QgsGeos class
Does vector analysis using the geos library and handles import, export, exception handling*.
Contents
Base classes
- class QgsGeometryEngine
- Contains geometry relation and modification algorithms.
Public static functions
-
static auto addPart(QgsGeometry& geometry,
GEOSGeometry* newPart) -> QgsGeometry::
OperationResult - Adds a new island polygon to a multipolygon feature.
-
static auto asGeos(const QgsGeometry& geometry,
double precision = 0) -> geos::
unique_ptr - Returns a geos geometry - caller takes ownership of the object (should be deleted with GEOSGeom_destroy_r)
-
static auto asGeos(const QgsAbstractGeometry* geometry,
double precision = 0) -> geos::
unique_ptr - Returns a geos geometry - caller takes ownership of the object (should be deleted with GEOSGeom_destroy_r)
- static auto fromGeos(const GEOSGeometry* geos) -> std::unique_ptr<QgsAbstractGeometry>
- Create a geometry from a GEOSGeometry.
- static auto geometryFromGeos(GEOSGeometry* geos) -> QgsGeometry
- Creates a new QgsGeometry object, feeding in a geometry in GEOS format.
-
static auto geometryFromGeos(const geos::
unique_ptr& geos) -> QgsGeometry - Creates a new QgsGeometry object, feeding in a geometry in GEOS format.
- static auto polygonize(const QVector<const QgsAbstractGeometry*>& geometries, QString* errorMsg = nullptr) -> QgsGeometry
- Creates a GeometryCollection geometry containing possible polygons formed from the constituent linework of a set of geometries.
Constructors, destructors, conversion operators
- QgsGeos(const QgsAbstractGeometry* geometry, double precision = 0)
- GEOS geometry engine constructor.
Public functions
- auto centroid(QString* errorMsg = nullptr) const -> QgsPoint* override
- Calculates the centroid of this.
- auto clip(const QgsRectangle& rectangle, QString* errorMsg = nullptr) const -> std::unique_ptr<QgsAbstractGeometry>
- Performs a fast, non-robust intersection between the geometry and a rectangle.
- auto closestPoint(const QgsGeometry& other, QString* errorMsg = nullptr) const -> QgsGeometry
- Returns the closest point on the geometry to the other geometry.
- auto combine(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> QgsAbstractGeometry* override
- Calculate the combination of this and geom.
- auto combine(const QVector<QgsAbstractGeometry*>& geomList, QString* errorMsg) const -> QgsAbstractGeometry* override
- Calculate the combination of this and geometries.
- auto combine(const QVector<QgsGeometry>& geometries, QString* errorMsg = nullptr) const -> QgsAbstractGeometry* override
- Calculate the combination of this and geometries.
- auto contains(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> bool override
- Checks if geom contains this.
- auto convexHull(QString* errorMsg = nullptr) const -> QgsAbstractGeometry* override
- Calculate the convex hull of this.
- auto crosses(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> bool override
- Checks if geom crosses this.
- auto delaunayTriangulation(double tolerance = 0.0, bool edgesOnly = false, QString* errorMsg = nullptr) const -> QgsGeometry
- Returns the Delaunay triangulation for the vertices of the geometry.
- auto difference(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> QgsAbstractGeometry* override
- Calculate the difference of this and geom.
- auto disjoint(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> bool override
- Checks if geom is disjoint from this.
- auto distance(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> double override
- Calculates the distance between this and geom.
- void geometryChanged() override
- Should be called whenever the geometry associated with the engine has been modified and the engine must be updated to suit.
- auto hausdorffDistance(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> double
- Returns the Hausdorff distance between this geometry and geom.
- auto hausdorffDistanceDensify(const QgsAbstractGeometry* geom, double densifyFraction, QString* errorMsg = nullptr) const -> double
- Returns the Hausdorff distance between this geometry and geom.
- auto intersection(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> QgsAbstractGeometry* override
- Calculate the intersection of this and geom.
- auto intersects(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> bool override
- Checks if geom intersects this.
