How to find the starting point in Starshot module?

When i read the Starshot module documentation, I don’t understand this sentence very well.
“ it is automatically found by summing the image along each axis and finding the center of the full-width, 80%-max of each sum ”

Can anyone help me explain this sentence?thanks

This has to do with the automatic center approximation. Pylinac needs a good guess of the starshot center (although not exact). From there, it creates the ring-shaped profile, which in turn detects the star lines. The star lines are reconstructed and then the true center is found from the line intersections.

The summing of each image axis is a very quick and convenient way to get that good guess. An image is worth a thousand words, so I’m attaching a summed image axis. You can tell that finding the FW80M is relatively easy and gives a pretty good guess. This is because all the star lines intersect at iso and thus the peak is very pronounced. Do this for both x and y and you have your position.

starshot axis sum.png