Implements a method in QgsGeometry and a processing algorithm to
calculate the pole of inaccessibility for a surface, which is the
most distant internal point from the boundary of the surface. This function
uses the 'polylabel' algorithm (Vladimir Agafonkin, 2016), which is an iterative
approach guaranteed to find the true pole of inaccessibility within a specified
tolerance. More precise tolerances require more iterations and will take longer
to calculate.
This adds a new input type for expression inputs. Expression
inputs can be linked to a parent layer so that the builder
shows the correct fields and layer variables.
It's designed for two use cases:
1. to be used when an algorithm specifically requires an expression,
eg Select by Expression and Extract by Expression.
2. to be potentially used as a replacement input instead of string
or number literals in algorithms. Eg - if the simplify algorithm
tolerance parameter was replaced with an expression paremeter, then
this expression would be evaluated for every feature before
simplifying that feature. It would allow parameters to be calculated
per feature, as opposed to the current approach of calculating
a parameter once before running the algorithm. It would also
mean algorithms like "variable distance buffer" would no longer
be needed, as a single "buffer" algorithm could then be used
for either a fixed distance, field based, or expression based
distance.
Tags are used while searching in the toolbox. This should help with
finding algorithms when the exact name is not known, eg
you could search for "envelope" or "bounds" and find the
'Polygon from Layer Extent' algorithm.
At the moment it's quite hard to discover algorithms which exist
when you don't know what their called and have to instead search
for every possible naming variant which could exist...
With a new option to prefer to snap to closest point on geometry.
The old behaviour was to prefer to snap to nodes, even if a node
was further from the input geometry than a segment. The new option
allows you to snap geometries to the closest point, regardless
of whether it's a node or segment.
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.
