Hmmm, no, this is not correct. I was able to re-access the database and did an experiment with numerical data. First I exported the raw data and then exported interpolated data using the 3 available methods: linear, natural and step. Comparing the 4 traces, I can see that the natural interpolation simply uses the "last known value" (i.e. the value of an interpolated point is assigned the value of the logged point immediately preceding it in time). The step interpolation is identical. The linear interpolation is just that: a linear interpolation of the surrounding points.
This is a bit surprising. I at least expected the natural and step methods to yield different results.
I just found a description of the methods in the MAX online help:
"Natural interpolation examines the data type, and uses linear interpolation for numeric data and step interpolation for Boolean data. Linear interpolation is used with numeric data and connects each logged data point with a line from point to point, creating a linear set of values between each logged point. Step interpolation reports the logged value until a new data point is logged, creating a step between logged values. The Boolean value always defaults to this method, regardless of the interpolation method you selected."
I am not getting what is described here, so there must be a bug in my version MAX (4.5.0f0). It doesn't matter anyway for me as I will just use linear interpolation from now on, which appears to work.
PorridgeMan.
