QgsGenericNumericTransformer class

QgsPropertyTransformer subclass for scaling an input numeric value into an output numeric value.

Reference

Base classes

class QgsPropertyTransformer: Abstract base class for objects which transform the calculated value of a property.

Public static functions

static auto fromExpression(const QString& expression, QString& baseExpression, QString& fieldName) -> QgsGenericNumericTransformer*: Attempts to parse an expression into a corresponding QgsSizeScaleTransformer.

Constructors, destructors, conversion operators

QgsGenericNumericTransformer(double minValue = 0.0, double maxValue = 1.0, double minOutput = 0.0, double maxOutput = 1.0, double nullOutput = 0.0, double exponent = 1.0): Constructor for QgsGenericNumericTransformer.

Public functions

auto clone() const -> QgsGenericNumericTransformer* override: Returns a clone of the transformer.
auto exponent() const -> double: Returns the exponent for an exponential expression.
auto loadVariant(const QVariant& transformer) -> bool override: Loads this transformer from a QVariantMap, wrapped in a QVariant.
auto maxOutputValue() const -> double: Returns the maximum calculated size.
auto minOutputValue() const -> double: Returns the minimum calculated size.
auto nullOutputValue() const -> double: Returns the size value when an expression evaluates to NULL.
void setExponent(double exponent): Sets the exponent for an exponential expression.
void setMaxOutputValue(double size): Sets the maximum calculated size.
void setMinOutputValue(double size): Sets the minimum calculated size.
void setNullOutputValue(double size): Sets the size value for when an expression evaluates to NULL.
auto toExpression(const QString& baseExpression) const -> QString override: Converts the transformer to a QGIS expression string.
auto toVariant() const -> QVariant override: Saves this transformer to a QVariantMap, wrapped in a QVariant.
auto transform(const QgsExpressionContext& context, const QVariant& value) const -> QVariant override: Calculates the transform of a value.
auto transformerType() const -> Type override: Returns the transformer type.
auto value(double input) const -> double: Calculates the size corresponding to a specific input value.

Function documentation

static QgsGenericNumericTransformer* QgsGenericNumericTransformer::fromExpression(const QString& expression, QString& baseExpression, QString& fieldName)

Attempts to parse an expression into a corresponding QgsSizeScaleTransformer.

Parameters
expression	expression to parse
baseExpression	will be set to the component of the source expression which is used to calculate the input to the property transformer. This will be set to an empty string if a field reference is the transformer input.
fieldName	will be set to a field name which is used to calculate the input to the property transformer. This will be set to an empty string if an expression is the transformer input.
Returns	corresponding QgsSizeScaleTransformer, or nullptr if expression could not be parsed to a size scale transformer.

QgsGenericNumericTransformer::QgsGenericNumericTransformer(double minValue = 0.0, double maxValue = 1.0, double minOutput = 0.0, double maxOutput = 1.0, double nullOutput = 0.0, double exponent = 1.0)

Constructor for QgsGenericNumericTransformer.

Parameters
minValue	minimum expected input value
maxValue	maximum expected input value
minOutput	minimum value to return
maxOutput	maximum value to return
nullOutput	value to return for null inputs
exponent	optional exponential for non-linear scaling

double QgsGenericNumericTransformer::exponent() const

Returns the exponent for an exponential expression.

bool QgsGenericNumericTransformer::loadVariant(const QVariant& transformer) override

Loads this transformer from a QVariantMap, wrapped in a QVariant.

You can use QgsXmlUtils::readVariant to read it from an XML document.

double QgsGenericNumericTransformer::maxOutputValue() const

Returns the maximum calculated size.

double QgsGenericNumericTransformer::minOutputValue() const

Returns the minimum calculated size.

double QgsGenericNumericTransformer::nullOutputValue() const

Returns the size value when an expression evaluates to NULL.

void QgsGenericNumericTransformer::setExponent(double exponent)

Sets the exponent for an exponential expression.

Parameters
exponent	exponent

void QgsGenericNumericTransformer::setMaxOutputValue(double size)

Sets the maximum calculated size.

Parameters
size	maximum size

void QgsGenericNumericTransformer::setMinOutputValue(double size)

Sets the minimum calculated size.

Parameters
size	minimum size

void QgsGenericNumericTransformer::setNullOutputValue(double size)

Sets the size value for when an expression evaluates to NULL.

Parameters
size	null size

QString QgsGenericNumericTransformer::toExpression(const QString& baseExpression) const override

Converts the transformer to a QGIS expression string.

The baseExpression string consists of a sub-expression reflecting the parent property's state.

QVariant QgsGenericNumericTransformer::toVariant() const override

Saves this transformer to a QVariantMap, wrapped in a QVariant.

You can use QgsXmlUtils::writeVariant to save it to an XML document.

QVariant QgsGenericNumericTransformer::transform(const QgsExpressionContext& context, const QVariant& value) const override

Calculates the transform of a value.

Parameters
context	expression context
value	input value to transform

Derived classes must implement this to perform their transformations on input values

double QgsGenericNumericTransformer::value(double input) const

Calculates the size corresponding to a specific input value.

Returns	calculated size using size scale transformer's parameters and type