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95 lines
4.7 KiB
Markdown
95 lines
4.7 KiB
Markdown
# Example (JKQTPlotter): Draw an Artistic Image with a Parametrized Scatter Graph {#JKQTPlotterParamScatterImage}
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This project (see `./examples/paramscatterplot_image/`) demonstrates the capabilities of `JKQTPXYParametrizedScatterGraph` to display parametrized scatters in a rectangular arrangement. See the test program in [`examples/paramscatterplot`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/paramscatterplot) for a basic example of the capabilities of `JKQTPXYParametrizedScatterGraph`.
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In this example, we load an image, convert it to greyscale and store it, together with x/y-coordinate-vectors in the datastore. Then a `JKQTPXYParametrizedScatterGraph` is used to draw the image as a pointilistic artwork, where each pixel is represented by a disk. The color of the disk is chosen from a color-palette, based on the grey-value. The size of each disk is chosen from the inverse grey value.
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First we prepare the data, as described above. The image is loaded and then converted to the required data vectors.
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```.cpp
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// 2.1 load image
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QImage image(":/example.bmp");
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QVector<double> imageVector, pointSizes;
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QVector<double> X,Y;
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// 2.2 convert image to greyscale, stored in a vector in row-major order
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double maxSymbolSize=30; // maximal diameter of symbols in pt
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for (int y=0; y<image.height(); y++) {
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for (int x=0; x<image.width(); x++) {
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// calculate grey-value image vector
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imageVector.push_back(qGray(image.pixel(x,y)));
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// calculate point sizes from inverse grey value and scaling between 0 and maxSymbolSize
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pointSizes.push_back(static_cast<double>(255-qGray(image.pixel(x,y)))/255.0*maxSymbolSize);
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// calculate X/Y-coordinates (y mirrored, so image is upright)
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X.push_back(x);
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Y.push_back(image.height()-1-y);
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}
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}
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// 2.3 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 columnG=ds->addCopiedColumn(imageVector, "greyscaleImageData");
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size_t columnS=ds->addCopiedColumn(pointSizes, "pointSizes");
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```
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Now we can use th datavectors to add a `JKQTPXYParametrizedScatterGraph`:
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```.cpp
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JKQTPXYParametrizedScatterGraph* graph1=new JKQTPXYParametrizedScatterGraph(&plot);
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graph1->setXColumn(columnX);
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graph1->setYColumn(columnY);
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graph1->setSizeColumn(columnS);
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graph1->setSymbolType(JKQTPFilledCircle);
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graph1->setColorColumn(columnG);
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graph1->setColorPalette(JKQTPMathImageMATLAB);
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graph1->setDrawLine(false);
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graph1->setTitle("");
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plot.addGraph(graph1);
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```
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For illustrative purposes, the original image is shown at the bottom-left:
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```.cpp
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JKQTPImage* graph2=new JKQTPImage(&plot);
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graph2->setImage(image);
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graph2->setX(0);
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graph2->setY(0);
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graph2->setWidth(10);
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graph2->setHeight(10);
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plot.addGraph(graph2);
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```
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Finally the plot is styled and the axis aspect ratios are fixed:
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```.cpp
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// scale the plot so the graph is contained and format the coordinate system
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plot.getXAxis()->setAxisLabel("x-axis");
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plot.getYAxis()->setAxisLabel("y-axis");
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plot.getXAxis()->setDrawGrid(false);
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plot.getYAxis()->setDrawGrid(false);
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// max. size is the size of the image
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plot.setXY(0,image.width()-1,0,image.height()-1);
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plot.setAbsoluteXY(0,image.width()-1,0,image.height()-1);
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// ensure that axis aspect ratio and coordinate system aspect ratio are maintained
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plot.getPlotter()->setMaintainAspectRatio(true);
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plot.getPlotter()->setAspectRatio(1);
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plot.getPlotter()->setMaintainAxisAspectRatio(true);
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plot.getPlotter()->setAxisAspectRatio(1);
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```
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The full test appication combines all these variants and the result looks like this:
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You can modify the example above in several ways, e.g. by choosing another symbol (e.g. a star):
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... or by changing the color palette and the symbol:
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... or even to set a different symbol for each pixel, based on the values in `columnS` (simply add `graph1->setSymbolColumn(columnS)`):
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