Layer builder

Help to build layers that fits Niva's index computation requirements using a CSV file and a root folder to match layers. The CSV contain informations on which features to extract from which layer and what buffer to apply on these features.

algorithm id: niva:layerbuilder

Parameters¶

Name	Optionnal	Type	Description
ROI	False	QgsVectorLayer	Region of interest.
CSV	False	STRING / File Path	Path to CSV that contain features extraction informations. CSV structure is explained below.
FOLDER	False	STRING / Folder Path	Path to root folder. Layers will be match recursively from this folder.

Outputs¶

Name	Type	Description
OUTPUT	QgsVectorLayer	Output layer with extracted features.

OUTPUT layer contain the following fields:

Name	Type	Description
type	STRING	Feature type from CSV file.

CSV structure¶

CSV file should use ';' as columns separator to not interfer with QgsExpression parsing that could contain ',' . All csv columns are displayed in the following table:

Columns¶

Name	Description	Optionnal
pattern	Regular expression to match layers in folder (i.e building.shp will match every file that contain 'building' and that end with the .shp extension).
filter	Expression to filter features from layer. Thise expression should respect QgsExpression format (same as used in Expression panel). i.e. NATURE = 'road', this expression wil extract all features where NATURE field is road.	True, let empty to gather all features.
formula	Expression to compute distance for buffer. Thise expression should respect QgsExpression format (same as used in Expression panel). i.e WIDTH 1.5* will apply on each feature a buffer with distance: feature's width (based on it's field WIDTH) * 1.5. Buffer expression can be fix: 1.5	True, let empty for no buffer.
type	The feature type (i.e building). This will fill the type field on output layer.	False
default_values	Contain default values for fields used in buffer formula in cas of the feature's value for this field is NULL. The algortihm will first try to fill the feature's field with median of this field on layer (after filtering) and if no value found fill with defautl value. i.e. with formula WIDTH 1.5* and default values WIDTH=5. If multiple fields are used in formula juste write Field1=Value1,Field2=Value2 without space.	False but should be filled only if field are used in formula, else let it empty.

Example¶

pattern	filter	formula	type	default_values	effect
CEMETERY.shp			cemetery		Gather all features of CEMETERY layers with no buffer.
PYLONE.shp		0.5	pylon		Gather all features of PYLON layer and apply a fix buffer of 0.5m.
CONSTRUCTION.shp	"NATURE = 'Windmill'"	2.5	windmill		Gather all features of CONSTRUCTION layer that have 'Windmill' for field NATURE and apply a buffer of 2.5m.
CONSTRUCTION.shp	"NATURE != 'Windmill'"	0.5	isolated_construction		Gather all features of CONSTRUCTION layer that don't have 'Windmill' for field NATURE and apply a buffer of 0.5m.
TRANSPORTS.shp	"NATURE IN ('Sorting Area', 'Parking')"		transports_area		Gather all features of TRANSPORTS layer that have either 'Sorting Area' or 'Parking' for field NATURE.
ROAD.shp	"NATURE = 'path'"	WIDTH	path	WIDTH=0.5	Gather all features of ROAD layer that have 'path' for field NATURE and apply a buffer of WIDTH. if feature's WIDTH is NULL, fill with median or 0.5m if no values.
ROAD.shp	"NATURE = 'Highway'"	WIDTH	Highway	WIDTH=9.5	Gather all features of ROAD layer that have 'Highway' for field NATURE and apply a buffer of WIDTH. if feature's WIDTH is NULL, fill with median or 9.5m if no values.
TRAIN.shp		NB_LINES * 1.25	train_line	NB_VOIES=2	Gather all features of TRAIN and apply a buffer of 1.25 NB_LINES. if feature's NB_LINES is NULL, fill with median or 2 if no values.