PyQGIS Documentation - Linfiniti Geo Blog

CHAPTER
FIVE
GEOMETRY HANDLING
Points, linestrings, polygons (and more complex shapes) are commonly referred to as geometries. They are represented
using QgsGeometry class.
To extract information from geometry there are accessor functions for every vector type. How do accessors work:
asPoint() returns QgsPoint
asPolyline() returns a list of QgsPoint items
asPolygon() returns a list of rings, every ring consists of a list of QgsPoint items. First ring is outer, subsequent
rings are holes.
You can use QgsGeometry.isMultipart() to find out whether the feature is multipart. For multipart features
there are similar accessor functions: asMultiPoint(), asMultiPolyline(), asMultiPolygon().
There are several options how to create a geometry:
• from coordinates:
gPnt = QgsGeometry.fromPoint(QgsPoint(1,1))
gLine = QgsGeometry.fromPolyline( [ QgsPoint(1,1), QgsPoint(2,2) ] )
gPolygon = QgsGeometry.fromPolygon( [ [ QgsPoint(1,1), QgsPoint(2,2), QgsPoint(2,1) ] ] )
• from well-known text (WKT):
gem = QgsGeometry.fromWkt("POINT (3 4)")
• from well-known binary (WKB):
g = QgsGeometry()
g.setWkbAndOwnership(wkb, len(wkb))
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