- auto isEqual(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> bool override
- Checks if this is equal to geom.
- auto isSimple(QString* errorMsg = nullptr) const -> bool override
- Determines whether the geometry is simple (according to OGC definition).
- auto lineLocatePoint(const QgsPoint& point, QString* errorMsg = nullptr) const -> double
- Returns a distance representing the location along this linestring of the closest point on this linestring geometry to the specified point.
- auto mergeLines(QString* errorMsg = nullptr) const -> QgsGeometry
- Merges any connected lines in a LineString/MultiLineString geometry and converts them to single line strings.
- auto overlaps(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> bool override
- Checks if geom overlaps this.
- auto pointOnSurface(QString* errorMsg = nullptr) const -> QgsPoint* override
- Calculate a point that is guaranteed to be on the surface of this.
- void prepareGeometry() override
- Prepares the geometry, so that subsequent calls to spatial relation methods are much faster.
- auto relate(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> QString override
- Returns the Dimensional Extended 9 Intersection Model (DE-9IM) representation of the relationship between the geometries.
- auto relatePattern(const QgsAbstractGeometry* geom, const QString& pattern, QString* errorMsg = nullptr) const -> bool override
- Tests whether two geometries are related by a specified Dimensional Extended 9 Intersection Model (DE-9IM) pattern.
- auto reshapeGeometry(const QgsLineString& reshapeWithLine, EngineOperationResult* errorCode, QString* errorMsg = nullptr) const -> std::unique_ptr<QgsAbstractGeometry>
- Reshapes the geometry using a line.
- auto shortestLine(const QgsGeometry& other, QString* errorMsg = nullptr) const -> QgsGeometry
- Returns the shortest line joining this geometry to the other geometry.
- auto singleSidedBuffer(double distance, int segments, int side, int joinStyle, double miterLimit, QString* errorMsg = nullptr) const -> std::unique_ptr<QgsAbstractGeometry>
- Returns a single sided buffer for a geometry.
- auto splitGeometry(const QgsLineString& splitLine, QVector<QgsGeometry>& newGeometries, bool topological, QgsPointSequence& topologyTestPoints, QString* errorMsg = nullptr) const -> EngineOperationResult override
- Splits this geometry according to a given line.
- auto subdivide(int maxNodes, QString* errorMsg = nullptr) const -> std::unique_ptr<QgsAbstractGeometry>
- Subdivides the geometry.
- auto symDifference(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> QgsAbstractGeometry* override
- Calculate the symmetric difference of this and geom.
- auto touches(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> bool override
- Checks if geom touches this.
- auto voronoiDiagram(const QgsAbstractGeometry* extent = nullptr, double tolerance = 0.0, bool edgesOnly = false, QString* errorMsg = nullptr) const -> QgsGeometry
- Creates a Voronoi diagram for the nodes contained within the geometry.
- auto within(const QgsAbstractGeometry* geom, QString* errorMsg = nullptr) const -> bool override
- Checks if geom is within this.
Function documentation
static QgsGeometry::
Adds a new island polygon to a multipolygon feature.
| Parameters | |
|---|---|
| geometry | geometry to add part to |
| newPart | part to add. Ownership is NOT transferred. |
| Returns | OperationResult a result code: success or reason of failure |
static geos::
Returns a geos geometry - caller takes ownership of the object (should be deleted with GEOSGeom_destroy_r)
| Parameters | |
|---|---|
| geometry | geometry to convert to GEOS representation |
| precision | The precision of the grid to which to snap the geometry vertices. If 0, no snapping is performed. |
static geos::
Returns a geos geometry - caller takes ownership of the object (should be deleted with GEOSGeom_destroy_r)
| Parameters | |
|---|---|
| geometry | geometry to convert to GEOS representation |
| precision | The precision of the grid to which to snap the geometry vertices. If 0, no snapping is performed. |
static std::unique_ptr<QgsAbstractGeometry> QgsGeos::
Create a geometry from a GEOSGeometry.
| Parameters | |
|---|---|
| geos | GEOSGeometry. Ownership is NOT transferred. |
static QgsGeometry QgsGeos::
Creates a new QgsGeometry object, feeding in a geometry in GEOS format.
