Data Loading

Using Plugins

xRHEED uses a flexible plugin system to load RHEED images and provide geometry information for each experiment.

A plugin should:

• Load a specific data format (e.g., .raw, .png, .bmp).

• Provide RHEED geometry by defining an ATTRS dictionary with keys such as:

  • plugin: Name of the plugin.

  • screen_sample_distance: Distance from sample to screen (in mm).

  • screen_scale: Pixel-to-mm scaling factor.

  • screen_center_sx_px: Horizontal center of the image (in pixels).

  • screen_center_sy_px: Vertical position of the shadow edge (in pixels).

  • beam_energy: Electron beam energy (in eV).

  Note

  The screen center values are approximate and may vary between experiments.

• Return an ``xarray.DataArray`` with: - sx (horizontal) and sy (vertical) coordinates, both in millimeters. - Coordinates sorted so the image is oriented with the shadow edge at the top (i.e., the image is “facing down”). - The sy values covering the image should be negative at the top of the image.

Example plugin attributes:

ATTRS = {
    "plugin": "UMCS DSNP ARPES raw",
    "screen_sample_distance": 309.2,  # mm
    "screen_scale": 9.04,  # pixels per mm
    "screen_center_sx_px": 740,  # horizontal center of an image in px
    "screen_center_sy_px": 155,  # shadow edge position in px
    "beam_energy": 18_600,  # eV
    "alpha": 0.0,  # default azimuthal angle
    "beta": 2.0,   # default incident angle
}

Note

There is a helper function dataarray_from_image() that might be used to create DataArray from a numpy image, using ATTRS scaling and centers. Plugins may use or override this.

Manual

While writing and using a dedicated plugin is the recommended approach, you can also load RHEED images manually (BMP, PNG, TIFF, or other formats) using the same load_data() function, but without providing plugin.

In this mode, you must provide the essential calibration parameters directly as keyword arguments:

• screen_sample_distance: Distance from sample to screen [mm].

• screen_scale: Pixel-to-mm scaling factor.

• beam_energy: Beam energy [eV].

Optional parameters include screen_center_sx_px, screen_center_sy_px, alpha, and beta. The resulting xarray.DataArray follows the same conventions as plugin-loaded images (coordinates in mm, shadow edge at the top).

Example usage:

import xrheed

rheed_image = xrheed.load_data(
    "example.bmp",
    screen_sample_distance=309.2,
    screen_scale=9.04,
    beam_energy=18_600,  # eV
)

This ensures that all loaded images, whether via a plugin or manually, are consistent and ready for further analysis and visualization in xRHEED.

Returned DataArray

• The data should be an xarray.DataArray with coordinates:

  • sx: horizontal axis, in mm

  • sy: vertical axis, in mm

• The image should be oriented so the shadow edge is at the top (negative sy values).