I am working with the polyline of google, I would like to give a set of coordinates and generate the correct polyline and viceversa. In particular in the end i would like to url encode the result (the polyline). When I insert a polyline like:

code = '((akntGkozv@kcCka@us@y{DfvAm{BnuCj_Aus@fzG))'

I use the polyline package: https://pypi.org/project/polyline/, and first I decode the polyline in order to see the coordinates:

coordinates = polyline.decode(code)
print(coordinates)
>> [(3e-05, -0.0001), (-0.0001, -7e-05), (-0.0002, -0.0002), (45.46221, 35.36626), (45.4621, 35.36617), (45.48328, 35.39727), (45.48317, 35.39718), (45.5172, 35.39707), (45.51711, 35.39816), (45.51723, 35.39814), (45.5172, 35.38418), (45.51823, 35.3843), (45.51821, 35.38428), (45.49413, 35.37398), (45.52816, 35.37387), (45.52807, 35.32855), (45.5281, 35.32845), (45.52823, 35.32848), (45.52813, 35.32861)]

and everything here is fine, the problems comes when I try to encode the coordinates back to the polyline (which is my ultimate goal since in the end i would like to give some coordinates and obtain the corresponding polyline)

new_code = polyline.encode(coordinates)
print(new_code)
>> ERXERXakntGkozvETPkcCkaETPusETPyEWBDfvAmEWBBnuCj_AusETPfzGERYERY

Which is slightly different from the original and if put back in the url it doesnt work!

So my question here are:

1. what kind of encoding is new_code? I have tried to encode it in percentage url using urllib.parse.quote(new_code) but the result is exactly the same, maybe I neeed to specify some particular encoding style but i didnt found anything.

2. The polyline that I used is a square inside the city of Milan (so only 4 points, maximum 5, are required to identify this area), but the coordinates results from the polyline.decode gives me back a list with 19 points with coordinates that are not even close to the city of Milan. Why?

CodePudding user response：

Ok so basically all of my problems came from the fact that the string i was considering: ((akntGkozv@kcCka@us@y{DfvAm{BnuCj_Aus@fzG)) contains (( and )) which are not part of the polyline but are simply two (( and )) inserted by the particular url of the site I was using. A simple replace and an encode return the correct polyline:

code = '((akntGkozv@kcCka@us@y{DfvAm{BnuCj_Aus@fzG))'
code = code.replace('(', '').replace(')', '')
code = urllib.parse.unquote(code)
print(code)
>> irotG_hzv@woBmE}i@yjE`oBwkDf|ChRhMzeG}~BxcB

Which infact, if put inside the polyline.decode returns exactly the coordinates that I have used:

coordinates = polyline.decode(code)
print(coordinates)
>> [(45.46869, 9.15088), (45.48673, 9.15191), (45.4936, 9.18452), (45.47567, 9.21216), (45.45051, 9.20907), (45.44822, 9.16701), (45.46869, 9.15088)]

Which are exactly 7 (now i have changed the shape so a sixtagon instead of a square) and points exactly in the city of Milan