Class: QgsSizeScaleTransformer

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

Class Hierarchy

Inheritance diagram of qgis.core.QgsSizeScaleTransformer

Base classes

QgsPropertyTransformer

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

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[source]

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[source]

Returns the exponent for an exponential expression.

See also

setExponent()

See also

type()

Return type:

float

static fromExpression(expression: str | None)[source]

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[source]

Returns the maximum calculated size.

See also

minSize()

Return type:

float

minSize(self) float[source]

Returns the minimum calculated size.

See also

setMinSize()

See also

maxSize()

Return type:

float

nullSize(self) float[source]

Returns the size value when an expression evaluates to NULL.

See also

setNullSize()

Return type:

float

setExponent(self, exponent: float)[source]

Sets the exponent for an exponential expression.

Parameters:

exponent (float) – exponent

See also

exponent()

setMaxSize(self, size: float)[source]

Sets the maximum calculated size.

Parameters:

size (float) – maximum size

See also

maxSize()

See also

setMinSize()

setMinSize(self, size: float)[source]

Sets the minimum calculated size.

Parameters:

size (float) – minimum size

See also

minSize()

See also

setMaxSize()

setNullSize(self, size: float)[source]

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

Parameters:

size (float) – null size

See also

nullSize()

setType(self, type: QgsSizeScaleTransformer.ScaleType)[source]

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[source]

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[source]

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

See also

setType()

Return type:

QgsSizeScaleTransformer.ScaleType