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How to convert Scale to Z Position?

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Joshua NortheastHow to convert Scale to Z Position?
by on Jan 12, 2013 at 4:37:21 am

Hello, I've filmed a shot were I zoom into a spot on the ground. I 2D tracked it in Mocha because I couldn't get a solid track in Boujou. I imported the track to after effects, applied it to a NULL and parented it to a picture of a flag pole I modelled in Blender. The track is pretty good, but when it zooms in and the image scales up, the flag pole pixelates. I can't just render the image from blender in a larger frame size because After Effects won't handle it. So, I thought of a workaround. I convert the 2D track to a 3D camera in After Effects, Export the AE camera to Blender and render it out. I successfully parented the 2D position to the 3D camera via expressions, but, I just don't know how to convert the scale value to a z position value. Because without doing that, the flag pole stays the same size when the camera zooms in. I've attatched the project file with the first 5 seconds of the footage to minimise download size (14mb).

http://dl.dropbox.com/u/67578544/Flag%20Pole%20Track.zip

P.S. I've included both the Transform Data and the Corner Pin from Mocha.

Joshua Northeast
Jnortheast Films


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Darby EdelenRe: How to convert Scale to Z Position?
by on Jan 12, 2013 at 6:49:32 am

Deriving Z position from scale requires two bits of information:

1) Camera field of view/focal length/zoom

2) A reference point, e.g. [100,100] scale = 1000 pixels away

Since you described your shot as a "zoom" this means that #1 is a moving target. This makes it impossible to do without knowing the zoom at every frame.

Most camera trackers will allow you to solve for a variable field of view which would give you this information, but my guess is that any camera tracker that could calculate that information accurately should also be able to solve the camera and therefore render the exercise completed.

However, if your camera only zooms and you don't get any closer/farther from your subject then you're set with a scale. Zooming = scaling.

How large would you need to render your flagpole from Blender in order for this to work? AE is much more capable of handling large image layers since the transition to 64-bit .

Darby Edelen


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Roland R. KahlenbergRe: How to convert Scale to Z Position?
by on Jan 12, 2013 at 7:49:40 am

It looks like your version of mocha allows for the scale value to vigorously exceed 100%. This was a known issue with certain versions of mochaAE. Using mochaPro 3.1, my scale value maxed out at 100.5%

TO fix your issue, you can divide the Null's scale value by 2.5 using an Expressions script - value/2.5. THe value of 2.5 is taken from looking at the value graph of the scale property which maxes out at about 250%.

HTH
RoRK

Intensive mocha & AE Training in Singapore and Other Dangerous Locations

Imagineer Systems (mocha) Certified Instructor
& Adobe After Effects ACE/ACI (version 7)


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Roland R. KahlenbergRe: How to convert Scale to Z Position?
by on Jan 12, 2013 at 1:01:10 pm

I should add that I got good camera solves using either AE's 3D Camera Solver or mochaAE/mochaPro V3.0 (or newer - V3.1 is the latest).

More importantly, your insert layer is a raster image which will bloat up, pixelate regardless if scale (2D layer) or camera distance (z-position) is used for its eventual screen resolution. IOW, a raster image will pixelate under both considerations.

As Darby has suggested earlier, you should start with a higher rez file. When you create this insert layer, set it to the size/rez where it is at its highest required rez for the shot.

HTH
RoRK

Intensive mocha & AE Training in Singapore and Other Dangerous Locations

Imagineer Systems (mocha) Certified Instructor
& Adobe After Effects ACE/ACI (version 7)


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