How can I determinethe lineardistance from a point to the edge of a circle ?

Please see the following image (I want the distance of the blue lines)

distanceToCircle.png

I have something that works, but uses an active that is moved every frame to the edge of the circle (fastloop for 180 angles) that opens another fastloop that moves another active pixel by pixel until it reaches the point.

It kind of works, but I know it uses more resources then it should... And there should be a math formula for this.

Here I've found some useful links:

https://stackoverflow.com/questions/...r-from-tangent

http://paulbourke.net/dome/fisheye

Not needed right now, but I would really like to know if Angular fisheye (figures 2 and 3) could be calculated with Fusion events