Pixel position of a data point

[gabe0]

Hello all,

I would like to know where the mouse position location of a data point is relative to the graph. Basically, the reverse action of this person's post:

WPF graph display point value on hover

http://forums.ni.com/t5/Measurement-Studio-for-NET/WPF-graph-display-point-value-on-hover/m-p/243395...

Instead of getting data point,  would like the mouse position. I am overlaying shapes over the graph and would like to know where a specific point in the graph is in pixel location coordinates.

Thank you.

---

[phansen · Accepted solution]

From your question, I assume you have a data value you want to translate (as opposed to a mouse event args, which already has a GetPosition method).

You can use the DataToScreen method to get a screen position within the plot area, and use the DesiredPlotAreaMargin to offset that screen position to reference the outer graph control (i.e. point.X += margin.Left; point.Y += margin.Top).

You can also use the DataToRelative method to get a relative position for a data point, and then position an object in the Children collection (much like a PointAnnotation😞

XAML

xmlns:ni="http://schemas.ni.com/controls/2009/xaml/presentation"
xmlns:niPrimitives="http://schemas.ni.com/controls/2009/xaml/presentation/primitives"
...
<ni:Graph x:Name="graph">
    <ni:Graph.Children>
        <Ellipse x:Name="dataMarker"
                 Width="10"
                 Height="10"
                 Stroke="Black"
                 StrokeThickness="2"
                 niPrimitives:RelativePanel.RelativeHorizontalAlignment="Center"
                 niPrimitives:RelativePanel.RelativeVerticalAlignment="Center"
                 />
    </ni:Graph.Children>
</ni:Graph>

Code

Point relative = graph.DataToRelative( dataValue );
RelativePanel.SetRelativeHorizontalPosition( dataMarker, relative.X );
RelativePanel.SetRelativeVerticalPosition( dataMarker, relative.Y );

[gabe0]

Thank you for the quick reply! One last question, how do I set the PlotAreaMargins?

Thanks,

[phansen]

If you want to set the plot area margin, instead of just reading the desired value, you can use the PlotAreaMargin property.

[gabe0]

Are the plot area margins the distance from the bounds of a plot to the edge of each Axes? I'm looking to get that offset value from the graph. 

Thanks,

Gabe

[phansen]

There is a single margin for the "plot area", which is the central part of the graph where data is drawn. In addition to the plot area, the graph allocates space around the plot area to display the coordinate axes. The DesiredPlotAreaMargin property indicates the desired size for all the axes, but you can override the desired size by specifying an explicit PlotAreaMargin.

Could you explain what you mean by "from the bounds of a plot to the edge of each axis"? Are you referring to the "plot area", or to the data values for an individual plot? Could you describe how you are using the margin value?

[gabe0]

The space around the plot area to display coordinate axes is what I mean by from the bounds of a plot to the edge of each axes. So you did answer my question, thank you. So, where can I set the plot area margin because I don't see the property anywhere.

Thanks.

[phansen]

PlotAreaMargin is a property of the graph (i.e. "<ni:Graph PlotAreaMargin="42" ...>" in XAML, or "graph.PlotAreaMargin = new Thickness( 42 );" in code).

[gabe0]

Okay, I'm using ni:Graph and it doesn't show up. I'm using MS2013, is this a new feature?

Thanks.

[phansen]

Ah, yes: I believe this was added in Measurement Studio 2015.