First, we need a function to rotate a point around origin.
When we rotate a point (x,y) around origin by theta degrees, we get the coordinates:
(x*cos(theta)-y*sin(theta), x*sin(theta)+y*cos(theta))
If we want to rotate it around a point other than the origin, we just need to shift it so the center point becomes the origin.
Now, we can write the following function:
from math import sin, cos, radians
def rotate_point(point, angle, center_point=(0, 0)):
"""Rotates a point around center_point(origin by default)
Angle is in degrees.
Rotation is counter-clockwise
"""
angle_rad = radians(angle % 360)
# Shift the point so that center_point becomes the origin
new_point = (point[0] - center_point[0], point[1] - center_point[1])
new_point = (new_point[0] * cos(angle_rad) - new_point[1] * sin(angle_rad),
new_point[0] * sin(angle_rad) + new_point[1] * cos(angle_rad))
# Reverse the shifting we have done
new_point = (new_point[0] + center_point[0], new_point[1] + center_point[1])
return new_point
Some outputs:
print(rotate_point((1, 1), 90, (2, 1)))
# This prints (2.0, 0.0)
print(rotate_point((1, 1), -90, (2, 1)))
# This prints (2.0, 2.0)
print(rotate_point((2, 2), 45, (1, 1)))
# This prints (1.0, 2.4142) which is equal to (1,1+sqrt(2))
Now, we just need to rotate every corner of the polygon using our previous function:
def rotate_polygon(polygon, angle, center_point=(0, 0)):
"""Rotates the given polygon which consists of corners represented as (x,y)
around center_point (origin by default)
Rotation is counter-clockwise
Angle is in degrees
"""
rotated_polygon = []
for corner in polygon:
rotated_corner = rotate_point(corner, angle, center_point)
rotated_polygon.append(rotated_corner)
return rotated_polygon
Example output:
my_polygon = [(0, 0), (1, 0), (0, 1)]
print(rotate_polygon(my_polygon, 90))
# This gives [(0.0, 0.0), (0.0, 1.0), (-1.0, 0.0)]