arc_center_from_rad_value.py

import math
from FreeCAD import Vector
import Part

def calcRadCenter(v1,radius,v2,cw):
    '''
    calculates centerpoint for arc move that uses only radius value
    and is missing I,J,K coords.v1 = start pt of arc,v2 =end pt of arc
    '''
    chord = v2.sub(v1)
    l = Part.makeLine((v1.x,v1.y,v1.z),(v2.x,v2.y,v2.z))
    sagitta = radius-math.sqrt(math.pow(radius,2)- math.pow(l.Length/2.0,2))
    if cw:
        perp = chord.cross(Vector(0,0,1))
    else:
        perp = chord.cross(Vector(0,0,-1))
    startpoint = v1.add(chord.multiply(0.5))
    perp.normalize()
    centerpt = startpoint.add(perp.multiply(radius-sagitta))
    return centerpt

def calcIJK(v1,centerpt):
    '''
    return relative IJK values from a previous point (vector) to the center of an arc
    (also a vector)
    '''
    return centerpt.sub(v1)