Blend shape question
 

I have modeled a dinosaur that will have facial animation so I am going to have to make some blend shapes. My question is this; should I seperate his head from his body or should I use his entire 1 piece geometry even though I'm only altering the face? I don't want to have to seperate its face from the rest of the geometry unless there is a reason that I should.

do i seperately.
detatch the head from body.

Heres a little trick for you to save on a lot of memory.

Before you make you blendshapes, cut off your head. Then combine the body and the head back again and merge the vertex's. Important - When combining the body and the head, make sure you select the head first.

What this does is re-order the vertex's so that the head uses all the first vertex's and the body uses the higher numbered vertex's.

Now you can make your blendshapes with just the head. When you make the blendshape node turn off Check Topology so that maya will not check the number of vertex's and because you re-ordered all the vertex numbers so the head contains the first few, all will work fine.

Richard

Awesome answer, Richard. thanks for the information!

By the way, I enjoyed going to your website. Very nice work.

I've had some time for this info to sink in an now I have a question: I assume that you make copies of the head once you cut it off and before you combine and merge it back onto the body. Why is it important that the head vertexs be renumbered with the lower numbers and the body be numbered with the higher vertex numbers. What does this do for you?

Won't the blend shaped have different vertex numbers than the head once the head is renumbered?

The idea is to re-order the vertex numbers so that you have the head as all the first numbers. The reason for this is that you can now duplicate the mesh and delete the body to make your head blendshapes. The blendshape node will move only the head verts because that is all that is in the blendshape. Blendshapes move the same vertex numbers in the target that are in the base shape, so if you vertex's are ordered differently between the 2 you'll get a very messed up shape. This trick simple makes sure all the vertex numbers are first for the head so you can delete the body.

All this trick really does is save you a lot of memory for blend shapes, but this is the reason people like to cut the head off in the first place.

Richard

OK. That clears things up a lot. Thank you....

Richard! are you there?

I tried the trick you explained and all went well except for one small problem. The blend shape worked as I slid the slider up and down but something unexpected happened as well. About a dozen faces located on various parts of the models body began migrating toward the dinosaurs head. At the end of their travel, then ended up located on or near the cut I made when I seperated the head from the body.

To seperate the head, I simply used the "cut faces tool". I then selected the head then <shift> selected the body and "combined" the two pieces together. Then I merged the vertices at the cut.

To make blend shapes I duplicated the dinosaur model then selected the head faces, inverted the selection then deleted the body.

To keep some of my tests as clean as possible. I didn't even modify the blend targets. I just set up the blend shape and tested it. In all cases, some faces located on the feet and one hand began migrating toward the head as I explained earlier.

What did I do wrong? I started from scratch and ran the tests a half dozen times. All with the same results.

I also ran a test where I set up the blend shape using the dinosaurs entire geometry; head and body. That test worked perfectly which leads me to believe that the problem has to do with the fact that I cut the head from the body then re-attached it.

One last clue; For a couple of my tests, I only selected the dinos snout while deleting the rest of his head and body to make the blend shape. I stayed as far away from the area that I cut as I could. I just wanted to rule out the possibility that the cut was causing the problem. Well, something else unexpected happened. Faces began moving toward the snout but this time, most of these faces were located on the dinos head instead of on his feet, as was the case in earlier tests.

Is the Blending getting confused because of an error in the way the vertexs are numbered? I re-attached the head to the body the way you explained then I checked a dozen or so faces and the ones on the head were all much lower numbers than the ones on his body so I believe the renumbering worked.

Any ideas?

Thats strange, I just did the same thing on one of my characters and it worked fine. The only thing I can think of is the use of the cut faces tool. I don't do it that way, I just select the faces in the head and extract/seperate them (actually I use a script fro highend3d.com called detachSeperate which basically duplicates the mesh, then deletes the selected faces from the duplicate, and the non selected faces from the original). From here a combine and merge verts connects back the head which I can now duplicate and make blendshapes from, after I delete the body faces.
I'm going to guess that the faces that are causing you problems are the ones around the cut.
Try this, instead of using the cut polygon tool, select the head faces instead to cut them off. After cutting and combining, don't forget to delete history before you duplicate and make the blend shapes.
If all else fails, this trick only saves you memory so you could just duplicate the whole mesh and make blendshapes. When they are made you can delete the blendshapes from the maya file and the blendshape node will still work. This will also save you memory.

Richard

Thank you, Richard. I'll give your suggestiong a try right away..