QgsGeometryAnalyzer Class Reference

The QGis class provides vector geometry analysis functions. More...

#include <qgsgeometryanalyzer.h>

Public Member Functions
bool	simplify (QgsVectorLayer *layer, const QString &shapefileName, double tolerance, bool onlySelectedFeatures=false, QProgressDialog *p=0)
	Simplify vector layer using (a modified) Douglas-Peucker algorithm and write it to a new shape file.
bool	centroids (QgsVectorLayer *layer, const QString &shapefileName, bool onlySelectedFeatures=false, QProgressDialog *p=0)
	Calculate the true centroids, or 'center of mass' for a vector layer and write it to a new shape file.
bool	extent (QgsVectorLayer *layer, const QString &shapefileName, bool onlySelectedFeatures=false, QProgressDialog *p=0)
	Create a polygon based on the extent of all (selected) features and write it to a new shape file.
bool	buffer (QgsVectorLayer *layer, const QString &shapefileName, double bufferDistance, bool onlySelectedFeatures=false, bool dissolve=false, int bufferDistanceField=-1, QProgressDialog *p=0)
	Create buffers for a vector layer and write it to a new shape file.
bool	convexHull (QgsVectorLayer *layer, const QString &shapefileName, bool onlySelectedFeatures=false, int uniqueIdField=-1, QProgressDialog *p=0)
	Create convex hull(s) of a vector layer and write it to a new shape file.
bool	dissolve (QgsVectorLayer *layer, const QString &shapefileName, bool onlySelectedFeatures=false, int uniqueIdField=-1, QProgressDialog *p=0)
	Dissolve a vector layer and write it to a new shape file.
bool	eventLayer (QgsVectorLayer *lineLayer, QgsVectorLayer *eventLayer, int lineField, int eventField, QgsFeatureIds &unlocatedFeatureIds, const QString &outputLayer, const QString &outputFormat, int locationField1, int locationField2=-1, int offsetField=-1, double offsetScale=1.0, bool forceSingleGeometry=false, QgsVectorDataProvider *memoryProvider=0, QProgressDialog *p=0)
	Creates an event layer (multipoint or multiline) by locating features from a (non-spatial) event table along the features of a line layer.
QgsGeometry *	locateBetweenMeasures (double fromMeasure, double toMeasure, QgsGeometry *lineGeom)
	Returns linear reference geometry as a multiline (or 0 if no match).
QgsGeometry *	locateAlongMeasure (double measure, QgsGeometry *lineGeom)
	Returns linear reference geometry.

Detailed Description

The QGis class provides vector geometry analysis functions.

Member Function Documentation

bool QgsGeometryAnalyzer::buffer	(	QgsVectorLayer *	layer,
		const QString &	shapefileName,
		double	bufferDistance,
		bool	onlySelectedFeatures = false,
		bool	dissolve = false,
		int	bufferDistanceField = -1,
		QProgressDialog *	p = 0
	)

Create buffers for a vector layer and write it to a new shape file.

Parameters

layer	input vector layer
shapefileName	path to the output shp
bufferDistance	distance for buffering (if no buffer field is specified)
onlySelectedFeatures	if true, only selected features are considered, else all the features
dissolve	if true, merge all the buffers to a big multipolygon
bufferDistanceField	index of the attribute field that contains the buffer distance (or -1 if all features have the same buffer distance)
p	progress dialog (or 0 if no progress dialog is to be shown)

bool QgsGeometryAnalyzer::centroids	(	QgsVectorLayer *	layer,
		const QString &	shapefileName,
		bool	onlySelectedFeatures = false,
		QProgressDialog *	p = 0
	)

Calculate the true centroids, or 'center of mass' for a vector layer and write it to a new shape file.

Parameters

layer	input vector layer
shapefileName	path to the output shp
onlySelectedFeatures	if true, only selected features are considered, else all the features
p	progress dialog (or 0 if no progress dialog is to be shown)

bool QgsGeometryAnalyzer::convexHull	(	QgsVectorLayer *	layer,
		const QString &	shapefileName,
		bool	onlySelectedFeatures = false,
		int	uniqueIdField = -1,
		QProgressDialog *	p = 0
	)

Create convex hull(s) of a vector layer and write it to a new shape file.

