[Question][LineChart] getting y value from x

I have a first line displaying altitude (y axis) regarding distance (x axis)
This line is displayed with a curve to have something smooth (in that case some y data are interpolated between 2 distance points)

I have another line (but only points are displayed) displaying people location but I have only the distance for the data (not the altitude)

People location distance value is not always available on the altitude data (by example altitude is available for distance 3000m and 3500m but not for 3200m)

To display the people location on the right place, I need to get the interpolated value for the altitude line.

How to get this value ?

Start with the LineChart API and its handling of interpolated values between distance points. The issue names no files or tests, so first determine whether the library exposes the needed altitude value or whether a new API is required; done means an agreed, documented way to place the people-location points at the interpolated altitude.

Written by the indexing model from the issue text.