Ground Marks from Impacting Object

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Old 08 August 2009   #1
Ground Marks from Impacting Object

MAX2010_64

I have setup a PFlow (attached) where a blade repeatedly strikes the ground as it moves.

I am trying to create particles that define precisely where the blade is penetrating the ground. I know I am doing something wrong but can't figure out exactly what it is. As the blade goes through the ground... one half of the particles fall through while the other half stay on the ground as desired.

Thanks for taking a look (note: uses a Box3 Cache... don't know if that will be a problem).
Attached Files
File Type: zip particle_displace_test_01.zip (32.3 KB, 22 views)
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Old 08 August 2009   #2
I'd do it with collision spawn.

There are two ways you could try:

1. Spawn particles on the plane (you can limit it to the genral area, where the blade hits, to reduce the particle count) and define your sword as collision object. Where the sword intersects the plane, new particles will be spawned.

2. In essence the same as 1, but with switched roles. The blade is the emitter, and the plane the collision object.
 
Old 08 August 2009   #3
number 2 for sure.
Attached Files
File Type: zip particle_displace_test_02.zip (33.6 KB, 20 views)
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Old 08 August 2009   #4
Thanks for these ideas! Will give these methods a try (sound simpler than what I'm doing). I'm currently on some other projects.


But in the scene I posted...

I distributed non-rendering particles on a plane, set the blade as a collision object, when the blade swings and hits the particles it spawns new particles which have gravity force and are then set to collide on another plane object and stick in place (leaving the shape of the blade mark).

This 'rube-goldberg' method partially works... but the thing I don't understand is why only half of the newly created particles stick but the others fall through? It's like the particles hit by the blade on the downstroke fall through but those hit by the upstroke stick as desired.

Thanks again.
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Sincerely,

Mike Truly
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Truly Media
970.349.5651
www.trulymedia.com
 
Old 08 August 2009   #5
It could be by the time the collision registers the new particle is created past the point of collision. So in reality the spawn is happening underneath, iffy. More than likey it has to do with the collision object normals. In the example I posted it has half of the collision objects normals flipped, flip them back and check the result, it may look familiar.
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Old 08 August 2009   #6
Thanks John... will check it out.
__________________
Sincerely,

Mike Truly
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Truly Media
970.349.5651
www.trulymedia.com
 
Old 08 August 2009   #7
Finally getting back around to this.

John, thanks very much for your example! I rebuilt the flow based on yours and have it working about the same.

1. One thing that was a bit puzzling... in your example you have the ground plane mesh with half the faces with flipped normals. Mine is working setup the same way. But early on, I tried to use an object with a stack to do the same thing and it didn't seem to work. Stack was like Plane>Mesh Select>Normals but it did not give the desired result as with collapsing to Editable Mesh and flipping the faces. Weird.

2. Other issue I'm having is that there is a bit of a gap on each strike right as the blade approaches the dividing line of the flipped faces (the center of the blade swing). See attached image. Not sure how to get even distribution across this area.

Thanks again.
Attached Images
File Type: jpg blade_strike_gaps_in_middle.jpg (56.1 KB, 57 views)
__________________
Sincerely,

Mike Truly
-----------------------
Truly Media
970.349.5651
www.trulymedia.com
 
Old 08 August 2009   #8
Any particular reason why you're using an UDeflector? A standard deflector should do it. In my experience the Deflector is far more reliable than the UDeflector. Also it works in both direction, while the UDeflector depends on the normals of the mesh.
 
Old 08 August 2009   #9
Thanks for this info Philipp!

I was using that because that's what John used in his example. I see that a plain deflector does work with both directions of the swing.

But I still have the problem of the gap that occurs mid-swing (as the blade nears vertical).

Thanks again.
__________________
Sincerely,

Mike Truly
-----------------------
Truly Media
970.349.5651
www.trulymedia.com
 
Old 08 August 2009   #10
That one is actually not easy to solve. Since the particles on the blade will move parallel to the ground at the center, no particle will actually hit the deflector. Firstly you can increase the density of particles on the blade to narrow the gap. To get completely rid of it, you might have to use additional deflectors. (I would add small SDeflectors where the gaps are. The spawned particles will be offset from the ground, but if you render your texture from an ortographical camera, this difference will not be visible.)
 
Old 08 August 2009   #11
I noticed that too, I don't know why the select mesh + normals modifier gives that "gradient" type transition with the normals. It is odd.

Yeah, I think your only easy solution in that case is to raise the integration steps at render time, there will always be some gap where the collision normals change but with enough particles and a high enough integration step the effect should be minimal.

EDIT: Just saw the above posts " or just add some more deflectors"

As for Deflector vs. UDeflector reliability that is debatable, especially when using simple geometry, deflectors when not relying on normals sure, but the collision detection is the same.
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Last edited by JohnnyRandom : 08 August 2009 at 05:40 PM.
 
Old 08 August 2009   #12
OK, if I make another deflector just in the center gap area that is rotated to a slight angle from the main deflector... I can make some filler particles spawn there to fill the gap.

But I need a way to make the particles move to be on the same plane as the original deflector particles. Using a Gravity to try to make all the particles fall onto the same plane results in some particles sticking to a plane... but others fall through ignoring the Collision plane.

Sigh.
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Sincerely,

Mike Truly
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Truly Media
970.349.5651
www.trulymedia.com
 
Old 08 August 2009   #13
You have Box#3, I assume?

Create a simple data operator that adds a few world space units to the Z-axis after spawn.

In event 02 add the new data op, your existing force, and a a collision test. Create another Deflector or Udeflector with a new ground plane and choose Stop as the speed.



BTW Upon rethinking, instead of adding more deflectors to the scene, use the Udeflector + Shape I used earlier and simply extrude the edges 1.0 along the normals seam and that will alleviate the seam spawn issue without additional burden.
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Last edited by JohnnyRandom : 08 August 2009 at 06:30 PM.
 
Old 08 August 2009   #14
Thanks very much John! The Extrude edges trick filled the gap. Actually, I used Extrude Edges on an Editable Poly so I would get a little bit of an angle in this gap area and it filled nicely with no perceptable rise in the particles in this area.

Thanks again.
__________________
Sincerely,

Mike Truly
-----------------------
Truly Media
970.349.5651
www.trulymedia.com
 
Old 08 August 2009   #15
OK it's working great... so naturally I want it to do more.

I have set this up based on Allan McKays Procedural Footstep tutorial and it works great but is only giving me a single depth of the gouge (see attached). Ideally, I would like to have the gouge have varying depth.

Any idea how to accomplish this this? I think this is much more complex to accomplish.

Thanks!
Attached Images
File Type: jpg varying_depth_of_gouges.jpg (15.5 KB, 35 views)
__________________
Sincerely,

Mike Truly
-----------------------
Truly Media
970.349.5651
www.trulymedia.com
 
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