On Fri, May 02, 2014 at 01:47:50PM +0200, [email protected] wrote: > my question is the following. I have to calculate the roughness with its > error bar from images with 3 nm height islands on silicon oxide.
This is impossible. More precisely, it is impossible without any a priori information telling you what is the topography and what is the error/uncertainty of topography. If you calibrated the instrument (http://gwyddion.net/documentation/user-guide-en/caldata.html) and applied the calibration to the data then you would know a priori the random and systematic errors for each data point. Gwyddion would perform corrections and provide uncertainties of the statistical characteristics automatically in the Statistical Quantities tool (and a few other places). Otherwise you may be able to roughly estimate uncertainties of some statistical quantities only if you have a model to which the surface must conform. This allows you to state that all deviations are measurement errors. For instance, if you can say a part of the surface is so flat that all observed variations from plane are measurement errors, you can then estimate these errors. Since roughness itself is a random deviation from some mean shape, the situation is even more complex here. Generally, you need at least a statistical model of the roughness. You can try to just estimate type A uncertainties by repeated measurements, and this may be what you are doing, however - This is likely a small part of the total uncertainty; the main issue is not the variation between individual measurements but systematic errors due to noise, tip convolution effects, limited area effects, ... - The Row/Column Statistics tool does not do this anyway. So, what Row/Column Statistics does? It calculates the selected quantity for all rows or columns and displays the average value and inter-row or inter-column variation. This is not an error estimate! There is probably only a single quantity whose average tells something about the entire surface: the mean. The average of means is the mean for the entire surface. All other quantities would have to be combined in a more complex manner to obtain something describing the entire surface or they are purely 1D quantities. So the average does not correspond directly to a 2D quantity and the variation is not the error of some 2D quantity. I hope this, at least, clears up things. Regards, Yeti ------------------------------------------------------------------------------ "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available. Simple to use. Nothing to install. Get started now for free." http://p.sf.net/sfu/SauceLabs _______________________________________________ Gwyddion-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/gwyddion-users
