How to create a line in Shapely using starting point, length, and an angle

Question

I found this code but it requires both first and second point to create a line. How can I change it so it works with only first point, length of the line, and an angle?

from shapely.geometry import LineString
from shapely.geometry import Point

p = Point(5,5)
c = p.buffer(3).boundary
l = LineString([(0,0), (10, 10)])
i = c.intersection(l)

print i.geoms[0].coords[0]
(2.8786796564403576, 2.8786796564403576)

print i.geoms[1].coords[0]
(7.121320343559642, 7.121320343559642)

Answer 1

You have several options:

1. Calculate the coordinates of the second point using basic trigonometry:

   import math
   from shapely.geometry import LineString, Point
   
   start = Point(0, 0)
   length = 1
   angle = math.pi / 3
   
   end = Point(start.x + length * math.cos(angle),
               start.y + length * math.sin(angle))
   line = LineString([start, end])
   print(line)
   # LINESTRING (0 0, 0.5000000000000001 0.8660254037844386)
   

   If your angle is not in radians but in degrees, you should convert it first:

   angle = 60
   angle = math.radians(angle)
   

2. Make a horizontal line with the given start point and length, and then rotate it by given angle around the first point:

   from shapely.affinity import rotate
   from shapely.geometry import LineString, Point
   
   start = Point(0, 0)
   length = 1
   angle = math.pi / 3
   
   end = Point(start.x + length, start.y)
   line = LineString([start, end])
   line = rotate(line, angle, origin=start, use_radians=True)
   print(line)
   # LINESTRING (0 0, 0.5000000000000001 0.8660254037844386)
   

   Note that by default rotate function expects angles in degrees, so if we want to pass an angle in radians to it, we have to use the use_radians=True as shown above.

   Alternatively, we could also use translate function to get the endpoint:

   from shapely.affinity import translate
   end = translate(start, length)