Graphics Reference
In-Depth Information
calculator.setEllipsoid(crs.ellipsoidAcronym())
calculator.setEllipsoidalMode(crs.geographicFlag())
if geometry.isMultipart():
self.add(info, 'num_multi', 1)
parts = geometry.asGeometryCollection()
for sub_geometry in parts:
self.analyzeGeometry(sub_geometry, layer, info)
elif geometry.type() == QGis.Point:
self.add(info, 'num_points', 1)
elif geometry.type() == QGis.Line:
self.add(info, 'num_lines', 1)
self.add(info, 'tot_line_length',
calculator.measure(geometry))
elif geometry.type() == QGis.Polygon:
self.add(info, 'num_polygons', 1)
self.add(info, 'tot_poly_area',
calculator.measure(geometry))
self.add(info, 'tot_poly_perimeter',
calculator.measurePerimeter(geometry))
def add(self, info, key, n):
if key in info:
info[key] = info[key] + n
else:
info[key] = n
The
add()
method is just a helper method that adds a number to a dictionary entry if it
exists, and creates that entry if it doesn't. This allows us to use the
info
dictionary to
store the results as we calculate them.
As you can see, the
analyzeGeometry()
method makes use of a
Qg-
sDistanceArea
object to calculate the lengths and areas of a geometry. Note that our
analyzeGeometry()
method is recursive; if a geometry has multiple parts, each sub-
geometry might also have multiple parts, so we call
analyzeGeometry()
recursively
on each part to allow these nested geometries to be handled correctly.
When we call
analyzeGeometry()
on a given
QGSGeometry
, the results of the
analysis will be stored in the
info
dictionary. Let's add some code to the end of our
