Class: QgsSizeScaleTransformer

class qgis.core.QgsSizeScaleTransformer

Bases: QgsPropertyTransformer

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

QgsSizeScaleTransformer(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 – scaling type

  • minValue – minimum expected value

  • maxValue – maximum expected value

  • minSize – minimum size to return

  • maxSize – maximum size to return

  • nullSize – size to return for null values

  • exponent – exponent for Exponential scaling method

QgsSizeScaleTransformer(a0: QgsSizeScaleTransformer)

Methods

clone

rtype:

Optional[QgsSizeScaleTransformer]

exponent

Returns the exponent for an exponential expression.

fromExpression

Attempts to parse an expression into a corresponding QgsSizeScaleTransformer.

loadVariant

param definition:

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.

toExpression

param baseExpression:

toVariant

rtype:

Any

transform

param context:

transformNumeric

Applies base class numeric transformations.

transformerType

rtype:

QgsPropertyTransformer.Type

type

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

Attributes

Area

Exponential

Flannery

Linear

Area = 1
Exponential = 3
Flannery = 2
Linear = 0
class ScaleType

Bases: int

clone(self) QgsSizeScaleTransformer | None
Return type:

Optional[QgsSizeScaleTransformer]

exponent(self) float

Returns the exponent for an exponential expression.

See also

setExponent()

See also

type()

Return type:

float

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

  • 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.

be parsed to a size scale transformer.

loadVariant(self, definition: Any) bool
Parameters:

definition (Any)

Return type:

bool

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

toExpression(self, baseExpression: str | None) str
Parameters:

baseExpression (Optional[str])

Return type:

str

toVariant(self) Any
Return type:

Any

transform(self, context: QgsExpressionContext, value: Any) Any
Parameters:
Return type:

Any

transformNumeric(self, input: float) float

Applies base class numeric transformations. Derived classes should call this to transform an input numeric value before they apply any transform to the result. This applies any curve transforms which may exist on the transformer.

transformerType(self) QgsPropertyTransformer.Type
Return type:

QgsPropertyTransformer.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