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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:
.. code-block:: bash
agg_array.h:523: error: cast from ‘agg::int8u*’ to ‘unsigned int’ loses precision
Try:
.. code-block:: bash
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()
.. image:: images/geos_coast_agg.png
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()
.. image:: images/euro_coast_agg.png
See docstrings of :attr:`ContourWriterAGG` methods for argument descriptions.
.. _PIL: http://www.pythonware.com/products/pil/
.. _aggdraw: http://effbot.org/zone/aggdraw-index.htm
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