Global Navigation Satellite Systems (GNSS) are often used for obtaining heading measurement estimates. Most notably in navigation systems for mobile systems, the direction of travel is obtained from measuring the vehicle's velocity vector.
Inexpensive magnetometers currently available in digital compasses have an accuracy of 2-3° and depend on the accuracy of the world magnetic field model. While suitable for directions when travelling, the lack of accuracy and precision are significant drawbacks in other applications.
Gyro compassing is another way of measuring a heading which depends on accurately measuring the earth's angular velocity by an inertial measurement unit. Currently, a high accuracy inertial sensor and navigation system are available with a heading accuracy of 0.1 degrees when in motion. However, such systems are expensive and inertial navigation systems are ineffective for static applications, such as surveying. Furthermore, higher accuracy is desired for some applications.
A heading obtained from Real Time Kinematic (RTK) compassing—i.e., the vector obtained over a known baseline between two GNSS antennas—is another GNSS-based approach that does not require a velocity vector but often requires baselines of many meters to obtain the required accuracy. In many applications, this requires structural dimensions that are not practical.
For example, to obtain True North with an accuracy of 0.1°, known techniques use a highly accurate inertial sensor based system that may cost $100,000 or “gravity finder” devices along with multiple GPS systems collocated at distances of 100 m or more, as separate mobile elements, which make it impossible for applications, since the implementation is very expensive or very large and cumbersome, and the calibration process is complicated and typically requires more than one person.
A precision positioning and pointing instrument uses a combination of sensors that are compact and affordable with a calibration process that obtains an accurate True North. This enables a laser rangefinder to provide precise geolocation coordinates of an object of interest.
An aspect of the system is to perform manual calibration by a human operator who accurately directs a pointing device, such as a telescope, to a reflector that was placed at a required distance and engages a calibration process to determine True North which is then recorded.
Another aspect of the system is automatic continuous calibration using an automatic seeker calibration system. In this embodiment, the operator points the telescope towards an object of interest (OOI) for which an accurate bearing is required. During automatic calibration, the automatic calibration seeker acquires lock onto a calibration reflector of a calibration antenna assembly that was placed at a known distance and within the field of the view of an automatic calibration seeker to determine the True North. The automatic calibration seeker maintains lock onto the calibration reflector and provides updated calibration information to a processor as long as the calibration antenna assembly remains in the automatic calibration seeker's field of view, during which a precision positioning and pointing instrument (P3I) is continuously calibrated.
Following completion of the calibration process, the P3I operator directs the pointing device to the object of interest (OOI) to determine geodetic coordinates of the OOI and line-of-sight angles to the OOI which are transmitted via a communication device to the operator and other users.
These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings which are schematic and not necessarily to scale.
Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In this regard, the embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. In clearly describing features of the embodiments, descriptions of other features that are well known to one of ordinary skill in the art may be omitted.
The indefinite articles “a” and “an” do not exclude a plurality of the following noun. Any use of “and/or” includes all combinations of preceding and following items, including a single item among those items. The words “at least one” preceding a list of items denotes any one item in the list or any combination of the items in the list. For example, at least one of A, B and C includes A; B; C; A and B; A and C; B and C; and A, B and C, regardless of whether A, B or C is a plural noun.
The precision positioning and pointing instrument (P3I) can accurately estimate the geodetic coordinates (latitude and longitude) of an object of interest (OOI) 21 (
Relative angular positional information may be obtained passively by placing the mounting rail 2 and pointing device 9 on main gimbal set 3 that is instrumented with pitch encoder 4 and yaw encoder 5 as illustrated in
The P3I is used with a calibration antenna assembly that includes GNSS antenna 1B and calibration reflector 7. An enlarged drawing of an embodiment of the calibration antenna assembly is illustrated in
The sensor 19 constitutes equipment capable of tracking the calibration reflector 7 and may include an electro optical (EO) sensor, infrared sensor (IR), a laser range finder, a radio frequency (RF) based sensor (e.g. RADAR), or other known tracking technology. One example of an implementation could consist of a small EO device such as a CMOS camera continuously observing the reflector 7 coated with a pattern, such as a QR code or ArUco pattern, which are significantly more accurate for automatic image processing than a cross hair. Such cameras are available with a resolution of 3840×2160 pixels and a frame rate of 30 fps that can be used. This allows the software algorithm to close the controller loop, thereby orienting the seeker along the line of sight directly to the static reflector. Other sensors may be used to drive the seeker controller and to close the loop locking the seeker on the reflector.
