Tracking moving object in static scene(1 still camera)?

#1

Hi all

I have footage of a moving object shot from a static camera(camera NOT moving). I have limited software available - Autodesk MatchMover and also MAX built in Tracker. The Max one is junk. Matchmover needs 2 cameras to solve? Is that correct? Any way to get a solve with 1 camera and get the result into max with what I have or with some other free software? I already tried with MatchMover but can’t seem to get a solve with 11 points on my object.

Regards,
Morne

#2

What type of movement are we talking about?
does it move at a constant speed in one direction or are we talking about following a bumble bee? also, how long is the shot?

#3

The shot is about 10 seconds and I’m tracking a pipe carried and waved by an actor. (I will replace the pipe with something else in 3D)

#4

Are we talking about replacing a broomstick with a lightsabre kind of thing?

Or will the 3d object have more detail?
Since the camera doesn’t move, match move software won’t help you.

either way I sense some rotoscoping in your future.
Maybe post a rendering of the 3D object you want to composite…I may have a better understanding of what you are up against.

#5

hehehe no. I need to replace it with a shoulder missile launcher so the angles and perspectives and movement needs to fit. The rotoscoping part will only be to fix the fingers as the guy holds the pipe versus how the launcher is held. How would I “rotate” and match the 3D launcher object to “fit onto” the pipe is the question.

#6

I know that this tutorial set describes and shows how to do this sort of thing:

http://www.hollywoodcamerawork.us/vfx_index.html

And I thought SynthEyes has done this as well.

#7

Sytheyes will track rotation of an object in a static scene?
Wow. I’ll have to look into that!

#8

I believe that there was a tutorial on their site that dealt with motion capture.

#9

Given that the object has enough points to track (around 6 to8 i think), you can do the object tracking in syntheyes.

#10

as mentioned I only have Autodesk MatchMover and the built in tracker in max. I do not have syntheyes and since it is not a free program it is not an option with the current project.

#11

SynthEyes does have a demo - I “think” it’s a full version, but perhaps you can email them to find out. Then you can try it out on this project, and if it works well enough you can invest in the software. They are VERY good at tech support and I’ve heard nothing but praise of the software.

#12

again this is not an option. The demo doesn’t allow export of your solve so kinda pointless. Yes I know the software is great but again I don’t have it and there is no budget for it now. I need a solution with what I have.

#13

Generally, motion capture of that sort does need two or more cameras—the tracker must triangulate the object’s position in space, and if there is little or no paralax shift, there must instead be multiple different perspectives on the object.

That said, it is possible to get an object solve from a single camera, if the object being tracked has enough detail and shifts its orientation enough. I unfortunately do not know Matchmover, though, so I can’t help you with specific steps. I’ll walk through two ways of doing it in PFTrack, and maybe you can figure out how to get equivalent results with Matchmover.

First, for object tracking, create a mask around the object you want to track. Not too tight, as you want the software to be able to see the edges of your object, but tight enough that it won’t get confused by extraneous motion from your actor or other objects moving in the scene. Invert the mask so that it is masking out everything except the object to be tracked.

Create a new motion group, and set the camera to stationary.

Create several user features (aka supervised trackers) in the motion group you created and track each one the length of the clip. Once you have 6 - 8 such features, run a solve for object motion. Hopefully you’ll get some kind of reference that verifies the motion of your object.

Export your scene in your 3d program’s format, manipulate your geometry to match the point cloud, and parent the geometry to the cloud. It might now move the way you want it to.

The other way to do it is through geometry tracking. Start by modelling a tracking object that roughly matches the shape of the object to be tracked. In your tracking program, make a new motion group for your object, and set the camera to stationary. Import the tracking geometry and manipulate it so that it fits as perfectly as possible over the object you want to track. Track the scene; your geometry should reproduce the motion of the object you are tracking.

Export the scene, and in your 3d program, parent your rocket launcher model to the tracking geometry.

There are definitely some “gotchas” in this process, though. The smaller (or further away) the object you’re trying to track is, the less likely it is that you’ll get a good (or any) solve. Also, if there are an insufficient number of reference points on the object, it will be far more difficult. I learned recently that the sort of tracking markers that work great for a camera solve aren’t so good for geometry tracking–texture tends to be better than X’s made from tape in that case.

I don’t have any idea if any of that will be helpful to you working in Matchmover or not, but I hope it is.

#14

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