Using topojson.py?

Question

How do I use the topojson.py created by calvinmetcalf: https://github.com/calvinmetcalf/topojson.py

There is a test file at git, which I tried to modify, but unfortunately I don't really know the python syntax. So I don't know how to initialize the calsses etc.

import json
import unittest

from topojson.conversion import convert


class TestTopojson(unittest.TestCase):

    def setUp(self):
        with open(r"C:\Users\root\Desktop\2016\Bundeslaender.geojson") as f:
            self.square_geojson = json.load(f)

    def test_convert_geojson_to_topojson(self):
        tj = convert(self.square_geojson)
        self.assertEqual(tj['type'], 'Topology')



if __name__=="__main__":

    test1 = TestTopojson('test1')
    test1.setUp(test1)
    test1.test_convert_geojson_to_topojson

I'm looking for a good and simple step by step tutorial on using the topojson.py classes. I think that using python would be the best approach to easily convert geojson to topojson on a Windows machine ..

Answer 1

It's true that is not very clear. A simple example:

from topojson.conversion import convert
from topojson import geojson
import json

with open("test.geojson") as f:
  test_geojson = json.load(f)
print test_geojson
{u'type': u'FeatureCollection', u'features': [{u'geometry': {u'type': u'Polygon', u'coordinates': [[[-83.23145862723665, 42.61719935058299], [-83.2316352368618, 42.61737853618379], [-83.23166951279292, 42.61742295755952], [-83.23119346860754, 42.617678900083554], [-83.23097637034452, 42.6174586310034], [-83.23145862723665, 42.61719935058299]]]}, u'type': u'Feature', u'properties': {u'LOWPARCELID': u'1902226080'}}]}
# to TopoJSON
tj = convert(test_geojson)
print tj
{'objects': {'name': {u'type': 'GeometryCollection', 'geometries': [{u'type': u'Polygon', 'properties': {u'LOWPARCELID': u'1902226080'}, 'arcs': [[0]]}]}}, 'type': 'Topology', 'bbox': [-83.23166951279292, 42.61719935058299, -83.23097637034452, 42.617678900083554], 'arcs': [[[3042, 0], [-2548, 3736], [-494, 926], [6867, 5337], [3132, -4593], [-6957, -5406]]], 'transform': {'translate': [-83.23166951279292, 42.61719935058299], 'scale': [6.932117695749783e-08, 4.795974603069803e-08]}}
# to GeoJSON
print geojson(tj)
{'type': 'FeatureCollection', 'features': [{'geometry': {'type': u'Polygon', 'coordinates': [[[-83.23145863777262, 42.61719935058299], [-83.2316352681315, 42.617378528194166], [-83.23166951279292, 42.617422938918985], [-83.23119348427075, 42.617678900083554], [-83.23097637034452, 42.617458620970034], [-83.23145863777262, 42.61719935058299]]]}, 'type': 'Feature', 'properties': {u'LOWPARCELID': u'1902226080'}}]}

But it works only with GeoJSON files with a features key (FeatureCollection)

test =  { "type": "Polygon",
 "coordinates": [
   [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0] ]
   ]
}
tj = convert(test)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "topojson/conversion.py", line 22, in convert
output_dict = topology(input_dict, *args, **kwargs)
File "topojson/topology.py", line 20, in topology
[x0,x1,y0,y1]=bound(objects)
File "topojson/bounds.py", line 20, in bound
b.obj(objects)
File "topojson/mytypes.py", line 46, in obj
self.outObj[fName]=self.FeatureCollection(obj[fName])
File "topojson/mytypes.py", line 19, in FeatureCollection
for feature in collection['features']:
KeyError: 'features'

New

The result of setup.py build/install is not correct with the setup.py of the git repository

A correct structure for Python 2.7.x is

The init.py file is init.py

Then (with see "dir for humans")

import topojson
from see import see
see(topojson)
.geojson()     .topojson()
# therefore
from topojson.topojson.conversion import convert
from topojson.geojson import geojson

Answer 2

Maybe you already solved the problem but anyway...

I ported the TopoJSON code from JavaScript to Python, following the exact same format Mike uses in his library (along with his +300 tests).

To perform the conversion from GeoJSON to TopoJSON, just execute:

from pytopojson import topology


test = {
    "type": "Polygon",
    "coordinates": [
        [[100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0]]
    ]
}

topology_ = topology.Topology()
topojson = topology_({'my_geojson': test})) # You have to provide a name for the GeoJSON

If you print the TopoJSON you will get.

print(topojson)

{
   "type":"Topology",
   "objects":{
      "my_geojson":{
         "type":"Polygon",
         "arcs":[
            [
               0
            ]
         ]
      }
   },
   "arcs":[
      [
         [
            100.0,
            0.0
         ],
         [
            101.0,
            0.0
         ],
         [
            101.0,
            1.0
         ],
         [
            100.0,
            1.0
         ],
         [
            100.0,
            0.0
         ]
      ]
   ],
   "bbox":[
      100.0,
      0.0,
      101.0,
      1.0
   ]
}

You can also use the command-line tool located in the bin folder:

python geo2topo.py < geojson_file

To install it, you just have to run:

pip install pytopojson

Let me know if this was helpful to you!