Contents
How is the QGIS nnplugin used in nnjoin?
The QGIS NNPlugin can be used to join two vector layers (the input and the join layer). All geometry type combinations are supported. A feature from the input layer is joined to the nearest feature in the join layer. Join layer features with missing geometries are ignored.
When to ignore missing geometries in nnjoin?
Join layer features with missing geometries are ignored. The result of the join is a new vector layer with the same geometry type and coordinate reference system as the input layer. Joining layers with different Coordinate Reference Systems (CRS) is supported, as long as the join layer coordinate system is a projected CRS.
How are distance calculations done in nnjoin plugin?
A warning is given when the user attempts to join layers with different CRS. The join and distance calculations is performed using the join layer CRS. Joining layers with an unprojected CRS is allowed, but the distance calculations are then done using decimal degreees, and the distances returned will be in decimal degrees.
Can a QGIS plugin be used to join two vector layers?
The QGIS NNJoin Plugin. The QGIS NNPlugin can be used to join two vector layers (the input and the join layer). All geometry type combinations are supported. A feature from the input layer is joined to the nearest feature in the join layer.
How to use nnjoin as a geo in Python?
NNjoin joins two vector layers based on nearest neighbour relationships and it use GEOS as Shapely. In Python it is quicker to use a Spatial Index as Rtree (Nearest Neighbours). There are many examples of the use of this module with Shapely and Fiona on the Web and GIS SE.
How is the index used in nnjoin plugin?
For input layers with non-point geometries, the index is used to find a possible nearest neighbour based on the centroid of the input geometry. The geometry of this possible nearest neighbour is then used in combination with the input geometry to determine a search region.
How to write new processing algorithms in QGIS?
Within QGIS, you can use Create new script in the Scripts menu at the top of the Processing Toolbox to open the Processing Script Editor where you can write your code. To simplify the task, you can start with a script template by using Create new script from template from the same menu.
How to join attributes from nearest point in QGIS?
In QGIS 3.8 and above the “Join attributes by nearest” native tool in Processing Toolbox does the job easily! If you can live with just joining a single attribute from your “B” layer, take a look at the “Hub Distance” tool from the mmqgis plugin.
Can a non multi polygon join layer be excluded?
For non-multi polygon join layers and point input layers (including approximations), containing polygons can be excluded. The user can specify the prefix of the join layer attributes in the output layer. The user can specify the name of the attribute that will contain the distance to the nearest neighbour.