Display control device, image display system, mobile body, display control method and program

Abstract

A display control device configured to control the display position of an image in an image projection unit (30) configured to project the image onto a display object (101) of a mobile body (100), the display control device comprising: a position correction unit (4) configured to set a correction amount used to correct the display position; and a display control unit (51) configured to control the display position of the image based on the correction amount set by the position correction unit.wherein the position correction unit (4) is configured to: receive a detection value of an acceleration acting on the mobile body (100) and calculate an inclination angle (β) of the mobile body (100) based on the received detection value of the acceleration; and adjust the correction amount of the display position to control the display position of the image to be projected onto the display object (101) in accordance with the inclination angle (β), wherein the adjustment of the correction amount of the display position in the position correction unit (4) is carried out by adjusting the correction amount per predetermined time unit in accordance with a change in the inclination angle (β) in a predetermined period, wherein the position correction unit (4), when adjusting the correction amount of the display position, in a case where the change in the inclination angle (β) is equal to or greater than a predetermined value,sets a correction amount used each time to correct the display position that is less than a total correction amount up to a control target value, wherein the position correction unit (4) is further configured to: set the correction amount of the display position per unit of time by evenly dividing the total correction amount up to the control target value; or set the correction amount of the display position per unit of time to any value in a case where the change in the tilt angle (β) is equal to or greater than a predetermined value and equal to or greater than a predetermined change threshold; and set the correction amount of the display position per unit of time to decrease over time.if the change in the angle of inclination (β) is equal to or greater than the predetermined value and less than the change threshold value.

Description

TECHNICAL AREA The present disclosure relates to a display control device, an image display system, a mobile body, a display control method and a program. STATE OF THE ART US patent 2019 / 0139286A1 describes a head-up display that projects a virtual image onto the real-world view, depending on the vehicle's driving state. Vehicle information, including pitch, is detected by a first position sensor, and roll is detected by a second position sensor. A control unit manages the video display based on this vehicle information. A mirror reflects the video signal to project it onto a windshield or a combination display. A mirror actuator adjusts the mirror's angle and / or position. At least one of the display states of the virtual image within a video display area, or the mirror's angle and / or position, is adjusted by the controller based on the pitch and / or roll angles. CN 107 710 751 A describes a head-up display that shows an object as either a three-dimensional or two-dimensional image superimposed on the real landscape. A display control device acquires information about a moving object and peripheral information, estimates the relative distance between any obstruction and the moving object, and, if it detects that an obstruction exists between the object to be displayed and the moving object, or if it detects the possibility of such an obstruction, changes the display mode of the object to be displayed and instructs the head-up display accordingly. Another example of an image display system that projects and displays an image onto a display object is a head-up display device mounted on a mobile body such as a vehicle (see, for example, patent reference 1). The head-up display device described in patent reference 1 projects information from an image display device onto the windshield of a vehicle, thereby superimposing information within the viewer's field of vision. The head-up display device calculates the vehicle's tilt angle by detecting its acceleration and adjusts the display position of a projected image accordingly. Furthermore, a control device for a vehicle light is known that performs automatic level control to automatically adjust the beam direction of a vehicle headlight depending on the vehicle's tilt angle (see, for example, patent literature 2). Patent literature 2 discloses that an optical axis angle of a vehicle light is adjusted based on a change in the tilt angle when a vehicle stops and a change in the tilt angle while the vehicle is driving. CITATION LIST PATENT LITERATURE Patent literature 1: JP H01- 293 239 APatent literature 2: WO 2016 / 114 159 A1 SUMMARY OF THE INVENTION TECHNICAL PROBLEM In an image display system that uses a head-up display device or similar, there is a need for further improvement in the control of an image's display position. The present disclosure was developed in the related technology in view of the above circumstances, and one objective of it is to provide a display control device, an image display system, a mobile body, a display control method and a program that can improve the control of a display position of an image. SOLUTION TO THE PROBLEM As one aspect, the present disclosure provides a display control device configured to control a display position of an image in an image projection unit, which in turn is configured to project the image onto a display object of a mobile body, wherein the display control device comprises: a position correction unit configured to set a correction amount used for correcting the display position; and a display control unit configured to control the display position of the image based on the correction amount set by the position correction unit.The position correction unit is configured to: acquire a detection value of an acceleration acting on the mobile body and calculate an inclination angle of the mobile body based on the acquired detection value of the acceleration; and set the correction amount of the display position to control the display position