On Wed, Mar 01, 2017 at 12:10:39PM +0100, Alessandro Gambardella wrote:
> I have a question related to calculation of the Power Spectral Density
> as reported at page 69 of the manual. I cannot easily understand what
> exactely is that "h" that originates the nm^3 unit instead of the nm^4
> as reported elsewhere for the PSD. Is that h the maximum height in the
> processed image? Or is it maybe the image resolution in nm? I cannot
> find any h definition in the previous paragraphs of the manual.
Please see the FAQ
http://gwyddion.net/faq.php#faq015
Concerning the formula, h is the sampling step.
> I only need to transform the nm^3 as Gwyddyon calculates into nm^4 for
> my purposes.
I would advise against this. The values in nm⁴ you often encounter have
a normalisation that depend on sampling. So you cannot compare PSDFs
from different measurements (different area, different sampling step).
The way in which these PSDFs preserve Parseval's theorem is valid but
not useful.
Instead, try to figure out what exactly the software that produces PSDF
in nm⁴ does and then recalculate it to the actual density, the same as
used in Gwyddion.
Regards,
Yeti
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