# 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

Pycoast can add contours to either a PIL image object:

    >>> from PIL import Image
    >>> from pycoast import ContourWriter
    >>> 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 = ContourWriter('/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 ContourWriter
    >>> 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 = ContourWriter('/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 `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 `ContourWriter` must be replaced with your GSHHS_DATA_ROOT.

The resulting (not so pretty) image shows the effect of the various arguments. The `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 `level` keyword argument controls the detail level of the dataset used. It defaults to 1 for the lowest detail level.

Instead of a tuple for `area_def` a pyresample `AreaDefinition` object can be used.

See method docstrings for information about possible argument values see method docstrings.

Creating an image with coastlines only:

    >>> from PIL import Image
    >>> from pycoast import ContourWriter
    >>> 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 = ContourWriter('/home/esn/data/gshhs')
    >>> cw.add_coastlines(img, area_def, resolution='l')
    >>> img.show()