System and method for the creation of a terrain density model

• US 20040039498A1
• Filed: 08/23/2002
• Published: 02/26/2004
• Est. Priority Date: 08/23/2002
• Status: Active Grant

• Current Assignee: Applied Perception, Inc. (Thermo Fisher Scientific Incorporated)
• Original Assignee: Applied Perception, Inc. (Thermo Fisher Scientific Incorporated)
• Inventors: Jochem, Todd, Ollis, Mark
• Granted Patent: US 6,728,608 B2
• Time in Patent Office: Days
• US Class Current: 701/23
• CPC Class Codes: G01C 21/005 with correlation of navigation data from several sources, e.g. map or contour matching G01C21/30 takes precedence
• CPC Class Codes: G05D 1/024 in combination with a laser lasers per se H01S
• CPC Class Codes: G05D 1/0257 using a radar radar systems designed for anti-collision purposes between land vehicles or between land vehicle and fixed obstacles G01S13/931
• CPC Class Codes: G05D 1/0274 using mapping information stored in a memory device navigation using map-matching G01C21/30

Abstract

A system and method of constructing a density map is disclosed. The density map is a cellular grid representing local terrain, wherein each cell contains a density vector representing the density of portion of the terrain corresponding to the cell. The density map can be used to classify and characterize the surrounding terrain, which is useful in making a determination of the traversability of the terrain to mobile vehicles.

Claims

1. A method of constructing a density map for local terrain comprising the steps of:

dividing said local terrain into a grid of cells;

obtaining readings for at least a portion of said cells from one or more environmental sensors;

providing a vector for each of said cells in said grid for which readings are available, said vector representing the density of the terrain represented by each of said cells.

2. The method of claim 1 wherein said reading from said sensors are readings of the permeability of terrain corresponding to each of said cells to energy emitted from said one or more sensors.

3. The method of claim 1 further comprising the steps of:

determining, from said readings from said one or more sensors, the minimum elevation for those cells for which a reading is available; and

storing said minimum elevation data with said density vector for each of said cells.

4. The method of claim 3 further comprising the step of:

determining, from said readings from said one or more sensors, the maximum elevation for those cells for which a reading is available; and

storing said maximum elevation data with said density vector for each of said cells.

5. The method of claim 1 wherein a new density map is re-generated at periodic intervals.

6. The method of claim 5 wherein said density map is cleared prior the generation of a new map.

7. The method of claim 5 wherein a portion of the data in said density map is discarded and a portion is retained, and said retained data is used to establish a new density map.

8. The method of claim 7 wherein said portion of said data which is discarded is the oldest data and said portion of said data which is retained is the latest data.

9. The method of claim 1 wherein said step of obtaining permeability readings further comprises the steps of:

directing said one or more sensors to emit energy at specific wavelengths directed in a specific direction;

measuring the degree of said energy reflected back to said sensors and the time elapsed between the emission of said energy and the detection of said reflected energy; and

determining the percentage of said of said emitted energy which is reflected back from said local terrain corresponding to one or more of said grid cells located at varying distances from said sensors.

10. The method of claim 1 wherein said one or more sensors are located on a mobile platform and further comprising the step of:

normalizing said data received from said one or more sensors to compensate for motion of said mobile platform.

11. The method of claim 10 wherein said each of said grid cells is assigned grid coordinates and wherein said step of normalizing said data further comprises the steps of:

establishing a base reference for said grid coordinates based on the actual or estimated position of said mobile platform;

for each of said readings from said one or more sensors, adjusting the position of said reading to compensate for actual or estimated movement of said mobile platform since the establishment of said base reference.

12. The method of claim 11 further comprising the step of periodically re-establishing said base reference based on the actual or estimated position of said mobile platform.

13. The method of claim 12 further comprising the step of clearing said density map of all data prior to said establishment of a new base reference.

14. The method of claim 12 further comprising the step of re-normalizing any data retained in said density map to said new base reference.

15. The method of claim 1 further comprising the step of providing a classification of said local terrain for each of said cells based on an interpretation of all data associated with each of said cells.

16. The method of claim 15 wherein said classification provides an indication of whether or not a mobile vehicle could traverse an area of said local terrain associated with any one of said cells.

17. An apparatus for assisting the autonomous navigation of a mobile vehicle comprising:

one or more environmental sensors mounted on said vehicle;

a processor programmed to receive data readings from said one or more sensors; and

software for constructing a density map based on said readings;

wherein said density map contains cells representing physical areas in the local terrain surrounding said vehicle and further wherein each of said cells contains at least a minimum terrain elevation and a density vector.

18. The apparatus of claim 17 wherein each of said cells also contains a data element representing the maximum terrain elevation.

19. The apparatus of claim 17 wherein said density vector for each of said cells represents an indication of the permeability of the portion of the local terrain associated with each of said cells to energy emitted from each of said one or more sensors.

20. The apparatus of claim 17 wherein said software is capable of adjusting said readings from said one or more sensors to account for movement of said vehicle as said readings are taken.

21. The apparatus of claim 17 wherein said software periodically shifts said data in said density map to account for movement of said vehicle.

22. The apparatus of claim 17 further comprising:

software capable of interpreting said density map to establish a classification of said local terrain corresponding to each of said cells.

23. The apparatus of claim 17 wherein said classification of said local terrain is used to determine if said mobile vehicle can traverse said terrain.