Interpolation behind the Scatter chart with smooth lines

[Aks73]

Dear friends,

In short, I need to interpolate a series of measured values like Excel does in Scatter chart with smooth lines. Does anyone know how Excel actually interpolates values for this type of chart? I tried GROWTH() function, but the results are not satisfactory. It is probably some kind of piece-wise interpolation, but which one and how many successive points are used?

 

[Jon Peltier]

The smoothed lines are actually defined by a Bezier function. There used to be a page on xlrotor.com that described this, but I wonder if it's been removed over the years.

 

[Aks73]

Thank you for the clue, Jon. I was hoping that Excel could solve it easier, but, probably, there is no way to avoid programming. Just have to find some way to calculate positions of the control points for each segment to achieve proper smoothness.

 

[Jon Peltier]

I found a link to this file:
https://xlrotor.com/Smooth_curve_bezier_example_file.zip

I was vaguely familiar with it many years ago...

 

[Aks73]

Thank you so much, Jon!

 

[Jon Peltier]

I should also point you to this reply to a much earlier post:

Extract Excel Scatter Plot with connected by smooth lines Points

Hi there, I have a couple of points, and when i do a scatter plot with connected by smooth line plot, it seems like excel does a bezier splines interpolation. I am wondering am i able to extract the data plots from the data chart? for example if i have X - Y 0 - 5 180 - 0 360 - 5 i would like...

www.mrexcel.com

(yeah, so I obsessed on this for a while.)