Near eye display system and method for display enhancement or redundancy

Abstract

An apparatus provides a virtual display in an environment for various applications including avionic, naval, military, remote control, medical and other applications. The apparatus can be a near eye display, such as, a head up display (HUD) or head worn display (e.g., helmet mounted display (HMD), glasses-based, goggle-based, visor-based, etc.). The near eye display can include a combiner for providing one or more of: an image for a failed display, an image between two or more head down displays, or an image to direct attention to warnings or locations in the field-of-view of the combiner.

Description

BACKGROUND

The present specification relates generally to the field of displays. More specifically, the specification relates to virtual displays.

Virtual displays can provide information that is viewable in virtual space for a user of equipment, such as aircraft, ships, boats, naval craft, medical equipment, robotic equipment, remote vehicles, unmanned vehicle systems (UVSs), training simulators, entertainment systems, military equipment, land vehicles, etc. The information can include navigation parameters, guidance parameters, equipment parameters, location information, video information, remote views, symbology, etc.

Virtual displays can be Near Eye Displays (NEDs), such as Head Mounted Displays (HMDs) (e.g., head worn displays, helmet mounted displays and head worn displays) or Head Up Displays (HUDs) with a fixed combiner near the eye position. Virtual displays can be utilized to provide images to an operator or user (e.g., a pilot in a cockpit). In aircraft applications, HUDs generally include a fixed combiner, an optical projector, an image source, and a HUD computer. HMDs generally include a head worn or helmet mounted combiner, optical projection elements, an image source, a HMD computer, and a head orientation sensor. The HUD or HMD computer causes the image source to provide an image which is projected to a combiner. The combiner provides a collimated image to the pilot. The image can include enhanced vision images, flight symbology, targeting data, flight instrument data, synthetic vision images, head up display (HUD) data, etc.

Cockpit and other display technologies have utilized non-virtual displays such as gauges and panel displays (e.g., head down displays (HDDs) in the cockpit environment). The non-virtual display technology has migrated from a multiplicity of independent gauges to a few large panel, non-virtual displays (e.g., large format HDDs in the cockpit environment). The large format HDDs can represent and concentrate information that used to be apportioned to different gauges and smaller HDDs. While this display technology allows for denser and more flexible display of multiple information streams, the denser, larger display formats can present several drawbacks. First, as information density on each panel is increased, the failure of a single display panel can cause degradation in cockpit workflow, pilot workload, and the amount of information provided to the pilot. Second, the larger, denser displays cannot easily direct attention to particular warnings on the HDDs and/or to locations outside of the cockpit and/or off the HDDs. Third, larger displays cannot be designed to cover the entire cockpit area. Dead space or unused areas in the cockpit cannot be filled in with display information due to shape and size constraints. Large HDDs often include bezels which take up space in the cockpit and cannot display information for the pilot. Bezels associated with conventional HDDs can prevent a seamless display experience.

Thus, there is a need for a low cost, lightweight virtual display system for use with a heads down display (HDD). There is also a need for a virtual display system that provides a seamless display system. There is further a need for near eye display system and method that can be easily integrated in the design of a cockpit without requiring extra display space. There is further a need for a near eye display that can provide display redundancy in the event of a malfunction. There is also a need for a virtual display system and method that is optimized to direct attention to warnings in the cockpit or to locations outside of the cockpit. Yet further, there is a need for a near eye display system that displays types of information in positions that are appropriate for the particular type of information.

Accordingly, it would be desirable to provide a display system and/or method that provides one or more of these or other advantageous features. Other features or advantages will be made apparent in the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned advantages or features.

SUMMARY

An exemplary embodiment relates to an apparatus for providing a virtual display in an environment. The apparatus includes a number of head down image sources. The head down image sources are each disposed at a respective image source position and separated by a gap. The apparatus also includes a combiner configured to provide an image. The image being provided virtually at a location associated with the gap.

Another exemplary embodiment relates to an apparatus for providing a virtual display in an environment including at least one head down image source. The apparatus includes a computer and a combiner configured to provide an image in response to the computer. The image is associated with the image source when the image source is in a failed mode.

Another exemplary embodiment relates to an HMD or HUD for providing a virtual display in an environment. The HMD or HUD includes at least one head down image source, and a combiner. The combiner is configured to provide an image. The image is provided to replace an image associated with the image source. The image is provided when the image source is in a failed mode.

