Method for determining visibility

• US 7,274,386 B2
• Filed: 05/25/2001
• Issued: 09/25/2007
• Est. Priority Date: 07/15/2000
• Status: Expired due to Term

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Pochmuller, Werner, Kuehnle, Goetz
• Primary Examiner(s): Vo; Tung
• Application Number:
  US10/333,230
• Publication Number:
  US 20040046866A1
• Time in Patent Office: 2,314 Days
• Field of Search: 348/135, 348/136, 348/137, 348/145, 348/144, 348/150, 382/107, 382/104, 382/103, 356/338, 356/339
• US Class Current: 348/135
• CPC Class Codes: B60R 16/0237 circuits concerning the atmospheric environment meteorology G01W
• CPC Class Codes: G01N 21/538 for determining atmospheric attenuation and visibility
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves

Abstract

To determine the visual range of, in particular, a driver in a motor vehicle, a contrast ((c(x₁), c(x₂)) is measured from at least two measuring positions (x₁, x₂) of a measuring device situated at different distances from the object, and the ratio of the measured contrast values is converted to a visual range (δ), using the difference of the distances of the measuring positions from the object.

Claims

1. A method for determining a visual range, comprising:

in order to produce measured contrast values, measuring a contrast at an object from at least two measuring positions of a measuring device situated at different distances from the object; and

converting a change in the measured contrast values to the visual range;

wherein the visual range is determined according to the following relationship;

$\mathrm{\delta <br><br>}=\frac{x_2-x_1}{\ln <br><br>\left(c<br><br>\left(x_1\right)/c<br><br>\left(x_2\right)\right)}=\frac{x_2-x_1}{\ln <br><br>\left(c<br><br>\left(x_1\right)\right)-\ln <br><br>\left(c<br><br>\left(x_2\right)\right)}$

 

wherein δ

denotes the visual range, x₁ and x₂ are distances of the at least two measuring positions from the object, and c denotes contrast.

2. The method as recited in claim 1, wherein:

the converting is performed in accordance with a ratio of the measured contrast values and a difference of the distances of the at least two measuring positions from the object.

3. The method as recited in claim 1, wherein:

the method is used for measuring the visual range of a driver in a moving motor vehicle.

4. The method as recited in claim 1, wherein:

a distance of the measuring device from the object is measured absolutely at each measuring position using triangulation.

5. The method as recited in claim 3, further comprising:

determining a difference of the distances of the at least two measuring positions from the object by measuring a distance traveled by a motor vehicle between the at least two measuring positions.

6. The method as recited in claim 5, further comprising:

calculating a distance traveled by the motor vehicle in accordance with a speed signal present in the motor vehicle and a time reference.

7. The method as recited in claim 5, further comprising:

determining a distance traveled by the motor vehicle by measuring an angle of rotation covered by a vehicle wheel between the at least two measuring positions.

8. The method as recited in claim 3, wherein:

in each instance, the object is selected within a conical volume that has a predefined opening angle and at whose apex the motor vehicle is located, an axis of the conical volume corresponding to a direction of movement of the motor vehicle.

9. The method as recited in claim 8, wherein:

the conical volume is situated in front of the motor vehicle in a direction of travel.

10. The method as recited in claim 8, wherein:

the conical volume is situated in back of the motor vehicle in a direction of travel.

11. The method as recited in claim 8, wherein:

the conical volume is situated in back of the motor vehicle in a direction of travel, when a visual-range measurement at another object situated in front of the motor vehicle in the direction of travel fails.

12. The method as recited in claim 8, further comprising:

in order to conduct a contrast measurement, initially recording an image at each of the at least two measuring positions to produce images; and

subsequently selecting the object in a most recent of the images, and thereafter identifying the object in at least one older one of the images.

13. The method as recited in claim 1, further comprising:

conducting a contrast measurement at the object from at least three measuring positions situated at different distances from the object; and

determining the visual range using a fitting operation.

14. The method as recited in claim 1, wherein:

at least one of the measured contrast values obtained for the visual range is used for setting a maximum speed of a motor vehicle.

15. A measuring device for determining a visual range, comprising:

an arrangement, in order to produce measured contrast values, for measuring a contrast at an object from at least two measuring positions of a measuring device situated at different distances from the object;

an arrangement for converting a change in the measured contrast values to the visual range; and

one of a CCD image sensor and a CMOS image sensor;

wherein the visual range is determined according to the following relationship;

$\mathrm{\delta <br><br>}=\frac{x_2-x_1}{\ln <br><br>\left(c<br><br>\left(x_1\right)/c<br><br>\left(x_2\right)\right)}=\frac{x_2-x_1}{\ln <br><br>\left(c<br><br>\left(x_1\right)\right)-\ln <br><br>\left(c<br><br>\left(x_2\right)\right)}$

 

wherein δ

denotes the visual range, x₁ and X₂ are distances of the at least two measuring positions from the object, and c denotes contrast.

16. The measuring device as recited in claim 15, wherein:

the one of the CCD image sensor and the CMOS image sensor includes a nonlinear varying characteristic.

17. The measuring device as recited in claim 16, wherein:

the nonlinear varying characteristic is logarithmic.

18. The measuring device as recited in claim 15, further comprising:

an image memory for temporarily buffering images supplied by the one of the CCD image sensor and the CMOS image sensor.