For example I have a QChart with QLineSeries with some points. Chart plots lines between these points in view, but how can I access value of Y by X at place where no points are, i.e. if I have e.g. points (0,0) and (10,10) how can I get value of Y from chart for X=5 (Y must be 5 too)?
Update:
I suppose that plot represents mathematical function, i.e. one X has exactly one Y.