astra.utils.optics

astra.utils.optics#

Pure optics math shared across device-based and FITS-header-based code paths.

paired_devices.py derives plate scale from live Alpaca Camera/Telescope device properties, while pointer.py derives it from FITS header metadata (XPIXSZ/FOCALLEN). Both then need the same downstream math (plate scale, field of view, FWHM in pixels), so that math lives here as plain functions over floats/arrays with no device or FITS dependencies.

Functions

field_of_view(sensor_size, focal_length)

Calculate the field of view spanned by a sensor, without the small-angle approximation.

fov_from_plate_scale(num_pixels, ...)

Calculate field of view from a per-pixel plate scale (small-angle approximation).

fwhm_pixels(plate_scale_deg_per_pixel[, ...])

Calculate the expected FWHM in pixels for a given atmospheric seeing.

plate_scale(pixel_size, focal_length)

Calculate the plate scale in degrees per pixel.
astra.utils.optics.plate_scale(pixel_size: float | ndarray, focal_length: float) → ndarray[source]#

Calculate the plate scale in degrees per pixel.

Parameters:

  • pixel_size – Pixel size in meters. Scalar or array (e.g. [x, y]).

  • focal_length (float) – Focal length in meters.

Returns:

Plate scale in degrees per pixel, same shape as pixel_size.

astra.utils.optics.field_of_view(sensor_size: float | ndarray, focal_length: float) → ndarray[source]#

Calculate the field of view spanned by a sensor, without the small-angle approximation.

Parameters:

  • sensor_size – Sensor extent in meters. Scalar or array (e.g. [sx, sy]).

  • focal_length (float) – Focal length in meters.

Returns:

Field of view in degrees, same shape as sensor_size.

astra.utils.optics.fov_from_plate_scale(num_pixels: float | ndarray, plate_scale_deg_per_pixel: float) → ndarray[source]#

Calculate field of view from a per-pixel plate scale (small-angle approximation).

Parameters:

  • num_pixels – Number of pixels along one or more axes.

  • plate_scale_deg_per_pixel (float) – Plate scale in degrees per pixel.

Returns:

Field of view in degrees, same shape as num_pixels.

astra.utils.optics.fwhm_pixels(plate_scale_deg_per_pixel: float, seeing_arcsec: float = 1) → float[source]#

Calculate the expected FWHM in pixels for a given atmospheric seeing.

Parameters:

  • plate_scale_deg_per_pixel (float) – Plate scale in degrees per pixel.

  • seeing_arcsec (float) – Atmospheric seeing in arcseconds.

Returns:

float – Expected FWHM in pixels.