Extracting List of coordinates from string

Question

Hello Iv been at this all day but have ran into a problem.

I am reading in GeoJson file and trying to extract the coordinates so that I can later iterate throughout them to determine the size of my window to redraw the polygons, represented by a list of coordinates. Each polygon may have 4 - x coordinate pairs. When I read in the GeoJson I get a list containing only 1 element for each polygon instead of a list with a list of coordinates. I believe this is because the list reads: [[[-76.2671328, 38.4506304], [-76.2669856, 38.4505256], [-76.2668385, 38.4503701], [-76.2667281, 38.4502182], [-76.2664568, 38.4499759], [-76.2661993, 38.4497843], [-76.2660108, 38.4497192]...]] and there are multiple sets of [[]] which make the list think there is one element inside..?

So then i tried converting the list of coordinate to a string so I could remove the extra [[]] and extract the coordinate pairs and turn them back into a list. Here is the code:

import json
import re

with open('landareas.json') as f:
    landareas = json.load(f)

coordinates = []
polygons = []
for feature in landareas['features']:
    polygons.append(feature['geometry']['coordinates'])

print len(polygons)
for polygon in polygons:
    #print type(polygon)
    #print len(polygon)
    string =  str(polygon)  
    newCords = string[2:len(string)-1]
    print newCords
    coordinates.append(re.findall('[(.+?)]', newCords))

for coordinate in coordinates:
    print coordinate
    print   

So now when i do this all i get back is:

['.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.']

With all the numbers stripped out.. :(!

If someone could please help me out in a method to exact the coordinates into a list of coordinates for each polygon so that I can loop through a list of polygons with each containing a list of their coordinates, that would be greatly apprcieated!

My initial error which started this was:

File "polygon_LatLong_xy.py", line 33, in <module>
    for x,y in polygons[CORDINATES]:
TypeError: 'int' object is not utterable

from this python script:

import turtle as t
import json

RCID = 0
CORDINATES= 1

with open('landareas.json') as f:
    landareas = json.load(f)

polygons = []
for feature in landareas['features']:
    polygons.append([feature['properties']['RCID'], feature['geometry']['coordinates'] ])

map_width = 400
map_height = 400

minx = 180
maxx = -180
miny = 90
maxy = -90

for x,y in polygons[CORDINATES]:
    if x < minx: minx = x
    elif x > maxx: maxx = x
    if y < miny: miny = y
    elif y > maxy: maxy = y

dist_x = maxx - minx
dist_y = maxy - miny

x_ratio = map_width / dist_x
y_ratio = map_height / dist_y

def convert(point):
    lon = point[0]
    lat = point[1]
    x = map_width - ((maxx - lon) * x_ratio)
    y = map_height - ((maxy - lat) * y_ratio)
    #Python turtle graphics start in the middle of the screen 
    #so we must offset the points so the are centered
    x = x - (map_width/2)
    y = y -(map_height/2)
    return [x,y]

t.up()
first_pixel = None
for point in polygons[CORDINATES]:
    pixel = convert(point)
    if not first_pixel:
        first_pixel = pixel
    t.goto(pixel)
    t.down()
t.goto(first_pixel)
t.write(str(polygons[RCID]), align="center", font=("Arial",16,"bold"))
t.up()
t.done()

If its any help here is an excerpt from the geoJson file:

{
  "type": "FeatureCollection", 
  "features": [
    {
      "geometry": {
        "type": "Polygon", 
        "coordinates": [ <--- note the 
          [ <----------------two sets of brackets? could this be why?              
            [
              -76.0220181, 
              38.1321203
            ], 
            [
              -76.0219133, 
              38.1321847
            ], 
            [
              -76.0232178, 
              38.1312463
            ], 
            [
              -76.0230198, 
              38.1312923
            ], 
            [
              -76.0220181, 
              38.1321203
            ]
          ]
        ]
      }, 
      "type": "Feature", 
      "properties": {
        "TXTDSC": "                                                                                ", 
        "RCID": 3918, 
        "PRIM": 3, 
        "NINFOM": "                                                                                ", 
        "SORIND": "                                                                                ", 
        "RECDAT": "                                                                                ", 
        "AGEN": 550, 
        "GRUP": 1, 
        "SORDAT": "                                                                                ", 
        "OBJL": 71, 
        "NOBJNM": "                                                                                ", 
        "INFORM": "                                                                                ", 
        "LNAM": "0226088C104B1046", 
        "STATUS": "                                                                                ", 
        "RECIND": "                                                                                ", 
        "SCAMAX": null, 
        "NTXTDS": "                                                                                ", 
        "CONDTN": null, 
        "FIDS": 4166, 
        "SCAMIN": null, 
        "FIDN": 143396939, 
        "RVER": 1, 
        "OBJNAM": "                                                                                "
      }
    }, 

Answer 1

After reading more about re i was able to come up with this bit of code that found the x,y pairs and turn them back into a list of x,y pairs, though they are still represented as a string.

for feature in landareas['features']:
    string_listof_cords = str(feature['geometry']['coordinates'])
    #print string_cords
    string_listof_cords = string_listof_cords.replace(",", "")
    print(re.findall(r'\D\d*\.\d*\s\d*\.\d*', string_listof_cords))

However, in my searching I found a better way to do what I was initially trying todo, manipulate polygons from shape files, and have such aborted this method all together. Thanks for the help @ytpillai

Answer 2

I'm not complete sure about your code, but I think your problem is that when you get the string value of the coordinates (in the polygons.append(feature['geometry']['coordinates']) and coordinates.append(re.findall('[(.+?)]', newCords)), you don't convert them into a list first.

Let's say we have a string c = "1, 2" You can do biglist.append(c.split(","))

One more thing that might help is that you make a set of coordinates for each polygon.

#Make a condition that tells the program when to search for the next polygon
polygons = []
polygon = []
for x in landareas['features']:
    if polygonDone:
        polygons.append(polygon)
        del polygon[:]
    else:
        polygon.append(x['geometry']['coordinates'].split(","))