# High quality contours using AGG

The default plotting mode of pycoast uses PIL for rendering of contours. PIL does not support antialiasing and opacity. The AGG engine can be used for making high quality images using the aggdraw module.

First install the aggdraw module.

Tip: if the building of aggdraw fails with:

    agg_array.h:523: error: cast from ‘agg::int8u*’ to ‘unsigned int’ loses precision

Try:

    export CFLAGS="-fpermissive"

before building.

Using pycoast with AGG for making antialiased drawing:

    >>> 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, (proj4_string, area_extent), resolution='l', width=0.5)
    >>> img.show()

and making the not-so-nice image from the first example nice:

    >>> 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', width=0.5, outline_opacity=127)
    >>> cw.add_borders(img, area_def, outline=(255, 0, 0), width=3, outline_opacity=32)
    >>> img.show()

See docstrings of `ContourWriterAGG` methods for argument descriptions.