Class: QgsSizeScaleTransformer

QgsPropertyTransformer subclass for scaling a value into a size according to various scaling methods.

Class Hierarchy

Base classes

QgsPropertyTransformer

Abstract base class for objects which transform the calculated value of a property. Possible uses include transformers which map a value into a scaled size or color from a gradient.

Methods

exponent	Returns the exponent for an exponential expression.
maxSize	Returns the maximum calculated size.
minSize	Returns the minimum calculated size.
nullSize	Returns the size value when an expression evaluates to NULL.
setExponent	Sets the exponent for an exponential expression.
setMaxSize	Sets the maximum calculated size.
setMinSize	Sets the minimum calculated size.
setNullSize	Sets the size value for when an expression evaluates to NULL.
setType	Sets the size transformer's scaling type (the method used to calculate the size from a value).
size	Calculates the size corresponding to a specific value.
type	Returns the size transformer's scaling type (the method used to calculate the size from a value).

Static Methods

fromExpression

Attempts to parse an expression into a corresponding QgsSizeScaleTransformer.

Attributes

Area
Exponential
Flannery
Linear

class qgis.core.QgsSizeScaleTransformer

Bases: QgsPropertyTransformer

__init__(type: QgsSizeScaleTransformer.ScaleType = QgsSizeScaleTransformer.Linear, minValue: float = 0, maxValue: float = 1, minSize: float = 0, maxSize: float = 1, nullSize: float = 0, exponent: float = 1)

Constructor for QgsSizeScaleTransformer.

Parameters:

• type (QgsSizeScaleTransformer.ScaleType = QgsSizeScaleTransformer.Linear) – scaling type

• minValue (float = 0) – minimum expected value

• maxValue (float = 1) – maximum expected value

• minSize (float = 0) – minimum size to return

• maxSize (float = 1) – maximum size to return

• nullSize (float = 0) – size to return for null values

• exponent (float = 1) – exponent for Exponential scaling method

__init__(a0: QgsSizeScaleTransformer)

Parameters:

a0 (QgsSizeScaleTransformer)

Area = 1

Exponential = 3

Flannery = 2

Linear = 0

class ScaleType

Bases: int

exponent(self) → float

Returns the exponent for an exponential expression.

See also

setExponent()

See also

type()

Return type:

float

static fromExpression(expression: str | None)

Attempts to parse an expression into a corresponding QgsSizeScaleTransformer.

Parameters:

expression (Optional[str]) -> (Optional[QgsSizeScaleTransformer]) – expression to parse

Returns:

• corresponding QgsSizeScaleTransformer, or None if expression could not be parsed to a size scale transformer.

• baseExpression: the component of the source expression which is used to calculate the input to the property transformer. This an empty string if a field reference is the transformer input.

• fieldName: a field name which is used to calculate the input to the property transformer. This an empty string if an expression is the transformer input.

maxSize(self) → float

Returns the maximum calculated size.

See also

minSize()

Return type:

float

minSize(self) → float

Returns the minimum calculated size.

See also

setMinSize()

See also

maxSize()

Return type:

float

nullSize(self) → float

Returns the size value when an expression evaluates to NULL.

See also

setNullSize()

Return type:

float

setExponent(self, exponent: float)

Sets the exponent for an exponential expression.

Parameters:

exponent (float) – exponent

See also

exponent()

setMaxSize(self, size: float)

Sets the maximum calculated size.

Parameters:

size (float) – maximum size

See also

maxSize()

See also

setMinSize()

setMinSize(self, size: float)

Sets the minimum calculated size.

Parameters:

size (float) – minimum size

See also

minSize()

See also

setMaxSize()

setNullSize(self, size: float)

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

Parameters:

size (float) – null size

See also

nullSize()

setType(self, type: QgsSizeScaleTransformer.ScaleType)

Sets the size transformer’s scaling type (the method used to calculate the size from a value).

Parameters:

type (QgsSizeScaleTransformer.ScaleType) – scale type

See also

type()

size(self, value: float) → float

Calculates the size corresponding to a specific value.

Parameters:

value (float) – value to calculate size for

Return type:

float

Returns:

calculated size using size scale transformer’s parameters and type

type(self) → QgsSizeScaleTransformer.ScaleType

Returns the size transformer’s scaling type (the method used to calculate the size from a value).

See also

setType()

Return type:

QgsSizeScaleTransformer.ScaleType