Seeking advice from the medical animators...


Seeking help on this one…
I’m looking at a medical animation job that will require a close up view of a large polyp resectioning using a snare. ie. a wire is looped around some internal tissue, the wire loop is tightened until it cuts the tissue off. The scene needs to be realistic, and needs to show the interaction of the wire and the soft tissue. The job is made more difficult given the fact that we need to show this procedure cutting away various parts of the same growth - bit by bit.

To do this procedurally / dynamically really requires something like a combination of soft body dynamics and cloth (for the tearing). Based on some previous, somewhat similar work with cloth, my gut feeling is I’d be fighting a loosing battle trying to do this procedurally / dynamically.

I’m wondering what the best approach is here? Maybe I should just knukle down and fake it with FFD / cage mesh point level animation, swapping out meshes to simulate the cutting away as I go.

Any thoughts from the experts?


without knowing more, I might try using morph targets on a mesh. One with the fully formed polyp. And then one or more targets for the snare tightening. Add the jiggle effector (or delay effector set to spring and point deform mode) if yo need some organic wiggle.

The removed pieces could either be dents created with additional morph targets or a displace deformer with spherical falloff applied to the areas you want removed. Maybe have a hidden glob under the surface that would be the piece that is removed–which is revealed when the dents push in (kind of a cheat).


Joel - many thanks for sharing your expertise, most appreciated.

Yes - I’ve done a previous job with the snare itself using posemorphs - and that was fine. On that previous job I’d used cloth to do some pseudo ‘soft body’ dynamics and tearing of the tissue - along with some careful post production / editing to minimise that shot. Trying to control cloth to the extent I really needed proved next to impossible.

On this job there’s much more emphasis on the actual resectioning itself - hence my concern about trying to do it with cloth or dynamics. I think your suggestions of morph targets, effectors and displacement for the tissue sound like the best route forward.


And, to the extent possible, use filmmaking techniques (cuts, cutaways to detail, objects briefly obscuring the view) to mask changes in assets and techniques. Way too often we get caught up in faithfully simulating a complex set of events, when the real goal is to communicate, and filmmaking and editing techniques will help us make a tighter story with simpler techniques.

Of course, you know all this, and maybe the client is insisting upon an epic one-shot of the whole procedure… If so, my sympathies!


Yes - so true!!

I’m sure a few of my clients think “…this 3D stuff - it can’t be that much more difficult than Powerpoint? Can it?” : )


Although there are plenty of ways to get into simulation on an animation like this in c4d (and if you are able to work things out that way ,then great!) , my best recommendation would be to work out the most flexible method that allows you to most easily adapt to client changes, which will almost definitely happen. If its a simulation, you may need to go all the way back to square 1 and start again if the client wants to make changes. It also means lots of tests in order to get the desired action and timing. Nicks recommendation of using the “art of the edit” to get around potential pitfalls is an excellent idea (and one I try to go with when i can). Of course many of these medical device clients might lack the cinematic eye and insist on something literal and continuous (this happens a LOT as well).


Thanks Joel - yes, I think that’s good advice. I’ve certainly been there on the ‘simulation front’ before. Running innumerable tests, then a change comes along and the tests become invalid - repeat the cycle. That can consume so much time, and as you say, can lead to an inflexible position.


I often have to remind myself of this with my current feature length
personal animated film project.
It is not a matter of what is actually happening in the shot but indeed
what I wish to appear to be happening via my camera angles and even
switching cameras via the old Stage object and how I plan to comp it

Of course with client guided animation work,
any Dynamic simulation to achieve an effect is wrought with peril
as they are not aware of how many times you may have to run the sim to get the effect they are seeking.

Several years Ago I was approached unsolicited via email, to animate
of character involving simulating some on screen skateboarding video gameplay for a film project about the skate boarding culture in Jacksonville Florida USA.

The client had seen one of my old Demo reels on vimeo and was really
excited that he found an animator who did Ragdoll simulation of
catastrophic hits and falls of people.

I was mac based at the time and the only decent ragdoll
collision solution was a Python based Solver for the Vestigial Poser application.

A major aspect of the shot was where the player misses a jump
between two buildings and falls several stories to the ground and dies.

In the end the client kept “micro-directing” the actual ground impact
to the point where I stopped using the ragdoll solver and essentially
keyframed the bloody thing which was a bit frustrating.:banghead:

Here is the on screen bit that made the film.