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

# QwtLogTransform(3)

Logarithmic transformation.

## NAME

QwtLogTransform - Logarithmic transformation.

## SYNOPSIS

`#include <qwt_transform.h>`

Inherits **QwtTransform**.

### Public Member Functions

**QwtLogTransform** ()\
 Constructor.  virtual **~QwtLogTransform** ()\
 Destructor.  virtual double **transform** (double value) const\
 virtual double **invTransform** (double value) const\
 virtual double **bounded** (double value) const\
 virtual **QwtTransform** \* **copy** () const\

### Public Attributes

QT\_STATIC\_CONST double **LogMin** = 1.0e-150\
 Smallest allowed value for logarithmic scales: 1.0e-150.  QT\_STATIC\_CONST double **LogMax** = 1.0e150\
 Largest allowed value for logarithmic scales: 1.0e150.

## Detailed Description

Logarithmic transformation.

**QwtLogTransform** modifies the values using log() and 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 log2(), log10() or any other logarithmic scale.

## Member Function Documentation

### double QwtLogTransform::bounded (double value) const` [virtual]`

**Parameters:**

*value* Value to be bounded

**Returns:**

qBound( LogMin, value, LogMax )

Reimplemented from **QwtTransform**.

### QwtTransform \* QwtLogTransform::copy () const` [virtual]`

**Returns:**

Clone of the transformation

Implements **QwtTransform**.

### double QwtLogTransform::invTransform (double value) const` [virtual]`

**Parameters:**

*value* Value to be transformed

**Returns:**

exp( value )

Implements **QwtTransform**.

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

**Parameters:**

*value* Value to be transformed

**Returns:**

log( value )

Implements **QwtTransform**.

## Author

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