Splitting polygon into two equal parts from specific point to polygon dividing line?

Question

I want to split a polygon into two equal parts but I want from a specific point to the polygon dividing line.

How to do this using ArcGIS Desktop 10?

Answer 1

For that you need to

• find another point on the polygon outline (with reasonable accuracy, that is set to 0.01 m in below script)
• connect 2 points by line
• split polygon using this line

INPUT:

OUTPUT:

To make script below work, you’ll need to put three layers listed from the top down in your mxd table of content:

• empty polygon layer to store splitted parts
• point layer with single point
• source polygon layer

Note: Point has to be snapped to or sit outside of polygon boundary

import arcpy, traceback, os, sys
gr=(math.sqrt(5)-1)/2

try:
    def showPyMessage():
        arcpy.AddMessage(str(time.ctime()) + " - " + message)
    #golden section to find minimum
    def gss(a,b,tol):
        c=b-gr*(b-a)
        d=a+gr*(b-a)
        fc=f(c);fd=f(d)
        while abs(c-d)>tol:
            if fc<fd:
                b,d,fd=d,c,fc
                c=b-gr*(b-a)
                fc=f(c)
            else:
                a,c,fc=c,d,fd
                d=a+gr*(b-a)
                fd=f(d)
        return (b+a)/2
    def f(z):
        global two
        theP=outline.positionAlongLine (z).firstPoint
        splitter=arcpy.Polyline(arcpy.Array([point,theP]),SR)
        two=pgon.cut(splitter)
        intR=abs(two[0].area-two[1].area)/pgon.area*100
        arcpy.AddMessage(intR)
        return intR

    mxd = arcpy.mapping.MapDocument("CURRENT")
    layers = arcpy.mapping.ListLayers(mxd)
    (outputLR,pointLR,pgonLR) =layers[:3]
    g=arcpy.Geometry()
    point=arcpy.CopyFeatures_management(pointLR,g)[0].firstPoint
    SR = arcpy.Describe(pointLR).spatialReference
    pgon=arcpy.CopyFeatures_management(pgonLR,g)[0]
    outline=pgon.boundary();L=outline.length
    chainage=gss(0,L,0.01)
    doit=f(chainage)

    curT = arcpy.da.InsertCursor(outputLR,"Shape@")
    for item in two:
        curT.insertRow((item,))


except:
    message = "\n*** PYTHON ERRORS *** "; showPyMessage()
    message = "Python Traceback Info: " + traceback.format_tb(sys.exc_info()[2])[0]; showPyMessage()
    message = "Python Error Info: " +  str(sys.exc_type)+ ": " + str(sys.exc_value) + "\n"; showPyMessage()