Viewing camera calibrations (.cal file)

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verewhittome
Posts: 2
Joined: Wed Mar 27, 2019 2:40 am

Viewing camera calibrations (.cal file)

Post by verewhittome » Wed Mar 27, 2019 2:47 am

Hi,

Is there any way to convert the calibrations file into a legible format so that I can obtain all the camera calibrations (ideally intrinsic + extrinsic matrices) for a given set of data?

I'm working on a project where I need to be able to compare motion tracking data to synchronized camera data, with known calibrations. It was straightforward to extract the motion capture data along with corresponding video footage on the mocap system. However, the calibrations are exported as a .cal file which I can't find a way to legibly read.

Would be very grateful for any help on this!

steven.andrews
NaturalPoint Employee
NaturalPoint Employee
Posts: 526
Joined: Mon Jan 19, 2015 11:52 am

Re: Viewing camera calibrations (.cal file)

Post by steven.andrews » Wed Mar 27, 2019 11:37 am

Hello verewhittome,

Thank you for reaching out to the community regarding this question. Most camera calibration information is not accessible, and the .cal file is not something that can be converted or read.

Camera position and orientation information is accessible, but only through use of the Motive API. Among the methods available are those for retrieving the camera XYZ positions and an orientation matrix. This is the only calibration information that is shared.

Best,
Steven
--
Steven Andrews
OptiTrack | Senior Customer Support Engineer
help.naturalpoint.com
support@optitrack.com

verewhittome
Posts: 2
Joined: Wed Mar 27, 2019 2:40 am

Re: Viewing camera calibrations (.cal file)

Post by verewhittome » Tue Apr 02, 2019 1:12 am

Hi Steven,

Thanks so much for your reply. Obtaining the camera orientations and positions would be incredibly helpful if I could get them!

So just to confirm - if I did not have access to the Mocap system anymore (I am a student working on a research project and the system is shared across the university), then I would not be able to recover anything from the .cal files? I would need to find a computer with Motive installed, load in the .cal files and then use the API to extract orientations/positions?

Many thanks,
Vere

steven.andrews
NaturalPoint Employee
NaturalPoint Employee
Posts: 526
Joined: Mon Jan 19, 2015 11:52 am

Re: Viewing camera calibrations (.cal file)

Post by steven.andrews » Tue Apr 02, 2019 12:30 pm

My pleasure Vere,

That is mostly correct. You would need access to a Motive license in order to use the API, and the cameras would need to be accessible.

To access the calibration information, you would have to compile and run an application that uses the API, such as the Markers sample that is included with Motive. (C:\Program Files\OptiTrack\Motive\Samples\markers)

In the application, you would make a call to the LoadCalibration operation, providing the path to your calibration file. Once that is done, you can access the cameras, their positions and their orientations.

Cheers,
Steven
--
Steven Andrews
OptiTrack | Senior Customer Support Engineer
help.naturalpoint.com
support@optitrack.com

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