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from numpy import sqrt, dot, sin, dot, array, pi
from math import atan2
def two_point_arc_to_kiva_arc(p1, p2, theta):
"""
Converts an arc in two point and subtended angle format (startpoint,
endpoint, theta (positive for ccw, negative for cw)) into kiva format
(x, y, radius, start_angle, end_angle, cw)
"""
chord = p2-p1
chordlen = sqrt(dot(chord, chord))
radius = abs(chordlen/(2*sin(theta/2)))
altitude = sqrt(pow(radius, 2)-pow(chordlen/2, 2))
if theta>pi or theta<0:
altitude = -altitude
chordmidpoint = (p1+p2)/2
rotate90 = array(((0.0,-1.0),
(1.0, 0.0)))
centerpoint = dot(rotate90, (chord/chordlen))*altitude + chordmidpoint
start_angle = atan2(*(p1-centerpoint)[::-1])
end_angle = start_angle+theta
if theta<0:
start_angle, end_angle, = end_angle, start_angle
cw = False
radius = abs(radius)
return (centerpoint[0], centerpoint[1], radius, start_angle, end_angle, cw)
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