Method for calibrating a sighting system

{
  "publication_number": "US10018893B2",
  "country": "US",
  "kind": "B2",
  "title": "Method for calibrating a sighting system",
  "abstract": "The invention relates to a method for calibrating a sighting system comprising a viewfinder and an optic for detecting the position of an object in space, characterized in that it comprises the determination of a control law to apply to the viewfinder to aim at the object as a function of its position, said position being determined in a frame of reference of the detection optic and the control law comprising two angular controls and a focusing control of the viewfinder, expressed as a function of the relative positions between the object to aim at and an intersection point of all the lines of sight of the viewfinder, the method comprising the steps consisting in: aiming (100), with the viewfinder, at objects found at at least six different known positions in the frame of reference of the sighting system and noting the corresponding controls, from the positions of the object and the corresponding controls, determining (200, 200 ′) the position of the intersection point of the lines of sight and the control law by the minimization of a function of the second derivative of the control law.",
  "claims": [
    "1. A method for calibrating a sighting system, said sighting system comprising a viewfinder focusable and rotationally movable along two axes, a detection optic for detecting a position of an object in a frame of reference of the detection optic, and a processing unit including a processor to control the rotational movement and focus of said viewfinder, said method comprising: by operation of a motor which rotates said viewfinder along said two axes, pointing and focusing said viewfinder at reference objects located at at least six different known reference positions in the frame of reference of the detection optic and storing values representing corresponding angular and focusing controls applied to the viewfinder to complete said pointing and focusing, from the known reference positions of the reference objects and the stored values, determining an intersection point of all lines of sight of the viewfinder, and determining a control law including two angular controls and a focusing control to apply to the viewfinder to aim at an object as a function of the position of said object, wherein the two angular controls are functions of the relative positions of the object and the intersection point, and wherein said focusing control is a function of a distance between the intersection point and the object, wherein said control law is determined by the minimisation of a function of the second derivative of the control law, calibrating the sighting system by configuring the processing unit to determine from said control law the two angular control values and the focusing control value to apply for the viewfinder to be aimed at and focused on an object based on a position of said object in a frame of reference of the detection optic.",
    "2. The method for calibrating a sighting system according to claim 1, in which the step of determining the position of the intersection point and the control law comprises iteratively: determining a position of the intersection point corresponding to the two angular controls minimising the function of the second derivative of the control law, and once the position of the intersection point is determined, determining the two angular controls minimising the function of the second derivative of the control law.",
    "3. The method for calibrating a sighting system according to claim 2, in which the step of determining the position of the intersection point comprises the minimisation, as a function of said position, of the integral of the sum of the second derivatives of the angular controls.",
    "4. The method for calibrating a sighting system according to claim 2, in which the step of determining the position of the intersection point comprises the minimisation, as a function of said position, of the integral of the sum of the second derivatives of the relative angular positions between the reference object and the intersection point expressed as a function of the angular controls of the viewfinder.",
    "5. The method for calibrating a sighting system according claim 1, in which each angular control is a function of two angles of thin plate spline type.",
    "6. The method for calibrating a sighting system according to claim 5, in which each angular control is a function of two angles of regularised thin plate spline type.",
    "7. The method for calibrating a sighting system according to claim 2, in which the determination of the focus control is implemented during the determination of the angular controls or after the determination of the angular controls and the intersection point.",
    "8. The method for calibrating a sighting system according to claim 7, in which the determination of the focus control comprises the minimisation of the integral of the second derivative of the focus control.",
    "9. The method for calibrating a sighting system according to claim 1, in which the focus control is a function of cubic spline type.",
    "10. A sighting system, comprising: a viewfinder; a detection optic for detecting a position of an object to aim at; and a processing unit including a processor configured to perform the method according to claim 1, so as to configure said processing unit to determine from the control law the two angular control values and the focusing control value to apply for the viewfinder to aim at and focus on an object based on a position of said object in a frame of reference of the detection optic."
  ],
  "description_excerpt": "The invention relates to a method for calibrating a sighting system to aim at an object using a viewfinder, the position of the object being located in a frame of reference external to the viewfinder, and a system implementing said method.\n\nThe invention finds application in particular in the field of the acquisition of high resolution images in a precise position, such as the acquisition of images of biometric traits of individuals.\n\nThe calibration of a sighting system is the determination of a control law to apply to a viewfinder to make it possible, from a position of an object in a frame of reference external to the viewfinder, to orient said viewfinder so as to aim at the object.\n\nAn example of application is a system for acquiring images of biometric traits of individuals, such as for example iris images. In order to acquire high resolution images of the iris of an individual, the system requires a high resolution camera. Due to this important resolution, this camera cannot have a wide fixed field, but has to be movable in order to be able to aim at an iris of an individual.\n\nThe system thus also comprises two cameras of lower resolution, but wide field, and fixed, which can detect the position of an iris of an individual.\n\nThe position of the iris in the frame of reference of the wide field cameras has to be exploited by the high resolution camera in order to aim at the iris and then carry out its acquisition.",
  "cpc": [
    "G03B 13/18",
    "G01B 11/002",
    "G06T 2207/30244",
    "G06T 7/80",
    "H04N 23/63",
    "H04N 23/67",
    "H04N 5/23293"
  ],
  "ipc": [
    "G01B 11/00",
    "G03B 13/18",
    "H04N 5/232",
    "G06T 7/80",
    "H04N 5/225"
  ],
  "assignees": [
    "Morpho SA"
  ],
  "inventors": [
    "Benoit MALRAT",
    "Jean Beaudet"
  ],
  "filing_date": "2015-11-03",
  "publication_date": "2018-07-10",
  "grant_date": "2018-07-10",
  "priority_date": "2014-11-05",
  "application_number": "US-201514931571-A",
  "family_id": "52807871",
  "cited_by_count": 4,
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  ]
}