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CGI Integration for Ground Crash

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Eric KirkCGI Integration for Ground Crash
by on Jun 29, 2011 at 8:06:22 pm

Hello all,

I'm looking for a solution here on how to make a CGI item, in this case a rustic space ship, interact with the ground so when it comes in, it hits the ground, sliding toward the camera, coming to a stop in just in front of the camera but with the realistic pushing of the dirt.

We've all see this stuff before where the ship comes in, a rut is left in it's trail, and it comes to rest with mounds of dirt around the leading edge.

I just saw a movie recently but can't recall the name but a perfect example would be from the movie 300, where the rhino comes sliding in to a stop. It is shown here:







So, for this, I am planning on a simple setting, like a shot of the Arizona desert, in comes ship, and slides in. Not worried about explosions or anything at this point, just that point where the ship interacts with the ground.

I have particular if that helps and many of the trapcode plugins.

Appreciate your help.

Eric

Eric D. Kirk
http://www.kirkproductions.com


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Steve RenardRe: CGI Integration for Ground Crash
by on Jun 29, 2011 at 8:32:28 pm

I think to do it purely in CGI and get the look you want you're going to have to move to a proper 3D environment like Max, Maya, or C4D. But I don't think that's how that shot is typically done. A better bet is probably to get some footage of the ground being dug up like that, and then comp the ship in. I think that is how the shot is usually done, because the particle/dynamics system required to slam something into the ground and have it dig a trench like that is pretty complex to build.

The particle tools you're talking about are not intended for a dynamic reaction to a moving object the way you're talking about, at least as far as I know.

------------
Steve Renard
Media Director, Cicada Design Inc.
and Freelance Know-it-all
647-406-7991
srenard@cicadadesign.ca
http://www.cicadadesign.ca


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Eric KirkRe: CGI Integration for Ground Crash
by on Jun 29, 2011 at 9:40:20 pm

Hi Steve,

I am just looking for a way so I would be happy to attempt it without CGI. Now, my ship IS CGI of course.

The way you describe sounds like it would work. Any pointers on how to do that? The part that is fuzzy to me is what to use to actually dig up the ground. I assume you would ensure the camera is at your preferred angle and then push the dirt with something in the general shape of the ship and in a manner that "that" something occupies the same area of the ship and then roto it out and replace with ship?

Could use some advice on this.

Thanks,
Eric

Eric D. Kirk
http://www.kirkproductions.com


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Tudor "Ted" JelescuRe: CGI Integration for Ground Crash
by on Jun 30, 2011 at 11:55:23 am

I would recommend trying FreeForm Pro for this one. You can animate a displacement map to create the impression of dirt gathering up in front of the spaceship as it slides in and leaving the trench behind it. Apply that to a nice desert texture that has a feathered edge and you can match the perspective and camera move in AE's 3d space. Particular should help in adding bits and pieces flying in the air and dust.
This tutorial will help:
http://www.videocopilot.net/tutorials/blast_wave/

Tudor "Ted" Jelescu
Senior VFX Artist


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Eric KirkRe: CGI Integration for Ground Crash
by on Jun 30, 2011 at 12:07:09 pm

Hi Ted,

We talk a couple weeks back about Free form pro when I was talking about draining my lake. Hopefully that will fit in to your tutorial soon.

I bought FF Pro as a result. So, back to my dirt issue. I've watched Andrew's tutorial and it will certainly fit in (great tutorial too). My problem right now is just not exactly sure how to approach this with FF pro. I don't have a real good grip on how to use displacement maps to drive the dirt movement.

I was actually messing around with my desert image last night with FF but wasn't making any progress.

Appreciate any pointers on where to start.

Eric

Eric D. Kirk
http://www.kirkproductions.com


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Tudor "Ted" JelescuRe: CGI Integration for Ground Crash
by on Jun 30, 2011 at 1:34:40 pm

First set your layer to which you can apply FF Pro. A high file as wide as your comp maybe ( for HD let's say 1920 wide by 3000 high) textured with the desert. You will need to paint a trench and a pile of rocks and dust ( as it looks from above) and animate the pile growing and moving as the trench grows. Of course that would have to match the timing of the ship falling and sliding. One more thing- precomp the layer - make sure the precomp is the same size as the layer- and put a mask that will feather the edges. This way you can place this on top of a motion tiled layer with the desert texture on it and blend it in.
Then you need to create the animated displacement map. Use another layer the same size with the texture described above. Start with a 50% grey image. Draw the trench shape and paint it with a darker grey- the darker it is the deeper the trench will be. On the edges you may want to have a gradient from the darkest to a little over 50% and then back to 50%. Then animate the pile - a shape the grows in intensity from 50% to a lighter gray ( the closer to white the taller the pile) with a gradient on the edges that goes from the lighter gray to 50%.
That's the basic idea. You will obviously have to tweak the animated texture and displacement map. You can add a lot more detail in both- rocks rolling, ground cracking and so on.
Hope this gives you a starting point.

Tudor "Ted" Jelescu
Senior VFX Artist


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Eric KirkRe: CGI Integration for Ground Crash
by on Jun 30, 2011 at 1:57:16 pm

Ted,

Great run down on the process. I think between the two of you, hopefully I can get something together. I appreciate you taking the time to provide the detailed walk thru.

Eric

Eric D. Kirk
http://www.kirkproductions.com


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Steve RenardRe: CGI Integration for Ground Crash
by on Jun 30, 2011 at 1:28:55 pm

Hi Eric,

I've seen the discussion of using FFPro - it's not a package I'm familiar with so I'll leave that to Ted.

In terms of my technique, I would have to do some experimentation, but I would do it in miniature using a sand box or table and then something painted green or blue that I could key out that was, as you say, shaped something like the ship - maybe the end of a shovel handle or something like that. Shoot a still of the sand undisturbed, then shoot video of the object moving through the sand, and then pull the object away and shoot another still with nothing there, so that you have a good clean "before" and "after" plate with which to work in your composite.

Then you can comp your images into a desert shot, add the ship, add flying debris a la the Andrew Kramer tut, and away you go.

Of course, I'm speaking of all this like I've done it before, which I have not, but this is how I would approach it. Maybe over the long weekend I'll grab a camera and some of my son's sand toys and see what I can come up with!

Good luck!
Steve

------------
Steve Renard
Media Director, Cicada Design Inc.
and Freelance Know-it-all
647-406-7991
srenard@cicadadesign.ca
http://www.cicadadesign.ca


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Eric KirkRe: CGI Integration for Ground Crash
by on Jun 30, 2011 at 1:54:23 pm

Hi Steve,

Funny enough, I was playing with a miniature last night and a year or so ago, had a similar idea with the green object sliding through the sand/dirt. I had not however, considered the still before and after. Good idea.

If you do work something up in your trials and discover anything, appreciate any updates.

Thanks,

Eric

Eric D. Kirk
http://www.kirkproductions.com


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