Tracking Rex

Match Moving is used throughout Hollywood in almost current every film you see.  Many times you never know you are watching a Match Moved shot because it is done so prefectly.  Match Moving or "tracking a plate" is the art of shooting video or film, inserting 3d elements to create a seamless shot.  This process of tracking points on the video or film is a very time consuming process that had to be completed by hand.  With advances in software, better a faster methods of tracking a plate have been developed. We recently created a short animation using Motion Tracking software.

We shot our scene using a Canon Optura DV camera.  We felt that in order to really test the motion tracking software, we had to do a hand held shot with lots of zooming!  Our camera man climbed into a tree and zoomed in to the street, wobbled the camera as he slowly zoomed out, held the shot, then zoomed in quickly to the street.

Below is our text based rough story board of the animation

  1. T-rex is moving down the street, hunting, scanning the area.
  2. A car is driving down the street.
  3. T-rex stops, adjusting his stance as he lowers his head and roars.
  4. The driver hits the brakes, stopping inches away from T-rex
  5. The car drives away in reverse as T-rex continues to roar.

Step 1
We loaded up the video into our motion tracking software and looked for areas of the video where we could place our tracking points. We ended up with 10 tracking points.  We then converted the 2d tracking points into points in 3d space.  Then we load the 3d points on top of the video in order to line the street up with the ground plane.  Using a primitive object, we render a sequence to make sure that tracking data is correct and that the object does not slide around on the street.  Once this has been completed and approved, we export the camera data to Lightwave.

Step 2
When you open the Lightwave scene up the you will see that the camera is keyed at every keyframe. We then use the ground plane as the street in which we will animate our T-rex and Audi TT. We use the video plate as a background sequence and as a front projection sequence map for the street object.  From this point on, we placed our objects onto the ground plane and began to work out the timing for the shot. 

Step 3
Once we have completed the animation, created our texture maps and set up the lights, we are ready for rendering.  In order to save render time we render each element on a separate pass (one at a time).  This also allows us more control over the final shot. Our render passes included: T-rex (this included the overhead shadows from the leaves), T-rex's shadow on the street, Audi TT (this included the overhead shadows from the leaves) and the Audi TT's shadow on the street. We render the elements as a Targa 32 bit in order to include the alpha matte in each frame.

Step 4
We load all of our sequences into After Effects and start our compositing process. We start to add each layer to the timeline.  We adjust the color and transparency of the shadows so they look similar to the real shadows from the trees. Once we have all of the shadows composited with their elements we adjust the colors and levels of the T-rex and the Audi TT.

The final item is to add the background sequence on top of the T-rex layer and create a traveling mask for the car that is parked on the street. This will enable us to put T-rex and his shadow behind the parked car.  This helps to add a bit more realism to the shot.

We were very impressed with the motion tracking software.  You can accomplish the plate track in a very short time.  This enable you to get the shots tracked and completed more quickly, which saves time and money

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