Altitude over distance to scale with missing data points - how to prevent bottoming out?

I'm not sure your chart can automatically interpolate between known points; I would create a new (formula-based) range in the spreadsheet that automatically interpolates between the 2 nearest points if there is no known altitude, and then plot that range instead.

Just be sure I understand your data correctly: Does it look something like the attached? Don't mind the values, as they are randomly generated.

And you want to do a linear interpolation between the 2 known points in order to fill out the empty spaces?

It isn't pretty, but it works.

No problem.

The values in the distance column do not matter; you can change them to whaterever you want.

You can use the "Trace dependants" function under (Ribbon) "Formulas" on one of the distance cells; it will tell you that no cells, other than the other distances, depend on it.

Is just ticking the 'smoothed line' checkbox on the format data series line style window not an option?

Originally Posted by Richard Buttrey

Is just ticking the 'smoothed line' checkbox on the format data series line style window not an option?

Would that not just soften the sharp peaks of a line?

And I quiver as I enter into a discussion with Mr. Buttrey.

In what way isn't it working?

Could you upload a workbook and describe what you expect to see that the smoothed line doesn't give you.

Originally Posted by Søren Larsen

Would that not just soften the sharp peaks of a line?

And I quiver as I enter into a discussion with Mr. Buttrey.

I didn't know I had that sort of reputation

Indeed it would, you are of course correct the smoothing does just 'soften' the changes of direction.

Your solution of interpolating values will still lead to a peak and a change of direction. And unless the change in values of the intermediate points are something other than a constant then the line between the given points is still straight. But I struggle to understand what else the poster wants.

Originally Posted by Richard Buttrey

I didn't know I had that sort of reputation

Indeed it would, you are of course correct the smoothing does just 'soften' the changes of direction.

Your solution of interpolating values will still lead to a peak and a change of direction. And unless the change in values of the intermediate points are something other than a constant then the line between the given points is still straight. But I struggle to understand what else the poster wants.

Nothing I think. Except for an explanation of how to expand the formula downwards, which I'm still considering how to do in the best way.

With regards to reputation: I'm just comparing # of posts, and having other solutions by you in the back of my head. So don't worry, there is no "talking about you behind your back". Not to my knowledge anyway...

If you just replace the blanks in col C with =NA() (or delete those lines entirely) and untick smooth lines, the data will appear interpolated between points.

I figured the easiest way was to expand it for; perhaps this also will make it more easy for you to figure out how to expand later on. When you plot the range, then just choose the part containing values.

Do you really need to calculate the interpolated points?

Why not use the sparse data set and set the Hidden & Empty cells property to Connect data points with line. You can find this on the Select Data dialog > Hidden & Empty cells.

Better yet why not simply have a table of know x(distance) and y(altitude) points.

See attached for example charts based on original data and condensed data.