Parameter details for the program to generate a Fresnel diffraction pattern

Occult uses a program written by Bob Anderson to generate the Fresnel diffraction patterns

When executing the program, the program name must be preceded by the name of a file containing a set of parameters that the program uses to generate the Fresnel image. For example, a call like:

"C:\\FresnelFolder\Parameters.txt" OccultDiffractionApp.exe
where the file Parameters.txt contains the parameters, can be located anywhere, and must be identified in inverted commas containing the full path for the file.

This topic lists those parameters. Issues to note are:

Every line where a parameter is specified must end with a comma, except for the very last parameter
A colon must be present immediately following the keyword, with the value being located between the colon and comma
Everything on a line after '//' is a comment. Comments are ignored by the program.
Indenting is not important. This is only done merely for visual appearance of this list.
Braces { } must surround the set of parameters

The key words, and illustrative values, are highlighted

{

// Set window_size to 0 to suppress display of ground shadow (and possibly other plots as well).
window_size_pixels : 800, // Optional but - if omitted, a default size will be used, so plots will be produced.

// The title of the ground shadow display image. title :
"(9203) Myrtus 2025 Feb 22", // Optional

fundamental_plane_width_km : 40, // Required. Size of the FOV in Km
fundamental_plane_width_num_points : 2000, // Required, but overridden if an external image is supplied

// Distance to the asteroid can be specified either in au or in arcsec.
// If both are present, parallax_arcsec is used. // At least one must be present.

parallax_arcsec : 3.7711,
distance_au : 2.33,

// If you want an integrated (white light) ground shadow image, supply a path to a QE table file.
// Use the example QHY174 sensor response curve file as a template. When present,
// a ground shadow image will be generated for each entry in the table.
// Each image will be weighted by the QE value at that wavelength for summing with the other images.

// path_to_qe_table_file : "qhy174QEevery20nm", // Optional. See note below if you need to include folder paths

// If your path contains back slashes, you must escape them with another back slash. See example below ...
// Example: path_to_qe_table_file : "c:\\Users\\boban\\Dropbox\\GolandProjects\\OccultDiffraction\\qhy174QEevery20nm",

// If no QE table is provided, the ground image will be generated for the wavelength // specified below. This parameter is ignored if a QE table is provided.

observation_wavelength_nm : 500, // Required to be present, even if a QE table is provided.

// The next 3 values determine shadow speed and fundamental plane PA (not relevant
// for Occult usage except for cross checking comparison during development). They are used
// to extract a sample light curve from the diffraction shadow.

dX_km_per_sec : 5.074,
// Optional dY_km_per_sec : -0.904,
// Optional path_perpendicular_offset_from_center_km : -1.18, // Optional. Defaults to 0.0 See note below for details

// The path_perpendicular_offset_from_center_km parameter is interpreted such that
// positive values shift the observation path to the right of someone facing forward on the star path.

percent_mag_drop : 75, // Optional. If omitted, 100 will be used

// star_diam_on_plane_mas: 0.15, // Optional. If omitted, 0.0 is used (i.e., no finite star calculation)

// The following parameters control limb-darkening for the star.
// Either the star class or a limb-darkening coefficient can be specified.
// If both are supplied, the limb_darkening_coeff is used.
// If omitted completely, no limb-darkening is applied.

limb_darkening_coeff: 0.7,
// Optional star_class : "K", // Optional Valid values are O B A F G K M

// This section can be omitted if an external image is supplied.
// If included when an external image is supplied, the ellipse shape
// will be added (overlaid) on top of the external image.

main_body : {                 // Required if no external image is supplied
    x_center_km : 5.8,
    y_center_km : 0.6,
    major_axis_km : 17.6,
    minor_axis_km : 8.0,
    major_axis_pa_degrees : 98.3,
},

satellite : {                 // Optional
    x_center_km : -5.8,
    y_center_km : -0.6,
    major_axis_km : 7.5,
    minor_axis_km : 2.8,
    major_axis_pa_degrees : 94.0,

// Set path_to_external_image. This field should be omitted if no external image is supplied.
// External images must be square and the width is used as fundamental_plane_width_num_points
// and overrides any value supplied in that parameter. Any ellipses defined will be
// added on top of the external image. Most commonly the ellipses are left empty. /
/ The external image file format can be 8 bit grayscale png with
// asteroid pixels set to 0 and all background pixels set to 255. If the external image
// is an RGB type, it is converted to the gray 8 and the external image pixel at (0,0)
// is read and used as skyRef. This is used to set the gray 8 image to 0 everywhere /
/ this value is found in the external image and to 255 everywhere else. The scheme is
// simply if it's not 'sky', it is 'asteroid'.

path_to_external_image : "11293_2.png",
external_image_width_km : 21.8

}

An example parameter file created by Occult is:

{
   window_size_pixels : 0, //Displays ground shadow. Set to zero for no display
   fundamental_plane_width_km : 37,
   fundamental_plane_width_num_points : 1200,
   parallax_arcsec : 5.8850,
   path_to_qe_table_file : "D:/Occult 4/Fresnel/Program/Watec910_every_40nm.qe",
   observation_wavelength_nm : 600,
   dX_km_per_sec : -0.992,
   dY_km_per_sec : -0.416,
   percent_mag_drop : 100,
   limb_darkening_coeff: 0.50,
   star_diam_on_plane_mas: 0.00,
   // This section can be omitted if an external image is supplied.
   // If included when an external image is supplied, the ellipse shape
   // will be added (overlaid) on top of the external image.
   main_body : {
      x_center_km : -12.23,
      y_center_km : 1.62,
      major_axis_km : 10.00,
      minor_axis_km : 3.50,
      major_axis_pa_degrees : 68.0,
   },
   satellite : {
      x_center_km : 12.13,
      y_center_km : -4.72,
      major_axis_km : 1.40,
      minor_axis_km : 1.40,
      major_axis_pa_degrees : 75.0,
   },
   // path_to_external_image : "input.png", //optional
}

Format of the quantum efficiency tables

The format of the QE table (the quantum efficiency of the camera detector) used to calculate the Fresnel pattern having regard to the camera's color sensitivity, is of the form:

[
   [wavelength_nm, qe_percent],
   [wavelength_nm, qe_percent],
   [wavelength_nm, qe_percent],
   ...
   [wavelength_nm, qe_percent],
]

The wavelengths must be in ascending order.
qe_percent is just used as a weighting factor, and wavelength weights will ultimately be
normalized so that the sum of the weights is 1.0. As a result, QE percentage is not the
mandatory units to use: if you have other values that can be used to weight each
wavelength contribution, go ahead.

Five qe files are provided when the program is downloaded via Occult. Those files are:

Watec910_every_40nm.qe
Starlight_every_40nm.qe
Watec902_every_40nm.qe
qhy174QE_every_5nm.qe
qhy174QE_every_20nm.qe

They will be found in the folder Occult 4/Fresnel. The file names refer to an associated camera