This class will take ownership of the buffer.
static QgsGeometry QgsGeos::
Creates a GeometryCollection geometry containing possible polygons formed from the constituent linework of a set of geometries.
The input geometries must be fully noded (i.e. nodes exist at every common intersection of the geometries). The easiest way to ensure this is to first unary union these geometries by calling combine() on the set of input geometries and then pass the result to polygonize(). An empty geometry will be returned in the case of errors.
QgsGeos::
GEOS geometry engine constructor.
| Parameters | |
|---|---|
| geometry | The geometry |
| precision | The precision of the grid to which to snap the geometry vertices. If 0, no snapping is performed. |
std::unique_ptr<QgsAbstractGeometry> QgsGeos::
Performs a fast, non-robust intersection between the geometry and a rectangle.
The returned geometry may be invalid.
QgsGeometry QgsGeos::
Returns the closest point on the geometry to the other geometry.
QgsAbstractGeometry* QgsGeos::
Calculate the combination of this and geom.
QgsAbstractGeometry* QgsGeos::
Calculate the combination of this and geometries.
QgsAbstractGeometry* QgsGeos::
Calculate the combination of this and geometries.
bool QgsGeos::
Checks if geom contains this.
bool QgsGeos::
Checks if geom crosses this.
QgsGeometry QgsGeos::
Returns the Delaunay triangulation for the vertices of the geometry.
The tolerance parameter specifies an optional snapping tolerance which can be used to improve the robustness of the triangulation. If edgesOnly is true than line string boundary geometries will be returned instead of polygons. An empty geometry will be returned if the diagram could not be calculated.
QgsAbstractGeometry* QgsGeos::
Calculate the difference of this and geom.
bool QgsGeos::
Checks if geom is disjoint from this.
double QgsGeos::
Calculates the distance between this and geom.
double QgsGeos::
Returns the Hausdorff distance between this geometry and geom.
This is basically a measure of how similar or dissimilar 2 geometries are.
This algorithm is an approximation to the standard Hausdorff distance. This approximation is exact or close enough for a large subset of useful cases. Examples of these are:
- computing distance between Linestrings that are roughly parallel to each other, and roughly equal in length. This occurs in matching linear networks.
- Testing similarity of geometries.
If the default approximate provided by this method is insufficient, use hausdorffDistanceDensify() instead.
double QgsGeos::
Returns the Hausdorff distance between this geometry and geom.
This is basically a measure of how similar or dissimilar 2 geometries are.
This function accepts a densifyFraction argument. The function performs a segment densification before computing the discrete Hausdorff distance. The densifyFraction parameter sets the fraction by which to densify each segment. Each segment will be split into a number of equal-length subsegments, whose fraction of the total length is closest to the given fraction.
This method can be used when the default approximation provided by hausdorffDistance() is not sufficient. Decreasing the densifyFraction parameter will make the distance returned approach the true Hausdorff distance for the geometries.
QgsAbstractGeometry* QgsGeos::
Calculate the intersection of this and geom.
bool QgsGeos::
Checks if geom intersects this.
bool QgsGeos::
Checks if this is equal to geom.
If both are Null geometries, false is returned.
bool QgsGeos::
Determines whether the geometry is simple (according to OGC definition).
double QgsGeos::
Returns a distance representing the location along this linestring of the closest point on this linestring geometry to the specified point.
| Parameters | |
|---|---|
| point | point to seek proximity to |
| errorMsg | error messages emitted, if any |
| Returns | distance along line, or -1 on error |
Ie, the returned value indicates how far along this linestring you need to traverse to get to the closest location where this linestring comes to the specified point.
QgsGeometry QgsGeos::
Merges any connected lines in a LineString/MultiLineString geometry and converts them to single line strings.
| Parameters | |
|---|---|
| errorMsg | if specified, will be set to any reported GEOS errors |
| Returns | a LineString or MultiLineString geometry, with any connected lines joined. An empty geometry will be returned if the input geometry was not a LineString/MultiLineString geometry. |
bool QgsGeos::
Checks if geom overlaps this.
