I'm generating smoke with i3d and am getting single lines of distortion at a specific location in the render. As the smoke passes thru this location it looks like a shockwave passing thru the smoke. I have attempted using 256^3 resolution on the I3D, but this does not seem to resolve the issue. Likewise, any changes I have made to the metacloud or texfog SHOP do not have any effect on this problem. I am not using adaptive step, as I have not been able to get good results yet and the render times are already quite high. I have not have this occure in any past I3D work, but now have it in 2 different shots.
http://sfdm.ca.scad.edu/vsfx/student/jemonnat/ [sfdm.ca.scad.edu]


- Jeremy

Hmm, I started messing with i3d last night, and I think I ran into the same issue. Is this what you're getting? (I can't see the pics on your web page)



This image was rendered with Adaptive Step on, and a Step Size of 0.005 (the default is 0.05) and Max Steps set to 2000 (the default is 1000). From this angle it just looks like a single line going through the the middle, but from a different angle you can see it actually looks cross-shaped.
The same problem was also discussed in this thread, but I don't think there was a solution…
http://www.sidefx.com/forum/viewtopic.php?t=2273&highlight=i3d [sidefx.com]

Thats almost exactly what the artifacts look like. As the cloud moves through that area, the line remains stationary and distorts everything that passes through it. I have attempted runinng a higher resample (100) and it fixes the problem slightly and a lower resample (1) make it look like it's from an atari game. Adaptive step is my next approach, but it sounds as though this is a reoccuring issue. Its not a noticable in the QT's I posted, but it is definatly noticable at full rez, and esp on a projection screen. Thanks for the help.

*bump*

When you visualize the .i3d files with an iso surface you can actually see the lines. You probably need to turn up the divisions, I'm using 300^3.

this was also being discussed on the list serv and someone mentioned turning the oversample down to 1 rather than 10 on the i3d rop. i tried this out (after getting similar artifacts) and it seemed to fix it..

my other solution before i turned down the sampling was i changed my filter settings on the tex fog shader.. the best settings i found to get rid of the problem without losing detail in the cloud was to set it to filter Sinc and a width of 2. But this was just more of a coverup than a fix.. but still an alternative incase the oversample doesn't fix it for ya..

Thanks deecue, but this i3d was generated with Oversampling set to 1 (I also read that post on the list).

thanks guys. I tried all these approaches and found that adjusting the filter gave me the best reults for this particular situation. While changing the filter in the shader does blur the image, it looked much better than the oversampling of 1, especially at full resolution. I would think most people would want a clearer image, rather than a more pixelated one, which is what I got with turning down the oversampling. I will repost finished QT's if anyone's interested. Thanks again.
- J

Maybe it's a Houdini 6.x thing, because in 5.5.230 I don't have any problems.

same problem for me

Dajuice how did you get to see the lines on the surface?

Like this

1) Create a new Geo Object
2) Lay down an Iso Surface Sop
3) In the parameters change it to 3D texture and load your .i3d file
4) Turn up the divisions, the default is 10^3, change it to something like 200^3 to see the lines. Turning off Specular Highlights in you display options helps too.

I think the solutions mentioned, like lowering Oversampling or using different Filters are probably just quick fixes/cover ups. I think we'll keep running into this until the issue is addressed.

I think this has been already addressed for future releases (not 6.1 though).

Ahh, good to know.