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alpha-beta-soup/cartopy-nztm.py

Created August 29, 2019 21:32
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Cartopy CRS definition for NZTM2000
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cartopy-nztm.py
import cartopy
import shapely.geometry as sgeom
class NZTM(cartopy.crs.TransverseMercator):
def __init__(self):
'''
https://epsg.io/2193
https://www.linz.govt.nz/data/geodetic-system/datums-projections-and-heights/geodetic-datums/new-zealand-geodetic-datum-2000-nzgd2000
'''
inverse_flattening = 298.257222101
semimajor_axis = 6378137
semiminor_axis = -((inverse_flattening*semimajor_axis)-semimajor_axis)
globe = cartopy._crs.Globe(
semimajor_axis=semimajor_axis,
semiminor_axis=semiminor_axis
)
super(NZTM, self).__init__(central_longitude=173,
central_latitude=0,
scale_factor=0.9996,
false_easting=1600000,
false_northing=10000000,
globe=globe)
@property
def boundary(self):
x0, x1 = self.x_limits
y0, y1 = self.y_limits
return sgeom.LineString([(x0, y0), (x0, y1),
(x1, y1), (x1, y0),
(x0, y0)])
@property
def x_limits(self):
return (827933.23, 3195373.59)
@property
def y_limits(self):
return (3729820.29, 7039943.58)
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alpha-beta-soup commented Aug 29, 2019 •
edited

For example, in a Flask application, to return a PNG of NZ in NZTM to the client at http://host:port/map:

@app.route('/map')
def getmap():
    ax = matplotlib.pyplot.axes(projection=NZTM())
    ax.add_feature(cartopy.feature.LAND)
    ax.coastlines('10m', alpha=0.2)
    x0, y0 = 165.893555, -47.696163
    x1, y1 = 180.0, -34.016242
    ax.set_extent([x0, x1, y0, y1])
    plt.title('New Zealand Transverse Mercator (2000) with Cartopy')
    output = io.BytesIO()
    matplotlib.backends.backend_agg.FigureCanvasAgg(ax.figure).print_png(output)
    return Response(output.getvalue(), mimetype='image/png')

map

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