of the image to be projected onto the display object in accordance with the inclination angle, wherein the setting of the correction amount of the display position in the position correction unit is done by setting the correction amount per predetermined unit of time in accordance with a change amount of the inclination angle in a predetermined period.Furthermore, the position correction unit is configured to: set the correction amount used each time to correct the display position; set the display position correction amount per unit of time by dividing the total correction amount equally up to the control target value; or set the display position correction amount per unit of time to any value in a case where the change in the tilt angle is equal to or greater than a predetermined value and equal to or greater than a predetermined change threshold; and set the display position correction amount per unit of time to decrease over time when the change in the tilt angle is equal to or greater than the predetermined value and less than the change threshold. As one aspect, the present disclosure provides an image display system to be attached to a mobile body, wherein the image display system comprises: an image projection unit configured to project an image onto a display object of the mobile body; and the display control device described above. As one aspect, the present disclosure provides a mobile body containing the image display system described above, wherein the display object is a window pane of the mobile body. As one aspect, the present disclosure provides a display control method for controlling a display position of an image in an image projection unit configured to project the image onto a display object of a mobile body, wherein the display control method comprises the following steps: in a position correction unit configured to specify a correction amount used to correct the display position, taking a detection value of an acceleration acting on the mobile body and calculating an inclination angle of the mobile body based on the detected acceleration value;and adjusting the correction amount of the display position to control the display position of the image to be projected onto the display object in accordance with the tilt angle, wherein the adjustment of the correction amount of the display position is carried out by adjusting the correction amount per predetermined unit of time in accordance with a change amount of the tilt angle in a predetermined period. As one aspect, the present disclosure provides a program that causes a computer to execute each step of the display control procedure described above. ADVANTAGEOUS EFFECTS OF THE INVENTION According to the present disclosure, it is possible to improve the control of the display position of an image. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a conceptual diagram showing an example of a configuration of an image display system with a display control device according to one embodiment. Fig. 2 is a conceptual diagram of a vehicle with the image display system according to the embodiment. Fig. 3A is a graphical diagram illustrating gravitational acceleration that acts when the vehicle is upright at the time of stopping. Fig. 3B is a graphical diagram illustrating gravitational acceleration that acts when the vehicle is upright at the time of stopping. Fig. 4A is a graphical diagram illustrating acceleration of motion that acts when the vehicle is upright while in motion. Fig. 4B is a graphical diagram illustrating acceleration of motion that occurs when the vehicle is upright while in motion.Fig. 5A is a schematic representation of a vehicle viewed from one side and not inclined. Fig. 5B is a conceptual diagram showing the field of vision of a user driving the vehicle in a state shown in Fig. 5A. Fig. 6A is a schematic diagram of a vehicle viewed from one side and inclined upwards. Fig. 6B is a conceptual diagram showing the field of vision of a user driving the vehicle in a state shown in Fig. 6A. Fig. 7A is a schematic diagram of a vehicle viewed from one side and inclined downwards. Fig. 7B is a conceptual diagram showing the field of vision of a user driving the vehicle in a state shown in Fig. 7A. Fig. 8 is a flowchart illustrating the operation of the display position control at the time of stopping in the display control device according to the embodiment.Figure 9 is a flowchart illustrating the operation of the display position control during driving in the display control device according to the embodiment. Figure 10 is a flowchart illustrating the operation of the display position control in the display control device according to this embodiment during a transition from stopping to driving. Figure 11 is a table illustrating an example of a correction amount for a display position corresponding to a deviation of a tilt angle measurement during driving and a change in the tilt angle according to the embodiment. DESCRIPTION OF THE EXECUTION FORMS Embodiments in which a display control device, an image display system, a mobile body, a display control method, and a program are specifically disclosed according to the present disclosure are described in detail below with reference to the drawings, insofar as this is appropriate. However, unnecessary detailed descriptions may be omitted. For example, a detailed description of a known fact or a repeated description of an essentially identical configuration may be omitted. This serves to avoid unnecessary redundancy in the following description and to facilitate understanding by the person skilled in the art. The accompanying drawings and the following description serve to aid the person skilled in the art in understanding the present disclosure and are not intended to limit the subject matter specified in the claims. (Introduction to the present revelation) In an image display system that uses a head-up display device or similar, a user may experience visual discomfort when a control is performed to change the display position in accordance with a change in the tilt angle of a moving body, such as a vehicle. For example, in a case where the correction amount of the display position is large, the user may experience visual discomfort if the display position changes suddenly. Therefore, in the present disclosure, a display control device capable of improving