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Tracking Forward Motion in Open Area

 
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Zephrus



Joined: 10 Mar 2012
Posts: 3

PostPosted: Mon Mar 12, 2012 9:21 am    Post subject: Tracking Forward Motion in Open Area Reply with quote

Hello, wasn't sure if this should go in the VFX or General forum so I'm posting it here.

I'm attempting to use Syntheyes to track both lateral and forward motion in a larger sized "grassy" field.

First I'll say where I've been successful, and then tell you where it seems to be falling apart. First, as stated, I'm trying to track camera motion that moves forward (about 30 or 40 feet) in a grassy field (actually a currently dried up lake bed). Let's say this clear, grassy area is approximately 100 x 100 feet, with some far objects just beyond this area to the tune of about 35 to 50 feet, such as apartment sidings, windows, tree trunks and other stationary objects at the far end. There are no "side walls" as there would be in an enclosed space, so Syntheyes has take its cues mostly from things on the ground. There is very short grass (like astroturf) in a good portion of the field, which has light and dark patches which provide contrast. An assortment of patchy dirt areas, and a few rocks, small to medium size, anywhere from 2 or 3 inches in diameter to a foot or so in diameter.

So here's the issue: When I do a relatively smooth pan shot only, I can get the track solid as a rock in Syntheyes, with no artificial tracking markers set out. But when there is forward movement involved, the scale of the forward movement does not "lock," and I get a sliding of my ground plane and object when I proceed to composite in Cinema 4D.

I am wondering, is this more of a Syntheyes issue, a tracking marker issue, OR, is it a scale issue? After using Lightwave forever, I'm fairly new to C4D, as well as to camera tracking and Syntheyes in general. When I import my camera solution track into C4D, my plane and object do seem to be stable. However, they do not "approach" the camera at the correct scale, i.e. the plane and object are not moving towards the camera as quickly as the camera is obviously moving over the ground, and they do not "scale up" quickly enough to match the approach of the camera. As a result, the ground plane and object appear to slide away from the camera.

Just how important is it to match measurement units (this may be an immensely dumb noob question I realize) between Syntheyes and C4D? And if this is not the likely issue, do I simply need to throw out some tracking markers? I hope I've been precise in my explanation of the issue. Any help and feedback much appreciated. Thank you.
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borgus



Joined: 30 Dec 2009
Posts: 145
Location: bremen, germany

PostPosted: Mon Mar 12, 2012 10:21 am    Post subject: Reply with quote

hi Zephrus,

I think you should make absolutely sure that the track is rock solid
before exporting anything to a 3thrd party app. Make sure that
you set up a coordinate system in every case and try to get the
scaling as close as possible in SE. Test your solve with a test sequence
( go to "perspective" window, press "L" to look thourgh the cam, RMB ->"preview movie") to render out a test sequence or whatever to
see how good your solve is. Add some test objects as well as a ground
plane to the scene do better check the perspective, scale, camera path etc.
I'm not aware of a "gerneral" issue causing sliding in a 3D app after
solving with SE, so it's more likely a "user issue" Smile

hope that helped a bit Smile

cheers, Seb
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Zephrus



Joined: 10 Mar 2012
Posts: 3

PostPosted: Mon Mar 12, 2012 10:10 pm    Post subject: Reply with quote

Thank you for the advice, Seb! Will give it a shot Smile If by chance all else fails, do you think I show throw out some tracking markers (tennis balls or the like) that I can roto out later?
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borgus



Joined: 30 Dec 2009
Posts: 145
Location: bremen, germany

PostPosted: Tue Mar 13, 2012 4:01 am    Post subject: Reply with quote

hi zephrus,

depends on you shot... if it's gonna be an easy job to paint the
balls/markers out, then do it. If you think that you have enough
contrasty feautres in your sequence, then don't.
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