用于在多个多边形之间构建成本最低的路径的 Python 脚本 : How to speed up it?

Question

我创建了一个 python 程序，该程序使用 ArcGIS 的“CostPath”函数在 shapefile“selected_pa​​tches.shp”中包含的几个多边形之间自动构建最低成本路径 (LCP)。我的 python 程序似乎可以工作，但它太慢了。我必须构建 275493 个 LCP。不幸的是，我不知道如何加速我的程序(我是 Python 编程语言和 ArcGIS 的初学者)。或者是否有另一种解决方案可以使用 ArcGIS(我使用 ArcGIS 10.1)快速计算多个多边形之间的最低成本路径？这是我的代码:

# Import system modules
 import arcpy
 from arcpy import env
 from arcpy.sa import *

arcpy.CheckOutExtension("Spatial")

 # Overwrite outputs
 arcpy.env.overwriteOutput = True

 # Set the workspace
 arcpy.env.workspace = "C:\Users\LCP"

 # Set the extent environment
 arcpy.env.extent = "costs.tif"


rowsInPatches_start = arcpy.SearchCursor("selected_patches.shp") 

for rowStart in rowsInPatches_start:        

ID_patch_start = rowStart.getValue("GRIDCODE") 

expressionForSelectInPatches_start = "GRIDCODE=%s" % (ID_patch_start) ## Define SQL expression for the fonction Select Layer By Attribute

# Process: Select Layer By Attribute in Patches_start
arcpy.MakeFeatureLayer_management("selected_patches.shp", "Selected_patch_start", expressionForSelectInPatches_start)

 # Process: Cost Distance
outCostDist=CostDistance("Selected_patch_start", "costs.tif", "", "outCostLink.tif")

# Save the output 
outCostDist.save("outCostDist.tif")

rowsInSelectedPatches_end = arcpy.SearchCursor("selected_patches.shp") 

for rowEnd in rowsInSelectedPatches_end:

    ID_patch_end = rowEnd.getValue("GRIDCODE") 

    expressionForSelectInPatches_end = "GRIDCODE=%s" % (ID_patch_end) ## Define SQL expression for the fonction Select Layer By Attribute

    # Process: Select Layer By Attribute in Patches_end
    arcpy.MakeFeatureLayer_management("selected_patches.shp", "Selected_patch_end", expressionForSelectInPatches_end)

    # Process: Cost Path
    outCostPath = CostPath("Selected_patch_end", "outCostDist.tif", "outCostLink.tif", "EACH_ZONE","FID")

    # Save the output
    outCostPath.save('P_' +  str(int(ID_patch_start)) + '_' + str(int(ID_patch_end)) + ".tif")

    # Writing in file .txt
    outfile=open('P_' +  str(int(ID_patch_start)) + '_' + str(int(ID_patch_end)) + ".txt", "w")
    rowsTxt = arcpy.SearchCursor('P_' +  str(int(ID_patch_start)) + '_' + str(int(ID_patch_end)) + ".tif")
    for rowTxt in rowsTxt:
        value = rowTxt.getValue("Value")
        count = rowTxt.getValue("Count")
        pathcost = rowTxt.getValue("PATHCOST")
        startrow = rowTxt.getValue("STARTROW")
        startcol = rowTxt.getValue("STARTCOL")
        print value, count, pathcost, startrow, startcol
        outfile.write(str(value) + " " + str(count) + " " + str(pathcost) + " " + str(startrow) + " " + str(startcol) + "\n")
    outfile.close()

非常感谢您的帮助。

Answer 1

写入光盘所需的速度与计算成本可能是一个瓶颈，请考虑添加一个线程来处理所有写入。

这个:

for rowTxt in rowsTxt:
        value = rowTxt.getValue("Value")
        count = rowTxt.getValue("Count")
        pathcost = rowTxt.getValue("PATHCOST")
        startrow = rowTxt.getValue("STARTROW")
        startcol = rowTxt.getValue("STARTCOL")
        print value, count, pathcost, startrow, startcol
        outfile.write(str(value) + " " + str(count) + " " + str(pathcost) + " " + str(startrow) + " " + str(startcol) + "\n")

可以通过将 rowsTxt 设为全局变量并将线程从 rowsTxt 写入磁盘来转换为线程函数。完成所有处理后，您可以有一个额外的全局 bool 值，以便您的线程函数可以在您完成所有编写后结束，您可以关闭线程。

我目前使用的示例线程函数:

import threading
class ThreadExample:
   def __init__(self):
      self.receiveThread = None

   def startRXThread(self):
      self.receiveThread = threading.Thread(target = self.receive)
      self.receiveThread.start()

   def stopRXThread(self):
      if self.receiveThread is not None:
         self.receiveThread.__Thread__stop()
         self.receiveThread.join()
         self.receiveThread = None

   def receive(self):
       while true:
          #do stuff for the life of the thread
          #in my case, I listen on a socket for data
          #and write it out

因此对于您的情况，您可以向线程类添加一个类变量

self.rowsTxt

然后更新您的接收以检查 self.rowsTxt，如果它不为空，则按照您在上面从您那里获取的代码片段中所做的那样处理它。处理完后，将 self.rowsTxt 设置回 None。您可以在获取 rowsTxt 时使用主函数更新您的线程 self.rowsTxt。考虑为 self.rowsTxt 使用像列表这样的缓冲区，这样你就不会错过写任何东西。