Source code for qwt.transform
# -*- coding: utf-8 -*-
#
# Licensed under the terms of the Qwt License
# Copyright (c) 2002 Uwe Rathmann, for the original C++ code
# Copyright (c) 2015 Pierre Raybaut, for the Python translation/optimization
# (see LICENSE file for more details)
"""
Coordinate tranformations
-------------------------
QwtTransform
~~~~~~~~~~~~
.. autoclass:: QwtTransform
:members:
QwtNullTransform
~~~~~~~~~~~~~~~~
.. autoclass:: QwtNullTransform
:members:
QwtLogTransform
~~~~~~~~~~~~~~~
.. autoclass:: QwtLogTransform
:members:
QwtPowerTransform
~~~~~~~~~~~~~~~~~
.. autoclass:: QwtPowerTransform
:members:
"""
import numpy as np
[docs]
class QwtTransform(object):
"""
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) )
"""
def __init__(self):
pass
[docs]
def bounded(self, value):
"""
Modify value to be a valid value for the transformation.
The default implementation does nothing.
"""
return value
[docs]
def transform(self, value):
"""
Transformation function
:param float value: Value
:return: Modified value
.. seealso::
:py:meth:`invTransform()`
"""
raise NotImplementedError
[docs]
def invTransform(self, value):
"""
Inverse transformation function
:param float value: Value
:return: Modified value
.. seealso::
:py:meth:`transform()`
"""
raise NotImplementedError
[docs]
def copy(self):
"""
:return: Clone of the transformation
The default implementation does nothing.
"""
raise NotImplementedError
[docs]
class QwtNullTransform(QwtTransform):
[docs]
def transform(self, value):
"""
Transformation function
:param float value: Value
:return: Modified value
.. seealso::
:py:meth:`invTransform()`
"""
return value
[docs]
def invTransform(self, value):
"""
Inverse transformation function
:param float value: Value
:return: Modified value
.. seealso::
:py:meth:`transform()`
"""
return value
[docs]
class QwtLogTransform(QwtTransform):
"""
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
"""
LogMin = 1.0e-150
LogMax = 1.0e150
[docs]
def bounded(self, value):
"""
Modify value to be a valid value for the transformation.
:param float value: Value to be bounded
:return: Value modified
"""
return np.clip(value, self.LogMin, self.LogMax)
[docs]
def transform(self, value):
"""
Transformation function
:param float value: Value
:return: Modified value
.. seealso::
:py:meth:`invTransform()`
"""
return np.log(self.bounded(value))
[docs]
def invTransform(self, value):
"""
Inverse transformation function
:param float value: Value
:return: Modified value
.. seealso::
:py:meth:`transform()`
"""
return np.exp(value)
[docs]
class QwtPowerTransform(QwtTransform):
"""
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.
"""
def __init__(self, exponent):
self.__exponent = exponent
super(QwtPowerTransform, self).__init__()
[docs]
def transform(self, value):
"""
Transformation function
:param float value: Value
:return: Modified value
.. seealso::
:py:meth:`invTransform()`
"""
if value < 0.0:
return -np.pow(-value, 1.0 / self.__exponent)
else:
return np.pow(value, 1.0 / self.__exponent)
[docs]
def invTransform(self, value):
"""
Inverse transformation function
:param float value: Value
:return: Modified value
.. seealso::
:py:meth:`transform()`
"""
if value < 0.0:
return -np.pow(-value, self.__exponent)
else:
return np.pow(value, self.__exponent)
[docs]
def copy(self):
"""
:return: Clone of the transformation
"""
return QwtPowerTransform(self.__exponent)
