TopoJSON to GeoJSON converter

topo2geojson.py

"""
topo2geojson.py
Convert topojson to geojson

Example Usage:
  python topo2geojson.py data.topojson data.geojson 


The topojson tested here was created using the mbostock topojson CLI
created with --spherical coords and --properties turned on

Author: Matthew Perry (http://github.com/perrygeo)
Thanks to @sgillies for the topojson geometry logic
requires:
  https://github.com/sgillies/topojson/blob/master/topojson.py

Next steps: how can this be generalized to a robust CLI converter?
"""
import json
import sys
from topojson import geometry
from shapely.geometry import asShape

topojson_path = sys.argv[1]
geojson_path = sys.argv[2]

with open(topojson_path, 'r') as fh:
    f = fh.read()
    topology = json.loads(f)

# file can be renamed, the first 'object' is more reliable
layername = topology['objects'].keys()[0]  

features = topology['objects'][layername]['geometries']
scale = topology['transform']['scale']
trans = topology['transform']['translate']

with open(geojson_path, 'w') as dest:
    fc = {'type': "FeatureCollection", 'features': []}

    for id, tf in enumerate(features):
        f = {'id': id, 'type': "Feature"}
        f['properties'] = tf['properties'].copy()

        geommap = geometry(tf, topology['arcs'], scale, trans)
        geom = asShape(geommap).buffer(0)
        assert geom.is_valid
        f['geometry'] = geom.__geo_interface__
        
        fc['features'].append(f) 

    dest.write(json.dumps(fc))

toposimplify.sh

!#/bin/bash

echo "Convert ESRI File Geodatabase to a shapefile in Plate Carre/WGS84 (EPSG:4326)"

ogr2ogr -t_srs epsg:4326 -f "ESRI Shapefile" \
    ecoregions_original.shp EcoregionSummaries3.gdb.zip EcoSums_ForMatt

echo "Convert shapefile to topojson with simplification"
# -s <tolerance> measured in steridians
# see http://en.wikipedia.org/wiki/Steradian#SI_multiples
# alternatively, can specify proportion of points kept
# e.g. --simplify-proportion 0.1 \

# rm temp*
for tolerance in 1E-7 1E-8 1E-9 1E-10
    do
        topojson --spherical \
            --properties \
            -s $tolerance \
            -q 1E6 \
            -o temp_$tolerance.topojson \
            ecoregions_original.shp &&

        # Convert it to GeoJSON
        python topo2geojson.py temp_$tolerance.topojson temp_$tolerance.geojson &&

        # Optionally, convert GeoJSON to any OGR data source
        ogr2ogr -f "ESRI Shapefile" ecoregions_$tolerance.shp temp_$tolerance.geojson OGRGeoJson &

    done
    wait

thank you. (off topic) also planning to use this in another platform. any chance you guys know java? there is no lib to convert topojson to geojson in java, sadly.