Issue with datacube reciprocal space calibration

[alouiset]

Hi!
I want to recover the reciprocal space grid of a DataCube instance in $Å^{-1}$ with the k-space origin at the center of the diffraction pattern. But it looks like there is a problem with the DataCube.calibrate() method in reciprocal space.
After

datacube.get_probe_size()

qx0_mean and qy0_mean are well stored in datacube.calibration

Calibration( A Metadata instance called 'calibration', containing the following fields:

             Q_pixel_size:      0.00814368
             R_pixel_size:      1.04527
             Q_pixel_units:     A^-1
             R_pixel_units:     nm
             QR_flip:           False
             probe_semiangle:   2.0042072631527734
             qx0_mean:          127.4822069952262
             qy0_mean:          127.39945750064858
)

Then, when I set the pixel sizes:

Q_pixel_size = 0.00814368 # in Å^-1, calibrated on Si sample.
datacube.calibration.set_Q_pixel_size(Q_pixel_size)
datacube.calibration.set_Q_pixel_units('A^-1')

datacube.calibration.set_R_pixel_size(1.04527)
datacube.calibration.set_R_pixel_units('nm')

The reciprocal space grid is not centered at the origin like I expected:

print(datacube)
--> DataCube( A 4-dimensional array of shape (20, 160, 256, 256) called 'datacube',
          with dimensions:

              Rx = [0.0,1.04527,2.09054,...] nm
              Ry = [0.0,1.04527,2.09054,...] nm
              Qx = [-127.4822069952262,-127.4740633152262,-127.4659196352262,...] A^-1  (*non-linear*)
              Qy = [-127.39945750064858,-127.39131382064858,-127.38317014064857,...] A^-1  (*non-linear*)
)

print(datacube.qxx.min(), datacube.qxx.max())
--> -127.4822069952262 -125.40556859522621

Here, I expected datacube.qxx.min() and datacube.qxx.max() to be around -1 and +1, respectively, in $Å^{-1}$.

It looks like the problem comes from the DataCube.calibrate() method in datacube.py.
Lines 94 and 95

        dim_qx = -origin[0] + np.arange(self.Q_Nx) * qpixsize
        dim_qy = -origin[1] + np.arange(self.Q_Ny) * qpixsize

should be:

        dim_qx = ( -origin[0] + np.arange(self.Q_Nx) ) * qpixsize
        dim_qy = ( -origin[1] + np.arange(self.Q_Ny) ) * qpixsize

so qpixsize is taken into account after centering the reciprocal space origin in pixel unit.

This modification fixed the issue for me, but maybe the method is not intended to work as I want it to.
Is there something I misunderstood here or is it a problem indeed?

Thanks!