As illustrated in
In an embodiment, automatic directional calibration may be obtained actively through automatic calibration seeker 8, illustrated in
Manual directional calibration is achieved through directing the pointing device 9 toward antenna 1B and obtaining a calibration vector from the P3I to the calibration antenna assembly 1B, 7 by defining a directional angle from the first GNSS antenna 1A to the second GNSS antenna 1B with respect to True North, based on first and second signals from real-time kinematic global navigation satellite systems obtained by GNSS receivers 13A and 13B, and computed in the system processor 11.
The accuracy of a calibration vector depends on the accuracy by which the GNSS receivers 13A and 13B obtains coordinates of the first and second locations of first and second GNSS antennas 1A and 1B and on the distance between the P3I antenna 1A and the calibration antenna assembly antenna 1B which is called the baseline distance. To keep the baseline distance to the absolute minimum, GNSS augmentation methods may be employed, such as differential GNSS and carrier phase wavelength disambiguation and/or real time kinematic (RTK) GPS.
A GNSS receiver operating on the principle of RTK requires ingestion of correction data into the positioning solution. The RTK corrections consist of a stream of data that is transported in a Radio Technical Commission for Maritime Services (RTCM) format. The RTCM data is generated by an RTK base station (not shown) embedding a GNSS receiver with a known antenna location and a processor that computes the corrections. A GNSS receiver operating on the principle of RTK requires RTCM data from an RTK base station that is within 20 miles, with improved accuracy if closer. The most common way to obtain RTK correction data is to find a nearby RTK base station that broadcasts RTCM data over the networked transport of RTCM via internet protocol (NTRIP).
As illustrated in
In another embodiment, instead of receiving RTCM data via RF receiver 20, the P3I may generate RTK correction data. GNSS antenna 1B and GNSS receiver 13B of the calibration antenna assembly may generate RTK corrections internally in the processor 11 for use by GNSS receiver 13A. This eliminates the need to install an ad-hoc RTK base station in the vicinity when an RTK base station is not within 20 miles of the P3I, thereby reducing material, components and complexity of the system.
The processor 11 may also perform GNSS carrier phase disambiguation internally to further reduce the baseline (the distance between GNSS antennas 1A and 1B) by an order of magnitude compared to a standard RTK computation. Thus, an accuracy of 0.02° can be obtained with a baseline of three meters or less using 14-bit encoders. Using the same encoders, a baseline of 30 m provides an angle accuracy that is 10 times better. Higher accuracy can be obtained by increasing the baseline and increasing the number of bits in the encoder. For example, 0.005° angular accuracy can be obtained using a 16-bit encoder and about 10 m baseline, such as when a precise heading is required for an OOI 5 km away.
Once pointing device 9 is locked on reflector 7, the operator engages the calibration software. In an embodiment, triggering a switch on the electronic box panel causes software in processor 11 to determine True North using all collected data from the sensors. Then, first angular measurements of the main gimbal set are detected by main pitch and yaw encoders 4, 5 in the main gimbal set while pointing device 9 is aligned with the second antenna to calibrate main pitch and yaw encoders 4, 5. This enables processor 11 to determine a baseline from the first antenna 1A to the second antenna 1B in the geographical coordinate system aligned with True North.
After receiving feedback from the P3I indicating a successful calibration, the operator points 43 the pointing device 9 on the universal mounting rail 2 towards the desired direction, e.g., aligned with a desired object of interest (OOI) 21 (
In the embodiment illustrated in
The GNSS receivers 13A and 13B may also be fitted with a selective availability anti-spoofing module (SAASM).
