This algorithm calculates the area and percentage cover
by which features from an input layer are overlapped by
features from a selection of overlay layers.
New attributes are added to the output layer reporting
the total area of overlap and percentage of the input
feature overlapped by each of the selected overlay layers.
This is quite a common GIS task request, yet is full
of traps for inexperienced users, and the amount of
manual data work usually done by users to calculate
these figures can often lead to mistakes and inaccurate
results. It's nice to have a robust, fast, inbuilt
algorithm which allows this task to be done in a
single step without risk of human error.
There's two motivations for this:
- the existing one was getting massive and took ages to run, which was
a pain when developing. Smaller batches allow just a subset of test to
be run which is much faster.
- There's a random segfault on test exit which occurs on Travis. Rather
then disabling these absolutely critical tests altogether, I'm using
this as a method of bisecting exactly which alg is causing this.
populating batch processing dialog
This option adds news rows using the values from an expression
which returns an array. (As opposed to "Calculate by Expression",
which works only on existing rows).
The intended use case is to allow populating the batch dialog
using complex numeric series, e.g. those created by the "generate_series"
expression function.
For example, adding rows for a batch buffer using the expression
generate_series(100, 1000, 50)
(results in new rows with values 100, 150, 200, .... 1000)
This new option is available under the Autofill menu for a column. Selecting it allows users
to create a new QGIS expression to use to update the value inside that column. Existing
parameter values (including those from other columns) are available for use inside
the expression via @variables.
E.g. this allows setting output file names to complex expressions like
'/home/me/stuff/buffer_' || left(@input, 30) || '_' || @distance || '.shp'
to an explicit widget in the table
The double-click-header action is very hidden, and many users will
not stumble upon this. By moving it to an explicit "Autofill" widget at the
top of the table, we make this important action much more user
discoverable.
It also gives the possibility of other, parameter specific, autofill
actions (e.g. fill by expression, fill by file pattern)
- for algorithms that produce directory output, it is possible to test
that directory contents are exactly the same (recursively)
- added possibility to have a project file loaded before an algorithm is run
- documented the new additions (+ few existing ones)
