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MS Office Forum / Excel / Charting / April 2007Charts/XY(scatter)/Smooth lines option
I would appreciate your help in the following issue: We like to know what function the Excel developpers have used in Excel for Charts/XY(scatter)/smooth lines. It iseems to us that it is a B-spline but there are many of those around. Could you please provide us with the exact spline function used for interpolation in this Excel option and possibly the code Thanks a lot in advance Ian Excel actually uses Bezier curves, though they can be approximated by splines. Look for the Smooth_curve_bezier_example_file.xls download in the bottom part of this page on Brian Murphy's web site: http://www.xlrotor.com/resources/files.shtml - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions http://PeltierTech.com _______ >I would appreciate your help in the following issue: > [quoted text clipped - 7 lines] > Thanks a lot in advance > Ian Dear Jon, Thanks for the message. I followed your advise but it seems that the code in Brian's web site is only for 4 points. In Excel we can give any number of points without restrictions and Excel gives us the smoth line. I would appreciate your advise Thanks in advance Ian > Excel actually uses Bezier curves, though they can be approximated by > splines. Look for the Smooth_curve_bezier_example_file.xls download in the [quoted text clipped - 20 lines] > > Thanks a lot in advance > > Ian What are you using the smoothed lines for? Not to interpolate values between plotted points, I hope, because the curves hold no information about the values between the points. I haven't looked at Brian's workbook in a couple of years, so I forget how he did it. Couldn't you extend the formulas, or loop more in the code, or extend whatever technique he uses? - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions http://PeltierTech.com _______ > Dear Jon, > [quoted text clipped - 37 lines] >> > Thanks a lot in advance >> > Ian Dear Jon, I have a table of X and Y which are more than 4. Normally Bezier is for 4 points. By interpolating with Excel I can get a smooth line from several input points but not the values in between. In Brians code you can in fact take the interpolated values between the original interpolated points according to a step. However it has as an input only 4 points. It seems difficult to me how to extend it since it is not straight forward. I think Brian should have done it and if he can help I would very much appreciate Thanks again ian > What are you using the smoothed lines for? Not to interpolate values between > plotted points, I hope, because the curves hold no information about the [quoted text clipped - 52 lines] > >> > Thanks a lot in advance > >> > Ian As I recall, two adjacent points in the chart form the outer pair of points in the Bezier curve, and Brian includes algorithms for determining the inner two. You need to do the analysis between every adjacent pair of points in the series. - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions http://PeltierTech.com _______ > Dear Jon, > [quoted text clipped - 72 lines] >> >> > Thanks a lot in advance >> >> > Ian |
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