QgsCoordinateTransformContext class

Contains information about the context in which a coordinate transform is executed.

Reference
- Constructors, destructors, conversion operators
- Public functions

The context stores various information regarding which coordinate transforms should be used when transforming points from a source to destination coordinate reference system.

The highest priority transforms are those set using addSourceDestinationDatumTransform() and which the transform has a matching source to destination CRS pair.

Failing this, if the source CRS has a matching transform specified by addSourceDatumTransform() then this datum transform will be used. The same logic applies for destination CRS transforms set using addDestinationDatumTransform().

Constructors, destructors, conversion operators

QgsCoordinateTransformContext(): Constructor for QgsCoordinateTransformContext.
QgsCoordinateTransformContext(const QgsCoordinateTransformContext& rhs): Copy constructor.

Public functions

auto addSourceDestinationDatumTransform(const QgsCoordinateReferenceSystem& sourceCrs, const QgsCoordinateReferenceSystem& destinationCrs, int sourceTransformId, int destinationTransformId) -> bool: Adds a new sourceTransform and destinationTransform to use when projecting coordinates from the specified sourceCrs to the specified destinationCrs.
auto calculateDatumTransforms(const QgsCoordinateReferenceSystem& source, const QgsCoordinateReferenceSystem& destination) const -> QgsDatumTransform::TransformPair: Returns the pair of source and destination datum transforms to use for a transform from the specified source CRS to destination CRS.
void clear(): Clears all stored transform information from the context.
auto hasTransform(const QgsCoordinateReferenceSystem& source, const QgsCoordinateReferenceSystem& destination) const -> bool: Returns true if the context has a valid datum transform to use when transforming from the specified source CRS to destination CRS.
auto operator=(const QgsCoordinateTransformContext& rhs) -> QgsCoordinateTransformContext&: Assignment operator.
void readSettings(): Reads the context's state from application settings.
auto readXml(const QDomElement& element, const QgsReadWriteContext& context, QStringList& missingTransforms) -> bool: Reads the context's state from a DOM element.
void removeSourceDestinationDatumTransform(const QgsCoordinateReferenceSystem& sourceCrs, const QgsCoordinateReferenceSystem& destinationCrs): Removes the source to destination datum transform pair for the specified sourceCrs and destinationCrs.
auto sourceDestinationDatumTransforms() const -> QMap<QPair<QString, QString>, QgsDatumTransform::TransformPair>: Returns the stored mapping for source to destination CRS pairs to associated datum transforms to use.
void writeSettings(): Write the context's state to application settings.
void writeXml(QDomElement& element, const QgsReadWriteContext& context) const: Writes the context's state to a DOM element.

Function documentation

bool QgsCoordinateTransformContext::addSourceDestinationDatumTransform(const QgsCoordinateReferenceSystem& sourceCrs, const QgsCoordinateReferenceSystem& destinationCrs, int sourceTransformId, int destinationTransformId)

Adds a new sourceTransform and destinationTransform to use when projecting coordinates from the specified sourceCrs to the specified destinationCrs.

If either sourceTransformId or destinationTransformId is -1, then no datum transform is required for transformations for that source or destination.

Returns true if the new transform pair was added successfully.

QgsDatumTransform::TransformPair QgsCoordinateTransformContext::calculateDatumTransforms(const QgsCoordinateReferenceSystem& source, const QgsCoordinateReferenceSystem& destination) const

Returns the pair of source and destination datum transforms to use for a transform from the specified source CRS to destination CRS.

Returns an ID of -1 if a datum transform should not be used for the source or destination.

bool QgsCoordinateTransformContext::hasTransform(const QgsCoordinateReferenceSystem& source, const QgsCoordinateReferenceSystem& destination) const

Returns true if the context has a valid datum transform to use when transforming from the specified source CRS to destination CRS.

void QgsCoordinateTransformContext::readSettings()

Reads the context's state from application settings.

bool QgsCoordinateTransformContext::readXml(const QDomElement& element, const QgsReadWriteContext& context, QStringList& missingTransforms)

Reads the context's state from a DOM element.

Returns false if transforms stored in the XML are not available. In this case missingTransforms will be filled with missing datum transform strings.

void QgsCoordinateTransformContext::removeSourceDestinationDatumTransform(const QgsCoordinateReferenceSystem& sourceCrs, const QgsCoordinateReferenceSystem& destinationCrs)

Removes the source to destination datum transform pair for the specified sourceCrs and destinationCrs.

QMap<QPair<QString, QString>, QgsDatumTransform::TransformPair> QgsCoordinateTransformContext::sourceDestinationDatumTransforms() const

Returns the stored mapping for source to destination CRS pairs to associated datum transforms to use.

The map keys will be QgsCoordinateReferenceSystems::authid()s.

If either the source transform ID or destination transform ID is -1, then no datum transform is required for transformations for that source or destination.

void QgsCoordinateTransformContext::writeSettings()

Write the context's state to application settings.

void QgsCoordinateTransformContext::writeXml(QDomElement& element, const QgsReadWriteContext& context) const

Writes the context's state to a DOM element.