Merging point clouds IDs

[hbahnassi]

I have two cached point clouds that I would like to merge into a new one. I tried different methods to do so, however all of them are generating unstable IDs through time (e.g. a particle has ID of 7 at one frame, the next frame it changes to 6!).

The attached screenshot shows this issue.

Any idea how to get around this issue?

Thanks,
Homam

[Grahame_Fuller]

If there's no simulation region, then the Modeling region gets re-evaluated every frame as necessary when the inputs change. So, all the particles are "new" every frame which is why the IDs change.

I suggest that you cache out the two particle clouds, and append the caches together.

Alternatively in the Simulation region, you may be able to filter for new particles (Init = 0) and add them each frame.

[hbahnassi]

Regarding suggestion 1: Do you know which tool in XSI append caches and fix the IDs?
Suggestion 2: I’ll think about it, maybe it is easier to code a tool that append icecach files and fix their IDs.

Thanks,
Homam

[Grahame_Fuller]

Regarding suggestion 1: Do you know which tool in XSI append caches and fix the IDs?

You can use two Cache on File nodes set to Read Cache, with Append turned on.

http://download.autodesk.com/global/docs/softimage2013/en_us/userguide/index.html?url=files/ICE_cach...

[hbahnassi]

You can use two Cache on File nodes set to Read Cache, with Append turned on.

http://download.autodesk.com/global/docs/softimage2013/en_us/userguide/index.html?url=files/ICE_cach...

Again this approach results unstable IDs 😞

[Grahame_Fuller]

Again this approach results unstable IDs 😞

Oops! You're right...

The attached picture shows how to set up option 2.

[hbahnassi]

I'm sorry to say that in the case of cached point clouds this approach didn't work 😞 I tried caching the .init property as a workaround but unfortunately it seems it is not cachable.

[Grahame_Fuller]

Sorry if I wasn't clear, but I didn't mean to use caches for option 2. The tree I posted was meant to read from live particle simulations.

If you want to try it with caches, then I would try reading Init in the original trees, saving it as a custom attribute, and adding it to the cache. You may need to display it in the viewport to make sure it gets computed and cached properly.

[hbahnassi]

Interesting! Displaying ICE attribute in the viewport makes it cachable 😮 I wonder how much time it will take me to discover that by my own. Thanks a lot Graham for this tip 🙂

So now it works fine even with cached clouds. However with this approach I need to update the point positions in the merged cloud. Otherwise they’ll stay in their creation position. To do this I added another branch to the ICE tree where it checks the ID for the source cloud to get the point positions from the correct source. The issue I’m facing now is a context mismatch, because I’m trying to get the point position from the cached cloud and set it to the merged cloud.

The screenshot shows how I’m trying to update point positions. I’m not sure if this the best way to do it, any ideas are welcome 🙂

Thanks,

[Grahame_Fuller]

Well the PointVelocity should already be cached and should have been transferred when cloned, so you could just plug in a Simulate Particles node.

About showing values and caching, it works because ICE is lazy and if an attribute isn't used to affect something visible in the scene, then it isn't calculated so there's nothing to cache. Showing values is a way to force the calculations to be performed.

[hbahnassi]

I’m not sure why the ClonePoint ICE Tree is not working as expected.

I tried using it to merge cached clouds and another time by merging simulated clouds. In both cases the results are not what is expected. The attached screenshot shows the results in both cases.