---
name: "QwtTransform"
section: "3"
platform: "linux"
package: "libqwt-doc"
version: "6.1.4-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/QwtTransform"
---

# QwtTransform(3)

A transformation between coordinate systems.

## NAME

QwtTransform - 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

**See also:**

**transform()**

Implemented in **QwtPowerTransform**, **QwtLogTransform**, and **QwtNullTransform**.

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

Transformation function

**Parameters:**

*value* Value

**Returns:**

Modified value

**See also:**

**invTransform()**

Implemented in **QwtPowerTransform**, **QwtLogTransform**, and **QwtNullTransform**.

## Author

Generated automatically by Doxygen for Qwt User's Guide from the source code.