# Looking for a pythonic way to calculate the length of a WKT linestring

I was quite unsatisfied with Calculating Length of Linestrings in WGS84 in Miles. It kept me wondering if there is a more convenient, Pythonic way to calculate the length of a WKT linestring according to a given SRID.

I have in mind something like:

srid="WGS84"
line="LINESTRING(3.0 4.0, 3.1 4.1)"
print length(line, srid)


I'm looking for an accurate answer, not sin\cos approximations.

Any ideas?

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tomkralidis, this is a GIS website. your answer ignores that the this is a distance between geospatial coordinates (look up SRID). shapely in of itself cannot compute geospatial distances as it has no knowledge of map projection. –  Bill Gale Oct 18 at 1:32

The geopy module provides the Vincenty formula, which provides accurate ellipsoid distances. Couple this with the wkt loading in Shapely, and you have reasonably simple code:

from geopy import distance

line_wkt="LINESTRING(3.0 4.0, 3.1 4.1)"

# a number of other elipsoids are supported
distance.VincentyDistance.ELLIPSOID = 'WGS-84'
d = distance.distance

# convert the coordinates to xy array elements, compute the distance
dist = d(line.xy[0], line.xy[1])

print dist.meters

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+1, would have +10 if I could. Saved my team hours of programming. –  Adam Matan Dec 1 '10 at 22:03

You could also use Shapely's length property, i.e.:

from shapely.wkt import loads

print l.length

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I'd use ogr2ogr (http://www.gdal.org/ogr/index.html) to do it directly but if you really must use python then there are python bindings (http://pypi.python.org/pypi/GDAL/) to let you do it.

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