Vector geometry¶

Add geometry attributes¶

Computes geometric properties of the features in a vector layer and includes them in the output layer.

It generates a new vector layer with the same content as the input one, but with additional attributes, containing geometric measurements based on a selected CRS.

The attributes added to the table depend on the geometry type and dimension of the input layer:

• for point layers: X (xcoord), Y (ycoord), Z (zcoord) coordinates and/or M value (mvalue)
• for line layers: length and, for the LineString and CompoundCurve geometry types, the feature sinuosity and straight distance (straightdis)
• for polygon layers: perimeter and area

Default menu: Vector ‣ Geometry Tools

Aggregate¶

Takes a vector or table layer and creates a new layer by aggregating features based on a group by expression.

Features for which group by expression returns the same value are grouped together.

It is possible to group all source features together using constant value in group by parameter, example: NULL.

It is also possible to group features by multiple fields using Array function, example: Array(“Field1”, “Field2”).

Geometries (if present) are combined into one multipart geometry for each group. Output attributes are computed depending on each given aggregate definition.

This algorithm allows to use the default aggregates functions of the QGIS Expression engine.

Boundary¶

Returns the closure of the combinatorial boundary of the input geometries (i.e. the topological boundary of the geometry).

Only for polygon and line layers.

For polygon geometries , the boundary consists of all the lines making up the rings of the polygon.

Boundaries (black dashed line) of the source polygon layer

For lines geometries, the boundaries are their end points.

Boundary layer (red points) for lines. In yellow a selected feature.

Bounding boxes¶

Calculates the bounding box (envelope) of each feature in an input layer. Polygon and line geometries are supported.

Black lines represent the bounding boxes of each polygon feature

Allows features in-place modification

Buffer¶

Computes a buffer area for all the features in an input layer, using a fixed distance.

It is possible to use a negative distance for polygon input layers. In this case the buffer will result in a smaller polygon (setback).

Buffer (in yellow) of points, line and polygon

Allows features in-place modification

Default menu: Vector ‣ Geoprocessing Tools

Parameters¶

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	Input vector layer
Distance	DISTANCE	[number ] Default: 10.0	Buffer distance (from the boundary of each feature). You can use the Data Defined button on the right to choose a field from which the radius will be calculated. This way you can have different radius for each feature (see Variable distance buffer (Graphical Modeler only)).
Segments	SEGMENTS	[number] Default: 5	Controls the number of line segments to use to approximate a quarter circle when creating rounded offsets.
End cap style	END_CAP_STYLE	[enumeration] Default: 0	Controls how line endings are handled in the buffer. One of: 0 — Round 1 — Flat 2 — Square Round, flat and square cap styles
Join style	JOIN_STYLE	[enumeration] Default: 0	Specifies whether round, miter or beveled joins should be used when offsetting corners in a line. Options are: 0 — Round 1 — Miter 2 — Bevel
Miter limit	MITER_LIMIT	[number] Default: 2.0	Controls the maximum distance from the offset curve to use when creating a mitered join (only applicable for miter join styles). Minimum: 1.
Dissolve result	DISSOLVE	[boolean] Default: False	Dissolve the final buffer. If True (checked), overlapping buffers will be dissolved (combined) into a new feature. Standard and dissolved buffer
Buffered	OUTPUT	[vector: polygon] Default: [Create temporary layer]	Specify the output (buffer) layer. One of: Skip output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to PostGIS Table… The file encoding can also be changed here.

Centroids¶

Creates a new point layer, with points representing the centroids of the geometries of the input layer.

The centroid is a single point representing the barycenter (of all parts) of the feature, so it can be outside the feature borders. But can also be a point on each part of the feature.

The attributes of the points in the output layer are the same as for the original features.

The red stars represent the centroids of the features of the input layer.

Allows features in-place modification

Default menu: Vector ‣ Geometry Tools

Check validity¶

Performs a validity check on the geometries of a vector layer.

The geometries are classified in three groups (valid, invalid and error) and for each group, a vector layer with its features is generated:

• The Valid output layer contains only the valid features (without topological errors).
• The Invalid output layer contains all the invalid features found by the algorithm.
• The Error output layer is a point layer that points to where the invalid features were found.

