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#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Copyright © Cloud Linux GmbH & Cloud Linux Software, Inc 2010-2019 All Rights Reserved
#
# Licensed under CLOUD LINUX LICENSE AGREEMENT
# http://cloudlinux.com/docs/LICENSE.TXT
# Implementation of Ramer-Douglas-Peucker algorithm
__all__ = ['ramerdouglas']
def ramerdouglas(line, dist):
"""Does Ramer-Douglas-Peucker simplification of a curve with `dist`
threshold.
`line` is a list-of-tuples, where each tuple is a 2D coordinate
Usage is like so:
>>> myline = [(0.0, 0.0), (1.0, 2.0), (2.0, 1.0)]
>>> simplified = ramerdouglas(myline, dist = 1.0)
"""
if len(line) < 3:
return line
(begin, end) = (line[0], line[-1]) if line[0] != line[-1] else (line[0], line[-2])
begin_end_x = end[0] - begin[0]
begin_end_y = end[1] - begin[1]
dist_sq = []
dist_append = dist_sq.append
for curr in line[1:-1]:
begin_curr_x = curr[0] - begin[0]
begin_curr_y = curr[1] - begin[1]
dist_append((begin_curr_y * begin_end_x - begin_curr_x * begin_end_y)**2 /
(begin_end_x**2 + begin_end_y**2))
maxdist = max(dist_sq)
if maxdist < dist ** 2:
return [begin, end]
if len(dist_sq) > 500:
pos = len(dist_sq) // 2
else:
pos = dist_sq.index(maxdist)
return (ramerdouglas(line[:pos + 2], dist) +
ramerdouglas(line[pos + 1:], dist)[1:])