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Fitting a Flexible Cubic Model

Contour plots are often an excellent alternative to 3D presentations where the object is to model three-dimensional data. Obviously, they can be used ‘just like a map’ where you may have a set of spot-heights (z-values) at various locations on the xy-plane.

The final example generates the most ‘satisfying’ map, from a purely visual point of view. This allows SharpPlot to fit a cubic regression surface in the x-direction, then apply a little flexibility to this to finalise the shape of the surface. No underlying model is assumed in the y-direction.

This combination of modelfit and flexibility is a good approach when you know that the z-value is composed of several effects, some of which are expected to obey a known model, but some of which are effectively ‘random’ values.

SharpPlot sp = new SharpPlot;

zdata = new int[] {100,15,27,117,19,112};
xdata = new int[] {17,31,29,21,30,24};
ydata = new int[] {190,270,310,300,190,230};

sp.Heading = "Cubic Model with False Colours";
sp.SetAltitudeColors(new Color[]{Color.SlateBlue,Color.Navy,Color.Green,Color.Red,
         Color.Orange,Color.Yellow});

sp.ContourPlotStyle = (ContourPlotStyles.ValueTags|ContourPlotStyles.ExplodeAxes|
         ContourPlotStyles.AltitudeShading|ContourPlotStyles.Curves);
sp.SetMarkers(Marker.Bullet);

sp.SetOrderOfFit(3,0);
sp.Flexibility = 8;
sp.MeshDensity = 3;

sp.DrawContourPlot(xdata,ydata,zdata);

Worked Examples

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