Upon further investigation my python exporter did in fact work. I tested the script on a set of static points and it worked fine. There appears to be an issue with directly reading points from non-file-cached dop sim. For some reason, writing the points to disk (geo rop) and reading them back in before running the export script made it work.
It's particularly bizarre since the sim scrubs properly in maya no problem from memory. This only happens on cooking a branched node chain.
I can try to isolate and reproduce the issue, if it's indeed a bug ill make an RFE
cheers 8)
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Houdini Engine for Maya » Python Callbacks inside an asset in Engine
- icarus551
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Houdini Engine for Maya » Python Callbacks inside an asset in Engine
- icarus551
- 22 posts
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I have an asset that takes some inputs and runs a bullet simulation to generate contact data. This point data needs to then be exported to a plain text file for other purposes. Currently I have a python sop with a button that, when pressed, runs a callback function to read the input geo and format it to a file. This works fine within houdini but upon trying to run my export callback from engine in maya it appears to output nothing, as in theres nothing being returned from ‘pts = hou.pwd().geometry().points()’
I'm not sure how something like this is evaluated in the Engine context, could someone explain what the best way to do this is?
I'm not sure how something like this is evaluated in the Engine context, could someone explain what the best way to do this is?
SI Users » Cloth and Finite element solver the same thing?
- icarus551
- 22 posts
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Technical Discussion » Best way to visualize a compressor
- icarus551
- 22 posts
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You could probably modulate particle massdensity so that when the fluid needs to be compressed you scale it to something closer to air, which would in turn make it more susceptible to compression
Technical Discussion » Blowtorch in Pyro ?
- icarus551
- 22 posts
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You really don't need to use a fluid sim for a blow torch effect. You can generate the shape in sops and create a volume from that, using the pyro shader for the render.
Technical Discussion » Importing Arrays in shop/cvex context
- icarus551
- 22 posts
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I'm doing some investigation into how far cvex shaders can go in terms of data shuffling. Currently I can write a float array to a geometry attribute and later import it back in vop sops via the import function. This function doesn't exist in the shading/cvex context though, is there another way to import float arrays into cvex?
Technical Discussion » "Advect by Volume" position advection in DOP POPs?
- icarus551
- 22 posts
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alejandroriviera
What was misleading for me is I looked really hard in the whitewater solver, but not much in the whitewater _object_, which contained the velocity field attachment. DOPs can be “here be dragons” land for me sometimes…
imre
In the whitewater solver they sample the vel field as a force to then do the integration with the powerful geometry vop dop hiden node.
I'm very courious about this node in H13, because all pop's finally will have a force integrator written with dops toolbox(H12.5) or HDK, we will see.
I can't imagine it being much different than the existing Gas Integrator dop, you have plenty of options in that to begin with.
Technical Discussion » Retiming simulation changes sim behaviour
- icarus551
- 22 posts
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What you're describing in op is what linear interpolation between cached frames. You can think of it as looking at a polygon circle. The motion is a smooth circle but since you are discretizing the motion into specific points it has to interpolate between what are essentially “keyframes” of motion.
You can either do what earlier posts suggest which is generating more “key” frame data to linearly interpolate from, or alternatively load the position data into CHOPS and apply some filtering to smooth the motion. It'll be slow if you have a lot of points obviously.
You can either do what earlier posts suggest which is generating more “key” frame data to linearly interpolate from, or alternatively load the position data into CHOPS and apply some filtering to smooth the motion. It'll be slow if you have a lot of points obviously.
Technical Discussion » pyro slowed down after frame 100
- icarus551
- 22 posts
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If you have buoyancy enabled the combination of upwards velocity and diffusion/cooling of temperature will cause the fluid to kind of float where the temperature has been reduced to where gravity is stronger than buoyancy. Try reducing the rate of cooling and temperature diffusion
Technical Discussion » Rigid Body Collisions Basics
- icarus551
- 22 posts
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Try increasing the Feedback Scale in the flip solver under Volume Motion / Solver.
Also make sure the object is a mutual affector in the merge you have.
Also make sure the object is a mutual affector in the merge you have.
Technical Discussion » Definitive method for FLIP retimeing
- icarus551
- 22 posts
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I'm not sure what you would accomplish with a .sim file, aside from sop-dop pipe speed, as opposed to fields in .bgeo form.
It might be worth investigating the attract fluid otls since you essentially want to enforce a “goal” surface field and velocity field given a specific timescale and frange between each frame.
The accuracy of these would be questionable though since those fields are so heavily modified by the particle body, you're really only indirectly controlling the particles in this manner.
