Rasterio example

about.md

python-powered.json

python_powered.py

# python_powered.py
#
# Turns the 15 features in the Python logo
#
#   http://www.python.org/community/logos/python-powered-h-140x182.png
#
# into a GeoJSON feature collection.

import json
import subprocess

import rasterio
from rasterio import features


with rasterio.drivers():
    
    with rasterio.open('python-powered-h-140x182.png') as src:
        blue = src.read_band(3)
    
    # Set every non-background pixel to 0 and then mask out the
    # white background.
    blue[blue < 255] = 0
    mask = blue != 255

    # transform to world coordinates so that we can map it
    transform = [-35.0, 0.5, 0.0, 40.5, 0.0, -0.5]

    # Get shapes from the positive part of the image.
    shapes = list(features.shapes(blue, mask=mask, transform=transform))

    # Burn those shapes into a new image.
    image = features.rasterize(
                ((g, 255) for g, v in shapes),
                out_shape=blue.shape, fill=0, transform=transform )

    # Write the new image out.
    kwargs = src.meta
    kwargs['count'] = 1
    kwargs['driver'] = 'GTiff'
    with rasterio.open('result.tif', 'w', **kwargs) as dst:
        dst.write_band(1, image)

subprocess.call(['open', 'result.tif'])

# Write the shapes out to GeoJSON.
results = ({
        'type': 'Feature', 
        'properties': {'raster_val': v}, 
        'geometry': s }
    for i, (s, v) 
        in enumerate(shapes) )

collection = {
    'type': 'FeatureCollection', 
    'features': list(results) }

with open('python-powered.json', 'w') as dst:
    json.dump(collection, dst)

rasterio_features_roundtrip.ipynb

Did you use a world file or some other projection source for your source image? For me, GDAL reports ERROR 6: No translation an empty SRS to PROJ.4 format is known. and I get a pretty whacky geojson representation.