The platepars_all_recalibrated.json file - markmac99/ukmon-pitools GitHub Wiki

RMS creates two scientific data files, one being the FTPdetectinfo file, and the other the platepars_all_recalibrated.json file. What is in the latter?

When you first set up the camera you installed a 'platepar' file. This file is used by RMS to map each frame to the sky (platesolving in astronomical language).

The initial platepar was manually generated using the SkyFit2 utility as explained here, and contains details of the date, time and location that the reference image was taken plus details of the mathematical model that was used to map the sky onto the image. The model takes into account distortion due to lens effects and refraction near the horizon.

During image processing, RMS adjusts the model for each individual detection to allow for small movements of the camera during the night. These could be caused by wind, thermal effects, or by vibrations due to traffic, people or animals. Our cats love jumping on the observatory roof...

The results of automated recalibration are stored in the platepars_all file. For each FF file containing detections, RMS creates a section in the file indexed by the FF name, followed by the platepar data for that frame. There should be one section for each frame that could be recalibrated.

The file is a text file but the data is stored as JSON, a structured language that allows computers to read the information back into a dictionary. This allows RMS to quickly find the platepar for each frame and apply it correctly. It is also used by server-side trajectory and orbit solvers.

{
    "FF_UK0006_20211102_174908_806_0058624.fits": {
        "F_scale": 13.520390641244425,
        "Ho": 135.20043085888028,
        "JD": 2458574.3507742244,
        "RA_H": 0,
        "RA_M": 0,
        "RA_S": 0,
        "RA_d": 94.22186489381463,
        "UT_corr": 0,
        "X_res": 1280,
        "Y_res": 720,
        "alt_centre": 43.770235145870494,
        "asymmetry_corr": false,
        "auto_check_fit_refined": false,
        "auto_recalibrated": true,
        "az_centre": 237.3768284193804,
        "dec_D": 0,
        "dec_M": 0,
        "dec_S": 0,
        "dec_d": 17.694786627963694,
        "distorsion_type": "poly3+radial",
        "distorsion_type_list": [
            "poly3+radial",
            "radial3",
            "radial5",
            "radial7"
        ],
        "distortion_type": "poly3+radial",
        "distortion_type_list": [
            "poly3+radial",
            "poly3+radial3",
            "poly3+radial5",
            "radial3-all",
            "radial4-all",
            "radial5-all",
            "radial3-odd",
            "radial5-odd",
            "radial7-odd",
            "radial9-odd"
        ],
        "distortion_type_poly_length": [
            12,
            13,
            14,
            7,
            8,
            9,
            6,
            7,
            8,
            9
        ],
        "elev": 80.0,
        "equal_aspect": false,
        "extinction_scale": 1.0,
        "focal_length": 0,
        "force_distortion_centre": false,
        "fov_h": 88.7110928957436,
        "fov_v": 47.27339448758259,
        "gamma": 1.0,
        "lat": 51.8831,
        "lon": -1.30616,
        "mag_0": -2.5,
        "mag_lev": 10.154563281528736,
        "mag_lev_stddev": 0.20996039932775085,
        "measurement_apparent_to_true_refraction": false,
        "poly_length": 12,
        "pos_angle_ref": 33.53411779239954,
        "refraction": true,
        "rotation_from_horiz": -2.893204872647113,
        "star_list": [],
        "station_code": "UK0006",
        "version": 2,
        "vignetting_coeff": 0.0007130535612064279,
        "vignetting_fixed": false,
        "x_poly": [
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            -5.4811452701488584e-06,
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            -7.580837453080252e-05,
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        ],
        "x_poly_fwd": [
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        "x_poly_rev": [
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            -1.7370832608325836e-05,
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        ],
        "y_poly": [
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            3.2570594828794683e-07,
            -6.56696485149919e-05,
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        ],
        "y_poly_fwd": [
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        ],
        "y_poly_rev": [
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        ]
    },
    "FF_UK0006_20211102_174919_056_0058880.fits": {
        "F_scale": 13.520390641244425,