topic Re: geopy.distance vincenty - pairs of coordinates in Python Snippets Questions

geopy.distance vincenty - pairs of coordinates

Nicole_Ueberschär — Thu, 02 Nov 2017 12:07:28 GMT

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...

Re: geopy.distance vincenty - pairs of coordinates

DanPatterson_Retired — Thu, 02 Nov 2017 12:43:06 GMT

Use this Vincenty then.... for comparison

Re: geopy.distance vincenty - pairs of coordinates

XanderBakker — Thu, 02 Nov 2017 12:53:13 GMT

The X property of a point always corresponds to Longitude and the Y always to Latitude. As far as I can see geopy 1.11.0 : Python Package Index seems to use a tuple of coordinates where the first element is the Latitude and the second is Longitude). So the answer would be yes...

Re: geopy.distance vincenty - pairs of coordinates

DanPatterson_Retired — Thu, 02 Nov 2017 17:50:36 GMT

of course, you can edit their code and swap the coordinates yourself

coords = [45, -75]

coords[::-1]
Out[5]: [-75, 45]

Re: geopy.distance vincenty - pairs of coordinates

Nicole_Ueberschär — Sun, 26 Nov 2017 08:47:21 GMT

Hi Dan, the python file is empty 😞

Re: geopy.distance vincenty - pairs of coordinates

DanPatterson_Retired — Sun, 26 Nov 2017 09:18:10 GMT

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

Re: geopy.distance vincenty - pairs of coordinates

Nicole_Ueberschär — Sun, 26 Nov 2017 09:30:34 GMT

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

Re: geopy.distance vincenty - pairs of coordinates

DanPatterson_Retired — Sun, 26 Nov 2017 09:51:02 GMT

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

Re: geopy.distance vincenty - pairs of coordinates

Nicole_Ueberschär — Sun, 26 Nov 2017 20:29:27 GMT

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...

Re: geopy.distance vincenty - pairs of coordinates

DanPatterson_Retired — Wed, 06 Dec 2017 10:45:56 GMT

closed?

Re: geopy.distance vincenty - pairs of coordinates

XanderBakker — Sun, 12 Dec 2021 08:58:11 GMT

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?

Re: geopy.distance vincenty - pairs of coordinates

XanderBakker — Sun, 12 Dec 2021 08:58:13 GMT

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.

Re: geopy.distance vincenty - pairs of coordinates

DanPatterson_Retired — Wed, 06 Dec 2017 14:11:04 GMT

longitude first then latitude... that is the problem with geowhater that I noted before and proposed a simple solution if anyone wanted to edit their code

coords = [45, -75]
coords[::-1]
Out[5]: [-75, 45]

Re: geopy.distance vincenty - pairs of coordinates

XanderBakker — Wed, 06 Dec 2017 14:20:14 GMT

You are (as always) completely right. I assumed that the code would use the coordinates in lat, lon order (as the OP mentioned), but it uses them the "right way" as X , Y and I provided Y, X. Switching the order did the trick and returns the expected values.

:--------------------------------------------------------:
:Vincenty inverse...
:Longitude, Latitude
:From: (-75.60019300, 6.23927000)
:To: (-74.07436300, 4.72356700)
:Distance: 238078.892 m
:Bearings...
: Initial 134.67 deg
: Final 134.82 deg
: Iterations taken.... 4
:--------------------------------------------------------:

Re: geopy.distance vincenty - pairs of coordinates

DanPatterson_Retired — Wed, 06 Dec 2017 14:25:43 GMT

You had already mentioned this in one of you previous comments as well...

The X property of a point always corresponds to Longitude and the Y always to Latitude

I belong to the Long/Lat... aka... X/Y, column/row... school

Re: geopy.distance vincenty - pairs of coordinates

XanderBakker — Wed, 06 Dec 2017 14:43:14 GMT

Don't get met wrong, I really feel weird if I have o specify something like Y, X, but I was focused on the way vincenty and geopy works with lat, long and therefore specified it incorrectly in your code, not noticing the correct example you provided that was not including point in the South Pole.. Anyway thanks for pointing out my mistake!