Calculating angles between line segments (Python) with math.atan2
The easiest way to get at this problem is using the dot-product.
Try this code (I've commented practically everything):
import math
def dot(vA, vB):
return vA[0]*vB[0]+vA[1]*vB[1]
def ang(lineA, lineB):
# Get nicer vector form
vA = [(lineA[0][0]-lineA[1][0]), (lineA[0][1]-lineA[1][1])]
vB = [(lineB[0][0]-lineB[1][0]), (lineB[0][1]-lineB[1][1])]
# Get dot prod
dot_prod = dot(vA, vB)
# Get magnitudes
magA = dot(vA, vA)**0.5
magB = dot(vB, vB)**0.5
# Get cosine value
cos_ = dot_prod/magA/magB
# Get angle in radians and then convert to degrees
angle = math.acos(dot_prod/magB/magA)
# Basically doing angle <- angle mod 360
ang_deg = math.degrees(angle)%360
if ang_deg-180>=0:
# As in if statement
return 360 - ang_deg
else:
return ang_deg
Now try your variations of lineA and lineB and all should give the same answer.
An alternative solution using the formula:
where 'm1' is the slope of line 1 and 'm2' the slope of line 2. If line 1 is defined by the points P1 = [x1, y1] and P2 = [x2, y2], then slope 'm' is:
By using the formulas above you can find the angle in degrees between two lines as follows:
def slope(x1, y1, x2, y2): # Line slope given two points:
return (y2-y1)/(x2-x1)
def angle(s1, s2):
return math.degrees(math.atan((s2-s1)/(1+(s2*s1))))
lineA = ((0.6, 3.6), (1.6, 3))
lineB = ((1.6, 3), (2, 3.6))
slope1 = slope(lineA[0][0], lineA[0][1], lineA[1][0], lineA[1][1])
slope2 = slope(lineB[0][0], lineB[0][1], lineB[1][0], lineB[1][1])
ang = angle(slope1, slope2)
print('Angle in degrees = ', ang)
Too much work. Take the absolute value of the arccosine of the dot product of the two vectors divided by each of the lengths of the lines.