I Need An Expression To Constrain A Particle Grid To A Poly Surface

[georgep1]

I need a particle creation expression that will constrain the Z location of a particle grid to a poly surface. I want the X and Y locations of the particles to remain in a grid.

Here is the tricky part: The poly surface resembles swiss cheese and has a lot of holes in it. I only want particles to show up on the surface itself, so that if there is a hole in the surface, there are no particles in that area.

So basically I want my swiss cheese-like poly surface to appear as if it is covered in particles that are spaced in an even grid.

If anyone could offer any help on achieving this it would be greatly appreciated.

Thanks.

[ptb]

It would be better to make a Nurbs Cheese (or an invisible instance), then make it a goal for the particles and animate the goalU and goalV prameters

[georgep1]

Thanks but unfortunately this is not possible. for what im trying to do, it has to be the poly.

Anyone?

[ptb]

QUOTE(georgep1 @ 09/01/08, 05:57 PM) [snapback]290812[/snapback]
Thanks but unfortunately this is not possible. for what im trying to do, it has to be the poly.

Anyone?

how will you animate your cheese? will it bend? or what is supposed to happen?
Else you could just parent the particleshape to the poly and delete the particles manually in the holes.

Another way i just thought of is to attach a hair system (just the follicles) and attach z of the particle to each follicle. You see, it's hard to retrieve poly surface information.

then again you could use deformers to achieve the effect, like i said - depends on what's supposed to happen.

[joojaa]

Why cant you just use the poly object as goal? I mean just delete the parts were the holes are form the goal verson shuffle some pointsaround on the surface and you ahve perfect control of amount and position.

Or use a second surface thats a wrapped poly. Better yet use the nurbs as the wrappee.

QUOTE
Thanks but unfortunately this is not possible.

I hate it when people say that, you description, before or after does not actually mean its not possible Your just shuting down a avenue of search that might be worth investigating. An that might work. So say rather i dont see thet working out very well instead. But see heres the problem. We must trust what you say because thets the only way we are communicating. So you may have inadvartedly closed of the true solution with thet sentence.

PS: this happens a lot and the right answer is not allways the obvious. So for a morbid example what is the purpose of bulletproof glass? To stop bullets? Hardly, its to protect. But protect what? If its whts on the other side of the bullet proof glass. So the best possible bulet proof glass is one thats indestructible by ANY means. Failing that one thats bullet proof only form one side. After all what good is a bullet proof glass if you can see the attacker placing a bomb on the other side of your glass. Now atleast he will think twice of doing so as you can shoot him and he can not. On the other hand if its purpose is to stop violence then its not a solution at all.

[georgep1]

thanks for the comments. I probably wasnt clear enough in my initial post. The part that will change is the size, number, and location of the holes in the surface. the particles will be used to instantiate an object that will be placed along the surface in a grid arrangement, but will be absent when there is a hole in the surface. The tricky part is that I want the objects to appear and disappear as the holes in the surface become bigger and smaller and appear and dissapear.

Also, the final result of this is not an animation. I am trying to view the way different configurations of this scheme look quickly and efficiently. It would take a very long amount of time to individually model different schemes.

I am not opposed to using a nurbs surface, but I found it impossible to automate parts of the nurbs surface that are trimmed away. For example: imagine a bumpy surface that is constantly changing shape, and all the bumps that protude past a certain plane get trimmed away and become holes. I am using the displaceD plugin to create the bumpy surface. I turned the history on and set the trimming plane to intersect the bumpy surface for a curve on surface and set the trim tool to keep and selected a part of the surface that doesnt trim away, but the problem is as soon as more than one part of the surface goes past the trimming plane at the same time, it just chooses one part to trim instead of trimming all the parts past the plane. With a poly surface I can just use the cut faces tool with the history on.

Thanks for the suggestions and if anyone can help me pull this off or give me any advice I would really appreciate it.

[joojaa]

make it 2 pass render, first render a map for the homes So they are black rest are white then emit form the grid, but kill all ones that emit from black.

Emit form the poly after the holes have been deleted in history delete particles emitted form border edges.

let teh renderer handle this.

[georgep1]

thanks for the great idea. Ill try this out as soon as things at work die down which should be in about a week. I may have some follow up questions on how to implement that technique once i start getting into it.

Is there a way to automatically delete particles emmitted from border edges? I was thinking of adjusting the poly tesselation to my desired grid and just making it a soft body and then instantiating my objects to the particles but the problem I had was that the new vertices around the holes that werent in line with the grid would also become particles.
If there is a way to automatically delete these please let me know, or if its possible to write a script to do this please give me some pointers or send me in the right direction.

Thanks a lot!