Your are absolutely right, that is a difficult task and I have no solution for it, but I try to discuss my opinion. I would say that the 3-point levelling is a nice technique when only used for a small part of the image or to say it that way: scanner range. Not only but especially when using a tube scanner you get parabolic or higher order parts into the "background" which then are hard to evaluate. Reasons as you all know can be the tube geometry itself, creep, hysteresis and so on. A purely plain averaging over three points therefore is somehow misleading.
Unfortunately I have no suggestions what the best way could be to overcome this but have you tried to calculate the higher order deviations out of your images? Ideally if you do a cross section over the entire image, each single staircase step should be of slope 0. If not further corrections will be needed to your data. As Peter said: a "thickness bar" or at least two more thin lines on both hand sides of the chosen profile would be great for the profiling tool anyway. Regards -- Markus Am 27.11.2008 um 08:39 schrieb Scott Webster: > This is changing the subject a little... > > But I too often use Gwyddion to determine step heights in my images. > I have been using the three-point level tool on one terrace in order > to try to make that (and the other) steps flat. Then I use the 1-D > statistical height distribution tool. Ideally the distribution > consists of a series of peaks that correspond to the different heights > of the steps (these can be measured with the "distance" tool after you > accept the height distribution). > > I believe that this method should in theory be more accurate than > analyzing sections, or at least it should do some more averaging for > you, so you don't have to look at so many section lines. There are > some papers written on this. > > Unfortunately, I find that my results are quite dependent on exactly > how the three-point level is done. Just a slight change of one of the > points or the averaging size changes the result, and it is quite > difficult to notice that it is not ideal. The image looks like a nice > staircase of steps in either case, and the histogram has peaks in it. > > Section lines have their own problems, as noise in the data causes the > section line to not look like a perfect "staircase" and therefore be > harder to interpret. > > Does anyone have any tips on using Gwyddion to reliably determine step > heights? In any event, the improvement suggested by Peter Eaton would > be nice, but I'm not sure it is the "holy grail." > > Scott > > On Wed, Nov 26, 2008 at 8:47 AM, Peter Eaton > <[EMAIL PROTECTED]> wrote: >> Dear Gwyddion Devleopers, >> I would like to make a request for a feature in Gwyddion. It is >> really a >> fairly simple (I hope) change to a current feature. >> Currently, researchers in my group use the "Extract Profiles" >> Feature, to >> measure step heights, a lot. When you select a profile, you have >> the option >> of changing "thickness" from 1 to 128 pixels. I guess what this >> does is to >> (mean) average a number of lines, it says in the documentation: >> "Profiles can be of different "thickness" which means that more >> neighbour >> data perpendicular to profile direction are used for evaluation of >> one >> profile point for thicker profiles. " >> This is really useful. But the problem is that it's not very visual, >> because the user cannot see where the lines being averaged are. It >> would be >> great if when the "thickness" is more than 1, instead of a line, a >> rectangle, showing where the lines being averaged are on the >> image. THis >> way, we can maximise the "width" of the profile, while avoiding >> unwanted >> "features". >> >> Ideally, the rectangle would also have some clear indication of >> which axis >> is along the profile length (e.g. a central line with arrowheads), >> because >> when you have "drawn" a square by this technique, it is easy to get >> confused and think the averaging axis is the profile length axis, >> etc. >> Thanks once again for the great software! >> pete. >> >> >> >> ________________________________ >> BigSnapSearch.com - 24 prizes a day, every day. Search now >> --------------------------------------------------------------------- >> ---- >> This SF.Net email is sponsored by the Moblin Your Move Developer's >> challenge >> Build the coolest Linux based applications with Moblin SDK & win >> great >> prizes >> Grand prize is a trip for two to an Open Source event anywhere in >> the world >> http://moblin-contest.org/redirect.php?banner_id=100&url=/ >> _______________________________________________ >> Gwyddion-users mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/gwyddion-users >> >> > > ---------------------------------------------------------------------- > --- > This SF.Net email is sponsored by the Moblin Your Move Developer's > challenge > Build the coolest Linux based applications with Moblin SDK & win > great prizes > Grand prize is a trip for two to an Open Source event anywhere in > the world > http://moblin-contest.org/redirect.php?banner_id=100&url=/ > _______________________________________________ > Gwyddion-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/gwyddion-users ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Gwyddion-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/gwyddion-users
