Qwt User's Guide  6.1.2
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QwtRasterData Class Referenceabstract

QwtRasterData defines an interface to any type of raster data. More...

#include <qwt_raster_data.h>

Inheritance diagram for QwtRasterData:
Inheritance graph

Public Types

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

Public Member Functions

 QwtRasterData ()
virtual ~QwtRasterData ()
virtual void setInterval (Qt::Axis, const QwtInterval &)
const QwtIntervalinterval (Qt::Axis) const
virtual QRectF pixelHint (const QRectF &) const
 Pixel hint. More...
virtual void initRaster (const QRectF &, const QSize &raster)
 Initialize a raster. More...
virtual void discardRaster ()
 Discard a raster. More...
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

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,
ConrecFlags  flags 
) const

Calculate contour lines

rectBounding rectangle for the contour lines
rasterNumber of data pixels of the raster data
levelsList of limits, where to insert contour lines
flagsFlags 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 ( )

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 

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.

areaArea of the raster
rasterNumber of horizontal and vertical pixels
See Also
initRaster(), value()
const QwtInterval & QwtRasterData::interval ( Qt::Axis  axis) const
Bounding interval for a axis
See Also
QRectF QwtRasterData::pixelHint ( const QRectF &  area) const

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.

areaIn 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::Axis  axis,
const QwtInterval interval 

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

intervalBounding interval
See Also

Reimplemented in QwtMatrixRasterData.

virtual double QwtRasterData::value ( double  x,
double  y 
) const
pure virtual
the value at a raster position
xX value in plot coordinates
yY value in plot coordinates

Implemented in QwtMatrixRasterData.