cutting a mesh with a knife?

[Dave Black]

Ok, there are a few ways to go about this, but since you're doing(I'm assuming) a slow, methodical cut, it's going to be hard.

First, you're right about animated booleans...

You may be able to fix the progressive morph:

Try manually fixing the smoothing groups on the faces that abutt the cutting line. Probably what is causing the the "raised bump", is the smoothing groups. Just have a look real quick, as it could be an easy fix.

I'll check back later. I'm sure we can figure this one out.

-3DZ

:D

[Rivendale]

I havn't tried this myself, but I guess you could use a morph for the opening of the cut, and to hide the open edges you could clone your mesh, weld the cut, scale it up very very slightly and animate an opacity-map going along with the cut.
Hope you understand, if you have any questions I can explain more what I mean.

[gman]

3DZealot,
thanks for the help, the open edge is smoothed out completely now and the prog morph is less predictably following a raised edge.

regards

[gman]

Just another question. I'd like to figure out a way of doing this so i dont have to be dictated by the edges. I want to be a bit more accurate so i can cut with smooth contours and intersect faces in any shape across the skin.

[Dave Black]

Glad that helped a bit...

As for what you are looking to do, there really is'nt a good way to get that effect. Boolean operations and NURBS trims are really the only way to get 2 non-similar shapes to intersect properly. Normally, they work ok, but since we are dealing with animation, we get alot of shading errors.

I remember in the movie "ICE AGE", alot of the effects of the ice breaking/cracking were perfect. I used to study it frame-by-frame to see if I could catch any on the tricks they used, but I could'nt find anything.

Perhaps there are still a few more options.

Can you briefly explain the final product? Does the skin have to flap back? Are there any dynamics effects(soft bodies simulations, fluid simulations)? How fast is the shot? How many shots are there going to be?

I know we can sort it out...

-3DZ

:D

[Rivendale]

Did you try my suggestion? I tried it and it should work good for what you are doing. Here's what you could do:
Make a blend material, put your skinmaterial in the top slot and in the opacity slot put a opacity map that makes the area that will be affected by the cut visible and fade out to the sides.
Make the second slot of the blend material totally invisible by setting opacity to 0.
I the mask slot, put a gradient ramp, make the interpolation solid and animate the ramp so that it wipes over the cutting area at the (exact)same rate as the cut.
Clone your mesh and delete all the polygons except the ones aroud the cut, move it up/out slightly, just enough so that it will render on top of your main mesh. Assign your blend material and turn off shadowcasting for this mesh.
This way you can do whatever you want with the underlying mesh because it wont be visible until the knife cuts the mesh. The tricky part is to match the cut animation with the gradient ramp.

Hope this helps:)

[gman]

Rivendale,
Your idea is good for just the cutting action but after the cut i need to use tools on the open cut and stretch back the skin.
thanks for your feedback.

3DZealot,
The operation requires a cut shaped like a 'C' that travels from the shoulder point of the bicep and down the outside of the arm to the elbow, the skin will then flap over revealing the muscles, which i will need to slice thru also, then the skin will be retracted back tightly. I could reshape the faces but i was hoping i could do this technique quickly, i was trying to think of a way using a spline snapped to the mesh and then inserting it into the mesh, and then using the prog' morh but i want to maintain good topology. Do you think this is plausible?

thanks

[Dave Black]

You might want to try the conform compound object type. Play with moving the operands a bit. Just a thought...It would take some effort, but that may be a possibility.

I have an idea for the animation. You could use a cloth simulation tool, or a softbody tool. That would get you the animation...sort of.

I'm still rolling the cutting method around in my brain...

Let's list a few things as possibilities:

1. Animated FFD modifier
2. Progressive morphs
3. Animated booleans

That's a hard one. I think that it's one of those tasks that has to be done the hard way. I wish this thread would get more hits. I've never really had to do something like this, so unfortunatly, my answers are just speculation.

What version of max are you using? If it's R5, you could possibly use a mesher function to capture the animated boolean, then possibly reset the offending smoothing groups...

ARRRGGHHH!!!

...I'll be back...

-3DZ

:D

[Stroker]

Been giving it some thought. Came up with how I would do it.

I would use two different systems/animations:
1) Cutting of the mesh
2) Peeling the flesh back

I would model with splines. Rather good control over the where the cut will be and mesh density were needed. Model the cut in with only a slight gap. Close the gap, then key-frame it open.

For peeling it back, switch it all over to a cloth simulator. Use what ever method the cloth uses to bind verts along the cut, them peel them back and let the rest follow.

If you set up two different Max scenes that are pixel perfect, the transition between the two should not be noticable at all. Although, if you really wanted to, you could do it all in one scene with two different cameras, then switch between them at the appropriate time.

I do have some thoughts on Reactor cloth and attach2RB, but I'm not sure just yet.

edit:
Did some messing around. I would do the whole thing with splines in one shot.

[gman]

I'm using max 5.1. I'm using anatomically correct models created with a 3d scanner so I can't really go in and do much remodelling, this is the main reason why i need to figure a way to intersect faces without damaging the smooth cut. I used a boolean with a smooth modifier applied to it and created a cut with no vert popping but the model is faceted from the smooth, do you know why? or how i can use this modifier properly to do this?

I'll try your idea using conform and get back to you.

thanks.

[PiXeL_MoNKeY]

Scalpel from Cebas may be your answer:

http://www.trinity3d.com/xcart/customer/product.php?productid=44&cat=1&page=5

[gman]

Wow I think I want scalpel!
thanks.

I still think A lot of helpful techniques can be learnt here so I will continue to find an alternative there must be a way in max....I must strive on......I must.

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