QwtRasterData (3) - Linux Man Pages


QwtRasterData -

QwtRasterData defines an interface to any type of raster data.


#include <qwt_raster_data.h>

Inherited by QwtMatrixRasterData.

Public Types

enum ConrecFlag { IgnoreAllVerticesOnLevel = 0x01, IgnoreOutOfRange = 0x02 }
Flags to modify the contour algorithm.
typedef QMap< double, QPolygonF > ContourLines
Contour lines.
typedef QFlags< ConrecFlag > ConrecFlags
Flags to modify the contour algorithm.

Public Member Functions

QwtRasterData ()
virtual ~QwtRasterData ()
virtual void setInterval (Qt::Axis, const QwtInterval &)

const QwtInterval & interval (Qt::Axis) const

virtual QRectF pixelHint (const QRectF &) const
Pixel hint.
virtual void initRaster (const QRectF &, const QSize &raster)
Initialize a raster.
virtual void discardRaster ()
Discard a raster.
virtual double value (double x, double y) const =0

virtual ContourLines contourLines (const QRectF &rect, const QSize &raster, const QList< double > &levels, ConrecFlags) const

Detailed Description

QwtRasterData defines an interface to any type of raster data.

QwtRasterData is an abstract interface, that is used by QwtPlotRasterItem to find the values at the pixels of its raster.

Often a raster item is used to display values from a matrix. Then the derived raster data class needs to implement some sort of resampling, that maps the raster of the matrix into the requested raster of the raster item ( depending on resolution and scales of the canvas ).

Member Enumeration Documentation

enum QwtRasterData::ConrecFlag

Flags to modify the contour algorithm.


Ignore all vertices on the same level.
Ignore all values, that are out of range.

Member Function Documentation

QwtRasterData::ContourLines QwtRasterData::contourLines (const QRectF &rect, const QSize &raster, const QList< double > &levels, ConrecFlagsflags) const [virtual]

Calculate contour lines


rect Bounding rectangle for the contour lines
raster Number of data pixels of the raster data
levels List of limits, where to insert contour lines
flags Flags to customize the contouring algorithm


Calculated contour lines

An adaption of CONREC, a simple contouring algorithm. http://local.wasp.uwa.edu.au/~pbourke/papers/conrec/

void QwtRasterData::discardRaster () [virtual]

Discard a raster. After the composition of an image QwtPlotSpectrogram calls discardRaster().

The default implementation does nothing, but if data has been loaded in initRaster(), it could deleted now.

See Also:

initRaster(), value()

void QwtRasterData::initRaster (const QRectF &area, const QSize &raster) [virtual]

Initialize a raster. Before the composition of an image QwtPlotSpectrogram calls initRaster(), announcing the area and its resolution that will be requested.

The default implementation does nothing, but for data sets that are stored in files, it might be good idea to reimplement initRaster(), where the data is resampled and loaded into memory.


area Area of the raster
raster Number of horizontal and vertical pixels

See Also:

initRaster(), value()

const QwtInterval & QwtRasterData::interval (Qt::Axisaxis) const [inline]


Bounding interval for a axis

See Also:


QRectF QwtRasterData::pixelHint (const QRectF &area) const [virtual]

Pixel hint. pixelHint() returns the geometry of a pixel, that can be used to calculate the resolution and alignment of the plot item, that is representing the data.

Width and height of the hint need to be the horizontal and vertical distances between 2 neighbored points. The center of the hint has to be the position of any point ( it doesn't matter which one ).

An empty hint indicates, that there are values for any detail level.

Limiting the resolution of the image might significantly improve the performance and heavily reduce the amount of memory when rendering a QImage from the raster data.

The default implementation returns an empty rectangle recommending to render in target device ( f.e. screen ) resolution.


area In most implementations the resolution of the data doesn't depend on the requested area.


Bounding rectangle of a pixel

Reimplemented in QwtMatrixRasterData.

void QwtRasterData::setInterval (Qt::Axisaxis, const QwtInterval &interval) [virtual]

Set the bounding interval for the x, y or z coordinates.


axis Axis
interval Bounding interval

See Also:


Reimplemented in QwtMatrixRasterData.

virtual double QwtRasterData::value (doublex, doubley) const [pure virtual]


the value at a raster position


x X value in plot coordinates
y Y value in plot coordinates

Implemented in QwtMatrixRasterData.


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