Pixels for Apriltag Detection?

I’m interested in trying to engineer the selection of lens for our navigation cameras, rather than trial-and-error. Given a focal length, I can compute the image size of an Apriltag at a given distance. Does anyone have any good estimate for how large an Apriltag image needs to be, in pixels, before it’s “reliably detectable”?

We were able to detect the tags at 4 pixels per square or 32 pixels across white border to white border for the full 8 inches.
Detection became unreliable after that.

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Props to the folks who developed the Apriltag algorithm; good quad detection over that few pixels is pretty impressive.

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I threw together an Apriltag “eye chart” that I use for tuning camera settings. These aren’t standard size, but give you an idea of how small a tag your setup can detect. Each successive group of tags is 1/2, 1/3, and 1/4 the size of the ID:0 tag.

AprilTags_16h5_eyechart.pdf (139.5 KB)

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