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64 lines
3.0 KiB
Markdown
64 lines
3.0 KiB
Markdown
# Example (JKQTPlotter): Vector Field Plot Example {#JKQTPParametrizedVectorFieldGraphExample}
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This project (see [`paramvectorfield`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/paramvectorfield) demonstrates the use of JKQTPParametrizedVectorFieldGraph to visualize a vector field with additional information encoded in the color of the vectors.
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The source code of the main application is (see [`paramvectorfield.cpp`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/paramvectorfield/paramvectorfield.cpp).
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Here is a short summary of the important parts of the code:
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```.cpp
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// 1. setup a plotter window and get a pointer to the internal datastore (for convenience)
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JKQTPlotter plot;
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JKQTPDatastore* ds=plot.getDatastore();
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// 2. make up some arbitrary data to be used for plotting
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// this generates a 2D grid of x/y-coordinates and then calculates dx=cos(y)*sqrt(x/3.0) and dy=sin(x)*sqrt(x/3.0)
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const auto columnXY=ds->addLinearGridColumns(NX, 0, 6, NY, -3, 3,"x","y");
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const auto columnDX=ds->addCalculatedColumnFromColumn(columnXY.first, columnXY.second, [](double x,double y) { return sin(y)*sqrt(x/3.0); });
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const auto columnDY=ds->addCalculatedColumnFromColumn(columnXY.first, columnXY.second, [](double x,double y) { return cos(x)*sqrt(x/3.0); });
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// now we also calulate a column that encodes some other information that can be color-coded
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const auto columnC=ds->addCalculatedColumnFromColumn(columnXY.first, columnXY.second, [](double x,double y) { return sqrt(fabs(y)); });
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// 3. create JKQTPVectorFieldGraph to display the data:
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JKQTPParametrizedVectorFieldGraph* graph1=new JKQTPParametrizedVectorFieldGraph(&plot);
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graph1->setXYColumns(columnXY);
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graph1->setDxColumn(columnDX);
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graph1->setDyColumn(columnDY);
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graph1->setColorColumn(columnC);
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graph1->setTitle(QObject::tr("$\\vec{f}(x,y)=\\bigl[\\sin(y)\\cdot\\sqrt{x/3}, \\cos(x)\\cdot\\sqrt{x/3}\\bigr]^\\mathrm{T}$"));
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// 4. add the graphs to the plot, so it is actually displayed
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plot.addGraph(graph1);
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```
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The result looks like this:
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By default, the color of the drawn vector is determined from the color column provided to the graph object.
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But you can also choose to not provide a color column and instead set
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```.cpp
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graph1->setVectorColorMode(JKQTPParametrizedVectorFieldGraph::ColorFromMagnitude);
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```
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Now the color encodes the actual length (or magnitude) of the vectors:
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Alternatively
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```.cpp
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graph1->setVectorColorMode(JKQTPParametrizedVectorFieldGraph::ColorFromAngle);
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```
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will color-encode the rotation angle (in radians, 3 o'clock is 0rad) of the vectors:
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