;finds loop length from radius

function loop_length, x1, x2, y1, y2

;dist = diameter or distance between the center of footpoints
dist = sqrt((x1-x2)^2+(y1-y2)^2)

;changes radius from arcseconds to cm
r = (dist * 72498958.3)/2.

circum = 2. * !pi * r

loop_length = circum / 2.

return, loop_length

end