Is there a simple way / ready-to-go function to calculate the azimuth of 2D-polygons in a GeoPandas DataFrame? My goal is to eventually compute azimuth angles of building footprints.

Most of the functions I have found explicitly calculate the azimuth for a line, which is not what I am looking for. I have been thinking along the following lines to calculate the azimuth of a polygon using its normal vector (2 dimensions). Is my approach going into the right directions? I am a bit unsure how to adjust for the quadrants, also my results seem a bit odd.

azimuth = 90 - math.degrees(math.atan2(normal[1], normal[0]))
if azimuth >= 360.0:
    azimuth -= 360.0
elif azimuth < 0.0:
    azimuth += 360.0
  • How is the normal defined for the polygon? Depending on that algorithm, (first three points?) using the 2 component defining the normal could give you arbitrary azimuths? – Dave X Nov 29 '20 at 14:15
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    You don't provide the inputs or outputs, or what you expected, but bearing calculations don't work on angular units (geographic coordinate system). Instead you need a function which solves the second (aka Inverse, aka Reverse) Problem of Geodesy – Vince Nov 29 '20 at 14:17
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    What have you tried so far using geopandas? Could you add your code attempts? How do you use a footprint in the script? You can calculate four different azimuths for a footprint which has four edges – Kadir Şahbaz Nov 29 '20 at 14:27
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    Can you add a screenshot/drawing of what you want to calculate? – BERA Nov 29 '20 at 15:15

You could try something like this:

import geopandas as gpd
import shapely
import math

df = gpd.read_file('/home/bera/GIS/Data/testdata/ak_riks.shp')

g = df.iloc[2].geometry
a = g.minimum_rotated_rectangle
l = a.boundary
coords = [c for c in l.coords]
segments = [shapely.geometry.LineString([a, b]) for a, b in zip(coords,coords[1:])]
longest_segment = max(segments, key=lambda x: x.length)

p1, p2 = [c for c in longest_segment.coords]
angle = math.degrees(math.atan2(p2[1]-p1[1], p2[0]-p1[0])) #https://stackoverflow.com/questions/42258637/how-to-know-the-angle-between-two-points

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