ZBrushCentral

mesh extract question

ZBrush Usage Questions
#1

I want to mesh extract the face of a model I have. Mesh extract under the subtools seems to extract the surface in both directions and the thicker you extract it the less detail you get.

Is there a way to mesh extract in one direction so that the face (of my model) details stay the same and the extraction goes the other way however thick I choose? I don’t care about the other sides details, just the face part.

Any help would be greatly appreciated and if anyone has a better tool or suggestion that would help too. I’m bassically trying t shell out the face from behind so that it becomes a certain thickness.

#2

On approach that pops to mind is the morph target->create diff mesh. This way you first store a morph target, then hide all polys except for the face, and go to Tool->Deformation->Inflate and inflate it by a negative amount (snapshot before the operation can help as a nice visual reference for the amount of inflation undergone). Then hit create diff mesh and there will be a new one with thickness between the orginal face and the ‘deflated’ mesh which you controlled. Although I have’t time to check now, I can’t say for sure if the details are fully preserved with this method, but I’m guessing they are.

#3

Extraction only goes in one direction – that of the surface normals for the masked polygons. But if your surface is really thin you will most likely end up having masked both the front and back faces. In that case, extraction would go in two directions. Pixolator has said that there will soon be a feature that will ignore back facing polys when painting a mask. This will allow you to mask one side of a thin surface, giving the results that you’re looking for.

#4

rhumba, I’ll try it and see if I can get it to work that way. Thank you for your idea.

aurick, That makes scense and I will be waiting for that feature to come. Thank you for informing me.

Yes I was using it on just a surface so it went in both directions. I tried masking just the face which made it just a thin surface.

#5

I am new to this so where do I find the buttons for:

snapshot
diff mesh

Thank you.

#6

I found the diff mesh button, but I am only able to use it if I mask an area and not hide it. Once I do as you said it seams to work with some bugs. The new diff mesh seams to be see through. I can see two surfaces and I see through the first and see the second surface below. As I spin the model I see only the under lying surface while the surface facing me is always see through. weird.

#7

aurick,

Where do I change the direction of the surface normals?

#8

That’s just a fancy way of saying “the direction in which the polygon faces”. So the extraction takes place straight out from your surface. To change the surface normals, you therefore have to change the angle of the polygons. In other words, resculpt the mesh. :wink:

#9

So you are say I would have to resculpt the entire mesh. Redo the whole thing just to change the surface normals? Even if I rescuplted it The norms I’m sure would still point in the same direction (outward probably). Other programs seem to have a button that just flips the surface normal from pointing in the direction that they are to the opposite direcction. Is there nothing like that in Zbrush?

#10

You can flip a model’s surface normals using Tool>Display Properties>Flip. This applies to the whole model. There is not a way in ZBrush to flip only some of a model’s normals.

#11

Thank you. That helps me out.
Here is a question though. If I were to flip the surface normals, could I then exctract it in the opposite direction since the normals are flipped? or does that not really do anything?

#12

Just looking trough the threads regarding mesh extraction and I’m having the same problem.

The mesh is extracted in both directions of the normal. Not sure if this has been fixed since the previous posts…not found anything yet.

As a test, I create a PM3Dsphere. Mask it and extract. If you then hide part of the sphere through the extraction, you can see that the extract is in both directions.

Is this an error? I see that there is the diff mesh workaround but from what Aurick was saying , it should only extract along the normal.

Ideally I’d just like to use extract rather than messing about with snapshots etc.

Any ideas as to why its doing this?

El-d

extract.jpg

#13

I don’t know if it is fixed yet, but I was still wondering the same thing. It would be nice to choose if the extract went in both directions or in only one direction.

#14

If you use Tool>Deformation>Size after extracting, you can compensate for this.

Basically, create your extraction at half the thickness that you would normally do. Then use Size with no masking to enlarge the extracted mesh. This can be used to move the interior portion out.

#15

Cheers Aurick… Problem is that the first few times I tried it crashed so seems a little unstable. Just tested again, it appears that if you don’t clear the mask on the original object then it fails.

Oh no. If you type in a value in the size it crashes.

Seems like you have to use the slider and then type values which isn’t very helpful.
I think the problem is that I want to type in half the thickness as a set value wheras the size slider is +/- 100. Looks like I can size it roughly with the slider and then tweak it slowly by typing in fractional size increments but its not ideal.

I suggest the addition of +/- direction options on the next update.

El-d

Edit: Just trying again and keeps crashing on sizing.

#16

I have never had a crash during sizing.

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#17

Zbrush 3.1 - zapplink installed also.
multithreading on.
Compact mem : 2768
max poly :8.99

PC : dell XP64 Pro SP 1
Intel xeon 2.8
3 Gb ram
nvidia quadro Fx 5500

test :
1 : create polysphere
2: mask paint a section on the surface
3: Subtools, extract.
4: clear mask
5: select sub tool
6: slide the sizer …and typically it didn’t crash this time.
repeated as above on the same polysphere and it crashed on me.

tried again, crashed

tried again… increased size by large amount and ok
repeated on same polysphere with large increment and ok
repeated on same polysphere with small increment (3) and crashed

tried again : size 20 , crashed
tried again : size 30 , crashed

tried again : size 51 ok, repeated , 41 ok, 33 crashed

tried various, typing sliding and seems to be random for the crashing.

Ahaa figured it. It only happens if I size the model after extracting without moving/rotating the model/display.

Hope it helps find the bug…and whilst your fixing it maybe you could add the ability to decide how much in or out it goes :wink:

Keep up the good work.

El-d

#18

Duplicated. Thanks.

#19

It’s taken a while to get back to this subject, but it appears to work pretty well with version 3.5r3. I tried it on the demohead.

I used backface masking and flipped the norms. Then I masked the head and extracted it. It did go it the right direction (inward). Then I had to clean up the new mesh on the inside a bit. Then I projected detail back onto it, cleaned it up a bit and it was a solid object that was hollowed out.

I also tried it with remesh all. It worked, but the head was more solid. The other method made it so the whole head was around the same thickness all throughout.

:slight_smile: