WO1996016836A1

WO1996016836A1 - Optical infrared safety system for vehicles

Info

Publication number: WO1996016836A1
Application number: PCT/US1995/014937
Authority: WO
Inventors: Michael Yaron
Original assignee: Exeter Professional Services, Inc.
Priority date: 1994-11-15
Filing date: 1995-11-15
Publication date: 1996-06-06
Also published as: JPH10509828A; CA2205383A1; AU4163396A

Abstract

A system for detecting vehicles in a host vehicle's (10) environment. The system preferably comprises at least one light emitting device (310) attached to the host vehicle for illuminating the host vehicle's (10) environment. The system further comprises at least one beam-forming device (430) interfaced with a light-emitting device (310) to illuminate the environment. Even more preferably, at least one photo-sensitive device (360) attached to the host vehicle for receiving the reflected light from the vehicle (200) in the host vehicle's (10) environment is provided. The system utilizes optical or infrared light thereby achieving a low cost and efficient vehicle-safety protection system.

Description

OPTICAL INFRARED SAFETY SYSTEM FOR VEHICLES

This application is a continuation-in-part of United States Patent Application Serial Number 08/340,496, filed on November 15, 1994, entitled OPTICAL SAFETY SYSTEM FOR VEHICLES.

Field of the Invention

This invention relates generally to safety systems for vehicles. More particularly, the present invention relates to imaging the outside, field of view of vehicles with active optical infrared sensors so that the operators of the vehicles can drive the vehicles safely.

Background of the Invention

One of the most important and critical aspects in operating a vehicle is having a clear view of the rear of the vehicle. Having a clear view of the rear of the vehicle, and indeed the entire outside of the vehicle, allows an operator of the vehicle to obtain an awareness of the environment, which thereby prevents accidents from happening ner. obstacles cr events in the environment are not perceived. As is known, in order to obtain a clear view of the outside of the vehicle, a series of mirrors is placed at strategic locations on the vehicle to allow the operator of the vehicle to gain sensitivit to the activity in the surrounding environment . Such mirrors are generally called "rear view" mirrors and "side view" mirrors .

Unfortunately, the above-referenced mirror systems do not automatically give the operator of the vehicle a sensitivit and awareness of the environment. Additionally, the vehicles have "blind spots" -- that is, spots outside the vehicle which cannot be viewed through the mirrors -- and so, the operator generally cannot be totally cognizant of the environment in which the vehicle is operating. Additionally, an operator's ability to perceive objects in the blind spot or dead zone is usually distorted due to the optical aberrations which a mirror produces. The well known warning on side-view mirrors "objects appear closer than they really are" is but one manifestation of these kinds of observations. There has not heretofore been a solution to the above- referenced problems, although several U.S. patents have issued which disclose various kinds of camera systems to view the outside of a vehicle. For example, U.S. Patent No. 5,096,287, Kakinami et al . , discloses a video camera for an automobile mounted on an arm which carries a rear view mirror. Similarly, U.S. Patent No. 5,305,012, Faris, teaches an electro/optical system and method for modulating light rays propagating towards an optical element such as an aperture stop in a camera. The camera system disclosed in Paris may be used for automotive, navigational, robotic, and recreational purposes. Additionally, U.S. Patent No. 5,262,813, Scharton, discloses an impact trigger mechanism for a camera mounted in a vehicle. Upon sudden impact or acceleration of the vehicle, a shutter on the camera is activated, which takes a picture of the impact.

It has been further discovered that the aerodynamic shape and texture of many vehicles make these vehicles appear stealth-like at various observation angles. The stealthiness of a vehicle is particularly acute when attempting to detect vehicles with narrow beam optical or infrared (IR) sensors. However, narrow beam sensors are necessary in order to prevent false alarms for a safety system which are a result of the road or other unrelated objects. Furthermore it would be desirable to use optical or IR sensors, since they offer a relatively low- cost and radiation-safe solution as compared to other radiation measures. The aforementioned patents and the art as a whole do not solve the problem of stealthiness of vehicles or false alarms. Nor has the prior art heretofore utilized optical or IR sensors to detect the vehicles in blind spots or other dangerous conditions.

The above-referenced patents do not contemplate a system which can bus images of the outside rear or side views of a vehicle to the operator of the vehicle which will allow the vehicle to be driven safely to avoid obstacles in the vehicle's blind spot or dead zone. Thus, the above-referenced patents fail to solve the problems provided in the art extant with typical mirror systems to view the outside of a vehicle. There therefore remains a long-felt need in the art for systems and methods to allow vehicle operators to safely view the outside rear or side environment of the vehicle, and specifically in blind spot.

fliiTrnnar-y of the Invention

The aforementioned long-felt needs are met and problems solved by systems for detecting vehicles in a host vehicle's environment. The systems preferably comprise at le one light-emitting device, attached to the host vehicle, for illuminating the host vehicle's environment with light which will be reflected from a vehicle in the environment. The syst preferably further comprises at least one beam-forming device interfaced with the light-emitting device for forming a beam from the light emitted by the light-emitting device and to illuminate the environment. Even more preferably, the system comprises at least one photo-sensitive device attached to the host vehicle for receiving the reflected light from the vehicl in the host vehicle's environment.

Yet more preferably, the system comprises means for impressing a modulated signal on the light-emitting device so that the light-emitting device can produce a beam of light. Even more preferably, an array of light-emitting devices is provided in accordance with the present invention. Yet more preferably, the array of light-emitting devices is either an array of light-emitting diodes or an array of optical or infrared lasers. Still more preferably, the system comprises transmitter circuit and a receiver circuit. Yet still more preferably, the beam-forming devices are optical plastic lenses interfaced with either the light-emitting array or a receiving array.

The optical/IR system provided in accordance with the present invention provides a low-cost system for detecting vehicles in a host vehicle's environment. These devices could be adapted for automotive, marine, trucking, or aeronautical applications. The invention will be best understood by those with ordinary skill in the art by reading the following detailed description of preferred embodiments in conjunction with the drawings which are first described briefly below.

Brief Description of the Drawings

Figure 1 is a perspective view of an automobile having a video safety system provided in accordance with the invention. Figure 2 is a perspective view of an automobile which comprises a video safety system provided in accordance with the present invention wherein more than one camera is utilized.

Figure 3 is a perspective view of the inside of an automobile compartment showing a video monitor which has displayed thereon the rear field of view of the automobile.

Figures 4A and 4B are elevational and plan views respectively of the fields of view of the rear of an automobile having a safety system in accordance with the present invention.

Figure 5 is a perspective view of an automobile having a video monitoring system in accordance with the present invention powered by solar energy.

Figure 6 illustrates optical ray reflection beams which are developed in accordance with the present invention.

Figures 7A and 7B illustrate bean formation for detecting vehicles in the dead zone of the host vehicle provide in accordance with the present invention. Figures 8A and 8B illustrate beam width when an optical or IR beam utilizes a road surface to direct bouncing waves.

Figure 9 depicts yet another beam configuration to pinpoint a non-stealthy area in the host vehicle's environment. Figure 10 illustrates an emitting array for providing a beam to reflect off a vehicle in the host vehicle's environment.

Figure 11 illustrates a receiving array for receiving a reflected beam. Figure 12A is yet another preferred embodiment of a beam generator provided in accordance with the present invention.

Figure 12B is yet a further preferred embodiment of receiving devices and displays provided in accordance with the present invention.

Detailed Description of Preferred Embodiments

Referring now to the drawings wherein like reference numerals refer to like elements, Figure 1 shows a vehicle 10 which incorporates a video protection system of the present invention. As will be recognized by those with skill in the art, vehicle 10 could be an automobile, a truck, a recreational vehicle or any other type of motorized vehicle that travels the - 7 -

roads and which is operated by an individual who must be aware of his or her outside environment. For convenience throughout, vehicle 10 will be referred to as an automobile hereinafter.

The automobile 10 has a passenger compartment 20 which comprises an operator's seat 30 and room for other individuals shown generally at 40. As is known, the operator of automobile 10 sits in his or her position 30 and drives the vehicle down the highways and roadways in a preferably safe fashion. To achieve sufficient safety, the operator must constantly be aware of the outside environment 50 of the vehicle. Since the operator faces forward when driving, it is clear that the front portion of the environment shown generally at 60 is in clear view and the operator will typically be able to operate the vehicle safely in a forward direction. However, since the operator does not face backward or to the side, the rearward portion 70 of the environment and side portion 75 of the environment are often obscured, and cannot be easily viewed without forcing the operator to crane his or her neck when viewing behind the vehicle or without the aid of mirrors systems which have not adequately allowed the operator to obtain a clear view of the rear portion 70 and side portion 75 of the environment where blind spots may occur.

In accordance with the invention, an optical safety system is provided to the automobile of Figure 1 so that the operator can view the outside rear or side environments. In a preferred embodiment, a sensor 80 is situated on an exterior surface of the vehicle. The sensor 80 can be any kind of sensor which picks up the presence of obstacles in the environment such as video sensors, radar, motion sensors, and the like. In a preferred embodiment, the sensor is a camera which provides images of the environment. For convenience and without intending to limit the invention in any way, sensor 80 may be referred to as a "camera" hereinafter.

More preferably, a receiver 90 in the interior 20 of the automobile is interfaced to sensor 80. The receiver is preferably adapted to receive data from the sensor which, in th case of a camera, is a video image and the receiver will then b a video monitor. The camera is adapted to view from about a 0° to about a 180° field of view. The video monitor 90 is desirably placed in conspicuous view of the operator of the automobile to give the operator of the automobile a view of the rear field of view 70 and side field of view 75 of the automobile.

The camera 80 and the video monitor 90 are linked together through a series of cables 100. Preferably, both the camera and the video monitor are powered by the automobile's battery, shown generally at 110. However, it will be recognize by those with skill in the art that the video monitor and camer may have their own separate sources of power, such as internal batteries. It is further recognized that any type of camera with a wide angle lens to give about a 0° to 180° field of view can be utilized. Furthermore, any type of video monitor or receiver which is small and compact and which can interface on the dashboard of the automobile can be linked to camera 80 to provide images to the operator. It is further envisioned that should a series of mirrors also be employed to provide the operator with a rear view of the outside environment, the video monitor 90 may even be placed on the rear view mirror typically found in the standard location on the windshield 120. In a preferred aspect of the invention, the camera 80 is mounted on the roof of automobile 10 in a forward position substantially in the center of the roof as shown on Figure 1. However, it will be recognized that the camera can be mounted at any convenient location on the automobile so long as the proper fields of view 70 and 75 are obtained and imaged by the camera 80.

Referring to Figure 2, the same automobile 10 has yet another configuration of the optical safety system provided in accordance with the present invention. In the embodiment of Figure 2, two cameras are positioned on the sides of automobile 10 and each one is individually linked to monitor 90 so that different views of the fields of view 70 and 75 of the automobile can be bussed to monitor 90. In this fashion, the monitor could be computer controlled to integrate a composite picture obtained from both cameras 80, or the screen of monitor 90 could be segmented to show different images obtained from each of the cameras in segmented portions of the screen. With either possibility, complete fields of view 70 and 75 are obtained by the camera system so the operator can drive the automobile 10 safely.

Referring now to Figure 3, the interior 20 of automobile is illustrated. The operator of the automobile at position 30 is able to view the forward field of view 60 of the automobile through windshield 120. Video monitor 90 is placed conveniently on a dashboard 130 and mounted securely thereon. monitor display unit or bar graph could also be mounted to the windshield or sun visor in a manner similar to the way in whic radar detectors are mounted. On the video monitor 90, images the rear field of view 70 and/or the side field of view 75 may be displayed. The operator therefore need only fix his or her eyes for a brief moment on the image of video monitor 90 to obtain a full understanding of the activities in the outside environment, particularly in the fields of view 70 and 75 of t automobile 10.

Thus, the optical safety system of the present invention provides a simple and efficient apparatus for allowi the operator of the vehicle to view the fields of view 70 and 75. Furthermore, video monitor 90 is a much more reliable device for providing an image of the rear of the automobile 10, and does not distort the image such as the right rear view mirror tends to do in conventional mirror systems. Thus, since the image of the fields of view 70 and 75 on monitor 90 is preferably clear and not distorted, a more realistic picture of the activities in the environment are provided to the operator, thereby ensuring that the operator drives the automobile 10 safely.

Referring to Figure 4A, yet a third preferred embodiment is shown wherein camera 80 is placed in the inside compartment 20 of the automobile 10. In this fashion, the camera 80 can view the fields of view 70 and 75 through the bac windshield of the automobile 10. As can be seen, the field of view 150 makes an angular image of the outside rear environment of vehicle 10 from the point at which camera 80 is mounted in the automobile 10, to the visual limit of camera 80 in the fields of view 70 and 75. In Figure 4B, the various fields of view obtained by the different camera placements of Figures 1 and 2 are shown. When the two cameras 80 are placed on either sides of automobile 10, the rear fields of view 160 are created by the two rear cameras so that a large portion of the entire fields 70 and 75 of view are imaged. When camera 80 is placed on the outside, top surface in the center of the roof of car 10 the field of view shown at 170 of the environment is obtained. The different camera placements 80 thus produce different fields of view and therefore, different images of the rear environment. Depending upon the particular images desired to be displayed on video monitor 90, the particular camera placement can be chosen. It has been found that it is most desirable to obtain the rear field of view 170 which is up to about a 180° view of the environment with respect to the camera 80. This is the widest field of view which produces the greatest image of the rear environment, and therefore, gives the operator of automobile 10 the most information for safely operating the automobile 10.

Referring now to Figure 5, the vehicle 10 may have the two cameras 80 placed equidistantly apart on the roof of the automobile. This provides a wider field of view than the fields of view 160, but probably not as great a field of view as that shown at 170. In addition, the optical safety system shown in Figure 5 is solar powered by a series of solar cells 180 which are embedded in the roof of automobile 10. The solar cells 180 provide enough power to energize both the cameras 80, and the video monitor 90 through the cables 100. It will be recognized that the solar cells 180 can be placed at any convenient location on the automobile 10 and that the cables 100 will have a length sufficient to run power from the solar cells 180 to th cameras 80 and video monitors 90.

Thus, the optical safety system of the present invention provides operators of vehicles with an efficient and comprehensive means for viewing the rear and side fields of vie of the vehicle during the operation of the vehicle. The system of the present invention assists prior mirror systems cannot alone adequately provide the operator of the vehicle with a goo image of the rear environment. The aforementioned results have not been achieved in the art. Hereinafter, the sensors are not referred to as cameras but are the optical or IR sensors which are described more fully below. Preferably, the sensors are mounted on any optimal position in the host vehicle. A further preferred embodiment of this invention is a optical/IR active sensor for detecting vehicles in a host vehicle's environment. In a most preferred embodiment, the invention is aimed at detecting vehicles or objects situated in the blind spots (side view, rear view, or any other mirrors) of the host vehicle's environment. In order to accomplish this result, a vehicle-mounted, multi-beam optical or IR active sensor which provides a reliable, consistent and low cost solution to the problem of detecting other vehicles that are situated in blind spots (sometimes referred to as the "dead zone") of the mirrors of the host vehicle is provided.

It is particularly desirable to use optical or IR sensors, since the aerodynamic shape and texture of most vehicles make them appear stealthy at various observation angles. Narrow beams are desired, therefore, to prevent false alarms from the road or other unrelated objects and optical or IR sensors offer a low cost, small-size solution to this problem as compared to other protection measures. Furthermore, since the optical or IR regime is basically in the .1 to 10 microns wavelength area, the optical and IR waves do not generate secondary electric currents on the surface of the vehicles in the host environment, and therefore, the vehicles tend to reflect nearly all of the energy in the IR waves that impinge on them. Therefore, optical ray reflection beams are preferably provided in accordance with the present invention to overcome the stealthy signatures of vehicles in a host vehicle's environment.

Referring to Figure 6, the host vehicle 10 has mounted thereon an IR or optical sensing unit 190 which outputs a beam of light in the rear 70 and side 75 environments of the vehicle 200 in the host vehicle's 10 environment. The beam 210 is emitted from the sensor assembly and reflects 220 from a surface of the vehicle 200. Referring to Figures 7A and 7B, in Figure 7A, a single beam is pointed backward relative to the host vehicle and is aimed to intercept at long distances reflections from the frontal objects of the vehicle in the blind spot of the host vehicle 10. Thus, the front headlight, the grill, and other items of vehicle 200 generate a substantial reflection shown generally at 230 in the optical or IR frequency range when illuminated with the beam 210 pointed approximately + or - 45° from the boresight of vehicle 200. When vehicle 200 moves forward, the reflecting objects would therefore become invisibl to the beam 210 of Figure 7A, and the remaining surface of the vehicle is quite stealthy.

Figure 7B depicts yet another beam 210 perpendicular to host vehicle 10 which can take over approximately where the beam of Figure 7A can no longer provide detection. Thus, the beam 210 of Figure 7B points head on to the vehicle 200 in the blind spot and provides a dependable reflection. The beams of Figures 7A and 7B therefore provide a split transmit and split receive beam which can be modified to ensure that the vehicle 200 is detected at all times. thus, figure 7A illustrates the split beam at a 45° orientation while Figure 7B illustrates the split beam at 90° .

Figures 8A and 8B depict a third possible beam orientation which provides detector that can be assisted by a road surface. When a road is smooth, it also reflects the incident IR beam 210. Thus, the beam reflected by the road can be used to assist in a detection of the vehicle 200 in the blin spot. Referring specifically to Figure 8A, when a narrow transmitted beam to 210 is oriented to illuminate the lower sid of vehicle 200, the transmitted or reflected beam 240 is naturally broader and thus, can detect both the direct reflecte wave and the wave that bounces 250 from the road. Similarly Figure 8B detects a wider transmitted beam 210, which generates a direct wave 260 and a bounced wave 270 to detect vehicle 200. It will be recognized that by those with skill of the art that different combinations of transmitted and receive beams can be used for the purpose of detecting either or both of the direct and bouncing reflected waves. It should be cautioned, however, that if the beams of Figures 8A and 8B are made too wide, they will eventually generate a permanent false alarm and will not aid in detecting the vehicle 200. In another preferred embodiment, a beam configuration to detect vehicle 200, is illustrated in Figure 9. In this embodiment, beam 210 is oriented to point at the rotating wheels of vehicle 200 since the wheels are not stealthy as and other aerodynamic surfaces of vehicle 200. In this manner, directed beam 210 can provide vehicle detection efficiently.

Optical or IR beams provided in accordance with the present invention can be formed of simple plastic lenses which are approximately .1 to .2 inches in diameter. Such plastic lenses can be produced at an exceedingly low cost. In contrast, a microwave or RF lens is much larger and more costly, as is a sonar beam lens, for example. Thus, it is advantageous in accordance with the present invention to utilize optical or IR systems for beam forming.

Referring to Figure 10, a circuit 280 for transmitting a beam from sensor system 190 is shown. The circuit preferably comprises an electronic modulation device 290 for impressing one of a variety of electronic signals shown generally at 300 on the circuit to produce the beam. The circuit further preferably comprises a series of light emitting devices 310, which may be light emitting diodes, lasers, or other devices which emit optical or IR light when impressed with the signal 300.

The modulated signal is preferably fed through a series of biasing resistors shown at 320 which will bias the light emitting devices 310. The light which is emitted from light emitting devices 310 is preferably channelled through a beam-forming device 325, which is peripherally simply a small plastic lens which forms a beam 330 to illuminate the environment of the host vehicle. It will be recognized by thos with skill in the art that the light-emitting devices 310 could be formed in an array of light-emitting devices and may be modulated according to any particular or desirable modulation scheme such as a square wave which is designed for the sensor system 190.

Figure 11 illustrates a preferred embodiment of an optical or IR receiver for receiving the reflected beam of light. The light 340 which is reflected from the vehicle in th host vehicle's environment is also received by a beam-forming device such as a plastic lens 350. An array of photosensitive devices 360 is provided to receive the incoming beam. It will be recognized by those with skill in the art that the array 360 can be comprised of a series of photosensitive diodes or other photosensitive transistors, for example. Preferably, a filter 370 is interfaced to the photosensitive receivers 360, which is matched to the defined waveform of the transmitter of Figure 10 A low-noise amplifier 380 is provided to filter the signal whic can be displayed on a display unit or indicator unit 390 which could either show a picture of the vehicle in the host vehicle's environment, or simply indicate that a vehicle is present. In a further preferred embodiment, an electronic bar graph unit may be used to provide an indication that a vehicle is in the host vehicle's blind spot or dead zone.

Figure 12A is yet another preferred embodiment of transmitter 280. In the embodiment of Figure 12A, a square wave generator 400 feeds a field effect transistor 410 that drives an array of light-emitting diodes shown generally at 420. There are n diodes in the array and preferably beam formers, such as lenses 430, are provided corresponding to each of the light- emitting diodes in the array. A beam of light 440 is thus output from the array and illuminates the environment.

Figure 12B illustrates a further preferred embodiment of a receiver circuit 450 interfaced to a display or indicator circuit 460. The incoming reflected beam 470 is focused by a series of beam-forming devices 480 which are interfaced to a corresponding number of phototransistors 490. A matching filter 500 which is preferably an LC circuit biases with voltage V_cc and feeds a low noise amplifier 510 which filters the signals generated by phototransistors 490. Preferably, an RC circuit 510 provides a low impedence path to ground for each of the photosensitive transistors 490. A low-noise amplifier 520 feeds a series of comparators 530 which turn on corresponding diodes 540. Each of the diodes output a signal 550 to drive a display unit which may display an image of the vehicle in the host vehicle's environment, or provide indication that the vehicle exists in the blind spot of the host vehicle. The circuits and beam forming devices provided in accordance with the present invention provide an efficient and low-cost optical or infrared sensing device for detecting vehicles in a host vehicle's environment. Thus, the opportunit to provide a safety device for host vehicles which have blind spots is economically achieved by utilizing systems and methods provided in accordance with the present invention. Such low cost and efficient results have not heretofore been achieved in the art. There have thus been described certain preferred embodiments of optical safety systems for vehicles provided in accordance with the present invention. While preferred embodiments have been described and disclosed, it will be recognized by those with skill in the art that modifications ar within the true spirit and scope of the invention. The appende claims are intended to cover all such modifications.

Claims

CLAIMSWhat is claimed is:

1. A system for detecting vehicles in a host vehicle's environment comprising: at least one light emitting device attached to the host vehicle for illuminating the host vehicle's environment with light which will be reflected from a vehicle in the environment; at least one beam forming device interfaced with the light emitting device for forming a beam from the light emitted by the light emitting device to illuminate the environment; and at least one photo-sensitive device attached to the host vehicle for receiving the reflected light from the vehicle in the host vehicle's environment.

2. The system recited in Claim 1 further comprising a means for impressing a modulated signal on the light-emitting device so that the light-emitting device can produce a beam of light.

3. The system recited in Claim 1 further comprising an array of light-emitting devices for illuminating the host vehicle's environment with light which will be reflected from the vehicle in the environment.

4. The system recited in Claim 3 further comprising a square wave form generator for impressing a signal on the array of light-emitting device.

5. The system recited in Claim 4 wherein the light emitting devices are light-emitting diodes.

6. The system recited in Claim 5 further comprisin a field-effect transistor for driving the light-emitting diode

7. The system recited in Claim 1 wherein the beam- forming device is a plastic lens.

8. The system recited in Claim 1 further comprisin an array of photo-sensitive devices interfaced with the beam- forming device for generating an electrical signal in response to the reflected beam.

9. The system recited in Claim 8 wherein the array of photo-sensitive devices comprises an array of phototransistors.

10. The system recited in Claim 9 further comprising a display unit for displaying an image of the vehicle in the host vehicle's environment.

11. The system recited in Claim 10 wherein the display unit comprises a plurality of comparators in correspondence with the photo-transistors.

12. The system recited in Claim 11 further comprising a plurality of diodes interfaced with each of the comparators for generating output signals which will be displayed to form the image of the vehicle in the host vehicle's environment.

13. A system for detecting a vehicle in a host vehicle's environment comprising: an array of light emitting devices which will illuminate the environment with beams of light that will reflect from the vehicle in the environment. means for impressing a modulated signal on the array of light emitting devices so that the array of light emitting devices can produce a beam of light; and a receiving device attached to the host vehicle for receiving the reflected light.

14. The system recited in Claim 13 further comprising at least one beam-forming device interfaced with the array of light-emitting devices for forming beams from the light emitted by the light-emitting devices to illuminate the environment.

15. The system recited in Claim 14 wherein the means for impressing a modulated signal impresses a square wave on the system.

16. The device recited in Claim 15 wherein the beam- forming device is a plastic lens.

17. The system recited in Claim 16 wherein the light emitting array comprises an array of light-emitting diodes.

18. A method of detecting a vehicle in a host vehicle's environment comprising the steps of: illuminating the environment with beams of light which can be reflected by the vehicle in the environment; receiving the reflected beams of light; and displaying an image of the vehicle in the host vehicle's environment.