Another exemplary embodiment relates to an apparatus in an environment. The environment includes a number of image sources. The image sources are each disposed at a respective image source position and are separated by a gap. The apparatus includes an image source and a combiner. The combiner is configured to provide an image from the image source. The image is provided virtually at a location associated with the gap.

Another exemplary embodiment relates to an apparatus that includes a near-eye display system including an image source and a combiner. The image source provides an image on the combiner for directing the attention of the user to a display or instrument in the field of view.

Other exemplary embodiments relate to methods for performing the operations associated with the systems and apparatuses described above.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, wherein like numerals denote like elements, which are briefly described below:

FIG. 1 is a schematic general block diagram of a virtual display system including a near eye combiner in accordance with an exemplary embodiment;

FIG. 2 is a more detailed block diagram of the virtual display system illustrated in FIG. 1, including a near eye waveguide combiner in accordance with another exemplary embodiment;

FIG. 3 is a more detailed block diagram of the virtual display system illustrated in FIG. 1, including a near eye head worn combiner in accordance with another exemplary embodiment;

FIG. 4 is a side view schematic illustration of an exemplary image source and near eye combiner for the virtual display system illustrated in FIG. 2 in accordance with another exemplary embodiment; and

FIG. 5 is a general flow diagram of a process used by the virtual display system illustrated in FIG. 1 in accordance with still another embodiment.

DETAILED DESCRIPTION

Before describing in detail the particular improved system and method, it should be observed that the invention includes, but is not limited to, a novel structural combination of components and not in the particular detailed configurations thereof. Accordingly, the structure, software, optics, methods, functions, control and arrangement of components have been illustrated in the drawings by readily understandable block representations and schematic drawings in order not to obscure the disclosure with structural details which will be readily available to those of ordinary skill in the art having the benefit of the description herein. Further, the invention is not limited to the particular embodiments depicted in the exemplary diagrams, but should be construed in accordance with the language of the claims.

With reference to FIG. 1, a virtual display system 10 provides a virtual image at one or more locations in an environment 11. System 10 can be part of a head up display (HUD) system, a head worn display system, a helmet mounted display (HMD) system, or other worn display system. Virtual display system 10 can be utilized in various applications, including but not limited to aviation, medical, naval, targeting, ground-based vehicle, military, remote control, etc. In one embodiment, virtual display system 10 is configured for use in smaller cockpit embodiments, for use in remote vehicle or aircraft applications, for use in ships or boats, or for use in simulators or other training devices. System 10 can be utilized for two dimensional or three dimensional virtual images.

Virtual system 10 is disposed in environment 11 which can be a cockpit, bridge, operating room, etc. Environment 11 can have a window 19 or port to an environment 21 external to environment 11 in one embodiment. For example, environment 11 can be an aircraft cockpit, and environment 21 can be the real world viewable through the windshield canopy of the cockpit. In one embodiment, environment 11 is a windowless cockpit environment.

In one embodiment, system 10 can include image source 12, image source 14, and a Near-Eye Display (NED) system 24. Image source 12 and image source 14 can be head down displays (HDDs) in a cockpit environment in one embodiment. Image sources 12 and 14 can be liquid crystal displays, CRT displays, gauges, etc. In one embodiment, image sources 12 and 14 are large format displays covering a portion of the cockpit environment. Dead spaces and gaps where sources 12 and 14 are not located are present in the cockpit environment in one embodiment.

Near eye display system 24 provides at least one virtual image in one embodiment. Near eye display system 24 can be a head worn display system or a fixed combiner display system in certain embodiments. In one embodiment, the virtual image replaces, augments, and/or complements an image provided by at least one of sources 12 and 14.

Near eye display system 24 includes a computer 26, an image source 28, optics 32 and a combiner 30. Images from image source 28 are projected via optics 32 to combiner 30 which can be a head worn combiner or a fixed combiner in one embodiment. System 10 can include a view tracker 36 for providing gaze information associated with the user (e.g., pilot) to computer 26 in one embodiment.

