I see we talk at cross purposes. Sorry for that confusion.
By offset I am talking about the offset at the image center.
What I wanted to say is, that my FFT image doesn't have a center at (0,0) after
postprocessing the data field.
But this is somehow achieved in the gwyddion fft-module.
I just realize this when comparing the fft images of my test data obtained with
the gwyddion module and with the
output of gwy_data_field_fft_postprocess(). The center in my plugin-generated
fft image is simply not the center
of the coordinate system which I expect after applying
gwy_data_field_fft_postprocess().
my offsets:
-2,565e+09 and 2,555e+09
They seem to be what you expect them to be.
in the image: left edge -> x = 5,58952e+06
right edge -> x = 5,11441e+09
So in between there is no 0...same for the y coordinate. I don't do much on
these data but gwy_data_field_2dfft and gwy_data_field_fft_postprocess.
On 0, "David Nečas (Yeti)" <[email protected]> wrote:
> On Mon, Sep 15, 2014 at 01:21:59PM +0200, Mathias Müller wrote:
> > I already use the function as it is meant to be used and the sample data is
> > fine, since the gwyddion fft-module displays everything correctly.
> > But when getting data points via:
> >
> > gwy_selection_get_object(selection, ID, pos)
>
> I don't understand what you are trying to accomplish. The selection is
> just a set of real (as opposed to pixel) coordinates. If you have a
> selection point saying it has coordinates (0,0) it has these
> coordinates. You can use this selection in connection with some data
> field to do something. Only in this combination the coordinates mean
> something in some data field. If you shift the data field origin, (0,0)
> will still mean ‘wherever (0,0) is in this field now’.
>
> > This puzzles me. Somehow my (x,y) offsets are not corrected after
> > having them postprocessed. I apply it right after gwy_data_field_2dfft
> > as you do in prof_psdf.
>
> Which offsets? For data field offsets, try printing
>
> gwy_data_field_get_xoffset(dfield)
> and
>
> gwy_data_field_get_xoffset(dfield) + gwy_data_field_get_xreal(dfield)
>
> They should be approximately the same with opposite signs (it depends on
> the pixel size parity).
>
> For selections, they will contain the coordinates you stored to them.
>
> Regards,
>
> Yeti
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