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138 lines
4.5 KiB
Markdown
138 lines
4.5 KiB
Markdown
# Example (JKQTPlotter): Secondary Axes {#JKQTPlotterSecondaryAxes}
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This project (see [`second_axis`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/second_axis) shows how to plot with multiple axes.
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The source code of the main application is (see [`second_axis.cpp`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/second_axis/second_axis.cpp).
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In the code we take these step to set up a plot with two secondary axes and three graphs:
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1./2. create a plotter and create columns with different dataset:
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```.cpp
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// 1. create a plotter window and get a pointer to the internal datastore (for convenience)
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JKQTPDatastore* ds=plot.getDatastore();
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// 2. now we create two columns for key and value
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size_t columnX=ds->addLinearColumn(40, 0,10,"x");
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size_t columnY1=ds->addColumnCalculatedFromColumn(columnX, [](double x) { return x; }, "y1");
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size_t columnY2=ds->addColumnCalculatedFromColumn(columnX, [](double x) { return cos(x); }, "y2");
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size_t columnY3=ds->addColumnCalculatedFromColumn(columnX, [](double x) { return x*x; }, "y3");
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```
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3. create a second y-axis and set its formating options, so it only draws an axis on the right
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```.cpp
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auto yAxisRef2=plot.getPlotter()->addSecondaryYAxis(new JKQTPVerticalAxis(plot.getPlotter(), JKQTPPrimaryAxis));
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plot.getYAxis(yAxisRef2)->setDrawGrid(false);
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plot.getYAxis(yAxisRef2)->setDrawMode1(JKQTPCADMnone);
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plot.getYAxis(yAxisRef2)->setDrawMode2(JKQTPCADMcomplete);
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plot.getYAxis(yAxisRef2)->setDrawMode0(JKQTPCADMnone);
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plot.getYAxis(yAxisRef2)->setShowZeroAxis(false);
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```
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... and ctreate third y-axis
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```.cpp
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auto yAxisRef3=plot.getPlotter()->addSecondaryYAxis(new JKQTPVerticalAxis(plot.getPlotter(), JKQTPPrimaryAxis));
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plot.getYAxis(yAxisRef3)->setDrawGrid(false);
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plot.getYAxis(yAxisRef3)->setDrawMode1(JKQTPCADMnone);
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plot.getYAxis(yAxisRef3)->setDrawMode2(JKQTPCADMcomplete);
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plot.getYAxis(yAxisRef3)->setDrawMode0(JKQTPCADMnone);
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plot.getYAxis(yAxisRef3)->setShowZeroAxis(false);
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```
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... reformat the major y-axis, so it does not draw on the right and thus the secondary axis yAxisRef2 replaces it there. If this step is omitted, the secondary axes stack on the right of the primary.
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```.cpp
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plot.getYAxis()->setDrawMode2(JKQTPCADMnone);
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plot.getYAxis()->setColor(graph1->getLineColor());
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```
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3. create graph in the plot, which plots the dataset:
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3.1 the first graph uses the default (primary) x/y-axes
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```.cpp
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JKQTPXYLineGraph* graph1=new JKQTPXYLineGraph(&plot);
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graph1->setKeyColumn(columnX);
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graph1->setValueColumn(columnY1);
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plot.addGraph(graph1);
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plot.getYAxis()->setAxisLabel("graph1");
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```
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3.2 the second graph uses the default (primary) x-axis, but the secondary axis yAxisRef2 as y-axis
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```.cpp
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JKQTPXYLineGraph* graph2=new JKQTPXYLineGraph(&plot);
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graph2->setKeyColumn(columnX);
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graph2->setValueColumn(columnY2);
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plot.addGraph(graph2);
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```
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tell graph2 to use this axis
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```.cpp
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graph2->setYAxis(yAxisRef2);
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```
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set axis color to match graph2's color
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```.cpp
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plot.getYAxis(yAxisRef2)->setColor(graph2->getLineColor());
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```
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set axis label
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```.cpp
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plot.getYAxis(yAxisRef2)->setAxisLabel("graph2");
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```
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3.3 the third graph uses the default (primary) x-axis, but the secondary axis yAxisRef3 as y-axis
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```.cpp
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JKQTPXYLineGraph* graph3=new JKQTPXYLineGraph(&plot);
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graph3->setKeyColumn(columnX);
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graph3->setValueColumn(columnY3);
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plot.addGraph(graph3);
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plot.getYAxis(yAxisRef3)->setColor(graph3->getLineColor());
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plot.getYAxis(yAxisRef3)->setAxisLabel("graph3");
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graph3->setYAxis(yAxisRef3);
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```
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4. autoscale the plot so the graph is contained. This auto-scales all axes using the graphs (and their data) as assigned to the axes, i.e.:
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- all 3 graphs for x-axis,
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- graph1 for primary y-axis,
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- graph2 for secondary axis yAxisRef2
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- graph3 for secondary axis yAxisRef3
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```.cpp
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plot.zoomToFit();
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```
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5. show plotter and make it a decent size
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```.cpp
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plot.setWindowTitle(title);
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plot.show();
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plot.resize(500,400);
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```
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The result looks like this:
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If we set seondary axes for the x-axis instead of the y-axis, i.e. use
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```.cpp
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// ...
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auto xAxisRef2=plot.getPlotter()->addSecondaryXAxis(new JKQTPHorizontalAxis(plot.getPlotter(), JKQTPPrimaryAxis));
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// ...
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```
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we get a plot like this:
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