require all input layers to be in the same CRS
The default behaviour is to assume that algorithms are well behaved
and can handle multi-CRS inputs, but algs have the option to
flag that they do not allow this and require the input CRS check.
Those algs should document that they require all inputs to have
matching CRS - processing 3.0 behaviour is to assume that algs
can handle this.
Geometries are passed as const reference and returned by value.
This make using the API easier and reduces the risk of ownership
problems.
The overhead is minimal due to implicit sharing.
Fix https://github.com/qgis/qgis3.0_api/issues/68
This adds a lot of flexibility to algorithms, as it makes output
sinks truely optional. For instance, the various "Extract by..."
algorithms could add a new optional sink for features which
'fail' the extraction criteria. This effectively allows these
algorithms to become feature 'routers', directing features onto
other parts of a model depending on whether they pass or fail
the test.
But in this situation we don't always care about these failing
features, and we don't want to force them to always be fetched
from the provider. By making the outputs truely optional,
the algorithm can tweak its logic to either fetch all features
and send them to the correct output, or only fetch
matching features from the provider in the first place (a big
speed boost).
I have got caught by the default set to WGS 84 when I loaded a layer
in projected CRS, set extent to layer's extent and... nothing got rendered
because map renderer was reprojecting to WGS 84.
This default is closer to the default in 2.x where reprojection is turned off.
QgsProcessingFeatureSink, not all QVariant types
Only strings/QgsPropertys are valid anyway, so instead of strings
use static properties. This makes it clearer what possible
values are permitted for the underlying source/sink definition.
flexible QVariantMap creatOptions parameters which include an
optional fileEncoding value
More flexible, allows sinks to be created using any creation
option which is passed to the underlying provider