The attribute tables of the generated layers will contain some additional information (“message” for the error layer, “FID” and “_errors” for the invalid layer and only “FID” for the valid layer):

The attribute table of each generated vector layer will contain some additional information (number of errors found and types of error):

Left: the input layer. Right: the valid layer (green), the invalid layer (orange)

Default menu: Vector ‣ Geometry Tools

Types of error messages and their meanings¶

If the GEOS method is used the following error messages can occur:¶

Error message	Explanation	Example
Repeated point	This error happens when a given vertex is repeated.
Ring self-intersection	This error happens when a geometry touches itself and generates a ring.
Self-intersection	This error happens when a geometry touches itself.
Topology validation error
Hole lies outside shell
Holes are nested
Interior is disconnected
Nested shells	This error happens when a polygon geometry is on top of another polygon geometry.
Duplicate rings	This error happens when two rings (exterior or interior) of a polygon geometry are identical
Too few points in geometry component
Invalid coordinate	For a point geometry, this error happens when the geometry does not have a proper coordinate pair. The coordinate pair does not contain a latitude value and a longitude value in that order.
Ring is not closed

If the QGIS method is used the following error messages can occur:¶

Error message	Explanation	Example
Segment %1 of ring %2 of polygon %3 intersects segment %4 of ring %5 of polygon %6 at %7
Ring %1 with less than four points
Ring %1 not closed
Line %1 with less than two points
Line %1 contains %n duplicate node(s) at %2	This error happens when consecutive points on a line have the same coordinates.
Segments %1 and %2 of line %3 intersect at %4	This error happens when a line self intersects (two segments of the line intersect each other).
Ring self-intersection	This error happens when an outer or inner (island) ring / boundary of a polygon geometry intersects itself.
Ring %1 of polygon %2 not in exterior ring
Polygon %1 lies inside polygon %2	This error happens when a part of a MultiPolygon geometry is inside a hole of a MultiPolygon geometry.

Collect geometries¶

Takes a vector layer and collects its geometries into new multipart geometries.

One or more attributes can be specified to collect only geometries belonging to the same class (having the same value for the specified attributes), alternatively all geometries can be collected.

All output geometries will be converted to multi geometries, even those with just a single part. This algorithm does not dissolve overlapping geometries - they will be collected together without modifying the shape of each geometry part.

See the ‘Promote to multipart’ or ‘Aggregate’ algorithms for alternative options.

Default menu: Vector ‣ Geometry Tools

Concave hull (alpha shapes)¶

Computes the concave hull of the features in an input point layer.

Concave hulls with different thresholds (0.3, 0.6, 0.9)

Concave hull (k-nearest neighbor)¶

This algorithm generates a concave hull polygon from a set of points. If the input layer is a line or polygon layer, it will use the vertices.

The number of neighbors to consider determines the concaveness of the output polygon. A lower number will result in a concave hull that follows the points very closely, while a higher number will have a smoother shape. The minimum number of neighbor points to consider is 3. A value equal to or greater than the number of points will result in a convex hull.

If a field is selected, the algorithm will group the features in the input layer using unique values in that field and generate individual polygons in the output layer for each group.

Convert geometry type¶

Generates a new layer based on an existing one, with a different type of geometry.

Not all conversions are possible. For instance, a line layer can be converted to a point layer, but a point layer cannot be converted to a line layer.

Convex hull¶

Calculates the convex hull for each feature in an input layer.

See the ‘Minimum bounding geometry’ algorithm for a convex hull calculation which covers the whole layer or grouped subsets of features.

Black lines identify the convex hull for each layer feature

Allows features in-place modification

Default menu: Vector ‣ Geoprocessing Tools

Create layer from extent¶

Creates a new vector layer that contains a single feature with geometry matching the extent of the input layer.

It can be used in models to convert a literal extent (xmin, xmax, ymin, ymax format) into a layer which can be used for other algorithms which require a layer based input.

Create wedge buffers¶

Creates wedge shaped buffers from input points.

Wedge buffers

The native output from this algorithm are CurvePolygon geometries, but these may be automatically segmentized to Polygons depending on the output format.

Parameters¶

Label	Name	Type	Description
Input layer	INPUT	[vector: point]	Input point vector layer
Azimuth (degrees from North)	AZIMUTH	[number ] Default: 0.0	Angle (in degrees) as the middle value of the wedge
Wedge width (in degrees)	WIDTH	[number ] Default: 45.0	Width (in degrees) of the buffer. The wedge will extend to half of the angular width either side of the azimuth direction. Azimuth and width values of the wedge buffer
Outer radius	OUTER_RADIUS	[number ] Default: 1.0	The outer size (length) of the wedge: the size is meant from the source point to the edge of the wedge shape.
Inner radius Optional	INNER_RADIUS	[number ] Default: 0.0	Inner radius value. If 0 the wedge will begin from the source point.
Buffers	OUTPUT	[vector: polygon] Default: [Create temporary layer]	Specify the output vector layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to PostGIS Table… The file encoding can also be changed here.

