SHIP-HANDLING SIMULATOR USING MULTI-MOVABLE EYEPOINTS VISUAL SYSTEM
Yasuo ARAI (Marine Technical College, Japan)
Taro MINAMIYA (Institute for Sea Training, Japan)
Shigeyuki OKUDA (Marine Technical College, Japan)
Abstract: Recently, a ship-handling simulator is frequently used for seafarers' training and/or maritime researches intended for bridge team. Though, nautical environment includes a huge number of various situations and the members move in the bridge, so it is difficult for each member to judge a same situation in the visual environment simulated on the screen generated through one fixed eyepoint. The visual information, that presents same timing and same information for all of members, is required to survey navigation environment including human factors and/or to train bridge teamwork, etc. The authors basically studied on the differences of influences to human behavior between movable eyepoint system and conventional system that is fixed eyepoint system, not only with geometrical analysis but also with investigations of human behavior which was observed to measure accuracies for ship operator to grasp the movement and relative motion of image, and proposed the basic new visual system for ship-handling simulator. In this paper, the Multi-Movable Eyepoints system (MME system) as a new simulator's visual system in order to resolve problems in conventional system is introduced: the performance and function are discussed using the example of MME system designed for docking maneuver. Finally, it is concluded that the function of MME system designed for docking simulator will be strongly effective not only for training and/or investigation concerning bridge team operation but also for the performance of visual system such as the directivity and distortion of screen display, etc.
In recent years, a ship-handling simulator should be used for seafarers' training and/or maritime researches intended for bridge team composed of pilot, master, mates, crew, etc. Validation of conventional visual system or one fixed eyepoint system already executed., but visual system of ship-handling simulator is never appropriate for plural members of bridge team.
Nautical environment includes a huge number of various environments and the plural members to operate a ship move anywhere in the bridge, so it is difficult that each member judges a situation in the visual environment simulated on the screen through one fixed eyepoint or conventional visual system. The visual environment that has same timing and same accuracy for each member is required on evaluations for navigation environment and/or simulator training.
The image through one fixed eyepoint is greatly influenced by position and movement of the member's eyepoint. For example, abeam motion of the eyepoint makes parallax to bearing of the image, and the parallax makes an error to relative motion of the image. Each member should have own visual environment follows up the movement of own eyepoint.
The authors studied on the differences of influences to human behavior between movable eyepoint system and conventional system that is fixed eyepoint system. not only with geometrical analysis but also with investigations of human behavior which was observed to measure accuracies for ship operator to grasp the movement and relative motion of image, and proposed the basic new visual system for ship-handling simulator..
In this paper, the Multi-Movable Eyepoints system is proposed as a new simulator's visual system in order to resolve not only these mentioned problems but also visual distortions on screen brightness, etc., and validity of the system is discussed using an example to design the Full mission simulator which is able to simulate in restricted waters and docking maneuvering.
2. MULTI-MOVABLE EYEPOINTS SYSTEM
3D visual system for movable eyepoint, which can display the visual scene where eyepoint is measured by the position and azimuth sensor already developed as called CAVE (Cave Automation Virtual Environment), and also the virtual system has been developed using goggles. These systems have some limitations that movable space is very small, or cannot generate the perfect space include both control space for ship handling such as bridge mockup and the visual scene around the environment, so they cannot be used to train and/or to evaluate or to research the navigational environments in bridge team.
Now a day, in case of vehicle control, especially ship handling, the bridge team training and/or assessments performance of operators are considering and adapted, so the simulator should be able to simulate navigational environment for plural members to judge the situations, to gain the information properly, as she should keep up with the control of plural members or multi-movable eyepoints.
We have an updated technology that it is able to generate the control space just same as real bridge or bridge mockup using goggles, but in this case it needs to grasp the operation such as the manipulation of instruments, etc. using motion-capturing. Using this system, it is a heavy burden for operators to train and/or to operate, and it will cause the same problem to generate the image of members in simulation.
For the reasons mention above, the authors propose the new system that is able to generate the visual scenes for plural members in same control space such as bridge using proper sensors gathering the position and azimuth of each eyepoint.
Each scene is generated by computer graphics, and projected on the same screen separated with the time trigger or polarization.
Fig. 1 shows the concept diagram of 3D visual system for multi-movable eyepoints. This figure shows the situation in case of two members, and shows same numbers of projectors as members. The system can use one projection system for plural members using the time-sharing system.
Fig.1 Concept of Multi-Movable Eyepoints System
On board the ship operator moves in the bridge for watch keeping, so his/her eyepoint is moving and the visual image is changing according to his/her eyepoint motion. The information that ship operator can grasp at different position was discussed by Prof. Dr. Kobayashi, et al
On the other hand, the visual information generated by the fixed eyepoint in ship-handling simulator is different from real world. The visual information influences very greatly to maneuver, so it trends that the different images from real world will not give the accurate work-load and in case of plural operators information for each operators will be same and uniform. So, it trends not enough to activate function of teamwork.
Now, we discuss the latent influences of the visual images generated under fixed eyepoint because of changing position of eye-position, categorizing into;
(1) longitudinal motion,
(2) abeam motion,
(3) vertical motion and
(4) position of eyepoint.
2.2.1 Longitudinal motion
On board, the image changes moving along fore or aft, but because of static image under fixed eyepoint in simulator it is not able to generate the blind same as real world. The view size of an object or a target is not different at anywhere in the bridge.
In this case, the image size on the screen under fixed system is static, so in fore motion the view size will be enlarged and in aft motion it will be reduced as shown in Fig.2.
||Visual scaling of object on the screen with longitudinal motion (1m)
2.2.2 Abeam motion
On board, the image changes moving abeam and ship operator can grasp the relative motion among the visual information. But because of static image under fixed system in simulator it is not able to change the relative relationship between the near object such as fore mast and the far one such as a target ship or a lighthouse. So, it is very easy to grasp the relative motion of target ship under fixed system, and it decreases the workload of ship operator less than on board.
On the other hand, in the case of blind caused by mast or derrick where the object or target ship behind, even if ship operator moves to confirm the exist of object, he/she cannot find, so it will increase the work-load for ship operator.
2.2.3 Vertical motion
In bearing the azimuth of object using compass, the eyepoint moves vertically, or up/down, then the horizon keeps the height of eyepoint and the image range from ship operator moves vertically.
Visual depression of object on the screen with 20cm downward motion
In fixed system the horizon image on the screen moves upward and the angle of elevation or depression increases when the height of eyepoint decreases as shown in fig.3, and because of the image of objects moving upward the objects behind blind section sometimes will be able to be found.
2.2.4 Position of eyepoint
The circumstances in ship operation such as the number of members or the number and/or positions of eyepoints influence the workload of ship operators.
In real case, such as navigating through the narrow channel, the master and plural mates on the bridge grasp the visual information with the watch-keeping and report each other what he/she grasps, then master and other mates supplement their navigational information each other. It is important to simulate the situations that generate the workload of each ship operator correctly.
In case of plural members under fixed system, each bearing of one object or target ship includes the parallax with proportional to the abeam distance of each member, so there is some fear for the ship operator who receives the report to misjudge the selection of target. The parallax increases greater as the screen distance becomes smaller which is shown in Fig.4.
Fig.4 Parallax proportional to distance between two eyepoints
On the other hands, in former section 2.2.2 mentioned the blind situation does not change according to the position of operator in fixed system, it happens sometimes to report the existence of object that cannot be reported because of real blind.