Parameters

layer	input vector layer
shapefileName	path to the output shp
onlySelectedFeatures	if true, only selected features are considered, else all the features
uniqueIdField	index of the attribute field that contains the unique convex hull id (or -1 if all features have the same buffer distance)
p	progress dialog (or 0 if no progress dialog is to be shown)

bool QgsGeometryAnalyzer::dissolve	(	QgsVectorLayer *	layer,
		const QString &	shapefileName,
		bool	onlySelectedFeatures = false,
		int	uniqueIdField = -1,
		QProgressDialog *	p = 0
	)

Dissolve a vector layer and write it to a new shape file.

Parameters

layer	input vector layer
shapefileName	path to the output shp
onlySelectedFeatures	if true, only selected features are considered, else all the features
uniqueIdField	index of the attribute field that contains the unique id to dissolve on (or -1 if all features should be dissolved together)
p	progress dialog (or 0 if no progress dialog is to be shown)

bool QgsGeometryAnalyzer::eventLayer	(	QgsVectorLayer *	lineLayer,
		QgsVectorLayer *	eventLayer,
		int	lineField,
		int	eventField,
		QgsFeatureIds &	unlocatedFeatureIds,
		const QString &	outputLayer,
		const QString &	outputFormat,
		int	locationField1,
		int	locationField2 = -1,
		int	offsetField = -1,
		double	offsetScale = 1.0,
		bool	forceSingleGeometry = false,
		QgsVectorDataProvider *	memoryProvider = 0,
		QProgressDialog *	p = 0
	)

Creates an event layer (multipoint or multiline) by locating features from a (non-spatial) event table along the features of a line layer.

Note that currently (until QgsGeometry supports m-values) the z-coordinate of the line layer is used for linear referencing

Parameters

lineLayer	layer with the line geometry
eventLayer	layer with features and location field
lineField	join index in line layer
eventField	join index in event layer
outputLayer	name of output file (can be empty if a memory layer is used)
outputFormat	name of output format (can be empty if a memory provider is used to store the results)
unlocatedFeatureIds	out: ids of event features where linear referencing was not successful
locationField1	attribute index of location field in event layer
locationField2	attribute index of location end field (or -1 for point layer)
offsetField	attribute index for offset field. Negative offset value = offset to left side, positive value = offset to right side
offsetScale	factor to scale offset
forceSingleGeometry	force layer to single point/line type. Feature attributes are copied in case of multiple matches
memoryProvider	memory provider to write output to (can be 0 if output is written to a file)
p	progress dialog or 0 if no progress dialog should be shown

bool QgsGeometryAnalyzer::extent	(	QgsVectorLayer *	layer,
		const QString &	shapefileName,
		bool	onlySelectedFeatures = false,
		QProgressDialog *	p = 0
	)

Create a polygon based on the extent of all (selected) features and write it to a new shape file.

Parameters

layer	input vector layer
shapefileName	path to the output shp
onlySelectedFeatures	if true, only selected features are considered, else all the features
p	progress dialog (or 0 if no progress dialog is to be shown)

QgsGeometry * QgsGeometryAnalyzer::locateAlongMeasure	(	double	measure,
		QgsGeometry *	lineGeom
	)

Returns linear reference geometry.

Unlike the PostGIS function, this method always returns multipoint or 0 if no match (not geometry collection). Currently, the z-coordinates are considered to be the measures (no support for m-values in QGIS)

QgsGeometry * QgsGeometryAnalyzer::locateBetweenMeasures	(	double	fromMeasure,
		double	toMeasure,
		QgsGeometry *	lineGeom
	)

Returns linear reference geometry as a multiline (or 0 if no match).

Currently, the z-coordinates are considered to be the measures (no support for m-values in QGIS)

bool QgsGeometryAnalyzer::simplify	(	QgsVectorLayer *	layer,
		const QString &	shapefileName,
		double	tolerance,
		bool	onlySelectedFeatures = false,
		QProgressDialog *	p = 0
	)

Simplify vector layer using (a modified) Douglas-Peucker algorithm and write it to a new shape file.

Parameters

layer	input vector layer
shapefileName	path to the output shp
tolerance	(level of simplification)
onlySelectedFeatures	if true, only selected features are considered, else all the features
p	progress dialog (or 0 if no progress dialog is to be shown)

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The documentation for this class was generated from the following files:

• /tmp/buildd/qgis-2.6.0+wheezy1/src/analysis/vector/qgsgeometryanalyzer.h
• /tmp/buildd/qgis-2.6.0+wheezy1/src/analysis/vector/qgsgeometryanalyzer.cpp