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 add_shapefile_shapes method to plot all line shapes found in the file Metareas.shp. We then use the 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
>>> 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,
                            'test/test_data/shapes/Metareas.shp',
                            outline='red',width=2)
>>> cw.add_shapefile_shape(img, area_def,
                           'test/test_data/shapes/divisao_politica/BR_Regioes.shp',
                           3, outline='blue')
>>> cw.add_shapefile_shape(img, area_def,
                           'test/test_data/shapes/divisao_politica/BR_Regioes.shp',
                           4, outline='blue', fill='green')
_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 ogr2ogr (part of GDAL tools), e.g.

$ 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 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())