.shape4ae Track Data

Hey everyone,

I don’t know if this is really the right place, but I’ll just give it a shot and hope someone in here can help me with my problem :slight_smile:

I’m a student of Computer Vision and currently working on a Project where I need some tracking data. Since our University has some licenses of Mocha for AE I want to try to import the data from the exported .shape4ae files.

I have currently a hard time figuring out how After Effects handles Transformations. In the .shape4ae File, there are basically two things to be found.

First of all the keyframed data of the shape of the object (e.g. the points for the xspline shape) and secondly and what is more interesting to me the information about how this shape is transformed for every frame.

There are 8 categories of data for every frame:

Translation X, Translation Y, Scale, Rotation, Shear X, Shear Y, Perspective X, Perspective Y

I wonder now how all this data for a single frame can be put in a 3x3 homogenous transformation matrix as can be found here

http://doc.trolltech.com/4.6/qtransform.html

It doesn’t seem to be straight forward, especially the shearing. For the first frame in the sequence the values are set to perform no transform at all, so:

Translation X = 0

Translation Y = 0

Scale = 1

Rotation = 0

Shear X = 0

Shear Y = 1

Perspective X = 0

Perspective Y = 0

The fact that Shear Y is set to 1 makes no sense to me right now. The value should be set to 0 if this would be the value responsible for vertical shearing in a transformation matrix.

I hope that someone here can explain to me how these values are applied to create a transformation frome one point to another in after effects.

If it helps I can post a .shape4ae file in here.

Thanks a lot in advance!

Hey everyone,

I don’t know if this is really the right place, but I’ll just give it a shot and hope someone in here can help me with my problem :slight_smile:

I’m a student of Computer Vision and currently working on a Project where I need some tracking data. Since our University has some licenses of Mocha for AE I want to try to import the data from the exported .shape4ae files.
I have currently a hard time figuring out how After Effects handles Transformations. In the .shape4ae File, there are basically two things to be found.
First of all the keyframed data of the shape of the object (e.g. the points for the xspline shape) and secondly and what is more interesting to me the information about how this shape is transformed for every frame.
There are 8 categories of data for every frame:
Translation X, Translation Y, Scale, Rotation, Shear X, Shear Y, Perspective X, Perspective Y
I wonder now how all this data for a single frame can be put in a 3x3 homogenous transformation matrix as can be found here
http://doc.trolltech.com/4.6/qtransform.html

It doesn’t seem to be straight forward, especially the shearing. For the first frame in the sequence the values are set to perform no transform at all, so:
Translation X = 0
Translation Y = 0
Scale = 1
Rotation = 0
Shear X = 0
Shear Y = 1
Perspective X = 0
Perspective Y = 0

The fact that Shear Y is set to 1 makes no sense to me right now. The value should be set to 0 if this would be the value responsible for vertical shearing in a transformation matrix.
I hope that someone here can explain to me how these values are applied to create a transformation frome one point to another in after effects.
If it helps I can post a .shape4ae file in here.

Thanks a lot in advance!

Hi,

Whilst what you want to do is theoretically possible, you will find it very difficult to achieve.

The transformations encoded in the shape4ae data are in camera space, so you need to set up a camera, backproject the points you want to transform and apply the transformation in camera space.

The best reference for how we do this is:

If your university owns a copy of mocha v1 as distinct from mocha for After Effects, you can have a much easier life by using the XML Motion Matrices tracking data export format. This is not present in newer versions of mocha but will probably be back in soon.

Best regards,

J-P

Hi,
Whilst what you want to do is theoretically possible, you will find it very difficult to achieve.
The transformations encoded in the shape4ae data are in camera space, so you need to set up a camera, backproject the points you want to transform and apply the transformation in camera space.
The best reference for how we do this is:

If your university owns a copy of mocha v1 as distinct from mocha for After Effects, you can have a much easier life by using the XML Motion Matrices tracking data export format. This is not present in newer versions of mocha but will probably be back in soon.
Best regards,
J-P