# Select the most distant vertex from polygon's centroid using ArcPy [closed]

I have a polygon and the polygon's centroid. I want to select the most distant vertex from centroid (picture: point A). I used arcpy.FeatureVerticesToPoints_management to create a feature class containing points generated from polygon, but I don't know what to do next.

Could you help me?

Also I want to find intersection point (point B) of the outline of polygon and line created by centroid and the most distant point (line OA).

• As many of the answers have pointed out, you really have two questions here: (1) the most distant vertex, (2) finding intersection point B. I suggest that you break off #2 into a new Question, to give it the focus and attention it deserves (it is a very interesting problem in its own right!) :) Feb 4, 2015 at 22:13

Here's a pared down version of @crmackey's answer. The polygon layer is called 'POLY1', and should be the only thing you need to change to get an output point file of farthest vertices - it creates centroids on-the-fly:

``````>>> points = []
>>> with arcpy.da.SearchCursor("POLY1",['SHAPE@']) as cursor:
...     for row in cursor:
...         centroid = row[0].centroid
...         dist = 0
...         for part in row[0]:
...             for pnt in part:
...                 cent_vert_dist = arcpy.PointGeometry(pnt).distanceTo(centroid)
...                 if cent_vert_dist > dist:
...                     dist = cent_vert_dist
...                     far_point = arcpy.PointGeometry(pnt)
...         points.append(far_point)
...
>>> arcpy.CopyFeatures_management(points,'in_memory\points')
``````

Back-tracking to the intersection point opposite the farthest vertex is possible, but will require some additional trigonometry that I'm not prepared to get into, atm.

This worked for me. The script will create an output point feature class that returns the point that is farthest from the centroid for all polygons:

``````import arcpy
import os
import sys
import traceback
import math
from datetime import datetime as d
arcpy.env.overwriteOutput = True

def Message(msg):
print str(msg)

def findDistance(a,b):
x = abs(a[0] - b[0])
y = abs(a[1] - b[1])
return math.sqrt((x*x) + (y*y))

def iter_geom(g):
for i in xrange(g.partCount):
yield i, g.getPart(i)

def polyPoints(in_polys, out_points):
"""function to find the minimum or maximimum distance between points

Required:
in_polys -- source points for near analysis
out_points -- output nearest or farthest point from centroid
"""

startTime = d.now()
# grab xy coords
point_dict, cent_dict = {}, {}
with arcpy.da.SearchCursor(in_polys, ['OID@','SHAPE@']) as rows:
for row in rows:
points = []
for i, part in iter_geom(row[1]):
for pt in iter(lambda: part.next(), None):
points.append((pt.X, pt.Y))
point_dict[row[0]] = points
cent_dict[row[0]] = (row[1].centroid.X, row[1].centroid.Y)

# grab attributes
desc = arcpy.Describe(in_polys)
fields = [f.name for f in desc.fields if not f.required]
with arcpy.da.SearchCursor(in_polys, ['OID@'] + fields) as rows:
att_dict = {r[0]: r[1:] for r in rows}

# create dictionary to find nearest or farthest vertex from centroid
newpt_dict = {}
for oid, points in point_dict.iteritems():
c = cent_dict[oid]
dist_dict = {coords: findDistance(c,coords) for coords in points}
query_pt = max(dist_dict.values())
for k,v in dist_dict.iteritems():
if v == query_pt:
newpt_dict[oid] = (k, v)

# create output table
path, name = os.path.split(out_points)
if arcpy.Exists(out_points):
arcpy.Delete_management(out_points)
sr = desc.spatialReference
arcpy.CreateFeatureclass_management(path, name, 'POINT', in_polys, 'DISABLED', 'DISABLED', sr)
ifields = ['SHAPE@'] + fields + add_fields
with arcpy.da.InsertCursor(out_points, ifields) as irows:
for oid, pt_dist in newpt_dict.iteritems():
all_atts = (pt_dist[0],) + att_dict[oid] + (oid, pt_dist[1])
irows.insertRow(all_atts)
Message('Created: %s' %os.path.basename(out_points))
Message('(Elapsed time: %s)' %(str(d.now() - startTime)[:-3]))
return out_points

if __name__ == '__main__':

##    # stand alone
polys = r'C:\TEMP\Utility\Utilities.gdb\Parcels_small'
out = polys + '_farPoints'
polyPoints(polys, out)
``````