Delaunay triangulation¶

Creates a polygon layer with the Delaunay triangulation corresponding to the input point layer.

Delaunay triangulation on points

Default menu: Vector ‣ Geometry Tools

Outputs¶

Label	Name	Type	Description
Delaunay triangulation	OUTPUT	[vector: polygon]	The output (Delaunay triangulation) vector layer

Before and after the cleaning

Allows features in-place modification

Delete holes¶

Takes a polygon layer and removes holes in polygons. It creates a new vector layer in which polygons with holes have been replaced by polygons with only their external ring. Attributes are not modified.

An optional minimum area parameter allows removing only holes which are smaller than a specified area threshold. Leaving this parameter at 0.0 results in all holes being removed.

Before and after the cleaning

Allows features in-place modification

Densify by count¶

Takes a polygon or line layer and generates a new one in which the geometries have a larger number of vertices than the original one.

If the geometries have Z or M values present then these will be linearly interpolated at the added vertices.

The number of new vertices to add to each segment is specified as an input parameter.

Red points show the vertices before and after the densify

Allows features in-place modification

Default menu: Vector ‣ Geometry Tools

Densify by interval¶

Takes a polygon or line layer and generates a new one in which the geometries have a larger number of vertices than the original one.

The geometries are densified by adding regularly placed extra vertices inside each segment so that the maximum distance between any two vertices does not exceed the specified distance.

If the geometries have Z or M values present then these will be linearly interpolated at the added vertices.

Example

Specifying a distance of 3 would cause the segment [0 0] -> [10 0] to be converted to [0 0] -> [2.5 0] -> [5 0] -> [7.5 0] -> [10 0], since 3 extra vertices are required on the segment and spacing these at 2.5 increments allows them to be evenly spaced over the segment.

Densify geometry at a given interval

Allows features in-place modification

Dissolve¶

Takes a vector layer and combines its features into new features. One or more attributes can be specified to dissolve features belonging to the same class (having the same value for the specified attributes), alternatively all features can be dissolved to a single feature.

All output geometries will be converted to multi geometries. In case the input is a polygon layer, common boundaries of adjacent polygons being dissolved will get erased.

The resulting attribute table will have the same fields as the input layer. The values in the output layer’s fields are the ones of the first input feature that happens to be processed.

Dissolve the polygon layer on a common attribute

Default menu: Vector ‣ Geoprocessing Tools

Drape (set Z value from raster)¶

Uses values sampled from a band within a raster layer to set the Z value for every overlapping vertex in the feature geometry. The raster values can optionally be scaled by a preset amount.

If Z values already exist in the layer, they will be overwritten with the new value. If no Z values exist, the geometry will be upgraded to include the Z dimension.

Drop M/Z values¶

Removes M (measure) or Z (altitude) values from input geometries.

Eliminate selected polygons¶

Combines selected polygons of the input layer with certain adjacent polygons by erasing their common boundary. The adjacent polygon can be either the one with the largest or smallest area or the one sharing the largest common boundary with the polygon to be eliminated.

Eliminate is normally used to get rid of sliver polygons, i.e. tiny polygons that are a result of polygon intersection processes where boundaries of the inputs are similar but not identical.

Default menu: Vector ‣ Geoprocessing Tools

Explode lines¶

Takes a lines layer and creates a new one in which each line layer is replaced by a set of lines representing the segments in the original line.

Each line in the resulting layer contains only a start and an end point, with no intermediate vertices between them.

The original line layer and the exploded one

Allows features in-place modification

Extend lines¶

Extends line geometry by a specified amount at the start and end of the line.

Lines are extended using the bearing of the first and last segment in the line.

The red dashes represent the initial and final extension of the original layer

Allows features in-place modification

Parameters¶

Label	Name	Type	Description
Input layer	INPUT	[vector: line]	Input line vector layer
Start distance	START_DISTANCE	[number ]	Distance by which to extend the first segment of the line (starting point)
End distance	END_DISTANCE	[number ]	Distance by which to extend the last segment of the line (ending point)
Extended	OUTPUT	[vector: line] Default: [Create temporary layer]	Specify the output vector layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to PostGIS Table… The file encoding can also be changed here.

