LineAnnotation, top axis and other plot interaction

Sep 5, 2012 at 2:48 PM

Short version: Vertical LineAnnotation doesn't go all the way across the plot.

Long version: I'm using multiple PlotModels in a vertical stackpanel (WPF) to show a number of signals.  The top PlotModel has a top and bottom horizontal axis.  The remaining PlotModels only have a bottom axis. The top axis is time.  The bottom axes on all the graphs are a time index value that the data is referenced to, but is meaningless to the user.  Occasionally there are breaks in the time.  I wanted to show that by a vertical line where there was a time break.  I used a LineAnnotation to do that and it mostly works.  However, on the top plot the line starts at the top of the top axis and goes a little ways down into the plot area of the graph then stops, but ONLY if there is another PlotModel on the stackpanel that uses a vertical CategoryAxis (used for discrete signals).  If there are only analog signals (using a vertical LinearAxis), the line goes all the way down the plot like the rest of the graphs.  I've stepped through the LineAnnotation:Render code and it seems to form the points and clip correctly.  I'd appreciate any help in determining why this is doing this!


Sep 5, 2012 at 2:59 PM

Actually, if there are only PlotModels that use LinearAxis for their vertical axis, the top PlotModel LineAnnotation still stops a little short of the bottom horizontal axis, but it gets a lot closer.

Sep 5, 2012 at 5:25 PM

Are you creating the plots by XAML, or do you bind PlotModels to the Model property? Are you using DataTemplates? Could it be related to

Can you send an image how it looks? Or generated code (Ctrl+Alt+C) to reproduce the error?

Sep 5, 2012 at 7:17 PM

Thanks for the quick response.  I do this programmatically, not in XAML and don't use data templates.  I bind the plot model to the model properties:

foreach (PlotModel lPlotModel in graphData.PlotModels) 
    OxyPlot.Wpf.Plot lPlot = new Plot(); 
    lPlot.Model = lPlotModel;
    if (lPlotIndex == 0) { 
      // add extra space on first graph for top time axis
      lPlot.Height = graphData.PlotHeights[lPlotIndex] + 30; 
    else {
       lPlot.Height = graphData.PlotHeights[lPlotIndex]; 
    lPlot.HorizontalAlignment = System.Windows.HorizontalAlignment.Stretch; 
    lPlot.Margin = new Thickness(0, 0, 2, 0); 
// snipped out putting filter on axes to limit data range shown 
    // MainGraphDisplay is the stackpanel 
The code to create the line annotation looks like:
foreach (int lTimeBreak in lTimeBreaks)
    LineAnnotation lVertBar = new LineAnnotation();
    lVertBar.LineStyle = LineStyle.Solid;
    lVertBar.Color = OxyColor.FromRGB(255, 0, 0);
    lVertBar.Type = LineAnnotationType.Vertical;
    lVertBar.X = lTimeBreak;
    lVertBar.Layer = AnnotationLayer.AboveSeries;
    lVertBar.ClipByXAxis = false;

    foreach (PlotModel lPlotModel in PlotModels)

I'd love to attach a screenshot but haven't figured out how to.
Sep 5, 2012 at 9:12 PM

try creating a new instance of the LineAnnotation for each PlotModel.

Sep 6, 2012 at 1:43 AM

Good tip. I should have thought of that!


From: objo [email removed]
Sent: Wednesday, September 05, 2012 4:13 PM
Subject: Re: LineAnnotation, top axis and other plot interaction [oxyplot:394496]

From: objo

try creating a new instance of the LineAnnotation for each PlotModel.

Sep 6, 2012 at 1:50 AM
Edited Sep 6, 2012 at 1:50 AM

That did fix the problem.  It makes sense because the discrete signal plots were much shorter, so when the endpoints were determined it was a short line - the short line was being reused in the top graph since it was after all the same object.

Thanks a ton!