geopy.distance vincenty - pairs of coordinates

[Nicole_Ueberschär]

Hi folks, 

I managed to calculate the distance between two points (from two different feature classes) using the vincenty module from geopy.distance. 

For quite some time I struggled to find out why I got wrong distances. (even to realize it took me some time)

In the end I figured that the vincenty module requires the coordinates in Latitude/Longitude while the coordinates as they are stored in the feature class shape@xy are stored as Longitude/Langitude. 

Can someone confirm this? It doesn't make any sense to me why the vincenty module should require the coordinates the "wrong way" but I only get correct measures when using the coordinates switched to Latitude/Longitude...

[DanPatterson_Retired]

Use this Vincenty then.... for comparison

[Nicole_Ueberschär]

Hi Dan, the python file is empty 😞

[DanPatterson_Retired]

strange, it used to be there because people have used it.. I uploaded again, let me know

[Nicole_Ueberschär]

Thanks Dan! Unfortunately now it says it can't import the textwrapper functions. Will have to look at it at a later stage again.

I 

[DanPatterson_Retired · Accepted solution]

I use python 3... I forget some are still on legacy python

comment out line 50 and remove the word 'dedent' in line 163

And besides... you just don't 'run' it unless you want the demo to run.  the def is the main part, but don't forget the imports

[Nicole_Ueberschär]

Thank you! I will give it another try. 

Of course you are right, that I don't run the script by itself, I imported it to my script and run it from there...

[DanPatterson_Retired]

closed?

[XanderBakker]

Hi Dan Patterson ,

I just did a small test with your script and obtained this result:

:--------------------------------------------------------:
:Vincenty inverse...
:Longitude, Latitude
:From: (  6.23927000, -75.60019300)
:To:   (  4.72356700, -74.07436300)
:Distance: 175953.991 m
:Bearings...
:  Initial   344.70 deg
:  Final     346.16 deg
:  Iterations taken.... 2
:--------------------------------------------------------:‍‍‍‍‍‍‍‍‍‍‍

When I run this script using the distance and angle to in arcpy:

def main():
    import arcpy
    coords = [[6.239270, -75.600193], [4.723567, -74.074363]]
    sr = arcpy.SpatialReference(4326)

    pntg1 = arcpy.PointGeometry(arcpy.Point(*coords[0][::-1]), sr)
    pntg2 = arcpy.PointGeometry(arcpy.Point(*coords[1][::-1]), sr)

    methods = ['PLANAR', 'GEODESIC', 'GREAT_ELLIPTIC',
               'LOXODROME', 'PLANAR', 'PRESERVE_SHAPE']

    for method in methods:
        print "{0}\t{1}\t{2}".format('%14s' % method,
                                     *pntg1.angleAndDistanceTo(pntg2, method))

if __name__ == '__main__':
    main()
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

... it gives me this:

        PLANAR     134.674409847     238078.891905
      GEODESIC     134.674454363     238078.891905
GREAT_ELLIPTIC     134.674961722     238078.891908
     LOXODROME     134.750719983     238078.956191
        PLANAR     134.674409847     238078.891905
PRESERVE_SHAPE     134.674454363     238078.891905‍‍‍‍‍‍‍‍‍‍‍‍

Any idea why the distance is so different?

[XanderBakker]

And when using geopy:

def main():
    from geopy.distance import vincenty, great_circle
    medellin = (6.239270, -75.600193)
    bogota = (4.723567, -74.074363)
    print(vincenty(medellin, bogota).meters)
    print(great_circle(medellin, bogota).meters)

if __name__ == '__main__':
    main()‍‍‍‍‍‍‍‍‍

... I get this result:

238078.891889
238660.799202‍‍

Showing that vincenty is very close to what arcpy calculated.