Extract specific vertices¶

Takes a vector layer and generates a point layer with points representing specific vertices in the input geometries.

For instance, this algorithm can be used to extract the first or last vertices in the geometry. The attributes associated to each point are the same ones associated to the feature that the vertex belongs to.

The vertex indices parameter accepts a comma separated string specifying the indices of the vertices to extract. The first vertex corresponds to an index of 0, the second vertex has an index of 1, etc. Negative indices can be used to find vertices at the end of the geometry, e.g., an index of -1 corresponds to the last vertex, -2 corresponds to the second last vertex, etc.

Additional fields are added to the vertices indicating the specific vertex position (e.g., 0, -1, etc), the original vertex index, the vertex’s part and its index within the part (as well as its ring for polygons), distance along the original geometry and bisector angle of vertex for the original geometry.

Extract vertices¶

Takes a vector layer and generates a point layer with points representing the vertices in the input geometries.

The attributes associated to each point are the same ones associated to the feature that the vertex belongs to.

Additional fields are added to the vertices indicating the vertex index (beginning at 0), the feature’s part and its index within the part (as well as its ring for polygons), distance along original geometry and bisector angle of vertex for original geometry.

Vertices extracted for line and polygon layer

Default menu: Vector ‣ Geometry Tools

Filter vertices by M value¶

Filters away vertices based on their M value, returning geometries with only vertex points that have a M value greater than or equal to the specified minimum value and/or less than or equal to the maximum value.

If the minimum value is not specified then only the maximum value is tested, and similarly if the maximum value is not specified then only the minimum value is tested.

The red line represents the black line with only vertices whose M value is <=10.

Filter vertices by Z value¶

Filters away vertices based on their Z value, returning geometries with only vertex points that have a Z value greater than or equal to the specified minimum value and/or less than or equal to the maximum value.

If the minimum value is not specified then only the maximum value is tested, and similarly if the maximum value is not specified then only the minimum value is tested.

The red line represents the black line with only vertices whose Z value is <=10.

Fix geometries¶

Attempts to create a valid representation of a given invalid geometry without losing any of the input vertices. Already valid geometries are returned without further intervention. Always outputs multi-geometry layer.

Allows features in-place modification

Geometry by expression¶

Updates existing geometries (or creates new geometries) for input features by use of a QGIS expression.

This allows complex geometry modifications which can utilize all the flexibility of the QGIS expression engine to manipulate and create geometries for output features.

For help with QGIS expression functions, see the inbuilt help available in the expression builder.

Interpolate point on line¶

Creates a point geometry interpolated at a set distance along line or curve geometries.

Z and M values are linearly interpolated from existing values.

If a multipart geometry is encountered, only the first part is considered when calculating the substring.

If the specified distance is greater than the input feature’s length, the resultant feature will have a null geometry.

Interpolated point at 500m of the beginning of the line

Keep N biggest parts¶

Takes a layer with polygons or multipolygons and returns a new layer in which only the n largest polygons of each multipolygon feature are kept. If a feature has n or fewer parts, the feature will just be copied.

Clockwise from top left: original multipart feature, one, two and three biggest parts kept

Line substring¶

Returns the portion of a line (or curve) which falls between the specified start and end distances (measured from the beginning of the line).

Z and M values are linearly interpolated from existing values.

If a multipart geometry is encountered, only the first part is considered when calculating the substring.

Substring line with starting distance set at 0 meters and the ending distance at 250 meters.

Allows features in-place modification

Parameters¶

Label	Name	Type	Description
Input layer	INPUT	[vector: line]	Input line vector layer
Start distance	START_DISTANCE	[number ]	Distance along the input line to the start point of the output feature
End distance	END_DISTANCE	[number ]	Distance along the input line to the end point of the output feature
Substring	OUTPUT	[vector: line] Default: [Create temporary layer]	Specify the output line vector layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to PostGIS Table… The file encoding can also be changed here.

Lines to polygons¶

Generates a polygon layer using as polygon rings the lines from an input line layer.

The attribute table of the output layer is the same as the one from of the input line layer.

Default menu: Vector ‣ Geometry Tools

Merge lines¶

Joins all connected parts of MultiLineString geometries into single LineString geometries.

