Pyro emit from particles on geometry

[stig_olsen]

Hi,

 

I have set up a pyro dynamic that is driven by a some particles that swirls on a geometry box.

I would really appreciate if someone can take a look at it and tell me what I can do to improve this.

Its a system that lets the particles grow on a painted surface and the idea for me is to adapt this to other geometry later. Then I need to make the smoke and fire to look as realistic as it could be.

 

I have also noticed that the flames are a bit not sharp / blurry in a way when doing a couple of frames in the render view.

 

Im very new to Houdini so please explain to me a way that a newie can understand, I dont have a coding background, but use a lot of time to try to understand Houdini.

 

 

 

Thanks.

 

 

Stig

 

 

pyro_test_SO.hipnc

[Sierra62]

I just had a quick glance at your file. my first recommendation is to modify your fuel.  In all pyro simulations, modifying your fuel can make a huge difference.  To do so, I would go into your "create_fuel_volumes" node, look at the stamp points tab and change the sample distance.  The lower the value the closer it gets to the particle size.   Also, when using particles as a fuel source, the particle you see in the viewport is not the actual size of the particle. By default particles are much larger than appear.  To lower the size of them, add an attribute called pscale and set it to .1 or lower.  

 

The other thing to look at is your division size of your simulation.  A division size of .2 is going to result in a very low res sim.  To get a better look, lower this value quite a bit.  The exact value is going to depend on a balance of of look and performance.  If you where to set it to .02, it would be a very defined simulation, but your file size could easily get into multiple gigs per frame. 

 

This should be a good start. 

[stig_olsen]

Thank you!

 

It certainly helped, I thought .2 should be good enough, but .02 did the trick.

How can I add this pscale? I dont understand how to create and use attributes yet, I dont know why.

I know I can add a point sop, and change to add scale to get e $PSCALE attribute. I just dont know what to do with ut, and I dont undestand why it doesnt show up in the detail view.

 

Stig

[Hello world]

u can use the vopsop to manipulate any point attributes

[stig_olsen]

Hello world, can you please explain how?

 

Stig

[ophamletsen]

The documentation shows you a bunch of ways on how to create attributes.

They even have an example file specific to pscale. Take a look here:

http://www.sidefx.com/docs/houdini13.0/examples/nodes/vop/addattrib/pscaleVOPSOP

Edited April 10, 2014 by ophamletsen

[stig_olsen]

Ok thank you - I will read.

I have set the divisions to 0.02, but it still looks like crap. It looks nothing like what I see in the viewfinder at all and it is totally blown out. Any idea?

I render to $HIP/Houdini/Render/navn_v01.$F4.jpeg and have set the output device to jpeg. Im going to bring it into After Effects later, so it will not work with the houdini pic.

Ive also set the pixple samling to 10

 

Stig

[Sierra62]

I don't my houdini running at the moment so I can't look at your file to tell you exactly, but here are some recommendations.   Firstly, using jpeg is not recommended, and really neither is pic.  I believe only houdini supports pic.  The industry standard for rendering is using .exr.  This is a non compressed image that gives the option of multiple layers as well.

 

Secondly, when rendering fire, it is recommended to use micropolygon rendering and depth map shadows.  you set your shadows on the lights themselves.   When using depth map shadows, increase the matte size from 512x512 to probably 1024x1024.   this gives you more detail in your shadows.

 

I would also do a lot of different test with light locations and intensities to get the right look.  you will find that pyro can be very finicky when it comes to lighting.  It can quickly go from looking great to washed out by just moving lights around.

 

When in mantra, using pixel sampling of 10 is a bit ridiculous.  I would start with 4x4 and if needed I will go to 6x6.   increasing pixel samples is the quickest way to increase render times.  I would instead increase the max ray samples.   The the max ray samples are the amount of times mantra will sample the light rays to get to the noise level.  say your noise is at 0.01(recommended) and your ray samples are at 12,  mantra will keep sampling rays till it hits .01 or till it has sampled 12 times.  If it hits the noise level with only 4 samples it will still move on.   

 

The next thing with mantra and pyro is transparent samples. This will set how many samples into the volume mantra will go.  The higher the number the more render depth you get, but also the render time will increase a lot.  Increase this if your doing more transparent smoke as opposed to thick billowing smoke.

 

When it comes to rendering and working with the renders after for color correcting etc.  it is important to set up render passes.  These will act similiar to photoshop layers.   When doing pyro the ones I would recommend are:

 

alpha (af) from the drop down menu

 

smoke_mask (float)

this is basically the alpha channel for the smoke

 

smoke_color(vector)

This will put your smoke color on a different layer

 

fire_mask(float)

the alpha for fire

 

fire_color(vector)

the color layer for the fire.

[stig_olsen]

Thank you for a very informative answer, I appreciate that!

 

I have now done everything you said. I can see that it helps, but I still got some artifacts inside the fire.

It looks like som low pixel blocky artifacts. Any idea?

 

 

Stig

pyro_test_SO_v2.hipnc

[Sierra62]

I had a quick look at your scene, and the first thing to come to mind is that there is a problem with collision.  Since you have your fuel directly on your collision object it will cause some intersection errors.  When you set up a basic static object it generally creates the object larger than it is.  By increasing the sampling you can get a more accurate scan for your collision.  You can turn display collision in the static object to see it.   The other way to do it is to have your source object just a bit larger than your source.   

Try your pyro sim without collision to see if there is still artifacts.

 

you can also try adding sharpness to the sim itself.  In the pyro solver, under the shape tab turn on sharpening.  Don't be afraid to change these values from default, they can really change your look.

[stig_olsen]

wow, that actually worked - thanks!

 

To get rid of the noise on the edges of the smoke I need to pump up the pixel samples to 15. The noise level is set to 0.01. Do I really need to pump it up to 15, or is it any other options for getting rid of that noise?

 

Stig

[Sierra62]

I would try setting the noise lower to say .005 and increasing the max ray samples to 12 or 16.   if you can avoid it, try not to increase pixel samples too much.  Also increase volume quality to at least 1.  

 

If you are still having issues try tweaking the shader.  such as final amplitude, shadow density etc.

[stig_olsen]

Thanks,

 

I have done as you said and tweeked the shader a lot.

It looks pretty good now, but I still have a lot of noise especially near the edges and where it is transparency. I have tried to push the transparency slider without getting any improved noise reduction.

 

I have attached the last file

pyro_test_SO_v3.hipnc