Use a DateTime axis for an Oxyplot HeatMap

Question

I want to use a datetimeaxis for the Y-axis of an Oxyplot heatmapseries (in winforms). The API allows me to add the axis to the PlotModel, but does not do much good since the y-value is mapped off of the integral column index of a matrix of doubles - the y values come out to around Jan. 1900.

How can I use times for the y data on the heat map?

Answer 1

The workaround to make this happen is not too difficult. When setting up the chart, create 2 axes: one for the time, and another for the integral index of the HeatMapSeries input.

DateTimeAxis dateTimeAxis;
HeatMapSeries series;
....

//set up the time axis for y
dateTimeAxis = new DateTimeAxis();
dateTimeAxis.Position = AxisPosition.Left;
dateTimeAxis.Key = "dateTimeAxis";                        
plotModel.Axes.Add(dateTimeAxis);

//set up a shadow axis for the HeatMapSeries
var linearAxis = new LinearAxis();
linearAxis.Position = AxisPosition.Left;
linearAxis.Key = "linearAxis";
plotModel.Axes.Add(linearAxis);
series.YAxisKey = linearAxis.Key;

Next, the assigned y-axis will have to be hidden - but we can't access the YAxis property until the plot has been updated:

//hide the linear axis
plotModel.Updated += (sender, e) =>
{
    series.YAxis.IsAxisVisible = false;
};

Finally, when setting the heat map data, simply create the desired mapping from the matrix index to time. Then adjust the y-scale. For example:

public void UpdateData(double[,] data)
{
    series.Data = data;

    //adjust date/time axis
    int numOfMinutes = data.GetLength(1);            
    dateTimeAxis.Minimum = DateTimeAxis.ToDouble(DateTime.Now);
    dateTimeAxis.Maximum DateTimeAxis.ToDouble(DateTime.Now.AddMinutes(numOfMinutes));
 }

I have not yet seen a way to do this directly in OxyPlot