work

Postby coilbook » Mon Jul 31, 2017 6:52 pm

coilbook Mon Jul 31, 2017 6:52 pm
haze wrote:Assume for the moment that you have no animation in your scene. Looking at the volume node in octane, the node inspector will give you some numbers such as "abs. scat. emis: 6.51/4.10/3.00" at the top. These numbers give you the max values of each channel of the volume that is currently loaded. For example, max value of absorption is 6.15.

If you have no animation in your scene, then you would always set the volume ramp "Max Value" to 6.51 for this volume, and the whole colour range of the ramp will be displayed.

Now assume you have 2 volumes in an animation, and the max value of absorption is 6.51 in one of them, and say 3 in the other. If you left the ramp's "Max Value" on 6.51 then the colours of the volumes will be consistent for the same densities in both. However, on the volume with max absorption value of 3, you wont see the whole colour range. Similarly, if you have another volume in the sequence that has max absorption value of 12, then you'll see the whole colour range, but much of it will just be the colour on the max end of the ramp.

What I suggest is to scrub through the timeline, and look at the max values of the volumes. Pick a value that's suitably close to the max value that you see, but one that still gives you a reasonable spread of colours (ie, it really comes down to how you want to setup your ramp)



Thank you
We use Phoenix 3 and 3ds max could you tell me where to look up those values? Thank you
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Re: why do not absorbtion/scattering ramps work

Postby haze » Mon Jul 31, 2017 7:54 pm

haze Mon Jul 31, 2017 7:54 pm
I'll ask someone in the office who knows phoenixFD to have a look for you.

In the mean time, a workaround could be to export a VDB from the start, middle and end of the sequence and load them in octane to see the values.
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Re: why do not absorbtion/scattering ramps work

Postby coilbook » Mon Jul 31, 2017 8:19 pm

coilbook Mon Jul 31, 2017 8:19 pm
haze wrote:I'll ask someone in the office who knows phoenixFD to have a look for you.

In the mean time, a workaround could be to export a VDB from the start, middle and end of the sequence and load them in octane to see the values.


Thank you that way we can know what MAX GRID VALUE should be set to when we render fire with Phoenix when flame is small or very big.
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Re: why do not absorbtion/scattering ramps work

Postby BK » Tue Aug 01, 2017 5:57 am

BK Tue Aug 01, 2017 5:57 am
Hi guys :)

I am not really a Phoenix power user, however, my test worked fine with Volume Gradient ramp node. Please try setting up the volume gradient ramp shown below and let us know how it goes.
2017-08-01 17_48_32-Slate Material Editor.png


The attached file is created using a Demo version and the values will work according to unit setup. I hope you will find this helpful.
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oct_phoenix.7z
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