This invention relates to position determination systems. Specifically, the present invention relates to a method and apparatus for determining position of an offset feature.
Satellite positioning system (SATPOS) devices that determine position using the satellites of the US Global Positioning System (GPS) are commonly used for navigation of vessels, vehicles, airplanes, and other conveyances. SATPOS devices are also used for surveying, construction site planning and management, mining, oil and gas exploration and development, etc. Also, handheld SATPOS devices are used for personal navigation, data collection, data maintenance, etc.
SATPOS devices are quite effective for indicating the position of the SATPOS device. Position is typically indicated using either an alphanumeric indication of position or by displaying a map that indicates position. Alphanumeric indications of position typically include coordinates such as, for example, Latitude and Longitude, World Geodetic Survey (WGS) Coordinates, etc.
Map displays typically indicate position by an icon or other indicator visible on a map. One such map display, typically referred to as a moving map display, displays the position of the SATPOS in the center of the displayed map. Such map displays typically are oriented such that the top of the SATPOS device""s display indicates North (either magnetic North or true North). That is, irrespective of the direction in which the SATPOS device is actually oriented, North is shown at the top of the display. For users that intuitively know which direction is North, such maps are adequate for locating features displayed on the map. However, for users that do not know where North is, or when visibility is obscured such that the user cannot determine where North is, such maps are inadequate for guiding the user to a destination or feature on the map.
For many commercial applications of SATPOS systems, such as construction site planning and management, surveying, navigation, etc., it is essential that an operator be able to locate features displayed on the map. Such users typically operate a separate device for indicating direction such as a conventional magnetic compass.
Some SATPOS devices indicate the direction of movement of the SATPOS device, typically referred to as xe2x80x9cheading.xe2x80x9d Typically, heading is determined by analysis of determined position in relation to prior determinations of position as the SATPOS moves. Typically, SATPOS devices that indicate heading use a map display oriented such that the top of the SATPOS unit (e.g., the top of the unit""s display) corresponds to North(either magnetic North or true North).
Some prior art SATPOS devices orient the displayed map such that the top of the SATPOS unit (e.g., the top of the unit""s display) corresponds to the direction of movement calculated by the SATPOS device. This gives a good approximation of the user""s heading as long as the user continues to move and as long as the SATPOS unit is oriented in the direction of movement, allowing a user to easily determine the location of features visible on the display.
However, when the SATPOS device stops moving, determination of heading can no longer be made. Some SATPOS systems maintain the previous heading for orienting the moving map display for a given time interval. Other prior art SATPOS systems default to positioning North at the top of the map. This can be quite confusing to the user.
Recently, digital compasses have been developed that can indicate direction. However, digital compasses must be calibrated to properly align the digital compass prior to use. Also, each time that magnetic environment around the compass changes, the digital compass must be recalibrated. Digital compasses are typically calibrated by moving the digital compass in a full horizontal arc. The calibration process takes time and is prone to operator error. Also, calibration error can occur as a result of local magnetic anomalies.
Typically, extensive measuring equipment is utilized to determine the position of an offset feature which is inaccessible or which is inconvenient to access. Time and resources are spent. Moreover, more than one person is typically needed to accomplish the task.
What is needed is a method and apparatus for providing an accurate indication of heading to a user of a SATPOS device. Also, a method and apparatus is needed that meets the above needs and that accurately indicates direction when the SATPOS is not moving. Also, a method and apparatus is needed that is easy to use and that does not require a user to manually calibrate a compass. Also, a method and apparatus is needed that facilitates determining position of an offset feature without setting up extensive measuring equipment. The present invention meets the above needs.
The present invention provides a method and apparatus that accurately indicates direction and heading to a user of a satellite positioning system (SATPOS) device. The integrated position and direction system of the present invention includes a digital compass for indicating direction when the SATPOS is not accurately determining direction. In one embodiment, the digital compass is comprised of at least three sensors.
An integrated position and direction system is disclosed that includes a SATPOS having a receiver adapted to receive satellite position determining signals. The integrated position and direction system of the present invention also includes a digital compass that is adapted to determine direction.
The integrated position and direction system also includes a controller for controlling the operations of the integrated position and direction system. The controller is coupled to the SATPOS, the digital compass, and to a display.
In one embodiment of the present invention, when the SATPOS is moving, the direction of movement or xe2x80x9cheadingxe2x80x9d determined by the SATPOS is indicated on the display. When the SATPOS is not moving, the direction given by the digital compass is indicated on the display. Therefore, while the SATPOS is moving, the heading is indicated, and when the SATPOS is not moving, direction is indicated using the digital compass. Thus, the present invention provides a method and apparatus for providing an accurate indication of both heading and direction to a user of a SATPOS device.
In one embodiment, the digital compass is automatically calibrated by the SATPOS when the SATPOS is moving. This calibration can be initiated by the user or can be fully automatic. More particularly, the digital compass of the present invention is calibrated automatically, either as a result of user input (e.g., selection of an icon, pressing of a button, etc.), or as a result of user-defined criteria for automatic calibration. That is, the user can program the present invention to automatically calibrate the digital compass (e.g. when velocity exceeds a given threshold, whenever the SATPOS begins moving, periodically while the SATPOS is moving, when the difference between the SATPOS determined heading differs from the heading indicated by the digital compass by more than a predetermined threshold, etc.) Thus, the position and direction system of the present invention is easy to use because there in no need for a user to calibrate a compass as is required using a prior art compass alone.
The present invention also provides a method and apparatus for determining position of an offset feature. In one embodiment, an integrated position and direction system is described that includes a digital compass and a satellite positioning system, and which is operable to determine the position of an offset feature.
In one embodiment, the integrated position and direction system is oriented so as to indicate the direction to the offset feature at a first location and is operated to determine a first direction to the offset feature relative to the first location using the digital compass and to determine a first position using the satellite positioning system.
The integrated position and direction system is moved and placed at a different location, referred to hereafter as a xe2x80x9csecond locationxe2x80x9d. At the second location, the integrated position and direction system is oriented so as to indicate the direction of the offset feature relative to the second location and is operated (e.g., by pressing a button) to determine a second direction to the offset feature using the digital compass and to determine a second position using the satellite positioning system. The integrated position and direction system calculates the position of the offset feature using the first and second directions and the first and second positions.
These and other objects and advantages of the present invention will no doubt become apparent to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments that are illustrated in the various drawing figures.