According to an aspect of an embodiment, the described features, functions, operations, and/or benefits can be implemented by and/or use processing hardware and/or software executed by processing hardware. For example, processor 11 illustrated in
The many features and advantages of the embodiments are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the embodiments that fall within the true spirit and scope thereof. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the inventive embodiments to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope thereof.
Number | Name | Date | Kind |
---|---|---|---|
453158 | Paoli | May 1891 | A |
3191176 | Guier | Jun 1965 | A |
4741245 | Malone | May 1988 | A |
4870422 | Counselman, III | Sep 1989 | A |
4881080 | Jablonski | Nov 1989 | A |
5379045 | Gilbert et al. | Jan 1995 | A |
5617317 | Ignagni | Apr 1997 | A |
5717406 | Sanderford | Feb 1998 | A |
5777578 | Chang et al. | Jul 1998 | A |
6035254 | Nichols | Mar 2000 | A |
6064942 | Johnson et al. | May 2000 | A |
6304210 | Allison et al. | Oct 2001 | B1 |
6369755 | Nichols et al. | Apr 2002 | B1 |
6727849 | Kirk et al. | Apr 2004 | B1 |
6732051 | Kirk et al. | May 2004 | B1 |
7451059 | Malchi et al. | Nov 2008 | B2 |
7468695 | Williams | Dec 2008 | B1 |
8311757 | Lin | Nov 2012 | B2 |
8686900 | Whitehead et al. | Apr 2014 | B2 |
8705022 | Taylor et al. | Apr 2014 | B2 |
8904656 | Hohl et al. | Dec 2014 | B2 |
9372070 | Jancic et al. | Jun 2016 | B1 |
9551980 | Akcasu et al. | Jan 2017 | B2 |
9689673 | Bejeryd et al. | Jun 2017 | B2 |
10337833 | Knapp | Jul 2019 | B2 |
10795030 | Schipper et al. | Oct 2020 | B2 |
20060069469 | Campbell | Mar 2006 | A1 |
20070104353 | Vogel | May 2007 | A1 |
20140300886 | Zogg | Oct 2014 | A1 |
20180274910 | Heidemann | Sep 2018 | A1 |
20180295272 | Xue | Oct 2018 | A1 |
20190204123 | Zhao | Jul 2019 | A1 |
20190383609 | Simon | Dec 2019 | A1 |
20200357141 | Zhou | Nov 2020 | A1 |
Entry |
---|
Baseline or base line. (1992). In C. G. Morris (Ed.), Academic Press Dictionary of Science and Technology (4th ed.). Elsevier Science & Technology. Credo Reference: https://search.credoreference.com/content/entry/apdst/baseline_or_base_line/0 (Year: 1992). |
Bakula et al.; “Reliable Technology of Centimeter GPS/GLONASS Surveying in Forest Environments, IEEE Transactions on Geoscience and Remote Sensing”, vol. 53, No. 2, Feb. 2015, pp. 1029-1038. |
Gang Lu; “Development of a GPS Multi-Antenna System for Attitude Determination”, UCGE Reports No. 20073, Univ. of Calgary Dept. of Geomatics Engineering, Jan. 1995, pp. i-xvi, 1-179. |
Awange et al.; “Environmental Geoinformatics: Monitoring and Management”, Springer, 2013, pp. i-xx, 1-541. |
Linton; History of Navigation, A Wikipedia Compilation, pp. 1-156, 2013. |
Grewal et al.; “Global Positioning Systems, Inertial Navigation, and Integration”; John Wiley & Sons, pp. i-xix, 1-392. |
Hovde; “Compact Sensor System for Target Localization”, University of Oslo, Spring 2017, pp. i-x, 1-53. |
Lee et al.; “Study for Improving Target Coordinate Acquisition Accuracy from Long Distance by VRS RTK”, Journal of the KIMST, vol. 21, No. 4, 2018, pp. 471-480. |
“Target Coordinates. Everywhere. Anytime.”, STERNA, printed on Aug. 26, 2021 from www.militarysystems-tech.com/suppliers/military-optronic-equipment-systems-and-sensors/vectronix#supplier-profile. |
Number | Date | Country | |
---|---|---|---|
20240168176 A1 | May 2024 | US |