DPlot

I'm trying to create grain size distribution charts for some soil data, but my professor wants the lines to be curved. I tried using the curve fit, but that strays much to far from the actual data.

I guess what I am looking for is something similar to excels scatter plot with smooth (rounded) lines, but with the grain size distribution axes.

How can I accomplish this?

Probably your best bet is Edit>Equal Intervals with a fairly small interval and Interpolation Method=Cubic Spline. Unlike a curve fit, the cubic spline will always pass through your original data points.

One problem in your case will be that this command produces points at an equal spacing in X. So on a log scale with your grain size plot you'll get, for example, 100x as many points between 0.1-1 as you do from 10-100. I'd suggest using a small interval, then Edit>Decimate Points>Welch to get rid of unneeded points.

Thanks for the reply; however, the Equal Intervals option is not selectable (grayed out on the dropdown menu)

Anyway to force that option or is there something else I could try?

thanks

That command requires that your input have monotonically increasing X values (X1 < X2 < X3, etc.). My guess is the only problem is that your data is in reverse order. See if using Edit>Sort results in Equal Intervals being enabled.

ahhh, okay. The sort worked. I guess I had my data in decreasing grain size.

The cubic spline had curves that plotted off of the graph, but I found the quadratic to plot it much closer to what I needed.

Thanks for the help. I am very impressed at the speed that you reply to posts.

Great product by the way. I have no regrets about the investment I made in your product as a tool to help me with my educational goals.