道格拉斯-普克 Douglas-Peuker(DP算法)-python实现

#-*- coding:utf-8 -*-
"""
道格拉斯算法的实现
程序需要安装shapely模块
"""
import math
from shapely import wkt,geometry

class Point:
	"""点类"""
	x=0.0
	y=0.0
	index=0 #点在线上的索引

	def __init__(self,x,y,index):
		self.x=x
		self.y=y
		self.index=index

class Douglas:
	"""道格拉斯算法类"""
	points=[]
	D=1 #容差

	def readPoint(self):
		"""生成点要素"""
		g=wkt.loads("LINESTRING(1 4,2 3,4 2,6 6,7 7,8 6,9 5,10 10)")
		coords=g.coords
		for i in range(len(coords)):
			self.points.append(Point(coords[i][0],coords[i][1],i))

	def compress(self,p1,p2):
		"""具体的抽稀算法"""
		swichvalue=False
		#一般式直线方程系数 A*x+B*y+C=0
		A=(p1.y-p2.y)/math.sqrt(math.pow(p1.y-p2.y,2)+math.pow(p1.x-p2.x,2))
		B=(p2.x-p1.x)/math.sqrt(math.pow(p1.y-p2.y,2)+math.pow(p1.x-p2.x,2))
		C=(p1.x*p2.y-p2.x*p1.y)/math.sqrt(math.pow(p1.y-p2.y,2)+math.pow(p1.x-p2.x,2))

		m=self.points.index(p1)
		n=self.points.index(p2)
		distance=[]
		middle=None

		if(n==m+1):
			return
		#计算中间点到直线的距离
		for i in range(m+1,n):
			d=abs(A*self.points[i].x+B*self.points[i].y+C)/math.sqrt(math.pow(A,2)+math.pow(B,2))
			distance.append(d)

		dmax=max(distance)

		if dmax>self.D:
			swichvalue=True
		else:
			swichvalue=False

		if(not swichvalue):
			for i in range(m+1,n):
				del self.points[i]
		else:
			for i in range(m+1,n):
				if(abs(A*self.points[i].x+B*self.points[i].y+C)/math.sqrt(math.pow(A,2)+math.pow(B,2))==dmax):
					middle=self.points[i]
			self.compress(p1,middle)
			self.compress(middle,p2)

	def printPoint(self):
		"""打印数据点"""
		for p in self.points:
			print "%d,%f,%f"%(p.index,p.x,p.y)

def main():
	"""测试"""
	#p=Point(20,20,1)
	#print '%d,%d,%d'%(p.x,p.x,p.index)
	d=Douglas()
	d.readPoint()
	d.printPoint()
	d.compress(d.points[0],d.points[len(d.points)-1])
	print "========================\n"
	d.printPoint()
if __name__=='__main__':
	main()

参考博客

部分修改后：

#-*- coding:utf-8 -*-
"""
道格拉斯算法的实现
程序需要安装shapely模块
"""
import math
from shapely import wkt,geometry
import matplotlib.pyplot as plt

class Point:
	"""点类"""
	x=0.0
	y=0.0
	index=0 #点在线上的索引

	def __init__(self,x,y,index):
		self.x=x
		self.y=y
		self.index=index

class Douglas:
	"""道格拉斯算法类"""
	points=[]
	D=1 #容差

	def readPoint(self):
		"""生成点要素"""
		g=wkt.loads("LINESTRING(1 4,2 3,4 2,6 6,7 7,8 6,9 5,10 10)")
		coords=g.coords
		for i in range(len(coords)):
			self.points.append(Point(coords[i][0],coords[i][1],i))

	def compress(self,p1,p2):
		"""具体的抽稀算法"""
		swichvalue=False
		#一般式直线方程系数 A*x+B*y+C=0,利用点斜式,分母可以省略约区
		#A=(p1.y-p2.y)/math.sqrt(math.pow(p1.y-p2.y,2)+math.pow(p1.x-p2.x,2))
		A=(p1.y-p2.y)
		#B=(p2.x-p1.x)/math.sqrt(math.pow(p1.y-p2.y,2)+math.pow(p1.x-p2.x,2))
		B=(p2.x-p1.x)
		#C=(p1.x*p2.y-p2.x*p1.y)/math.sqrt(math.pow(p1.y-p2.y,2)+math.pow(p1.x-p2.x,2))
		C=(p1.x*p2.y-p2.x*p1.y)
		
		m=self.points.index(p1)
		n=self.points.index(p2)
		distance=[]
		middle=None

		if(n==m+1):
			return
		#计算中间点到直线的距离
		for i in range(m+1,n):
			d=abs(A*self.points[i].x+B*self.points[i].y+C)/math.sqrt(math.pow(A,2)+math.pow(B,2))
			distance.append(d)

		dmax=max(distance)

		if dmax>self.D:
			swichvalue=True
		else:
			swichvalue=False

		if(not swichvalue):
			for i in range(m+1,n):
				del self.points[i]
		else:
			for i in range(m+1,n):
				if(abs(A*self.points[i].x+B*self.points[i].y+C)/math.sqrt(math.pow(A,2)+math.pow(B,2))==dmax):
					middle=self.points[i]
			self.compress(p1,middle)
			self.compress(middle,p2)

	def printPoint(self):
		"""打印数据点"""
		for p in self.points:
			print "%d,%f,%f"%(p.index,p.x,p.y)

def main():
	"""测试"""
	#p=Point(20,20,1)
	#print '%d,%d,%d'%(p.x,p.x,p.index)
	
	d=Douglas()
	d.readPoint()
	#d.printPoint()
	#结果图形的绘制，抽稀之前绘制
	fig=plt.figure()
	a1=fig.add_subplot(121)
	dx=[]
	dy=[]
	for i in range(len(d.points)):
		dx.append(d.points[i].x)
		dy.append(d.points[i].y)
	a1.plot(dx,dy,color='g',linestyle='-',marker='+')

	
	d.compress(d.points[0],d.points[len(d.points)-1])

	#抽稀之后绘制
	dx1=[]
	dy1=[]
	a2=fig.add_subplot(122)
	for p in d.points:
		dx1.append(p.x)
		dy1.append(p.y)
	a2.plot(dx1,dy1,color='r',linestyle='-',marker='+')

	#print "========================\n"
	#d.printPoint()

	plt.show()

if __name__=='__main__':

	main()

结果：