If any parts of the input MultiLineString geometries are not connected, the resultant geometry will be a MultiLineString containing any lines which could be merged and any non-connected line parts.

Allows features in-place modification

Minimum bounding geometry¶

Creates geometries which enclose the features from an input layer. The features can be grouped by a field. The output layer will then contain one feature per group value with a geometry (MBB) that covers the geometries of the features with matching value.

The following enclosing geometry types are supported:

• bounding box (envelope)
• oriented rectangle
• circle
• convex hull

Clockwise from top left: envelope, oriented rectangle, circle, convex hull

Minimum enclosing circles¶

Calculates the minimum enclosing circles of the features in the input layer.

Enclosing circles for each feature

Allows features in-place modification

Multi-ring buffer (constant distance)¶

Computes multi-ring (donut) buffer for the features of the input layer, using a fixed or dynamic distance and number of rings.

Multi-ring buffer for a line, point and polygon layer

Allows features in-place modification

Multipart to singleparts¶

Splits multipart features in the input layer into singlepart features.

The attributes of the output layer is the same of the original ones but divided into single features.

Left the multipart source layer and right the single part output result

Allows features in-place modification

Default menu: Vector ‣ Geometry Tools

Offset lines¶

Offsets lines by a specified distance. Positive distances will offset lines to the left, and negative distances will offset them to the right.

In blue the source layer, in red the offset one

Allows features in-place modification

Oriented minimum bounding box¶

Calculates the minimum area rotated rectangle for each feature in the input layer.

Oriented minimum bounding box

Allows features in-place modification

Orthogonalize¶

Attempts to orthogonalize the geometries of the input line or polygon layer. This process shifts the vertices in the geometries to try to make every angle in the geometry either a right angle or a straight line.

In blue the source layer and in the red orthogonalized result

Allows features in-place modification

Point on Surface¶

For each feature of the input layer, returns a point that is guaranteed to lie on the surface of the feature geometry.

Allows features in-place modification

Parameters¶

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	Input vector layer
Create point on surface for each part	ANGLE_TOLERANCE	[boolean ]	If checked, a point will be created for each part of the geometry.
Point	OUTPUT	[vector: point] Default: [Create temporary layer]	Specify the output point vector layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to PostGIS Table… The file encoding can also be changed here.

Points along geometry¶

Creates points at regular intervals along line or polygon geometries. Created points will have new attributes added for the distance along the geometry and the angle of the line at the point.

An optional start and end offset can be specified, which controls how far from the start and end of the geometry the points should be created.

Points created along the source line layer

Points displacement¶

Given a distance of proximity, identifies nearby point features and radially distributes them over a circle whose center represents their barycenter. A convenient tool to scatter overlaid features.

Pole of inaccessibility¶

Calculates the pole of inaccessibility for a polygon layer, which is the most distant internal point from the boundary of the surface.

This algorithm uses the ‘polylabel’ algorithm (Vladimir Agafonkin, 2016), which is an iterative approach guaranteed to find the true pole of inaccessibility within a specified tolerance. A more precise tolerance (lower value) requires more iterations and will take longer to calculate.

The distance from the calculated pole to the polygon boundary will be stored as a new attribute in the output layer.

Pole of inaccessibility

Polygonize¶

Creates a polygon layer whose features boundaries are generated from a line layer of closed features.

The yellow polygons generated from the closed lines

Polygons to lines¶

Takes a polygon layer and creates a line layer, with lines representing the boundaries of the polygons in the input layer.

Black lines as the result of the algorithm

Default menu: Vector ‣ Geometry Tools

Project points (Cartesian)¶

Projects point geometries by a specified distance and bearing (azimuth).

Allows features in-place modification

Promote to multipart¶

Takes a vector layer with singlepart geometries and generates a new one in which all geometries are multipart.

Input features which are already multipart features will remain unchanged.

This algorithm can be used to force geometries to multipart types in order to be compatible with data providers that require multipart features.

Allows features in-place modification

Rectangles, ovals, diamonds (fixed)¶

Creates a buffer area for all the features in an input layer with different shape choice.

Parameters can vary depending on the shape chosen.

Different buffer shapes

Rectangles, ovals, diamonds (variable)¶

Creates a buffer area for all the features in an input layer with different shape choice.

Buffer shape parameters are specified through attribute of the input layer.

Different buffer shapes with different parameters

Remove duplicate vertices¶

Removes duplicate vertices from features, wherever removing the vertices does not result in a degenerate geometry.

