Question

Given a point (pX, pY) and a circle with a known center (cX,cY) and radius (r), what is the shortest amount of code you can come up with to find the point on the circle closest to (pX, pY) ?

I’ve got some code kind of working but it involves converting the circle to an equation of the form (x – cX)^2 + (y – cY)^2 = r^2 (where r is radius) and using the equation of the line from point (pX, pY) to (cX, cY) to create a quadratic equation to be solved.

Once I iron out the bugs it’ll do, but it seems such an inelegant solution.

Answer 1

where P is the point, C is the center, and R is the radius, in a suitable ‘mathy’ language:

V = (P - C); Answer = C + V / |V| * R; 

where |V| is length of V.

OK, OK

double vX = pX - cX; double vY = pY - cY; double magV = sqrt(vX*vX + vY*vY); double aX = cX + vX / magV * R; double aY = cY + vY / magV * R; 

easy to extend to >2 dimensions.