Array of Dots

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Here's an example grid image from a GoPro camera. This is a fairly old version that is mounted onto foam-core, and it has developed some bubbles in the process, so it isn't what we're really looking for!

Also notice that it does not entirely fill the camera image. The corners of the image are the most informative part of the image, so when there are no dots there, the calibration will necessarily be less accurate or not possible at all.

AGAIN : The array of dots must have a single repeating pattern. If it is irregular or has been glued from multiple pieces, you must use the Line Straightening method above, and create lines manually.

It can be problematic if the dots are larger and you are using a wide fisheye camera: the outer dots can be distorted, resulting in position determination errors. And of course with a wide- angle fisheye (some of which can go past 180 degrees), you have to get the camera closer and closer to the flat surface. So for wide-angle fisheyes, the Random Dots calibration is best .

To process array-of-dots images, begin by clicking Shot/Create Lens Grid Trackers.

Answer No to indicate that you have an array of dots. Delete any spurious trackers, likely using the tracker panel's Delete mode. If there are multiple frames in the calibration sequence that you can use, track forward into them. Data will be pulled from all frames on which the center tracker is valid. Either way, then select all trackers (control-A) and lock them.

NOTE : Be alert for mispositioned dots or lines at the edge of a vignetted image.

You can switch have the camera view display only dots, or turn off the image display, to check the trackers produced.

In earlier SynthEyes camera calibration documentation, we advised that you could film a sequence for calibration, wiggling the camera slightly to increase coverage near the edges of

the image. However, if you do that, you must be sure that the camera rotation is nodal, ie the rotation is about the nodal point of the camera lens.

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