Live-Charts | Simple, flexible, interactive & powerful charts, maps and gauges for Net | Chart library

The solution is relatively simple. The problem with LiveCharts is, that it not well documented. It gets you easily started by providing some examples that target general requirements. But for advanced scenarios, the default controls doesn't offer enough flexibility to customize the behavior or layout. There is no documentation about the details on how things work or what the classes of the library are intended for.

Once I checked the implementation details, I found the controls to be really horrible authored or designed.

Anyway, this simple feature you are requesting is a good example for the shortcomings of the library - extensibility is really bad. Even customization is bad. I wish the authors would have allowed templates, as this would make customization a lot easier. It should be simple to to extend the existing behavior, but apparently its not, unless you know about undocumented implementation details.
The library doesn't come in like a true WPF library. I don't know the history, maybe it's a WinForms port by WinForms devs. But it's free and open source. And that's a big plus.

The following example draws a cursor on the plotting area which snaps to the nearest chart point and higlights it, while the mouse is moving. A custom ToolTip follows the mouse pointer to show info about the currently selected chart point:

ViewModel.cs