Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C17/00—Compasses; Devices for ascertaining true or magnetic north for navigation or surveying purposes
  • G01C17/34—Sun- or astro-compasses

Definitions

• the present invention relates to azimuth direction finding in the field of navigation in surveying and military applications and more specifically to the implementation of a compass based on celestial observation.
• a celestial compass that uses and/or includes: (a) one or more imagers configured to image star positions in the sky, (b) a memory storing an "almanac” (an almanac, e.g. "Yale Catalogue”) listing the true position of stars and/or celestial bodies and/or sun and/or moon (herein after "stars") in the sky at any desired times (i.e.
• a processor coupled to the memory and programmed to process the star almanac data, the celestial compass global location, and the camera images of star positions to calculate the direction of the true north (geodetic North) or any other basis/datum direction by comparing the data on star location in the almanac to their location as imaged by the one or more imagers, and determining the orientation of the celestial compass relative to the global coordinate system (azimuth and elevation angles).
• the celestial compass can be leveled by a "common leveling apparatus".
• the tilt offset from the horizontal plane of the celestial compass can be determined by a tilt measuring device.
• a method of determining the direction of the true north can also be used to determine the elevation angle of a given target object with respect to the local horizon.
• the one or more imagers image the sky and determine the actual position of stars in the sky.
• the meaning of 'position' as used herein refers to two-axis angular coordinates in a spherical coordinate system relative to the point of view of the one of more imagers, also referred to as azimuth and elevation.
• each imager may include appropriate imaging technology so that stars can be imaged during the day as well as at night.
• the position of the celestial compass and measurement time may be determined via a Global Positioning System (GPS). Alternatively other navigation/positioning and timing methods and/or devices can be used.
• GPS Global Positioning System
• the processor calculates the orientation of the celestial compass relative to the global coordinate system (azimuth and elevation angles).
• the required accuracy of the true north determination by the celestial compass is achievable even in cases where the input parameters of position and time are not highly accurate. For example, a 1 kilometer error in the position of the celestial compass will affect the accuracy of the true north direction by less than a third of a milliradian.
• Fig. 1 is a perspective view of the local horizontal plane, the celestial compass at the center and the celestial sky above;
• Fig. 2 is a side view of the local horizontal plane, the celestial compass at the center and the field-of-view (FOV) of the celestial sky imaged by the celestial compass;
• FOV field-of-view
• Fig. 3 is a top-down view (from the zenith onto horizontal plane) of the local horizontal plane, the celestial compass at the center and the field-of-view (FOV) of the horizon as it is imaged by the celestial compass; and
• Fig. 4 is a diagram showing pictorially the process implemented by the processor of the celestial compass, the image it produces, comparison and adjustment using data from the star almanac and the final determination of the true north direction.
• the figures show a celestial compass 1 in accordance with embodiments of the invention.
• the celestial compass includes one or more imagers 21 to 23, for example CCD or C-MOS cameras, configured to produce an image 15 of the sky 3 or at least a suitably significant portion of the sky, with a view of several stars 4.
• Image 15 is compared to a star almanac, schematically depicted as a memory device 16 storing star position data for each star that can potentially be imaged by the celestial compass.
• a target object 10 within the field of view (FOV) of the imagers of the celestial compass can also be imaged by one of the imagers 21 to 23.
• the celestial compass 1 may rest on a platform that is adjusted to accurately orient the celestial compass in the local horizontal plane 2 with the aid of a leveling device 20.
• Such a device may be a spirit level.
• the angular offset of the celestial compass from the horizontal plane may be measured, and the offset used to correct the viewed image of the stars.
• This offset may be measured with a device that is capable of accurate angular measurements of offset from the horizontal plane.
• the celestial compass can derive its orientation in both azimuth and elevation. Nevertheless, in cases where only a small number of stars are visible, or indeed, when only one star can be imaged, for example the Sun in the daytime, knowledge that the celestial compass is accurately referenced to the horizontal plane significantly enhances the accuracy of determining the true north.
• the imagers 21 to 23 capture the angular position of the stars within their FOV.
• the position of a star within the FOV can be related directly to its angular position (azimuth and elevation) with respect to the reference point of the imager.
• the current invention also contemplates a set of imagers 21 to 23 jointly covering or exceeding the entire FOV of a hemisphere, thereby covering the entire sky.
• three imagers are depicted, where each imager has a FOV of 127° in the horizontal and a 92° FOV in the vertical. Therefore three imagers proved full coverage for the hemisphere of the sky.
• Alternatively a larger number of imagers with smaller individual FOV values are also possible, provided their combined FOV covers the hemisphere of the sky.
• a practical imager especially if it offers a large FOV, is likely to suffer optical aberrations that might lead to erroneous angular position values for imaged stars.
• the mechanical alignment of several imagers may introduce some relative alignment errors between imagers.
• the invention reduces these errors by carefully calibrating the images generated by the imagers against a calibration image with visible calibration objects accurately arranged on a calibration surface in the form of a complete hemispheric target under which the imager set of the celestial compass is placed for calibration.
• the calibration surface may extend to a portion of a hemisphere, and relative angular motion between the celestial compass and the calibrating target incorporated to scan the calibration target over the entire combined FOV of the imager array.
• the set of imagers may calibrated by viewing stars distributed across the entire FOV and comparing their position to those in the almanac.
• the location of pixels on the images obtained from the imagers 21 to 23 can be associated with the precise direction of the true north 7, and from this association any other pixels can be used to calculate a precise azimuth direction.
• Capturing an image of target 10 in the imaged dataset enables calculation of the target's precise azimuth 6, and optionally its elevation 8. As noted above, this requires knowledge of the relative angular offset of the reference plane of the celestial compass from the horizontal plane. Such knowledge can be obtained directly from the image of stars in the sky. Alternatively, using level 20, knowledge of the local horizontal plane is obtained, and processing of that datum with the azimuth 6 of target object 10 can determine the elevation angle 8 of the target object with respect to the local horizon. If, for whatever reason, the celestial compass 1 is not leveled on a local horizontal plane, a compensation angle can be calculated utilizing a leveling offset meter to be used in place of level 20.
• a sky imager images the stars and compares it with an almanac, whereby with an accurate knowledge of the day and time, and a GPS (i.e. accurate knowledge of position/location and time), one can accurately compute true north 7.
• the position/location used in the almanac is the position of compass 1 and imager/cameras 21 to 23.
• a processor (not shown) of the celestial compass extracts data from a star almanac data storage 16, such as the Yale Catalogue.
• the processor also extracts star positions from an image produced by the imagers 21 to 23.
• the processor compares the two (image matches) to compute the differential orientation between the almanac and image, to enable a computation of the true North.
• processor may be a suitably programmed computer.
• the invention contemplates a computer program being readable by a computer for executing the method of the invention.
• the invention further contemplates a machine-readable memory tangibly embodying a program of instructions executable by the machine for executing the method of the invention.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Astronomy & Astrophysics (AREA)
• General Physics & Mathematics (AREA)
• Navigation (AREA)

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• 2015
  • 2015-03-26 IL IL237963A patent/IL237963A0/en unknown
• 2016
  • 2016-03-13 SG SG11201707739RA patent/SG11201707739RA/en unknown
  • 2016-03-13 WO PCT/IL2016/050272 patent/WO2016151574A1/en active Application Filing
  • 2016-03-13 EP EP16767866.3A patent/EP3274657A4/de not_active Withdrawn
  • 2016-09-25 IL IL248033A patent/IL248033A0/en unknown

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