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Shapes from ESRI shape files
-------------------------------
Pycoast supports plotting of polygons and polylines from ESRI shapefiles,
currently only in lonlat coordinates format.
In the following example we use :attr:`add_shapefile_shapes` method to plot all line shapes
found in the file Metareas.shp. We then use the :attr:`add_shapefile_shape` (notice the singular)
to plot only the 3rd and 4th shape_id within the file BR_Regioes.shp.
>>> from pycoast import ContourWriterAGG
>>> from PIL import Image
>>> img = Image.new('RGB', (600, 600))
>>> proj4_string = '+proj=merc +lon_0=-60 +lat_ts=-30.0 +a=6371228.0 +units=m'
>>> area_extent = (-2000000.0, -5000000.0, 5000000.0, 2000000.0)
>>> area_def = (proj4_string, area_extent)
>>> cw = ContourWriterAGG(gshhs_root_dir)
...
>>> cw.add_coastlines(img, area_def, resolution='l', level=4)
>>> cw.add_shapefile_shapes(img, area_def,
'tests/test_data/shapes/Metareas.shp',
outline='red',width=2)
>>> cw.add_shapefile_shape(img, area_def,
'tests/test_data/shapes/divisao_politica/BR_Regioes.shp',
3, outline='blue')
>>> cw.add_shapefile_shape(img, area_def,
'tests/test_data/shapes/divisao_politica/BR_Regioes.shp',
4, outline='blue', fill='green')
.. image:: images/brazil_shapefiles_agg.png
Reproject unsupported shapefiles
********************************
If your shapefile is not in lonlat coordinates, then you can re-project your shape file using
:attr:`ogr2ogr` (part of GDAL_ tools), e.g.
.. code-block:: bash
$ ogr2ogr original.shp lonlat.shp -t_srs "+proj=latlong"
This should work if you have all the extra meta-files original.* included with your original.shp.
Please refer to the OGR_ documentation for more information.
Complex shape drawing
*********************
To further customize how shapes are drawn the
:meth:`~pycoast.ContourWriterAGG.add_shapes` can be used. This is the low-level
version of the ``add_shapefile_shape`` method described above. This method
takes an iterable of shape objects to draw with optional drawing parameters.
In combination with python generators this can provide a high performance
method for drawing multiple shapes with per-shape customization.
In the below example a custom generator function is defined to open a shapefile
and specify that each polygon should be blue and any other shape should be red.
>>> import shapefile
>>> def my_shapes_generator():
... sf = shapefile.Reader(filename)
... for shape in sf.shapes():
... if shape.shapeType == shapefile.POLYGON:
... kwargs = {'fill': (0, 0, 255)}
... else:
... kwargs = {'fill': (255, 0, 0)}
... yield (shape, kwargs)
... cw.add_shapes(img, area_def, my_shapes_generator())
.. _OGR: http://www.gdal.org/ogr2ogr.html
.. _GDAL: http://www.gdal.org/
.. _PIL: http://www.pythonware.com/products/pil/
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