Hi all,

I use the obj export in Houdini pretty often but there is one thing that i cant figure out.

Say I am transferring some attributes from one mesh to another ie updated UV's.

This model is then loaded into Zbrush (from whence it came), the base matching point by point, vertex by vertex. Yet when it is loaded into Zbrush, it is asking should I project the old details onto the new one because the topology has changed.

Even exporting the Lv 0 mesh from Zbrush, import into Houdini, export it right out into Zbrush it still says the topology has changed. Im confused to say the least, is there a setting or something i can do to stop this from happening, its kinda important.

And if anyone has an answer to my SSS question i would love someone/anyone to shed some light or point me in the right direction as to what i am doing wrong.
http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=25752 [sidefx.com]

As always, thanks for taking the time to read this.

-andrew

I don't have a chance to check it out with ZBrush, but Houdini Obj importer does some steps behind the scene to match obj with Houdini's standards. Most probably this is reverting faces (i.e. reverting vertices order). You could try to revert it again before export if exporter doesn't do it by itself. Sorry for being trivial, but In any case, make the simplest case, like box, and test in/out with it. Objs are easy to investigate.

hth,
skk.

Cheers, i will give it a go. I was even at the point of looking at the objs in a text editor.

I will come back with the results for the sake of reference.

Ok so i figured out specifically what the problem is.

If you export an object from Zbrush without Polygroups, import into H, then back to Zbrush. No problem.

Even if you reorder the points, Zbrush will detect it and a message in top left will say, “Mismatch points-order in the imported mesh was detected and auto-corrected. ” (which is nice).

However the moment you have more than one poly group in Zb and export that out (to H), and bring it back it says there has been a topological change.

So what is it that Houdini does to groups when you export?

Do a test with a box. Post the results of the .obj before and after.