It might be worth investigating the attract fluid otls since you essentially want to enforce a “goal” surface field and velocity field given a specific timescale and frange between each frame.
The accuracy of these would be questionable though since those fields are so heavily modified by the particle body, you're really only indirectly controlling the particles in this manner.
Technical Discussion » Houdini Multijoints
- icarus551
- 22 posts
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Use the glue network constraint, you generate your glue network externally and apply it to your fractured object, the example file shows it all.
http://www.sidefx.com/docs/houdini12.1/nodes/dop/gluenetworkconstraint [sidefx.com]
http://www.sidefx.com/docs/houdini12.1/nodes/dop/gluenetworkconstraint [sidefx.com]
Technical Discussion » Curl Calculation
- icarus551
- 22 posts
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Ahh cool, yes its definitely working in your scene. I'll look for why it wasn't working in mine. thanks!
Note: I was using vex gradient() instead of volume analysis sop, I wonder if theres a descrepancy between outputs.
Edit: vex gradient function and volume gradient sop give same result. prolly same code in hdk..
Note: I was using vex gradient() instead of volume analysis sop, I wonder if theres a descrepancy between outputs.
Edit: vex gradient function and volume gradient sop give same result. prolly same code in hdk..
Technical Discussion » Curl Calculation
- icarus551
- 22 posts
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johner
The VolumeAnalyis SOP should really have an option to calculate the curl, but in the meantime you can compute the gradient of each velocity component and calculate the curl by hand in VOPs (thereby doing a little extra work: nine derivatives instead of the six minimally required).
See attached for an example of computing the curl of a FLIP sim (and turn on the curl attribute visualization).
I was shown a similar solution which is correctly theoretically, but if you compare it against the dop computed curl they don't even look similar.
I ran a 2D smoke sim (xz axis) to compare. Curl vectors of a 2d field should all point along one axis (y axis). The dop computed curl does this but none of the sop solutions do.
Very mysterious.
Technical Discussion » Curl Calculation
- icarus551
- 22 posts
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After comparing against the dop generated curl, they definitely don't match (or are even close).
The mystery continues
The mystery continues
Technical Discussion » Curl Calculation
- icarus551
- 22 posts
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Symek, I think that is correct, I took the tensor-vector dot product of the gradient matrix and the normalized vector, then used that in a cross product with the vector, which first look appears to give a correct curl vector.
On a basic vortex velocity field it looks correct, but I need to check it out on a more complex field.
On a basic vortex velocity field it looks correct, but I need to check it out on a more complex field.
Technical Discussion » Curl Calculation
- icarus551
- 22 posts
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dennis.weil
Hi,
I've never seen the gradient expressed as a matrix. What did you do to get this result?
The Volume Gradient VOP or volumegradient() vex function return a gradient vector which should be exactly what you need.
-dennis
This is only in terms of scalar fields, a vector field will return a matrix (a vector consists of 3 scalars, so you have 3x the components)
I'm really looking to keep this simple and avoid using a wrapper around the gas analysis dop.
Technical Discussion » Curl Calculation
- icarus551
- 22 posts
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I'm looking to calculate curl of a vector field to visualize vorticity within a velocity field.
Curl is stated as the cross product of the vector and the gradient or
From a houdini standpoint the gradient of a vector field is a 3x3matrix, so I don't see how you could possibly do a cross product of a matrix and a vector.
I think I'm missing a key point here since I can't find any information online about this kind of implementation.
Can any math gurus help me out here? I know its available in dop context so I don't think it would be too difficult to get together in sops(vex).
Curl is stated as the cross product of the vector and the gradient or
From a houdini standpoint the gradient of a vector field is a 3x3matrix, so I don't see how you could possibly do a cross product of a matrix and a vector.
I think I'm missing a key point here since I can't find any information online about this kind of implementation.
Can any math gurus help me out here? I know its available in dop context so I don't think it would be too difficult to get together in sops(vex).
Technical Discussion » Bullet physics implementation and other stuff
- icarus551
- 22 posts
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Technical Discussion » fbx export mesh tessellation
- icarus551
- 22 posts
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im pretty new to houdini but what im currently trying to do is export a simulated fluid surface and import it into maya, but when i import the fbx file the fluid surface is completely faceted and nothing in maya as far as i know will solve the problem
i used standard fbx export options (and import options in maya)
attached is an example of the faceted geometry in maya.
is there a way to stop this from happening in the export?
i used standard fbx export options (and import options in maya)
attached is an example of the faceted geometry in maya.
is there a way to stop this from happening in the export?
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