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Usage

Pycoast can be used to add coastlines, borders and rivers to a raster image if the geographic projection of the image and the image extent in projection coordinates are known

images/BMNG_clouds_201109181715_areaT2.png

Pycoast can add contours to either a PIL image object:

>>> from PIL import Image
>>> from pycoast import ContourWriterAGG
>>> img = Image.open('BMNG_clouds_201109181715_areaT2.png')
>>> proj4_string = '+proj=stere +lon_0=8.00 +lat_0=50.00 +lat_ts=50.00 +ellps=WGS84'
>>> area_extent = (-3363403.31,-2291879.85,2630596.69,2203620.1)
>>> area_def = (proj4_string, area_extent)
>>> cw = ContourWriterAGG('/home/esn/data/gshhs')
>>> cw.add_coastlines(img, area_def, resolution='l', level=4)
>>> cw.add_rivers(img, area_def, level=5, outline='blue')
>>> cw.add_borders(img, area_def, outline=(255, 0, 0))
>>> img.show()

or to an image file:

>>> from pycoast import ContourWriterAGG
>>> proj4_string = '+proj=stere +lon_0=8.00 +lat_0=50.00 +lat_ts=50.00 +ellps=WGS84'
>>> area_extent = (-3363403.31,-2291879.85,2630596.69,2203620.1)
>>> area_def = (proj4_string, area_extent)
>>> cw = ContourWriterAGG('/home/esn/data/gshhs')
>>> cw.add_coastlines_to_file('BMNG_clouds_201109181715_areaT2.png', area_def, resolution='l', level=4)
>>> cw.add_rivers_to_file('BMNG_clouds_201109181715_areaT2.png', area_def, level=5, outline='blue')
>>> cw.add_borders_to_file('BMNG_clouds_201109181715_areaT2.png', area_def, outline=(255, 0, 0))

Where the :attr:`area_extent` is the extent of the image in projection coordinates as (x_ll, y_ll, x_ur, x_ur) measured at pixel edges.

The argument to :class:`~pycoast.cw_agg.ContourWriterAGG` must be replaced with your GSHHS_DATA_ROOT.

images/euro_coast.png

The resulting (not so pretty) image shows the effect of the various arguments. The :attr:`resolution` keyword argument controls the resolution of the dataset used. It defaults to 'c' for coarse. Increasing the resolution also increases the processing time. The :attr:`level` keyword argument controls the detail level of the dataset used. It defaults to 1 for the lowest detail level. See method docstrings for information about other possible argument values.

Example with tuple

Creating an image with coastlines only:

>>> from PIL import Image
>>> from pycoast import ContourWriterAGG
>>> img = Image.new('RGB', (425, 425))
>>> proj4_string = '+proj=geos +lon_0=0.0 +a=6378169.00 +b=6356583.80 +h=35785831.0'
>>> area_extent = (-5570248.4773392612, -5567248.074173444, 5567248.074173444, 5570248.4773392612)
>>> area_def = (proj4_string, area_extent)
>>> cw = ContourWriterAGG('/home/esn/data/gshhs')
>>> cw.add_coastlines(img, area_def, resolution='l')
>>> img.show()

images/geos_coast.png

Example with AreaDefinition

Instead of a tuple for :attr:`area_def` a pyresample :class:`~pyresample.geometry.AreaDefinition` object can be used. The code below produces the same image as above.

>>> from PIL import Image
>>> from pycoast import ContourWriterAGG
>>> from pyresample.geometry import AreaDefinition
>>> img = Image.new('RGB', (425, 425))
>>> area_def = AreaDefinition('my_area', 'Area Description', 'geos_proj',
...     {'proj': 'geos', 'lon_0': 0.0, 'a': 6378169.00, 'b': 6356583.80, 'h': 35785831.0},
...     425, 425,
...     (-5570248.4773392612, -5567248.074173444, 5567248.074173444, 5570248.4773392612))
>>> cw = ContourWriterAGG('/home/esn/data/gshhs')
>>> cw.add_coastlines(img, area_def, resolution='l')
>>> img.show()