In operation, near eye display system 24 provides images from image source 28 to a pilot or other operator so that he or she can simultaneously view the images and a real world scene in one embodiment. The images can include graphic and/or text information (e.g., flight path vector, target icons, symbols, fuel indicators, course deviation indicator, pitch indicator, etc.). The image can also include information from other sensors or equipment associated with environment 10 (e.g., a vertical traffic collision avoidance display, terrain avoidance and awareness display, a weather radar display, flight control sensors, an electronic flight bag, a navigation system, environmental sensors, etc. in an aircraft) in one embodiment. In addition, the images can include synthetic or enhanced vision images. In one embodiment, collimated light representing the image from image source 28 is provided on combiner 30 so that the pilot can view the image conformally on the real world scene through combiner 30.

Near eye display system 24, with or without view tracker 36, can be used to compensate for the partial or total failure of one or more head-down displays (e.g., sources 12 and 14) in one embodiment. When computer 26 receives an indication of malfunction associated with one of sources 12 or 14, computer 26 can cause information associated with the malfunctioning display (e.g. source 12 or 14) to be displayed on combiner 30. The indication of the malfunction or display fault can be provided from sources 12 or 14 or other systems including an integrated display control and monitoring system in one embodiment. In one embodiment, the indication can be manually input via a user interface. When computer 26 receives the indication of malfunction associated with both sources 12 and 14, computer 26 can cause information associated with the malfunctioning sources 12 and 14 to be displayed on combiner 30. The information associated with both sources 12 and 14 can be merged and redundant information eliminated to more clearly display the information. Near eye display system 24 can also provide information from malfunctioning gauges or other equipment when an indication of a fault or malfunction is received by computer 26 in one embodiment.

In one embodiment, upon failure of sources 12 or 14, which can be automatically detected or manually indicated, computer 26 instructs system 24 to display to the pilot the content of the failed source 12 or 14 or both whenever the pilot looks in the direction of the failed display in one embodiment. Computer 26 can use gaze information from view tracker 36 to determine when the pilot views the failed source 12 or 14 in one embodiment. In one embodiment, the field of view previously subtended by the failed source 12 or 14 is now filled by system 24, which now acts as a backup or redundant display system. Advantageously, system 24 leads to seamless continuation of cockpit operations and improved dispatch reliability for the aircraft in one embodiment.

In one embodiment, the HDDs (sources 12 and 14) are non-functional and simply are a target area so that when the user looks at the target area, information associated with the target area is provided. In this way, system 24 operates to provide a virtual head down display system according to one embodiment.

In one embodiment, near eye display system 24 can be used to enhance the awareness of information provided by sources 12 and 14 and to enhance awareness of aircraft operations. For example, indications can be displayed by system 24 (which is always within the wearer's field of view (FOV) in one embodiment) to direct the attention of user 20 to particular locations within the cockpit (warning messages on sources 12 and 14, or other instruments) or outside the cockpit (e.g., for traffic etc.). In one embodiment, arrows, chevrons, text or other indicia are provided on combiner 30 to direct the pilot's attention. Computer 26 can receive gaze information from tracker 36 and adjust the position of the arrow or other indicia as the pilot's view changes toward the warning message or traffic in one embodiment. Color can be added to or overlayed over monochromatic information provided by sources 12 and 14 using combiner 30 to augment the display of information in one embodiment.

In another embodiment, system 24 can be used to “fill in” the dead spaces in environment 11 associated with sources 12 and 14. The dead spaces can be associated with bezels or areas between sources 12 and 14 in one embodiment. The dead spaces or unused areas can also be located above, below, to the right, or to the left of sources 12 and 14 in one embodiment. Advantageously, system 24 provides information at locations where placement of displays is impracticable (e.g., due to non-rectangular or non-planar areas, or other areas not meeting the requirements of the display device installation) in one embodiment.

In addition, near eye display system 24 can provide information at locations between sources 12 and 14 to virtually provide the appearance of a seamless display in one embodiment. Eliminating display seams is advantageous when providing information that requires spanning multiple sources 12 and 14, for example wide field of view imagery, large maps, etc. according to one embodiment. System 24 can provide information to gaps between sources 12 and 14 to provide a seamless display experience in one embodiment. Computer 24 can use gaze information from tracker 36 to appropriately provide the information in virtual locations associated with dead spaces in the cockpit. In addition, HUD symbology can be provided when user 20 looks through combiner 30 through window 19 in one embodiment.

View tracker 36 is an optional component of system 24 in one embodiment. View tracker 36 can include sensors for head tracking and/or pupil tracking. In one embodiment, an eye sensor which picks up reflections of a pupil can be utilized for tracking position of the eye. Head position and pupil position from tracker 36 can be provided as gaze information to computer 26 so computer 26 can determine an appropriate virtual image for the pilot.

In one embodiment, view tracker 36 can be or include one or more camera-based sensors to provide gaze information. The cameras can be mounted on system 24 or the user for determining the content of the user's visual field (e.g., gaze information). The camera can be part of head tracker 36. In one embodiment, the camera associated with head tracker 36 can utilize marks within environment 11 to determine where user 20 is looking. Spatial registry software can be utilized to determine where a user is viewing.

Combiner 30 can be embodied as a head worn combiner or a fixed HUD combiner. In one embodiment, combiner 30 utilizes waveguide optics and diffraction gratings to receive collimated light provided by source 28 and provide collimated light to a user 20. In one embodiment, combiner 30 can be a goggle, glasses, helmet or visor-type combiner.

Image sources 12, 14, and 28 can be or include any type of devices for providing an image including but not limited to a CRT display, an LED display, an active matrix liquid crystal display (LCD), a light emitting diode, laser illuminator, etc. In one embodiment, image source 28 can be a micro LCD assembly or liquid crystal on silicon (LCOS) display and can provide linearly polarized light. Image source 28 can include a laser or LED backlight in one embodiment.

Image sources 12, 14 and 28 can provide information from a variety of sources. In one embodiment, image sources 12 and 14 can provide information from aircraft sensors, instruments, and systems including but not limited to one or more of a targeting computer, a HUD computer, a synthetic vision system (SVS), an enhanced vision system (EVS), a flight computer, a traffic collision avoidance system (TCAS), a terrain awareness and avoidance system (TAAS), a navigation system, an electronic flight bag system and a HUD/HWD computer.

Computer 26 can be a HUD computer or HWD computer and controls the provision of images by image source 28. Computer 26 can be a processing circuit or part of a processing circuit associated with other electronic components in environment 11. Computer 26 can receive data from various sensors, equipment, and subsystems and can receive data from image sources 12 and 14. For example, image sources 12 and 14 can provide an indication of a malfunction to computer 26.

Optics 32 can be collimating optics which can be a single optical component, such as a lens, or include multiple optical components. The collimating optics can be integrated with image source 28 in one embodiment. The collimating optics can also be separate or partially separate from image source 28.

With reference to FIG. 2, a display system 200 similar to display system 10 includes a combiner 230, optics 32, image source 28 and HUD computer 26. Combiner 230 is preferably a waveguide fixed combiner with a diffractive grating input and a diffractive grating output. Combiner 230 can disposed near the pilot's eyes as described in U.S. patent application Ser. No. 14/152,756 according to one embodiment. Combiner 230 can be flat or curved.

System 200 is employed in an aircraft environment 211 or a cockpit including a window 254 and a window 256 in one embodiment. In addition, environment 211 can include a control panel 202, a primary flight display 204, a navigation display 206, a navigation display 208, a primary flight display 210, an electronic flight bag display 212 and electronic flight bag display 214 each can be an HDD or part of an HDD in one embodiment. In one embodiment displays 204, 206, and 212 are provided on a single large panel HDD or a pair of HDDs. Primary flight display 210, a navigation display 208, and electronic flight bag display 214 can be redundant systems provided for a co-pilot, as shown in FIG. 2 according to one embodiment.

In operation, when the pilot's view 294 through combiner 230 is toward display 206, computer 26 causes image source 28 to provide information to combiner 230 that augments or replaces the information on display 206. The information can point to or highlight warnings on display 206 or off display 206 in one embodiment. In one embodiment, the information can replace the navigation display information on navigation display 206 when display 206 fails. In one embodiment, the information can fill in dead spaces near display 206 or between displays 204 and 206. A HUD computer 26 can provide the data for the image on source 28 using gaze information from view tracker 36 in one embodiment.

Pilot 220 can turn or rotate head position to view information on combiner 230 associated with primary flight display 204 according to view 292. Display 212 can provide electronic flight bag information. Pilot 220 can turn or rotate head position to view information on combiner 230 associated with display 212 according to view 290. Combiner 230 can augment or replace information on displays 212 and 204 in a similar manner to the augmentation and replacement described above with respect to display 206.

Although only three displays 212, 204, and 206 for a pilot are shown in FIG. 2, more image sources and fields of view can be provided. Displays 212, 204, and 206 can be provided below a glare shield 217 in one embodiment.

With reference to FIG. 3, a display system 300 similar to display system 10 includes a head worn combiner 330, optics 32, image source 28 and HWD computer 26 similar to computer 26. Combiner 330 can be a binocular or monocular combiner. Combiner 330 can be a substrate waveguide combiner with a diffractive grating input and a diffractive grating output in one embodiment. Combiner 330 can be provided on frames for glasses in one embodiment.

System 300 is employed in an aircraft environment 211 or a cockpit including a window 254 and a window 256 in one embodiment. In addition, environment 211 can include a control panel 202, a primary flight display 204, a navigation display 206, a navigation display 208, a primary flight display 210, an electronic flight bag display 212 and electronic flight bag display 214, each can be an HDD or part of an HDD in one embodiment. In one embodiment displays 204, 206, and 212 are provided on a single large panel HDD or a pair of HDDs. Primary flight display 210, a navigation display 208, and electronic flight bag display 214 can be redundant systems provided for a co-pilot, as shown in FIG. 3 according to one embodiment.

In operation, when the pilot's view 392 through combiner 330 is toward display 204, computer 26 causes image source 28 to provide information to combiner 330 that augments or replaces the information on display 204. The information can point to or highlight warnings on display 204 or off display 204 in one embodiment. In one embodiment, the information can replace the primary flight display information on primary flight display 204 when display 204 fails. In one embodiment, the information can fill in dead spaces near display 204 or between displays 206 and 204 or displays 212 and 204. HWD computer 26 can provide the data for the image on source 28 using gaze information from view tracker 36 in one embodiment.

Pilot 220 can turn or rotate head position to view information on combiner 330 associated with navigation display 206 according to view 394. Display 212 can provide electronic flight bag information. Pilot 220 can turn or rotate head position to view information on combiner 330 associated with display 212 according to view 390. Combiner 330 can augment or replace information on displays 212 and 206 in a similar manner to the augmentation and replacement described above with respect to display 204. Although only three pilot displays 212, 204, and 206 are shown in FIG. 3, more image sources and fields of view can be provided.

With reference to FIG. 4, a display system 400, similar to NED system 24, is configured for use in a cockpit environment 411. Display system 400 includes a HUD combiner 416 and an image source 413. Image source 413 includes a backlit liquid crystal display module 470 including a transmissive AMLCD display A very compact optical system 474 receives light from lens 472 and provides collimated light to combiner 416 (e.g., collimation via a catadioptric folded collimator in one embodiment). Generally, the collimated light input to combiner 416 has a small dimension in a vertical direction allowing a compact design. Combiner 416 includes a diffractive grating 476 for coupling light into the waveguide associated with combiner 416 and a diffractive grating 478 that ejects light out of combiner 416 to pilot 420. Gratings 476 and 478 are configured for pupil expansion. Image source 413 and combiner 416 can be attached to a ceiling of the cockpit or a bulkhead wall in certain embodiments.

With reference to FIG. 5, systems 10, 200, 300 and 400 can operate according to a process 500. Process 500 can be performed by computer 26 executing the software or instructions according to various embodiments. In one embodiment, process 500 receives a head position or eye position at an operation 502. At an operation 504, the virtual location of dead space is determined using the gaze information. At an operation 506, information is displayed virtually in the dead space.

In an operation 520, the status of a HDD is determined. If a head down display is malfunctioning, an image associated with the malfunctioning display can be provided at a virtual location associated with the malfunctioning display. In one embodiment, a malfunction is determined by a camera or other device which determines if a HDD (source 12) is black indicating it is non-functional. In one embodiment, the camera is part of view tracker 36. Alternatively, at an operation 524, the image associated with the malfunctioning display can be provided at another location.

At an operation 530, the presence of warnings on HDDs can be determined. If warnings are present on a HDD, symbols can be provided virtually to draw attention to the warning on the HDD at an operation 534. If a warning is provided outside a cockpit or off of a display HDD at an operation 532, an indication of the warning location can be virtually provided at an operation 536. The head position and eye position received at operation 502 can be used to determine the relative location of the warnings to provide an appropriate pointing indicator.

Although exemplary embodiments are described with respect to cockpit environments, the display technology described herein can be utilized in other environments including tiled display or panel display environments outside of the cockpit. For example, the systems 10, 200, 300 and 400 can be utilized to provide panoramic views in tile displays. For example, systems 10, 200, 300 and 400 can be utilized to provide large seamless map displays and redundant displays in other applications without departing from the scope of the claims. Systems 10, 200, 300 and 400 can be utilized to provide a large airport map panoramically covering several displays and providing information between scenes between the displays.

While the detailed drawings, specific examples, and particular configurations given describe preferred and exemplary embodiments, they serve the purpose of illustration only. The inventions disclosed are not limited to the specific forms shown. For example, the methods may be performed in any of a variety of sequence of steps or according to any of a variety of mathematical formulas. The hardware and software configurations shown and described may differ depending on the chosen performance characteristics and physical characteristics of the communications devices. For example, the type of system components and their interconnections may differ. The systems and methods depicted and described are not limited to the precise details and conditions disclosed. The figures show preferred exemplary operations only. The specific data types and operations are shown in a non-limiting fashion. Furthermore, other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the exemplary embodiments without departing from the scope of the invention as expressed in the appended claims.

Claims

1. An apparatus in an environment, the environment comprising a plurality of target areas, the target areas each disposed at a respective target area position and separated by a gap, the apparatus comprising: an image source; anda combiner configured to: receive an image from the image source; andprovide the image virtually at a location associated with the target areas and the gap when the combiner is viewed from a user position viewing the target areas;wherein the combiner is part of a head worn display.

2. The apparatus of claim 1, wherein the image comprises information associated with the target areas.

3. The apparatus of claim 1, wherein the image comprises head-up display (HUD) symbols provided virtually at a location outside of a windshield.

4. The apparatus of claim 1, wherein a first target area of the plurality of target areas is a first head down display source.

5. The apparatus of claim 1, further comprising: a head tracking device, wherein the image is provided in accordance with a head position.

6. The apparatus of claim 1, wherein the combiner is fixed to a helmet.

7. The apparatus of claim 6, wherein the combiner is a waveguide combiner.

8. An apparatus in an environment, the environment comprising a plurality of target areas, the target areas each disposed at a respective target area position and separated by a gap, the apparatus comprising: an image source; anda combiner configured to: receive an image from the image source; andprovide the image virtually at a location associated with the target areas and the gap when the combiner is viewed from a user position viewing the target areas;wherein a first target area of the plurality of target areas is a first head down display source, and wherein the first head down display source is at least one of non-functional, malfunctioning, and powered off.

9. An apparatus for providing a virtual display in an environment including a head down display source, the apparatus comprising: a computer configured to determine that the head down display source is in a failed mode; anda combiner configured to provide a virtual display of an image from an image source in response to the head down display source being in a failed mode, wherein the virtual display is provided at a location associated with the head down display source.

10. The apparatus of claim 9, wherein the image is comprised of primarily flight data and the combiner receives light from a real world scene.

11. The apparatus of claim 9, wherein the combiner is a near eye fixed waveguide combiner.

12. The apparatus of claim 9, further comprising: a head tracking device, wherein the image is provided in accordance with a head position.

13. The apparatus of claim 9, wherein the combiner is a head worn combiner.

14. The apparatus of claim 9, wherein the head down display source is a panel display image source.

15. A method for providing a virtual display in an environment, the method comprising: determining a status of a first head down display source in the environment; andproviding an image associated with the first head down display source at a virtual location based on the status, wherein the status indicates that the first head down display source is malfunctioning.

16. The method of claim 15, wherein the virtual location is a target location associated with the first head down display source.

17. The method of claim 15, wherein the virtual location correlates to dead space in the environment.

18. The method of claim 17, wherein the dead space comprises a gap between the first head down display source and a second head down display source.

19. The method of claim 15, wherein the status of the first head down display source is determined by a camera.