On Tue, May 06, 2014 at 02:48:56PM -0600, Casey LaMarche wrote: > What is interesting is that Gwyddion is showing a smaller frequency > than matlab, but I don't understand how this is possible.
Because Gwyddion cheats. More precisely, it avoids the artifacts caused in FFT filtering by value and derivative discontinuities at data edges (as the profile is not really a periodic function) by extending the data slightly to make it smoothly periodic before FFT filtering and then cutting off the extension again after the filtering. The net effect is that you get nice splitting into wavines and roughness also close to the data edges, matching well the human perception/expectation in this area. Taking it to the extreme, if you take profile like the one attached, Gwyddion can essentially put the straight line to wavines and the jumps to roughness – something that is impossible with naïve FFT filtering due to edge artifacts. Unless you require precise counting of waves (as you do in your example), this is what you want. If you need the exact algorithm, I am afraid there is no substitute for reading the code... Regards, Yeti
steps.dat
Description: Netscape Proxy Auto Config
------------------------------------------------------------------------------ Is your legacy SCM system holding you back? Join Perforce May 7 to find out: • 3 signs your SCM is hindering your productivity • Requirements for releasing software faster • Expert tips and advice for migrating your SCM now http://p.sf.net/sfu/perforce
_______________________________________________ Gwyddion-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/gwyddion-users
