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Trend surface with contour lines

The Cloud chart is essentially a scatter-plot in 3 dimensions (maybe you are running an experiment in which you vary pressure and temperature, and are interested in the yield of the result). Rather than fitting a line to show the relationship between input and output, you fit a plane (if the data is linear in both x and y) or a curved surface.

This example shows the analagous style to the ‘trendline’ available in the ScatterPlot. The surface is a gaussian-weighted smooth which can be controlled with the Flexibility property. With so few points, the sample sets the flex very low indeed, as otherwise the surface would resemble a series of plateaux around each point. With a realistically large data array (probably several hundred points) the default flexibility would be more suitable.

Contour lines are drawn at each Z-axis tickmark, and the ‘grid’ is computed at the intersection of each x-y tick. The MeshDensity property can be used to add more points into the mesh to make a smoother surface.

SharpPlot sp = new SharpPlot;
sp.SetMargins(24,32,18,6);

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 = "Trend\nSurface";
sp.HeadingStyle = HeadingStyles.Right;

sp.SetZTickMarks(50);  // Contour interval also

sp.CloudChartStyle = CloudChartStyles.WallShading|CloudChartStyles.TrendSurface|
         CloudChartStyles.Contours|CloudChartStyles.GridLines|
         CloudChartStyles.TiledSurface;

sp.Flexibility = 1;
sp.ZAxisStyle = ZAxisStyles.ForceZero;
sp.YAxisStyle = YAxisStyles.FlatText;
sp.SetFillStyles(FillStyle.Opacity30);
sp.SetPenWidths(0.8);

sp.SetMarkers(Marker.Node);
sp.DrawCloudChart(xdata,ydata,zdata);

Worked Examples

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