Reading data from a json using Python and using it to draw shapes-CodePudding

I have a COCO formatted json which if you are not familiar with COCO, is just a list of coordinates of 10 sided polygons (attached an example).

I need to create an array from these coordinates that will plot them on a 128 x 128 square as filled in polygons so that I can multiply it with another array.

I have so far tried skimage.draw polygons and matplotlib polygons. These work if I manually enter coordinates, but I don't know how to read the data in from the json and then use that as the coordinates.

Below is an example of the json.

{
"version": "4.6.0",
"flags": {},
"shapes": [
{
  "label": "blob",
  "points": [
    [
      75.14285714285714,
      83.71428571428571
    ],
    [
      72.23121416791264,
      82.67540136440437
    ],
    [
      70.48628641932781,
      80.12350546954684
    ],
    [
      70.57457698914924,
      77.03333552579737
    ],
    [
      72.46236188059122,
      74.58523142065489
    ],
    [
      75.42857142857144,
      73.71428571428571
    ],
    [
      78.34021440351594,
      74.75317006416705
    ],
    [
      80.08514215210077,
      77.30506595902457
    ],
    [
      79.99685158227935,
      80.39523590277405
    ],
    [
      78.10906669083737,
      82.84334000791652
    ]
  ],
  "group_id": null,
  "shape_type": "polygon",
  "flags": {}

I have tried:

f=open('139cm_2000_frame27.json') 
data=json.load(f) 
shapes=data["shapes"] 
for i in shapes: 
    print('points')

but it errors at 'points' Thank you so much!

CodePudding user response：

You can use the json library to work with json objects. If you need to load the json from a file use json.load() like so:

import json
with open('example.json', 'r') as f:
    versions = json.load(f)['versions']

and use loads when from a string:

import json
json_str = '{"versions": 10}'
versions = json.loads(json_str)['versions']

CodePudding user response：

Ok, you’ve managed to get some way. You now have to navigate the ‘dicts within lists within dicts’. This code will simply print out all the coordinates of all the shapes:

f=open('139cm_2000_frame27.json') 
data=json.load(f) 
shapes=data["shapes"] 
for i in shapes: 
    print(i['label'])   # prints the label first
    for c in i['points']:
        print(c)       # a list containing coordinates

(Sorry, but the single quoted strings are malformed. I’ll have to fix those later)