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from shapely.geometry import LineString, Point as ShapelyPoint
import math
def cut(line, distance):
""" Cuts a LineString in two at a distance from its starting point.
This is an example in the Shapely documentation.
"""
if distance <= 0.0 or distance >= line.length:
return [LineString(line), None]
coords = list(line.coords)
for i, p in enumerate(coords):
# TODO: I think this doesn't work if the path doubles back on itself
pd = line.project(ShapelyPoint(p))
if pd == distance:
return [
LineString(coords[:i+1]),
LineString(coords[i:])]
if pd > distance:
cp = line.interpolate(distance)
return [
LineString(coords[:i] + [(cp.x, cp.y)]),
LineString([(cp.x, cp.y)] + coords[i:])]
def cut_path(points, length):
"""Return a subsection of at the start of the path that is length units long.
Given a path denoted by a set of points, walk along it until we've travelled
the specified length and return a new path up to that point.
If the original path isn't that long, just return it as is.
"""
if len(points) < 2:
return points
path = LineString(points)
subpath, rest = cut(path, length)
return [Point(*point) for point in subpath.coords]
class Point:
def __init__(self, x, y):
self.x = x
self.y = y
def __add__(self, other):
return Point(self.x + other.x, self.y + other.y)
def __sub__(self, other):
return Point(self.x - other.x, self.y - other.y)
def mul(self, scalar):
return Point(self.x * scalar, self.y * scalar)
def __mul__(self, other):
if isinstance(other, Point):
# dot product
return self.x * other.x + self.y * other.y
elif isinstance(other, (int, float)):
return Point(self.x * other, self.y * other)
else:
raise ValueError("cannot multiply Point by %s" % type(other))
def __rmul__(self, other):
if isinstance(other, (int, float)):
return self.__mul__(other)
else:
raise ValueError("cannot multiply Point by %s" % type(other))
def __div__(self, other):
if isinstance(other, (int, float)):
return self * (1.0 / other)
else:
raise ValueErorr("cannot divide Point by %s" % type(other))
def __repr__(self):
return "Point(%s,%s)" % (self.x, self.y)
def length(self):
return math.sqrt(math.pow(self.x, 2.0) + math.pow(self.y, 2.0))
def unit(self):
return self.mul(1.0 / self.length())
def rotate_left(self):
return Point(-self.y, self.x)
def rotate(self, angle):
return Point(self.x * math.cos(angle) - self.y * math.sin(angle), self.y * math.cos(angle) + self.x * math.sin(angle))
def as_int(self):
return Point(int(round(self.x)), int(round(self.y)))
def as_tuple(self):
return (self.x, self.y)
def __cmp__(self, other):
return cmp(self.as_tuple(), other.as_tuple())
def __getitem__(self, item):
return self.as_tuple()[item]
def __len__(self):
return 2
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