# Coordinate tranformations

## QwtTransform

class `qwt.transform.``QwtTransform`

  A transformation between coordinate systems

  QwtTransform manipulates values, when being mapped between the scale and the paint device coordinate system.

  A transformation consists of 2 methods:

  > - transform
  > - invTransform

  where one is is the inverse function of the other.

  When p1, p2 are the boundaries of the paint device coordinates and s1, s2 the boundaries of the scale, QwtScaleMap uses the following calculations:

      p = p1 + (p2 - p1) * ( T(s) - T(s1) / (T(s2) - T(s1)) )
      s = invT( T(s1) + ( T(s2) - T(s1) ) * (p - p1) / (p2 - p1) )

  `bounded`(value)

    Modify value to be a valid value for the transformation. The default implementation does nothing.

  `transform`(value)

    Transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `invTransform()`

  `invTransform`(value)

    Inverse transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `transform()`

  `copy`()

    Returns: | Clone of the transformation

    The default implementation does nothing.

## QwtNullTransform

class `qwt.transform.``QwtNullTransform`
  `transform`(value)

    Transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `invTransform()`

  `invTransform`(value)

    Inverse transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `transform()`

  `copy`()

    Returns: | Clone of the transformation

## QwtLogTransform

class `qwt.transform.``QwtLogTransform`

  Logarithmic transformation

  QwtLogTransform modifies the values using numpy.log() and numpy.exp().

  Note

  In the calculations of QwtScaleMap the base of the log function has no effect on the mapping. So QwtLogTransform can be used for logarithmic scale in base 2 or base 10 or any other base.

  Extremum values:

  > - QwtLogTransform.LogMin: Smallest allowed value for logarithmic scales: 1.0e-150
  > - QwtLogTransform.LogMax: Largest allowed value for logarithmic scales: 1.0e150

  `bounded`(value)

    Modify value to be a valid value for the transformation.

    Parameters: | value (float) – Value to be bounded
    Returns: | Value modified

  `transform`(value)

    Transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `invTransform()`

  `invTransform`(value)

    Inverse transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `transform()`

  `copy`()

    Returns: | Clone of the transformation

## QwtPowerTransform

class `qwt.transform.``QwtPowerTransform`(exponent)

  A transformation using numpy.pow()

  QwtPowerTransform preserves the sign of a value. F.e. a transformation with a factor of 2 transforms a value of -3 to -9 and v.v. Thus QwtPowerTransform can be used for scales including negative values.

  `transform`(value)

    Transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `invTransform()`

  `invTransform`(value)

    Inverse transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `transform()`

  `copy`()

    Returns: | Clone of the transformation

class `qwt.transform.``QwtTransform`

  A transformation between coordinate systems

  QwtTransform manipulates values, when being mapped between the scale and the paint device coordinate system.

  A transformation consists of 2 methods:

  > - transform
  > - invTransform

  where one is is the inverse function of the other.

  When p1, p2 are the boundaries of the paint device coordinates and s1, s2 the boundaries of the scale, QwtScaleMap uses the following calculations:

      p = p1 + (p2 - p1) * ( T(s) - T(s1) / (T(s2) - T(s1)) )
      s = invT( T(s1) + ( T(s2) - T(s1) ) * (p - p1) / (p2 - p1) )

  `bounded`(value)

    Modify value to be a valid value for the transformation. The default implementation does nothing.

  `transform`(value)

    Transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `invTransform()`

  `invTransform`(value)

    Inverse transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `transform()`

  `copy`()

    Returns: | Clone of the transformation

    The default implementation does nothing.

class `qwt.transform.``QwtLogTransform`

  Logarithmic transformation

  QwtLogTransform modifies the values using numpy.log() and numpy.exp().

  Note

  In the calculations of QwtScaleMap the base of the log function has no effect on the mapping. So QwtLogTransform can be used for logarithmic scale in base 2 or base 10 or any other base.

  Extremum values:

  > - QwtLogTransform.LogMin: Smallest allowed value for logarithmic scales: 1.0e-150
  > - QwtLogTransform.LogMax: Largest allowed value for logarithmic scales: 1.0e150

  `bounded`(value)

    Modify value to be a valid value for the transformation.

    Parameters: | value (float) – Value to be bounded
    Returns: | Value modified

  `transform`(value)

    Transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `invTransform()`

  `invTransform`(value)

    Inverse transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `transform()`

  `copy`()

    Returns: | Clone of the transformation

class `qwt.transform.``QwtPowerTransform`(exponent)

  A transformation using numpy.pow()

  QwtPowerTransform preserves the sign of a value. F.e. a transformation with a factor of 2 transforms a value of -3 to -9 and v.v. Thus QwtPowerTransform can be used for scales including negative values.

  `transform`(value)

    Transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `invTransform()`

  `invTransform`(value)

    Inverse transformation function

    Parameters: | value (float) – Value
    Returns: | Modified value

    See also

    `transform()`

  `copy`()

    Returns: | Clone of the transformation