topic Re: how to make clusters from small polygons with constraint of boundary touching? in Developers Questions

how to make clusters from small polygons with constraint of boundary touching?

waqarahmad — Wed, 11 Mar 2015 19:06:11 GMT

I want to make some clusters from a bunch of small polygons with the constraint that each basic unit (polygon) in the resultant cluster must share a portion of its boundary with at least one other basic unit (polygon) in the same cluster. This is becuase of the reason that i want the resultant clusters contagious.

Re: how to make clusters from small polygons with constraint of boundary touching?

DarrenWiens2 — Wed, 11 Mar 2015 20:23:04 GMT

How do you want to deal with overlapping polygons (e.g. area of smaller polygon may fully overlap, but boundary may be far inside the larger polygon)?

Re: how to make clusters from small polygons with constraint of boundary touching?

DarrenWiens2 — Fri, 10 Dec 2021 20:08:33 GMT

You can pull out polygons intersecting at least one other polygon using the following script:

>>> polys = []
... outPolys = []
... with arcpy.da.SearchCursor("YOUR_POLYGON_LAYER_HERE","SHAPE@") as cursor:
...    for row in cursor:
...        polys.append(row[0])
... for i in range(len(polys)):
...    overlap = 0
...    for j in range(len(polys)):
...        if polys.distanceTo(polys) == 0:
...            overlap = overlap + 1
...    if overlap > 1:
...        outPolys.append(polys)       
... arcpy.CopyFeatures_management(outPolys,'in_memory\polys')

Re: how to make clusters from small polygons with constraint of boundary touching?

yosukekimura — Thu, 12 Mar 2015 00:41:19 GMT

I haven't tested, but

p.disjoint(q)

intead of

p.distanceTo(q)==0

may runs faster particularly when there are a bunch of polygon.

your method is O(n^2) so may have trouble with large number of polygons...

Re: how to make clusters from small polygons with constraint of boundary touching?

yosukekimura — Fri, 10 Dec 2021 20:08:35 GMT

Darren's method should work, and this is an alternative.

# make table of pair of zero distance
arcpy.GenerateNearTable_analysis(fcOrig, fcOrig, tblNear, "0", 
    "NO_LOCATION", "NO_ANGLE", "CLOSEST", "0")

if int(arcpy.GetCount_management(tblNear).getOutput(0)) > 0:
  # grab ids that showed up in the table 
  ids = set([ _[0] for _ in  arcpy.da.SearchCursor(tblNear,('IN_FID'))])

  # grab shape 
  oid = arcpy.Describe(fcOrig).OIDFieldName
  outpoly = [_[0] for _ in arcpy.da.SearchCursor(fcOrig, [ 'SHAPE@, oid]) 
      if _[1] in ids ]

  # save
  arcpy.CopyFeatures_management(outpoly, fcTouching)

Re: how to make clusters from small polygons with constraint of boundary touching?

waqarahmad — Thu, 12 Mar 2015 21:24:52 GMT

i have only polygons which touching EACH OTHER'S boundry