# QwtTransform - Man Page

A transformation between coordinate systems.

## Synopsis

`#include <qwt_transform.h>`

Inherited by QwtLogTransform, QwtNullTransform, and QwtPowerTransform.

### Public Member Functions

QwtTransform ()
Constructor.
virtual ~QwtTransform ()
Destructor.
virtual double bounded (double value) const
virtual double transform (double value) const =0
virtual double invTransform (double value) const =0
virtual QwtTransform * copy () const =0
Virtualized copy operation.

## Detailed Description

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 ) );

## Member Function Documentation

### double QwtTransform::bounded (double value) const [virtual]

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

Parameters

value Value to be bounded

Returns

value unmodified

Reimplemented in QwtLogTransform.

### virtual double QwtTransform::invTransform (double value) const [pure virtual]

Inverse transformation function

Parameters

value Value

Returns

Modified value

transform()

Implemented in QwtPowerTransform, QwtLogTransform, and QwtNullTransform.

### virtual double QwtTransform::transform (double value) const [pure virtual]

Transformation function

Parameters

value Value

Returns

Modified value