This algorithm updates existing geometries (or creates new
geometries) for input features by use of a QGIS expression. This
allows complex geometry modifications which can utilise all the
flexibility of the QGIS expression engine to manipulate and create
geometries for output features.
This algorithm allows you to extract specific nodes from geometries.
Eg you can extract the first or last node in the geometry.
The algorithm accepts a comma separated list of node indices to
extract, eg 0 = first node, 1 = second node, etc. Negative indices
can be used to extract nodes from the end of the geometry. Eg
-1 = last node, -2 = second last node.
segments shorter than a certain threshold or sharp corners
with an angle exceeding a threshold
Expose the angle threshold to processing smooth algorithm
Also:
- optimise QgsGeometry::smooth for new geometry classes
- Fix smooth does not work with geometries containing Z/M
This change allows users to choose which method to use when running
the simplify geometries algorithm, with choices of the existing
distance based (Douglas Peucker) algorithm, area based (Visvalingam)
algorithm and snap-to-grid.
Visvaligam in particular usually results in more cartographically
pleasing simplification over the standard distance based methods.
The existing polygoncentroids algorithm has been deprecated
(and hidden from the toolbox), and a new, generic centroids
algorithm added which works with lines and multipoints
Before the algorithm was written to optimise clipping a few
features against thousands of mask features. The revised algorithm
is optimised for clipping thousands of input features against
a few mask features.
Given that this second operation is much more likely, it makes
sense to optimise for this use case.
I've also applied some other optimisations like taking advantage
of spatial indexes on the providers, using prepared geometries
and also only applying an intersection operation if the geometry
isn't wholly contained by the mask geometry.
Benchmarks:
clipping roads layer with 1 million lines against 2 polygons
before: 5 mins 30 seconds
after: 10 seconds
clipping address layer with 5 million points against 2 polygons
before: 50 minutes
after: 30 seconds
This algorithm joins all connected parts of MultiLineString
geometries into single LineString geometries.
If any parts of the input MultiLineString geometries are not
connected, the resultant geometry will be a MultiLineString
containing any lines which could be merged and any non-connected
line parts.
