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QwtRasterData(3) Qwt User's Guide QwtRasterData(3)


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


#include <qwt_raster_data.h>

Inherited by QwtMatrixRasterData.

Public Types

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

Public Member Functions

QwtRasterData ()
Constructor. virtual ~QwtRasterData ()
Destructor. void setAttribute (Attribute, bool on=true)
bool testAttribute (Attribute) const
virtual QwtInterval interval (Qt::Axis) const =0
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.

Gaps inside the bounding rectangle of the data can be indicated by NaN values ( when WithoutGaps is disabled ).

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 ).

QwtMatrixRasterData implements raster data, that returns values from a given 2D matrix.

See also


Definition at line 42 of file qwt_raster_data.h.

Member Typedef Documentation

typedef QFlags<Attribute > QwtRasterData::Attributes

An ORed combination of Attribute values.

Definition at line 74 of file qwt_raster_data.h.

typedef QFlags<ConrecFlag > QwtRasterData::ConrecFlags

An ORed combination of ConrecFlag values.

Definition at line 86 of file qwt_raster_data.h.

Member Enumeration Documentation

enum QwtRasterData::Attribute

Raster data attributes. Additional information that is used to improve processing of the data.


The bounding rectangle of the data is spanned by the interval(Qt::XAxis) and interval(Qt::YAxis).

WithoutGaps indicates, that the data has no gaps ( unknown values ) in this area and the result of value() does not need to be checked for NaN values.

Enabling this flag will have an positive effect on the performance of rendering a QwtPlotSpectrogram.

The default setting is false.


NaN values indicate an undefined value

Definition at line 54 of file qwt_raster_data.h.

enum QwtRasterData::ConrecFlag

Flags to modify the contour algorithm.


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

Definition at line 77 of file qwt_raster_data.h.

Member Function Documentation

QwtRasterData::ContourLines QwtRasterData::contourLines (const QRectF & rect, const QSize & raster, const QList< double > & levels, ConrecFlags flags) 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.

Definition at line 286 of file qwt_raster_data.cpp.

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()

Definition at line 237 of file qwt_raster_data.cpp.

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()

Definition at line 221 of file qwt_raster_data.cpp.

virtual QwtInterval QwtRasterData::interval (Qt::Axis) const [pure virtual]


Bounding interval for an axis

See also


Implemented in QwtMatrixRasterData.

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.

Definition at line 267 of file qwt_raster_data.cpp.

void QwtRasterData::setAttribute (Attribute attribute, bool on = true)

Specify an attribute of the data


attribute Attribute
on On/Off /sa Attribute, testAttribute()

Definition at line 189 of file qwt_raster_data.cpp.

bool QwtRasterData::testAttribute (Attribute attribute) const


True, when attribute is enabled

See also

Attribute, setAttribute()

Definition at line 201 of file qwt_raster_data.cpp.

virtual double QwtRasterData::value (double x, double y) 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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Sun Jul 18 2021 Version 6.2.0