The tolerance parameter specifies the tolerance for coordinates when determining whether vertices are identical.

By default, Z values are not considered when detecting duplicate vertices. E.g. two vertices with the same X and Y coordinate but different Z values will still be considered duplicate and one will be removed. If the :guilabel;`Use Z Value` parameter is true, then the Z values are also tested and vertices with the same X and Y but different Z will be maintained.

Allows features in-place modification

Remove null geometries¶

Removes any features which do not have a geometry from a vector layer.

All other features will be copied unchanged.

The features with null geometries can be saved to a separate layer.

Reverse line direction¶

Inverts the direction of a line layer.

Before and after the direction inversion

Allows features in-place modification

Rotate¶

Rotates feature geometries by the specified angle clockwise. The rotation occurs around each feature’s centroid, or optionally around a unique preset point.

Allows features in-place modification

Segmentize by maximum angle¶

Segmentizes a geometry by converting curved sections to linear sections.

The segmentization is performed by specifying the maximum allowed radius angle between vertices on the straightened geometry (e.g the angle of the arc created from the original arc center to consecutive output vertices on the linearized geometry). Non-curved geometries will be retained without change.

Segmentize by maximum distance¶

Segmentizes a geometry by converting curved sections to linear sections.

The segmentization is performed by specifying the maximum allowed offset distance between the original curve and the segmentized representation. Non-curved geometries will be retained without change.

Set M value¶

Sets the M value for geometries in a layer.

If M values already exist in the layer, they will be overwritten with the new value. If no M values exist, the geometry will be upgraded to include M values and the specified value used as the initial M value for all geometries.

Set M value from raster¶

Uses values sampled from a band within a raster layer to set the M value for every overlapping vertex in the feature geometry. The raster values can optionally be scaled by a preset amount.

If M values already exist in the layer, they will be overwritten with the new value. If no M values exist, the geometry will be upgraded to include M values.

Parameters¶

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	Input vector layer
Raster layer	RASTER	[raster]	Raster layer with M values
Band number	BAND	[raster band] Default: 1	The raster band from which the M values are taken
Value for nodata or non-intersecting vertices	NODATA	[number ] Default: 0.0	Value to use in case the vertex does not intersect (a valid pixel of) the raster
Scale factor	SCALE	[number ] Default: 1.0	Scaling value: the band values are multiplied by this value.
Updated	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output vector layer (with updated M values). One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to PostGIS Table… The file encoding can also be changed here.

Set Z value¶

Sets the Z value for geometries in a layer.

If Z values already exist in the layer, they will be overwritten with the new value. If no Z values exist, the geometry will be upgraded to include Z values and the specified value used as the initial Z value for all geometries.

Simplify¶

Simplifies the geometries in a line or polygon layer. It creates a new layer with the same features as the ones in the input layer, but with geometries containing a lower number of vertices.

The algorithm gives a choice of simplification methods, including distance based (the “Douglas-Peucker” algorithm), area based (“Visvalingam” algorithm) and snapping geometries to grid.

Clockwise from top left: source layer and increasing simplification tolerances

Allows features in-place modification

Default menu: Vector ‣ Geometry Tools

Single sided buffer¶

Computes a buffer on lines by a specified distance on one side of the line only.

Buffer always results in a polygon layer.

Left versus right side buffer on the same vector line layer

Smooth¶

Smooths the geometries in a line or polygon layer. It creates a new layer with the same features as the ones in the input layer, but with geometries containing a higher number of vertices and corners in the geometries smoothed out.

The iterations parameter dictates how many smoothing iterations will be applied to each geometry. A higher number of iterations results in smoother geometries with the cost of greater number of nodes in the geometries.

Increasing number of iterations causes smoother geometries

The offset parameter controls how “tightly” the smoothed geometries follow the original geometries. Smaller values results in a tighter fit, and larger values will create a looser fit.

Blue: the input layer. Offset 0.25 gives the red line, while offset 0.50 gives the green line.

The maximum angle parameter can be used to prevent smoothing of nodes with large angles. Any node where the angle of the segments to either side is larger than this will not be smoothed. For example, setting the maximum angle to 90 degrees or lower would preserve right angles in the geometry.

Allows features in-place modification

Snap geometries to layer¶

Snaps the geometries in a layer either to the geometries from another layer, or to geometries within the same layer.

Matching is done based on a tolerance distance, and vertices will be inserted or removed as required to make the geometries match the reference geometries.