There are two things to consider here: 1.) The property configuration for the user interface such that the axis labels display date/time information, and 2.) the conversion factor between date/time and numeric values.
For 1.), look at the MajorDivisions property on the X axis (assuming you want the date/time labels on the X axis), then look at the LabelFormat property. The format string can be any of the standard .NET format strings that are supported by
DateTimeFormatInfo and there are several canned formats available in the LabelFormat editor at design-time.
For 2.), the DateTime/double conversion factor that the Measurement Studio graphs use is a double value of 0.0 is equivalent to DateTime.MinValue and a double interval of 1.0 is equivalent to 1 second. The NationalInstruments.DataConverter class will convert from/to double and TimeSpan with this conversion factor.
Here is an example that generates arrays of time and data values, configures the axis to display date/time labels, and plots the data in a ScatterGraph:
// Configure the X axis to display date/time labels.
xAxis1.MajorDivisions.LabelFormat = new FormatString(FormatStringMode.DateTime, "h:mm");
const int sampleCount = 60;
// Create an array of DateTime values that start at midnight and continues at
// one minute intervals for an hour.
TimeSpan interval = TimeSpan.FromMinutes(1);
DateTime[] times = new DateTime[sampleCount];
times[0] = DateTime.Today;
for (int i = 1; i < sampleCount; ++i)
times[i] = times[i - 1] + interval;
// Convert the array of DateTime values to an array of doubles for the graph.
double[] timeValues = (double[])DataConverter.Convert(times, typeof(double[]));
// Create an array of sample values to plot against the time values.
double[] dataValues = new double[sampleCount];
Random rnd = new Random();
for (int i = 0; i < sampleCount; ++i)
{
dataValues[i] = rnd.NextDouble() * 10;
}
// Plot the sample values against the time values on the ScatterGraph.
scatterGraph1.PlotXY(timeValues, dataValues);
Note that this example uses the ScatterGraph instead of the WaveformGraph because ScatterGraph plots an array of values against another array of values, but the WaveformGraph plots an array of values against a start time and a fixed interval.
Hope this helps.
- Elton
