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Far-ish Trackers
The tracker clean-up dialog detects trackers with too little parallax for an adequate distance measurement. Consider a tracker 1 meter from the camera, and the camera moving 10 cm to its right. The position of the tracker in the two images from the camera will be different, tens or hundreds of pixels apart. What if the tracker is 1 kilometer from the camera, and the camera moved the same 10 cm? The tracker may be located in exactly the same pixel in both images, and no distance can be determined to the tracker 1 km away.
Accordingly, far-ish-ness (you will not find this in the dictionary) can be measured in terms of the numbers of pixels of perspective, and the threshold is the number of pixels of perspective change produced by the camera motion over the lifespan of the tracker.
As you slowly increase the far-ish-ness threshold, you’ll see trackers further and further from the camera become labeled as far.
But, you may also find a few trackers close to the camera that are also labeled Far-ish, even at a low threshold. What has happened, that these nearby trackers are far-ish? Simple: either they are short–lived, or the camera was not translating much during their lifetime. For example, there may be many far-ish trackers there is a tripod- type “hold” region during a shot.
Far-ish trackers can not really be fixed. If the same feature is tracked earlier or later in the shot, a short-lived tracker might be combined with its longer-lived siblings. But otherwise, they may only be made Far (in which case their solve will only produce a direction), or they may be deleted.
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