Oh thanks for the hint, Yeti. I guess this fft_postprocess() can be applied without any modification. Could you add this function to the gwyddion API? It might be useful for others as well.
Cheers, /M On 0, "David Nečas (Yeti)" <[email protected]> wrote: > On Fri, Sep 12, 2014 at 03:32:04PM +0200, Mathias Müller wrote: > > in my C-code I want to apply the gwyddion fft-transformation to SPM data. > > > > the code sniplet is: > > > > data_field_fft_r = gwy_data_field_new_alike(data_field, TRUE); > > data_field_fft_i = gwy_data_field_new_alike(data_field, TRUE); > > gwy_data_field_2dfft(data_field,NULL,data_field_fft_r,data_field_fft_i,GWY_WINDOWING_NONE,GWY_TRANSFORM_DIRECTION_FORWARD,GWY_INTERPOLATION_ROUND,TRUE,1) > > ; > > gwy_data_field_2dfft_humanize(data_field_fft_r) ; > > > > where data_field is obtained from real space data. > > > > When displaying the artifical data, it looks pretty good, e.g. like a > > hexagonal structure. Comparing the coordinates within the differently > > obtained FFT images, it looks > > like all the x and y values are way larger in the c-code 2d-FFT (no window) > > then the one from the gwyddion module. I.e. the very center of the > > gwyddion-performed fft-image > > is nearly at (0.002,0.004) nm^-1. But the data reasulting from > > gwy_data_field_2dfft_humanize(data_field_fft_r) show a center at approx. > > (3.43886e-08,5.05459e-08)...I guess m^-1. > > Functions such as gwy_data_field_2dfft() only perform the transforms. > They do not set units nor real fiels dimensions. This is somewhat > unfortunate, but backward compatible. See for instance > fft_prosptocess() in the FFT module: > > > https://sourceforge.net/p/gwyddion/code/HEAD/tree/trunk/gwyddion/modules/process/fft.c#l182 > > Regards, > > Yeti ------------------------------------------------------------------------------ Want excitement? Manually upgrade your production database. When you want reliability, choose Perforce Perforce version control. Predictably reliable. http://pubads.g.doubleclick.net/gampad/clk?id=157508191&iu=/4140/ostg.clktrk _______________________________________________ Gwyddion-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/gwyddion-users
