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I have set of polygons whom I would like to check their compactness.

I'm working in Jupyter Notebook and my geometry is GeoPandas.
I would like to try Polsby-Popper test and Schwartzberg test (and other test that are here: https://fisherzachary.github.io/public/r-output.html ) but I can't find any simple way to do it.

I don't find way to create the necessary circles, e.g "circle whose area is equal to the area of the polygon " or "circle whose circumference is equal to the perimeter of the polygon ".

I have found script to do find smallest enclosing circle but it seems like it works with points and I have polygon in GeoPandas (https://www.nayuki.io/res/smallest-enclosing-circle/smallestenclosingcircle.py).

If anyone knows any library/package/ any idea of how I can create circles from given perimeter or area. It's important to say that I have around 70k polygons to check so I also have the memory issue.

My end goal is to get ideas how can I calculate this in Python in Jupyter Notebook.

Edit: I have found this library but struggling with install it/use it (https://jblindsay.github.io/wbt_book/available_tools/gis_analysis_patch_shape_tools.html) (https://github.com/jblindsay/whitebox-tools/blob/master/src/tools/gis_analysis/related_circumscribing_circle.rs)

Kadir Şahbaz
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ReutKeller
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  • You dont need the circle, at least for PP test https://gis.stackexchange.com/questions/271966/calculating-polsby-popper-score-using-arcgis-pro-field-calculator-gives-error-00 – BERA Sep 17 '20 at 13:20
  • @BERA I'm forbbiden from use arcgis for this task – ReutKeller Sep 17 '20 at 13:22
  • Ofc translate the formula to geopandas. You need geometry area and perimiter length – BERA Sep 17 '20 at 13:22
  • @BERA I need to calculate the circumscribing circle , otherwise is just the compactness ratio and not Polsby-Popper test or Schwartzberg – ReutKeller Sep 17 '20 at 13:35

1 Answers1

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You don't need to create circles. The formula is derived from the ratio you mentioned.

Use the following script. You can apply the other formulas easily.

import geopandas as gpd
from math import pi, sqrt

def pp_compactness(geom): # Polsby-Popper
    p = geom.length
    a = geom.area

    return (4pia)/(p*p)


def s_compactness(geom): # Schwartzberg
    p = geom.length
    a = geom.area

    return 1/(p/(2pisqrt(a/pi)))


gdf = gpd.read_file("file/path")


gdf["Polsby_Popper"] = gdf.geometry.apply(pp_compactness)
gdf["Schwartzberg"] = gdf.geometry.apply(s_compactness)


print(gdf)


geometry            Polsby_Popper   Schwartzberg


0   POLYGON ((552...    0.351956        0.593259


1   POLYGON ((552...    0.550202        0.741756


..               ...         ...             ...


130 POLYGON ((553...    0.434469        0.659142


131 POLYGON ((553...    0.706016        0.840248
Kadir Şahbaz
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  • thank you for your answer, if I understand from you, I missunderstood the calclation and the calculation is the polygon with itself and not with circles? – ReutKeller Sep 17 '20 at 15:03
  • The formula is derived from the ratio you mentioned. Don't worry about the ratio. There is a similar derivation in this post. – Kadir Şahbaz Sep 17 '20 at 15:08