Is there no way to disable the behavior by inheriting from some kind of Series?
I found a snippet of code on this forum that just happens to inherit HorizontalAnchoredCategorySeries and appears to allow the markers to overlap.

But the code seems like it is hacked together. I'll try to reference the post if I can find it.

Did you notice the initial project that was posted? The skinny lines should be collapsed later if based upon collision.

Hi Will,

Inheriting from a series is an option like in the example you provided but I wanted to steer away from it at first because in order to control how the markers are rendered you will basically have to handle rendering of the series yourself.  This will involve creating all the little components that make up the series in the plot area.  If you use the default rendering the series provides, it's going to render the markers as it does now.  It's definitely a viable option but it will require a decent amount of work.  The CustomLineSeries in your example isn't really a hack though, if you want to create your own custom series that example is a way you can do it.

As for the marker size and collision, the calculation for determining collision is not using the markers visual size.  Even if I adjust the marker's width and height to be the same as the content of the marker, line markers are still disappearing at the same time as circle markers.  In the source code, this code is the reason why: 

Rect markerRect = new Rect(x - 5, y - 5, 11, 11);

if (!double.IsNaN(x) && !double.IsNaN(y) && !double.IsInfinity(x) && !double.IsInfinity(y) && collisionAvoider.TryAdd(markerRect))
{
    // add marker
}

So you were right initially, the widths are being hard coded.  At present the options are to either create your own series or modify the source code.  I highly recommend submitting a product idea for this though so we can potentially add support to adjust this behavior in a future version.  If you submit this, please reference this forum thread so the Product Management team can look back at it.

Hmm.  It didn't seem to add a scrollbar to the code snippet from what I can see.  At the end of this if check is collisionAvoider.TryAdd(markerRect).

I'll consider submitting the product idea piece. But in the meantime, I had a question about that last project that I had posted:

<Style TargetType="local:CustomLineSeries">
            <Setter Property="Thickness" Value="2"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="local:CustomLineSeries">
                        <Canvas Name="RootCanvas"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

I don't understand why this is needed and referenced in the custom series. Can I avoid this by setting the DefaultStyleKey to LineSeries to gain this?
Is there no easy way to rid the xaml side such that it is consolidated into one piece? When attempting to use CustomLineSeries.cs in our code with that style placed in App.xaml resources, the series just simply does not show up. I'm having a hard time tracking down what is the actual issue as the code sample is sparse and incomplete for general usage. (But of course, its a sample).

--Whatever the style is doing it seems to related to this.Viewport getting set as well as this.RootCanvas. I guess for the custom series solution I figure out the connections between the style, series and the chart. Any useful information this would also be great.

Thanks for the quick responses.

At this time we have finally decided to modify the source to prevent the data point (marker) hiding.

Removing the collisionAvoider.TryAdd(..) check from CategoryFramePreparer.cs:PrepareMarker(..)still doesn't prevent the markers from being hidden.
I'm not sure whether this is a bug or if there is simply more than one spot that needs to be modified.

Please advise.

Hi Will,

Let me know if you have any further questions on this matter.