How to read Coordinates of a polygon from a text file which are encoded as [[x,y], [x1,y1], ....[xn,-CodePudding

I have text file coordinates.txt, which has data in the below format. I want to read coordinates in each line into python object list of list of float. Each of the bounds will have only 5 lat,long pairs.

{"id": "1b2e1366-9ac7-4220-8dc2-c333d3da6e42", "bounds": "[[-121.02662668533802, 38.39556098724271], [-121.01552400710878, 38.39556098724271], [-121.01552400710878, 38.38638931377034], [-121.02662668533802, 38.38638931377034], [-121.02662668533802, 38.39556098724271]]"}
{"id": "e2c02621-6685-435c-b1f0-07e0bca49870", "bounds": "[[-121.71606277115228, 38.424526411333495], [-121.70496009292305, 38.424526411333495], [-121.70496009292305, 38.41535473786112], [-121.71606277115228, 38.41535473786112], [-121.71606277115228, 38.424526411333495]]"}
{"id": "14d29a1f-e014-43fc-bfcf-b380126e8270", "bounds": "[[-120.64683157721372, 38.77860318996463], [-120.63572889898448, 38.77860318996463], [-120.63572889898448, 38.769431516492254], [-120.64683157721372, 38.769431516492254], [-120.64683157721372, 38.77860318996463]]"}

I'm using the below code to read the value for the key "bounds":

    with open(file = coordinates_file_path) as f:
        for line in f:
            coordinates = json.loads(line)['bounds']
            print(coordinates[0]) # this prints only the char `[`
            coordinates_data.append(coordinates)

What I want: coordinates to be a list of size 5, with each element being a list of size 2 of float. So that I can instantiate a Polygon() object as below:

>>> from geojson import Polygon

>>> Polygon([[(2.38, 57.322), (23.194, -20.28), (-120.43, 19.15), (2.38,   57.322), (2.39, 56.45)]])  
{"coordinates": [[[2.3..., 57.32...], [23.19..., -20.2...], [-120.4..., 19.1...], [2.3..., 57.3..]]], "type": "Polygon"}

But with the code I used above, coordinates is just a string of [[-121.02662668533802, 38.39556098724271], [-121.01552400710878, 38.39556098724271], [-121.01552400710878, 38.38638931377034], [-121.02662668533802, 38.38638931377034], [-121.02662668533802, 38.39556098724271]].

CodePudding user response：

Using python module ast did the trick for me


import ast
  
# initializing string representation of a list
ini_list = "[1, 2, 3, 4, 5]"
  
# printing initialized string of list and its type
print ("initial string", ini_list)
print (type(ini_list))
  
# Converting string to list
res = ast.literal_eval(ini_list)

Output:

initial string [1, 2, 3, 4, 5]
<class 'str'>
final list [1, 2, 3, 4, 5]
<class 'list'>

CodePudding user response：

You can try this:

import json

coordinates_file_path = "<filename>.txt"
with open(coordinates_file_path) as file:
    json_content = file.read().split("\n")
    
    for json_element in json_content:
        if json_element:
            json_converted = json.loads(json_element)
            bounds = json_converted["bounds"]

            # Remove the outer list brackets and split the 5 coordinates
            for coordinate in bounds.strip("[]").split("]"):
                # Remove inner list starting brackets and convert str to float
                coordinate = coordinate.strip("[, ").split(",")
                coordinate = list(map(float, coordinate))
                print(coordinate)

Not sure if this is the best way to do this, but it gets the job done. The coordinate variable contains a list of two floats which you can use to create your Polygons. Hope this helps!

Output:

[-121.02662668533802, 38.39556098724271]
[-121.01552400710878, 38.39556098724271]
[-121.01552400710878, 38.38638931377034]
[-121.02662668533802, 38.38638931377034]
[-121.02662668533802, 38.39556098724271]
[-121.71606277115228, 38.424526411333495]
[-121.70496009292305, 38.424526411333495]
[-121.70496009292305, 38.41535473786112]
[-121.71606277115228, 38.41535473786112]
[-121.71606277115228, 38.424526411333495]
[-120.64683157721372, 38.77860318996463]
[-120.63572889898448, 38.77860318996463]
[-120.63572889898448, 38.769431516492254]
[-120.64683157721372, 38.769431516492254]
[-120.64683157721372, 38.77860318996463]