How do I create and plot a ContourSeries with Oxyplot?

Question

I have a WPF application where I need to visualize y = y(x1, x2) where x1, x2 are linear coordinates. I can do this using the HeatMapSeries in Oxyplot, but when I want to plot two sets of data in the same window, heatmaps are not the proper tool. A couple of contour series would be better. Now, I have tried to achieve this in the same manner as with the HeatMapSeries, that worked pretty well:

public void PlotHeatMap (){

   OxyPlot.PlotModel model = new PlotModel { Title = "2-D data" };
   model.Axes.Add( new OxyPlot.Axes.LinearColorAxis { 
   Position = OxyPlot.Axes.AxisPosition.Right, 
   Palette = OxyPalettes.Jet( 500 ), 
   HighColor = OxyColors.Gray, 
   LowColor = OxyColors.Black } );

   OxyPlot.Series.HeatMapSeries heatmap = new OxyPlot.Series.HeatMapSeries {
     Data = ( Double[ , ] )data,
     X0 = x1min,
     X1 = x1max,
     Y0 = x2min,
     Y1 = x2max
    };

   model.Series.Add( heatmap );
}

Output from the HeatMapSeries

Now, when I try to use the ContourSeries instead, I just replace the HeatMapSeries with a ContourSeries:

public void PlotContour (){

   OxyPlot.PlotModel model = new PlotModel { Title = "2-D data" };
   model.Axes.Add( new OxyPlot.Axes.LinearColorAxis { 
   Position = OxyPlot.Axes.AxisPosition.Right, 
   Palette = OxyPalettes.Jet( 500 ), 
   HighColor = OxyColors.Gray, 
   LowColor = OxyColors.Black } );

   OxyPlot.Series.ContourSeries contour = new OxyPlot.Series.ContourSeries {
      ColumnCoordinates = arrayFromMinToMax1,
      RowCoordinates = arrayFromMinToMax2,
      ContourLevels = arrayOfLevels,
      ContourColors = arrayOfColors, // Same # elements as the levels' array
      Data = ( Double[ , ] )data
    };

   model.Series.Add( contour );
}

This just produce the output:

Output from the ContourSeries attempt

The x- and y-axes are there, and match the min and max coordinates, but I can see no contour lines. I suspect that there is something missing with setting up the Axis (should it be the same as for the HeatMapSeries??). I don't know how to proceed with this contour plot. Are there examples other than e.g. the ContourSeriesExamples at GitHub?

Thanks for any help!

Could it simply be that you are plotting the wrong region? Looking at the axes in your contour plot they appear to be flipped compared to the heat map plot. What if you set `ColumnCoordinates = arrayFromMinToMax2` and `RowCoordinates = arrayFromMinToMax1` instead? — Anders Gustafsson, May 18 '15 at 17:51
Thanks for pointing that out, Anders, but the result is the same. I updated the image, though. — Mats Isaksson, May 19 '15 at 06:47
If you look at the [HeatMapSeriesExamples](https://github.com/oxyplot/oxyplot/blob/develop/Source/Examples/ExampleLibrary/Series/HeatMapSeriesExamples.cs#L27) it even combines a heat map with contours, so contours should really be straightforward. Let the `ContourSeries` decide the levels and colors itself, i.e. remove the `ContourLevels` and `ContourColors` properties from the initializer, and see if this gives any improved resut. — Anders Gustafsson, May 19 '15 at 07:25
That's what I thought too. Straightforward! And combining heatmap with contour would actually be my first choice for my application. When I look at the scale of my empty contour plot and see it ranges from 0 to 100, while the data is the same as in the heatmap, i.e. 0 to 0.08. Is there a way this can be problematic? — Mats Isaksson, May 19 '15 at 08:11
I tested to rescale the *Peaks* example in the *ContourSeriesExamples*, and I also shifted it so that values were between -0.03 and 0.07. No problem displaying the contours. Can I recommend that you start with a simpler dataset and make `ContourSeries` work for that, then move on to your original dataset? By the way, why do you need to cast `data` to `double[,]`? — Anders Gustafsson, May 19 '15 at 08:52
One more thing, although I don't think it has any impact on your problem: you don't need to add a `LinearColorAxis` to your `PlotModel` when you are plotting a `ContourSeries`. Also, could you publish the `data` array somewhere, e.g. as a Gist on Github or on ideone.com? Maybe the "flows" in the data compicates things for the contour generator? — Anders Gustafsson, May 19 '15 at 09:16
Anders, the cast is necessary because data is of a user-defined type, sort of a matrix class. — Mats Isaksson, May 19 '15 at 12:05

score 3 · Answer 1 · answered May 19 '15 at 12:03

I finally found what was wrong - it was my mistake! The ColumnCoordinates and the RowCoordinates arrays must match the size of the DoubleArray Data! And I didn't make sure they were. Now the contour and heatmap align! Thanks Anders for support and pushing me into my own code!

HeatMap with Contour

How do I create and plot a ContourSeries with Oxyplot?

1 Answers1