[Gwyddion-users] Slope Distribution (Inclination Graph) ?

[Salman Manzoor]

Hi Gwyddion User!

I am trying to find a slope distribution (gwyddion also refers to this as
Inclination graph) from a height matrix that I obtained with AFM. Could
someone explain how does gwyddion exactly calculate the slope at each pixel
(without local plane fitting)? And what it does when you select the 'Use
Local Plane Fitting'? And when you use Local Plane Fitting, there is an
option to change the number of pixels, are these pixels selected as a
square neighbourhood or linear row/column pixels?

Thanks,

-Salman

[David Nečas (Yeti)]

Post by Salman Manzoor
I am trying to find a slope distribution (gwyddion also refers to this as
Inclination graph) from a height matrix that I obtained with AFM. Could
someone explain how does gwyddion exactly calculate the slope at each pixel
(without local plane fitting)? And what it does when you select the 'Use
Local Plane Fitting'? And when you use Local Plane Fitting, there is an
option to change the number of pixels, are these pixels selected as a
square neighbourhood or linear row/column pixels?

The module is decribed here

http://gwyddion.net/documentation/user-guide-en/statistical-analysis.html#slope-distribution

The derivatives used when local plane fitting is not used are calculated
from the minimum neighbourhood, i.e. the four neighbour pixels that
share a side with the central one, with the elementary discrete
differentation formula.

For local plane fitting, the neighbourhood is square and centered on the
pixel for odd sizes, shifted half-pixel up and to the left for even
sizes.

Regards,

Yeti