Swapping coordinates with Fiona

swap-coords.py

# Swapping x, y coords.

from descartes import PolygonPatch
from fiona import collection
from itertools import imap
import logging
from matplotlib import pyplot

log = logging.getLogger()

BLUE = '#6699cc'

# To begin: a few functions to swap geometry coordinates. They call each
# other semi-recursively. GeoJSON was designed to make this possible, BTW.

def swap_Point(coords):
    """Swaps x, y coordinate values, leaves z+ alone."""
    return tuple(coords[:2][::-1] + coords[2:])

def swap_LineString(coords):
    """Returns swapped LineString or Ring coordinates, preserving 
    order, number, and dimensionality."""
    # Calls swap_Point.
    return list(swap_Point(pt_coords) for pt_coords in coords)

def swap_Polygon(coords):
    """Returns swapped Polygon coordinates, preserving order, number,
    and dimensionality."""
    # Calls swap_LineString.
    return list(
        swap_LineString(ring_coords) for ring_coords in coords)

# The next function is applied to each record in the following
# processing code.

def swap(rec):

    """Returns a record after swapping its geometry's coordinate x,y."""

    # Use lexical dispatch on geometry type to get the proper translation
    # function.
    handlers = {
        'Point': swap_Point,
        'LineString': swap_LineString,
        'Polygon': swap_Polygon }
    try:
        g = rec['geometry']
        g['coordinates'] = handlers[g['type']](g['coordinates'])
        rec['geometry'] = g
        return rec
    except Exception, e:
        log.exception("Error processing record %s:", rec)

def draw(axes, rec):
    """Given matplotlib axes and a record, adds the record as a patch
    and returns the axes so that reduce() can accumulate more
    patches."""
    axes.add_patch(
        PolygonPatch(rec['geometry'], fc=BLUE, ec=BLUE, alpha=0.5, zorder=2))
    return axes

if __name__ = "__main__":

    # Set up the figure and axes.
    figure = pyplot.figure(1, figsize=(6, 6), dpi=90)
    axes = figure.add_subplot(111)

    with collection("docs/data/test_uk.shp", "r") as source:
        results = imap(swap, source)
        reduce(draw, results, axes)

    axes.autoscale(tight=True)
    figure.savefig('swap-coords.png')