pointcloud vopsop issue

[JoshJ]

I'm doing a very simple test with getting Cd from a point cloud in sops, using pciterate and a while loop. Rather than accumulating the color, I'd like to achieve something like "over", where the color from the next point either overwrites the previous color, or doesn't overwrite where color has already been absorbed.

Please have a look at the attached files, you will see the artifacts present. Thanks for any insight into getting this method working.

testing_pointclouds.hipnc

Edited December 28, 2011 by joshjordan

[3dbeing]

I thought for each would work here, but it errors out, saying no group 19? some times it doesn't error out but doesn't bring in the point color attr? or it does but it's 0? Not sure, so sop solver to the rescue...

testing_pointclouds_dops.hipnc

[JoshJ]

Thanks, however as a next step, I actually need to implement this in a shader (shop, material shader builder)... that's the reason for using this vops point cloud approach. As an initial prototype, I chose to first get it working in sops.

There's a thread here with an example file by pclaes:

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=20001&highlight=highest+distance

...which does some magic that I don't quite understand. I think something similar could determine if some points coming through the loop have already been colored.

And another example, have a look at this thread:

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=22645&highlight=point+cloud

the example file by tamte is named:

pcloudtest_age_fix.hipnc

In this example, some condition other than a simple pciterate is used to plug into the condition of the "if". Can we use something like this to test if a color has already been absorbed from another point? I tried something like this yesterday but never got anything working... I'm not sure if its because of a limitation of the system, or my own inexperience with using point clouds.

Edited December 28, 2011 by joshjordan

[eetu]

I think there was an image bombing shader in rdg's "a shader a day" thread, but I can't seem to find it (od[search] gives me an error).

It might be of relevance -- if you find it

[JoshJ]

I think there was an image bombing shader in rdg's "a shader a day" thread, but I can't seem to find it (od[search] gives me an error).

It might be of relevance -- if you find it

Thanks, yes I found that the other day as well. That approach, which I believe uses uv space as a base, is my second option if we can't get rid of these artifacts from the point cloud lookup.

Edited December 28, 2011 by joshjordan

[Erik_JE]

An idea is to randomly offset the pointcloud in Y direction and in your VOP iterate over all points and set the color to the point which is in allowed radius and has the highest Y value. Faking the circles actually being stacked on top of each other and not being in each other.

[JoshJ]

That's a great idea, I'd like to try it. I'm not really sure how to compare the values of the individual points in the iteration loop though...

[DanBode]

You could look up each point's number in the point cloud loop and store the lowest (or highest). You can use a compare vop after a pcimport to see if the current point number is lower than the previous minimum. If the current point number is lower than the previous lowest, store this point's color and number, otherwise store the previous color and lowest number. See attached.

testing_pointclouds_db.hipnc

[JoshJ]

DanBode, That's a great solution. That's what I was looking for. Thanks very much.

Edit:

I've tried to extend this further and support something like an "alpha channel" or "transparency" for the colored points. However, I can't figure out how to combine it with this approach. I am attaching another file which demonstrates the issue.

You can switch this node from 0 to 1, which will demonstrate the two approaches I'd like to combine:

/obj/grid_object1/vopsop1/while1/if1/switch1

Alternatively, any methods using the pointclouds in vops which may not solve the problem perfectly, but will minimize the artifacts, are also welcome.

pointclouds_overlap_with_alpha.hipnc

Edited December 28, 2011 by joshjordan

[edward]

FYI, for "smooth" results that interpolate everywhere, the BlendPose CHOP has a helpcard example that is similar for point positions (but can be used for any attribute in general).

[Mzigaib]

Hey thanks for the post and answers.

Did any of you know how to mix the colors without just overlap them?

Edited March 12, 2012 by Mzigaib

[Mzigaib]

I did manage to make each point color fade according through it's radius but I didn't manage a way to add or multiply the colors between each other.

Can anyone help?

testing_pointclouds_db_01.hipnc

[Mzigaib]

Did anyone succeeded to multiply or add the color between each other?

Edited April 26, 2012 by Mzigaib

[Mzigaib]

Did anyone succeeded to multiply or add the color between each other?

I did however make my circles follow radius size from the point cloud pscale attribute, I still got some chopped circles thou. If anyone knows how to improve this please share.

Thanks.

testing_pointclouds_db_02.hipnc

Edited April 26, 2012 by Mzigaib

[Mario Marengo]

A somewhat related old thread that may be useful.