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Calculate Trackable Pose from Corner Screen Coordinates

April 27, 2014 - 6:52pm #1

Hi all,

Does anyone know how to calculate the pose of a trackable (or camera in repect to a trackable) given the 4 screen cooridates of the trackable corners? I assume  Vuforia does this under the hood, but I wanted to expose this functionality to my application. Does anyone know if I can use Vuforia API to accomplish this, or what the math is behind this operation? Any insight would be greatly appreciated.

Thanks

Calculate Trackable Pose from Corner Screen Coordinates

May 2, 2014 - 12:44pm #6

I thought this might be possible if I could edit the camera frame or the feature points before they get consumed by Vuforia, but I believe I read in an earlier post that this is not possible either. 

Vuforia does not expose the feature points, as those are part of the "internal" processing...  technically you could still grab the camera frame and perform some CV processing on such image using some custom library (e.g. FastCV or OpenCV as you say); however this would not belong anymore to the domain of Vuforia per-se.

 

 

Calculate Trackable Pose from Corner Screen Coordinates

May 2, 2014 - 7:20am #5

Thank you for the reply. I have searched, and unfortunately the calculations appear farily non-trivial without importing some sort of external computer vision library (like FastCV or OpenCV) to solve the constraints. This also requires knowledge of the intrinsic parameters of the device camera, which I believe Vuforia already knows internally. It seems like I will be doing a lot of redundant work that the Vuforia engine already does very well. Is there perhaps a way for me to "trick" Vuforia into seeing a trackable between the user selected points? I thought this might be possible if I could edit the camera frame or the feature points before they get consumed by Vuforia, but I believe I read in an earlier post that this is not possible either. 

Calculate Trackable Pose from Corner Screen Coordinates

May 2, 2014 - 6:24am #4

All right, thanks for the explanation.

Vuforia does not expose (via the API) the internal maths to do that calculation (as they are "internal");  have you searched in some 3D maths or Compouter vision forums / websites, I think there are many which explain this kind of homography mathematics. ?

 

Calculate Trackable Pose from Corner Screen Coordinates

May 2, 2014 - 6:16am #3

I want to give our users a fall back mechanism if the trackable cannot be found in the camera frame. This can happen if the user is too far away from the marker or the exposure on the camera blows it out. In these cases I would like to allow the user to manually select the corners of the marker in the frame to calculate the initial pose of the trackable. From there we can continue to augment the experience using another technique like gyro tracking. I know Vuforia already does the homography calculations under the hood, so I would like to avoid re-writing that code seperately for this situation.

Calculate Trackable Pose from Corner Screen Coordinates

May 2, 2014 - 12:18am #2

Vuforia already delivers you the Trackable pose... not sure why you would need to compute it by yourself from the target corners.

 

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