Navigation for a vehicle by implementing two operating modes
A robotic lawnmower ( 100 ) for movable operation within a work area ( 205 ) has a satellite navigation device ( 190 ), a landmark scanner ( 193 ) and a controller ( 110 ). The controller causes the robotic lawnmower ( 100 ) to movably operate within the work area ( 205 ) in a first operating mode, the first operating mode being based on positions determined from satellite signals received by the satellite navigation device ( 190 ). The controller determines that a position cannot be reliably determined based on satellite signals received by the satellite navigation device ( 190 ), and in response thereto causes the robotic lawnmower ( 100 ) to movably operate within the work area ( 205 ) in a second operating mode. In the second operating mode, the controller receives scanning information from said landmark scanner ( 193 ) and identifies at least one landmark based on the received scanning information and determines a landmark-based position estimate. The controller defines a search space using the landmark-based position estimate, and the satellite navigation device ( 190 ) is reconstructed based on the defined search space. Once the satellite navigation device ( 190 ) has been reconstructed, the controller causes the robotic lawnmower ( 100 ) to again operate in the first operating mode.
1. A vehicle for movable operation, the vehicle comprising:
a satellite navigation device;
a landmark scanner; and
a controller, the controller being configured to:
cause the vehicle to movably operate in a first operating mode, the first operating mode being based on positions determined from satellite signals received by the satellite navigation device;
determine that a position cannot be reliably determined based on satellite signals received by the satellite navigation device, and, in response thereto, cause the vehicle to movably operate in a second operating mode;
wherein in the second operating mode, the controller is configured to:
receive scanning information from said landmark scanner;
identify at least one landmark based on the received scanning information, wherein being configured to identify the at least one landmark comprises being configured to detect the at least one object in said received scanning information and match the at least one object against landmarks in a landmark database;
determine a landmark-based position estimate based on the matched landmark;
define a search space using the landmark-based position estimate; and
reconstruct the work point for the satellite navigation device based on the defined search space.
2. The vehicle as defined in claim 1 , wherein the controller is further configured to cause the vehicle to again operate in the first operating mode once the work point for the satellite navigation device has been reconstructed.
3. The vehicle as defined in claim 1 , wherein the controller is configured to determine the landmark-based position estimate by:
identifying at least three landmarks and determining the landmark-based position estimate based on a triangulation or trilateration of said at least three landmarks.
4. The vehicle as defined in claim 1 , wherein the controller is configured to download new information about landmarks within a working area around the vehicle in response to the vehicle moving to new positions.
5. The vehicle as defined in claim 1 , wherein the satellite navigation device is a Global Navigation Satellite System device.
6. The vehicle as defined in claim 5 , wherein the satellite navigation device comprises a single-frequency carrier phase differential satellite signal receiver.
7. The vehicle as defined in claim 6 , wherein the controller is configured to recalibrate the satellite navigation device based on the defined search space by resolving an integer wavelength ambiguity for satellite signals received by the satellite navigation device.
8. The vehicle as defined in claim 1 , wherein the controller is configured, in the second operating mode, to define the search space by:
obtaining a pseudo range position estimate from satellite signals received by the satellite navigation device;
determining a coarse search space candidate from the pseudo range position estimate; and
defining the search space by reducing a scope of the coarse search space candidate based on the landmark-based position estimate.
9. The vehicle as defined in claim 7 , wherein the controller is configured, in the second operating mode, to:
estimate whether the defined search space will allow integer wavelength ambiguity resolution within a threshold time; and if so:
continue in the second operation mode at least for the duration of the threshold time; and if not:
stop an ongoing propulsion of the vehicle.
10. The vehicle as defined in claim 1 , wherein the controller is configured to store the landmark database in memory of the vehicle.
11. The vehicle as defined in claim 1 , wherein the controller is configured to query the landmark database stored in an external memory.
12. The vehicle as defined in claim 1 , wherein the landmark scanner is a camera, a laser, a radar, a sonar or an infra red sensor.
13. The vehicle as defined in claim 1 , wherein the vehicle further comprises a deduced reckoning navigation sensor, and wherein the controller is further configured to:
obtain a deduced reckoning position estimate by the deduced reckoning navigation sensor and
define the search space using the deduced reckoning position estimate in combination with the landmark-based position estimate.
14. The vehicle as defined in claim 13 , wherein the deduced reckoning navigation sensor is adapted to detect one or more of the following navigation parameters: position, speed, direction, tilt angle, and acceleration.
15. The vehicle as defined in claim 1 , the controller further being configured to:
measure a duration of the second operation mode;
determine whether a threshold time has been exceeded; and if so:
stop an ongoing propulsion of the vehicle.
16. The vehicle of claim 1 , wherein the vehicle is movably operated within a work area.
17. The vehicle of claim 1 , wherein the vehicle is a guided farming vehicle, a robotic work tool or a robotic lawnmower.
18. A robotic work tool system comprising a charging station and a robotic work tool according to claim 17 .
19. A method of controlling a vehicle for movable operation, the method comprising:
movably operating the vehicle in a first operating mode, the first operating mode being based on positions determined from satellite signals received by a satellite navigation device;
determining that a position cannot be reliably determined based on satellite signals received by the satellite navigation device;
in response thereto, movably operating the vehicle in the second operating mode, wherein movably operating in the second operating mode comprises:
receiving scanning information from said landmark scanner;
identifying at least one landmark based on the received scanning information, wherein identifying the at least one landmark comprises detecting the at least one object in said received scanning information and matching the at least one object against landmarks in a landmark database;
determining a landmark-based position estimate based on the matched landmark;
defining a search space using the landmark-based position estimate; and
reconstructing the work space for the satellite navigation device based on the defined search space.
20. A computer readable storage medium encoded with instructions that, when executed on a processor, perform the method according to claim 19 .