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60 lines
2.5 KiB
Markdown
60 lines
2.5 KiB
Markdown
# JKQtPlotter: Examples: Plotting Parametric Curves {#JKQtPlotterParametricCurves}
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This project (see `./examples/simpletest_parametriccurve/`) demonstrates how to draw parametric curves, using [`JKQTPxyLineGraph`}(../simpletest) and [`JKQTPxyParametrizedScatterGraph`](../simpletest_paramscatterplot).
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The source code of the main application can be found in [`jkqtplotter_simpletest_parametriccurve.cpp`](../simpletest_parametriccurve/jkqtplotter_simpletest_parametriccurve.cpp). First, the parametric curve (here a [logarithic spiral](https://en.wikipedia.org/wiki/Logarithmic_spiral)) is sampled into two columns containing the x- and y-values along the curve. In addition the radial distance from x=y=0 is added into a third column:
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```c++
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QVector<double> X, Y, R;
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const int Ndata=500; // number of plot points in each curve
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const double phiMax=4.0*M_PI;
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const double a=1;
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const double k=0.2;
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for (double phi=-phiMax; phi<=phiMax; phi+=phiMax/double(Ndata)) {
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const double x=a*exp(k*phi)*cos(phi);
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const double y=a*exp(k*phi)*sin(phi);
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X<<x;
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Y<<y;
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R<<sqrt(x*x+y*y);
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}
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// and copy it to the datastore
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size_t columnX=ds->addCopiedColumn(X, "x");
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size_t columnY=ds->addCopiedColumn(Y, "y");
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size_t columnR=ds->addCopiedColumn(R, "r");
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```
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Then simples graph just uses the columns X and Y to plot the curve:
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```c++
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JKQTPxyLineGraph* graph1=new JKQTPxyLineGraph(&plot);
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graph1->set_xColumn(columnX);
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graph1->set_yColumn(columnY);
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graph1->set_drawLine(true);
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graph1->set_symbol(JKQTPnoSymbol);
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graph1->set_title("one-colored spiral");
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plot.addGraph(graph1);
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```
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If you use `JKQTPxyParametrizedScatterGraph` instead of `JKQTPxyLineGraph`, you can also modify the color of the line-segments, connecting the datapoints:
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```c++
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JKQTPxyParametrizedScatterGraph* graph2=new JKQTPxyParametrizedScatterGraph(&plot2);
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graph2->set_xColumn(columnX);
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graph2->set_yColumn(columnY);
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graph2->set_colorColumn(columnR);
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graph2->set_palette(JKQTPMathImageMATLAB);
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graph2->set_symbol(JKQTPnoSymbol);
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graph2->set_drawLine(true);
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graph2->set_title("colored spiral");
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graph2->get_colorBarRightAxis()->set_axisLabel("color scale radius $r(\\phi)$");
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plot2.addGraph(graph2);
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```
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The result looks like this:
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... and with the line-color set by the radius:
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