Applying a Transformation to the Data Values Represented by a Scale
Different types of transformations can be applied to the data values that are represented by a given scale. These transformations are defined by means of transformer objects that are all instances of subclasses of the IlvChartCoordinateTransformer class. Several subclasses are provided in the Charts Library:
IlvChartCoordinateTransformerThis class is the base class permitting you to define transformations that consist of an elementary transformation, possibly followed by a logarithmic transformation.
The following subclasses are defined:
IlvSimpleChartTransformer has an identity transformation as the elementary transformation. This means that no transformation will be applied before the logarithmic transformation (if a logarithmic transformation is defined).IlvAffineChartTransformer has an affine transformation as the elementary transformation. This means that an affine transformation will be applied before the logarithmic transformation (if a logarithmic transformation is defined).The logarithmic transformation that is applied to the data values depends on the defined logarithmic base. If the logarithmic base is equal to 0 or 1, no logarithmic transformation is applied. Otherwise, the following transformation is applied:
c_transformed = log(c) / log(base)
where c is the initial coordinate, base is the logarithmic base, log is the natural logarithm, and c_transformed is the coordinate transformed using the logarithmic transformation.
The transformer object defining the transformation to be applied to a given coordinate is stored in the coordinate information object associated with the coordinate.
The following code lines show how to apply a logarithmic transformation to the data values represented along the abscissa of a chart.
IlvSingleScaleDisplayer* abscissaScale = chart->getAbscissaScale(); IlvChartCoordinateInfo* abscissaInfo = abscissaScale->getCoordinateInfo(); abscissaInfo->setTransformer(new IlvSimpleChartTransformer(10)); |
The base of the logarithmic transformation that will be applied is set to 10.
Warning: If you want the abscissa scale to be graduated with logarithmic graduations, you must also set a logarithmic scale steps updater on the scale. |
To set a logarithmic scale steps updater on the abscissa scale use the following code:
IlvLogScaleStepsUpdater* logUpdater = new IlvLogScaleStepsUpdater(abscissaScale); delete IlvScaleStepsUpdater::Set(abscissaScale, logUpdater); |
IlvZoomCoordinateTransformerThis class allows you to define a transformation that is applied locally on a part of the data to display that data as zoomed.
Warning: If such a transformer is set on a given coordinate a zoom scale steps updater must also be set on the scale representing this coordinate in order to compute the corresponding graduations for the scale. |
You can look at the lens.cpp file located in the $ILVHOME/samples/charts/lens/src directory for an example of how to use the IlvZoomCoordinateTransformer and IlvZoomScaleStepsUpdater classes.
Published date: 05/24/2022
Last modified date: 02/24/2022
