polygon problem

[interstellar]

Hi Everyone,

Can anyone help me figure out what I'm doing wrong?

I created an asteroid with ZBrush4 and used OBJ2FACT to convert the "Object" file into a "Fact" file. When I rendered the asteroid with "Smooth Across Faces" disabled, I got the image on the top left corner of this picture:

http://www.joetucciarone.com/a-problem.jpg

With "Smooth Across Faces" enabled, I got the image on the upper right. If you look carefully you can see some dark and white spots on the asteroid.

The bottom two images are closeup images of the same place on the asteroid; "Smooth Across Faces" is disabled in the bottom left image and it is enabled in the bottom right image. The dark and white artifacts turn out to be triangular polygons that are not rendering correctly with "Smooth Across Faces" enabled.

Any help would be very welcome!

Thanks,

Joe T

[Tomas Egger]

Ola Joe,

Try to re-import the model inside OBJ2FACT..

Experiment the Normal options to avoid the artifacts in the triangles.

Thanks

Tom

[interstellar]

Ola Joe,

Try to re-import the model inside OBJ2FACT..

Experiment the Normal options to avoid the artifacts in the triangles.

Thanks

Tom

Thank you very much, Tomas, for your quick reply! I'll do what you have suggested.

Joe T

[interstellar]

Hi Tomas,

In OBJ2FACT I used several "Calculate Normals" Angle values from 0 to 90 degrees and the strange polygons did not go away. My version of OBJ2FACT does not have a "Fix Rotated Normals" option; could that fix my odd polygons?

This is the first model I have made with ZBrush4; could this new version of ZBrush have produced a defective "object" file?

Joe T

[Tomas Egger]

Ola Joe,

Please, send me a OBJ file, since we are testing our new import system and I can look the OBJ2FACT issue too.

Thanks a lot

Tom

[AVTPro]

Hi Joe, Tomas.

It's not a Zb4 problem. It just looks like a few of the normals are reversed or flipped. It's not an uncommon 3D problem. As you mentioned, you don't have the lastest version of OBJ which has a feature to help with that issue.

There still may be a way to fix the normals by recalculating the surface with exporting and reimporting the fact models directly from EIAS. I think Option click or a "forced correct normals" option might be available on import.

I haven't used ZB4 in a while but I don't think it really likes or even uses triangles in ZB4. Use quads as much a possible and shy away from tris. Save the triangulation for the last import if possible. I'm guessing you triangulated in Obj/EI and not out of ZB? Unless you are using displacement maps I can't see a huge benefit to these triangles over quads. Keep your quad models and triangle in EIAS with Dicer or Encage. Last but not least, you can also use a normal averaging/smooth if you have other software that supports it but again, I believe just Exp/Imp from EI could force correct normals direction.

[interstellar]

Hi Joe, Tomas.

It's not a Zb4 problem. It just looks like a few of the normals are reversed or flipped. It's not an uncommon 3D problem. As you mentioned, you don't have the lastest version of OBJ which has a feature to help with that issue.

There still may be a way to fix the normals by recalculating the surface with exporting and reimporting the fact models directly from EIAS. I think Option click or a "forced correct normals" option might be available on import.

Hi Alonzo,

I appreciate your detailed response! Fortunately, I always export my models (from within ZBrush) with the "quads" option selected.

Onward to your suggestion of importing/exporting in EI: Of all the years I've imported models into EI, I have never selected options in the Import Window. In fact, I forgot there were options! This time, when I imported my FACT file, I selected "Recalculate Normals" (leaving the "Smooth Shading" at the default value of 40). That fixed 90% of the polygons. There are now just a handful of "bad" polygons left behind. I wonder if a different value for "Smooth Shading" would fix those?

Tomas, my asteroid model is a bit under 6 megabytes; would you still like to look at the "raw" object file? If so, how can I send it to you; it might work as an email attachment . . .

Sincerely,

Joe Tucciarone

[Tomas Egger]

Ola Joe,

Please, Zip (compress) it to me.

tom@eias3d.com

Thanks Alonzo..

Thanks

Tom

[Tomas Egger]

Ola Joe and Alonzo,

I just tested the Asteroid model in a few 3d appl., its a Zbrush problem, a bad OBJ export.

Thanks

Tom

[interstellar]

Ola Joe and Alonzo,

I just tested the Asteroid model in a few 3d appl., its a Zbrush problem, a bad OBJ export.

Thanks

Tom

Hi Everyone,

I just wanted everyone to know that the importer Tomas is developing for EIAS9 works beautifully! I sent him my asteroid "object" model and he emailed an image to me after he had run it through his importer. There wasn't a bad polygon on it.

That feature alone will make EIAS v9 worth it for me!

Joe T

[interstellar]

Hi Everyone,

I just did a simple test on my Mac Pro(OS 10.6.4; EIAS v8, ZBrush4): I made a 3D sphere in ZBrush4, applied a circular mask and subdivided the masked area (my ZBrush asteroids always start as spheres where crater rims get a higher density of polygons). Then, I used OBJ2FACT to convert the ZBrush ".obj" file into a ".fac" file. When I imported (with "Recalculate Normals" enabled) this sphere into EI, I saw "bad polygons":

http://www.joetucciarone.com/a-problem2.tiff

The EI Camera view on the right shows the circular area that was subdivided in ZBrush. The "bad polygons" (seen in the picture on the left) are triangles caused by the ZBrush "Geometry/Divide" tool. Inexplicably, not all of the triangles are bad.

I used this procedure many times over the years with ZBrush2 on my G5. I wonder if something has changed in ZBrush4?

I spent an hour looking on the ZBrush forums but there are thousands of posts and I could easily spend weeks searching for an answer there!

Joe T

[Tomas Egger]

Ola Joe,

This is the EIAS 9 new importer converting your model (default settings)..

But, Im intrigued with Zbrush4 export..

Thanks

Tom

[interstellar]

Hi Everyone,

Here is part of a note I just sent to Tomas:

***********

Success!

I imported my asteroid model into ZBrush4 and, following your suggestion, I disabled "Triangle" in the "Geometry" Tab before I exported it. After converting it in OBJ2FACT, I imported it into EI. When it was imported with "Recalculate Normals" disabled, I saw the bad polygons. However, I imported it a second time with "Recalculate Normals" enabled and "Smooth Shading" set to 40. I did not see any bad polygons on it at all! I rotated it a dozen different ways and still I saw no bad polygons anywhere.

***********

Tomas spent valuable time to help me with this. He bent over backward to look at my problem and he found the solution. Apparently, a procedure I had used successfully for years with ZBrush2 had to be changed slightly for use with ZBrush4.

Thank you Tomas!

Sincerely,

Joe Tucciarone