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Tracking for engine glows

Jan 7, 2013 1:24 AM

Hi,

 

I have been working on engine glows for the past few weeks, and though I am having a relatively good outcome, I was wondering what, in the forums point of view, the best way to track data for this type of shot would be?

 

I have filmed a miniature model. one specific shot has the camera still, and the model lowered over a period of time. The model is that of a spaceship modeled after an aeroplane. There are two engines, one on the back of each wing. As the model drops, the far engine becomes obscured by the ships body. (this is just one specific shot of many, but I am guessing that once I find a good method to track, it can be altered and used for most shots)

 

What I am currently doing is this:

 

1) Import the footage

2) Key footage

3) Track a area around the engine using MochaImportPlus.

4) Using MochaImportPlus, I create a "Move" null object

5) Selecting the Null and all the keyframes (by pressing "UU" to display them) I move the null to the position on the engine that looks right

6) I create a Point Light and in 3D space allign it to the corner of the null (Top Left) and parent it to that null

7) Using Video CoPilots Lens Flares, I use the point light as the flare emitter

 

This works quite well, and by duplicating the light, and attaching each one to its own null, the flares work quite nicely. The problem that I have, is that my tracking skills dont seem to be all that good, and the track slides throughout the shot. If at the start it is dead-centre to the engine, at the end it might be half an inch (whew - translating between centimeters and inches has just made my brain drip out of my ears!) higher. Also, along with the tracking data, is there an automated way to get the lens flare that attaches to it, to scale?

 

I admit that I have not done too much research around this yet, as I thought I would be able to use the knowledge I have so far to make the effect work. And as I said, the outcome is not terrible, with some cleaning up and moveing of keyframes, I get a reasonable result, but I am sure that there is a better way to do this. I am not looking for an easier way as such, but a better way!

 

Well, thanks in advance,

Pierre

 
Replies
  • Currently Being Moderated
    Jan 7, 2013 2:48 PM   in reply to Pierre Devereux

    Jeez, it's too bad it's a physical model and not in a 3D application. 

     

    You may want to consider the part of the model that eclipses the engines & glows:  it will need to be rotoed on a layer above them, and it will need a little light wrap (or reduced-size glow) to help sell it.  Not an especially easy task on the first go.

     
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  • Currently Being Moderated
    Jan 7, 2013 6:46 PM   in reply to Pierre Devereux

    I just tracked the headlights of this car as it goes through fog in Mocha to see if I could recreate your issue.  While the position and anchor point tracks seemed to track nicely, the scale got thrown off when it went through the fog and I had to add a couple manual keyframes to fix it:

    Mocha_Car.png

    Even then the scale of the Null Object woud jump a bit as it went through the fog.  In your case you may need to to two different tracks, one up until the light is eclipsed by the ship and one after it comes out from behind the model.  Also Dave is probably right about Rotoing out the part of the ship you want in front of the lights. 

     

    In my case I was able to fix the scale change in After Effects since the car is moving at a relatively steady speed in this shot.  I simply setup up some manual keyframes and used an expression pick whip to match the percentage of the light's Cone Angle to the percentage of the Scale.  If you're curious here's how I set it up:

    Mocha_Track_AE_Setup.png

    A) I copied and pasted the Anchor Point, Position, Rotation and Scale data from Mocha onto my Null.  Since The anchor point and position were the only bits of data that I needed for the shot, I deleted the others including rotation and scale which I fixed with some manual keyframes do to the steady motion of the vehicle.

    B) Then I manually set the anchor of my Null layer to 0 so that the corner matched the center of the headlight.

    C) Then I added two lights, an ambient light and a spot light, and I parented the spot light to the Null Object.  (This may work differently with Video Copilot Optical Flares, but my understanding is that they use lights as well so it might actually be pretty similar) 

    D) Then I option clicked on the Spot Light's Cone Angle to create an expression and I pick whipped the scale property of the Null object.  Now the light's Cone Angle will change to match the scale of the Null Object. 

    E) Finally I fiddled with the Scale keyframes and ended up having it start at 30% and finish at 60%.

     
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