QgsPoint* QgsGeos::
Calculate a point that is guaranteed to be on the surface of this.
May return a nullptr.
void QgsGeos::
Prepares the geometry, so that subsequent calls to spatial relation methods are much faster.
This should be called for any geometry which is used for multiple relation tests against other geometries.
QString QgsGeos::
Returns the Dimensional Extended 9 Intersection Model (DE-9IM) representation of the relationship between the geometries.
| Parameters | |
|---|---|
| geom | geometry to relate to |
| errorMsg | destination storage for any error message |
| Returns | DE-9IM string for relationship, or an empty string if an error occurred |
bool QgsGeos::
Tests whether two geometries are related by a specified Dimensional Extended 9 Intersection Model (DE-9IM) pattern.
| Parameters | |
|---|---|
| geom | geometry to relate to |
| pattern | DE-9IM pattern for match |
| errorMsg | destination storage for any error message |
| Returns | true if geometry relationship matches with pattern |
std::unique_ptr<QgsAbstractGeometry> QgsGeos::
Reshapes the geometry using a line.
| Parameters | |
|---|---|
| reshapeWithLine | the line used to reshape lines or polygons |
| errorCode | if specified, provides result of operation (success or reason of failure) |
| errorMsg | if specified, provides more details about failure |
| Returns | the reshaped geometry |
QgsGeometry QgsGeos::
Returns the shortest line joining this geometry to the other geometry.
std::unique_ptr<QgsAbstractGeometry> QgsGeos::
Returns a single sided buffer for a geometry.
| Parameters | |
|---|---|
| distance | buffer distance |
| segments | for round joins, number of segments to approximate quarter-circle |
| side | side of geometry to buffer (0 = left, 1 = right) |
| joinStyle | join style for corners ( Round (1) / Miter (2) / Bevel (3) ) |
| miterLimit | limit on the miter ratio used for very sharp corners |
| errorMsg | error messages emitted, if any |
| Returns | buffered geometry, or an nullptr if buffer could not be calculated |
The buffer is only applied to one side of the geometry.
EngineOperationResult QgsGeos::
Splits this geometry according to a given line.
| Parameters | |
|---|---|
| splitLine | the line that splits the geometry |
| newGeometries out | list of new geometries that have been created with the split |
| topological | true if topological editing is enabled |
| topologyTestPoints out | points that need to be tested for topological completeness in the dataset |
| errorMsg out | error messages emitted, if any |
| Returns | 0 in case of success, 1 if geometry has not been split, error else |
std::unique_ptr<QgsAbstractGeometry> QgsGeos::
Subdivides the geometry.
The returned geometry will be a collection containing subdivided parts from the original geometry, where no part has more then the specified maximum number of nodes (maxNodes).
This is useful for dividing a complex geometry into less complex parts, which are better able to be spatially indexed and faster to perform further operations such as intersects on. The returned geometry parts may not be valid and may contain self-intersections.
The minimum allowed value for maxNodes is 8.
Curved geometries are not supported.
QgsAbstractGeometry* QgsGeos::
Calculate the symmetric difference of this and geom.
bool QgsGeos::
Checks if geom touches this.
QgsGeometry QgsGeos::
Creates a Voronoi diagram for the nodes contained within the geometry.
Returns the Voronoi polygons for the nodes contained within the geometry. If extent is specified then it will be used as a clipping envelope for the diagram. If no extent is set then the clipping envelope will be automatically calculated. In either case the diagram will be clipped to the larger of the provided envelope OR the envelope surrounding all input nodes. The tolerance parameter specifies an optional snapping tolerance which can be used to improve the robustness of the diagram calculation. If edgesOnly is true than line string boundary geometries will be returned instead of polygons. An empty geometry will be returned if the diagram could not be calculated.
bool QgsGeos::
Checks if geom is within this.