84 lines
2.7 KiB
Python
84 lines
2.7 KiB
Python
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"""A more complex example which renders an infinite series of concentric
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circles centred on a point.
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The circles are represented by a Python iterator which will yield only the
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circles which intersect the query's bounding box. The advantage of this
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approach over a MemoryDatasource is that a) only those circles which intersect
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the viewport are actually generated and b) only the memory for the largest
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circle need be available since each circle is created on demand and destroyed
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when finished with.
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"""
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import math
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import mapnik
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from shapely.geometry import *
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def box2d_to_shapely(box):
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import shapely.geometry
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return shapely.geometry.box(box.minx, box.miny, box.maxx, box.maxy)
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class ConcentricCircles(object):
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def __init__(self, centre, bounds, step=1):
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self.centre = centre
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self.bounds = bounds
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self.step = step
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class Iterator(object):
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def __init__(self, container):
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self.container = container
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centre = self.container.centre
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bounds = self.container.bounds
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step = self.container.step
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if centre.within(bounds):
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self.radius = 0
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else:
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self.radius = math.ceil(centre.distance(bounds) / float(step)) * step
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def next(self):
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circle = self.container.centre.buffer(self.radius)
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self.radius += self.container.step
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# has the circle grown so large that the boundary is entirely within it?
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if circle.contains(self.container.bounds):
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raise StopIteration()
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return ( circle.wkb, { } )
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def __iter__(self):
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return ConcentricCircles.Iterator(self)
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class TestDatasource(mapnik.PythonDatasource):
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def __init__(self):
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super(TestDatasource, self).__init__(
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geometry_type=mapnik.DataGeometryType.Polygon
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)
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def features(self, query):
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# Get the query bounding-box as a shapely bounding box
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bounding_box = box2d_to_shapely(query.bbox)
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centre = Point(-20, 0)
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return mapnik.PythonDatasource.wkb_features(
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keys = (),
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features = ConcentricCircles(centre, bounding_box, 0.5)
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)
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if __name__ == '__main__':
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m = mapnik.Map(640, 320)
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m.background = mapnik.Color('white')
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s = mapnik.Style()
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r = mapnik.Rule()
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r.symbols.append(mapnik.LineSymbolizer())
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s.rules.append(r)
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m.append_style('point_style',s)
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ds = mapnik.Python(factory='TestDatasource')
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layer = mapnik.Layer('python')
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layer.datasource = ds
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layer.styles.append('point_style')
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m.layers.append(layer)
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box = mapnik.Box2d(-60, -60, 0, -30)
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m.zoom_to_box(box)
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mapnik.render_to_file(m,'map.png', 'png')
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