visibility by appropriately adjusting a correction amount of a display position in accordance with a change amount of a tilt angle, and an image display system comprising the display control device, are described by way of example. (Overview of the embodiment) In the following embodiment, a vehicle, such as an automobile, is taken as an example of a mobile body, and a configuration example for an image display system mounted on the vehicle and a display control device in the image display system is described. Fig. 1 is a conceptual diagram showing an example of a configuration of an image display system according to one embodiment. Fig. 2 is a conceptual diagram of a vehicle containing the image display system according to the embodiment. As shown in Figs. 1 and 2, an image display system 10 according to the present embodiment includes, for example, a head-up display (HUD) provided in a vehicle 100, which serves as an example of a mobile body. That is to say, the vehicle 100 comprises a main body of a mobile body and the image display system 10 provided in the main body of a mobile body. The image display system 10 is installed in the interior of the vehicle 100 to project an image from below onto a windshield 101 (for example, a window pane) of the vehicle 100. In the example shown in Fig. 2, the image display system 10 is arranged in a dashboard 102 below the windshield 101. As shown in Fig. 2, a user 200, when viewing the image display system 10, visually perceives a virtual image 300 projected through the windshield 101 into a target space 400 located in front of the vehicle 100 (outside the vehicle). The “virtual image” referred to here is an image formed by a divergent beam of light as if an object actually existed when the light emitted by the image display system 10 is deflected by a display object such as the windshield 101. Therefore, the user 200, who is driving the vehicle 100, can see the virtual image 300, which corresponds to an image projected by the image display system 10 superimposed on a real space extending in front of the vehicle 100.Therefore, according to the image display system 10, it is possible to cause the user 200 to visually perceive various types of driving assistance information, such as vehicle speed information, navigation information, pedestrian information, information about vehicles ahead, lane departure information, and vehicle status information, as the virtual image 300. Accordingly, the user 200 can visually perceive the driving assistance information simply by making a slight movement of their line of sight from a position where the line of sight is directed towards the front of the windscreen 101. In the image display system 10 according to the present embodiment, the virtual image 300 formed in the target space 400 comprises at least two types of virtual images, i.e., a first virtual image 301 and a second virtual image 302. The “first virtual image” referred to here relates, for example, to information indicating the direction of travel of the vehicle 100 as navigation information. The first virtual image 301 can be an arrow indicating a right turn or a left turn, displayed on a road surface 600.The first virtual image 301 of this type is a virtual image corresponding to an image displayed using augmented reality (AR) technology. It is superimposed and displayed at a specific position within a real-world scene (the road surface 600, a building, a surrounding vehicle, a pedestrian, and the like) as seen by the user 200. The "second virtual image" refers, for example, to information displaying the vehicle's status 100 as instrument information. The second virtual image 302 could display vehicle speed information or similar data, showing the current speed of the vehicle 100. Specific examples of the first virtual image 301 and the second virtual image 302 are described later. In the image display system 10, the virtual image 300, which is formed in the target space 400, is formed on a virtual plane 501 that intersects an optical axis 500 of the image display system 10. As shown in Fig. 1, the image display system 10 according to the present embodiment comprises a main unit 1 with an image projection unit 30. The image projection unit 30 generates an image 700 and projects the generated image 700 onto the front window 101, thereby generating the virtual image 300, which corresponds to the image 700 in the target space 400. The image projection unit 30 comprises an image generation unit 2 and a projection unit 3. The image generation unit 2 comprises a display area 20 and generates the image 700 on the display area 20. The image generation unit 2 projects the generated image onto the projection unit 3 by means of output light. The projection unit 3 projects the image projected by the image generation unit 2 onto the front window 101. In a state where the main unit 1, which contains the image generation unit 2 and the projection unit 3, is mounted, for example, on vehicle 100, the position of the main unit 1 changes with the position of vehicle 100 due to the load on vehicle 100. Since the image projection unit 30 is mounted in the main unit 1, the position of the image projection unit 30 is the same as the position of the main unit 1. Therefore, the position of the main unit 1 is also the position of the image projection unit 30. In particular, for example, if the vehicle 100 is in a forward-tilting position, such as when an occupant is in a front seat like the driver's seat, the main unit 1 is also in a forward-tilting position; in a case where the vehicle 100 is in a rearward-tilting position, such as when an occupant is in a rear seat or when luggage is placed in a trunk, the main unit 1 is also in a rearward-tilting position. If the position of the main unit 1 of the image display system 10 (a tilt angle of the image projection unit 30) changes, the position of the virtual image 300 projected by the image display system 10 in the target space 400 also changes.For this reason, for example, in a case where the vehicle 100 is in a forward-tilting or a backward-tilting position, the first virtual image 301 may be displayed in a superimposed manner at a position that differs from a certain position where the first virtual image 301 was originally intended to be superimposed in a real scene as seen by the user 200. Accordingly, a display position of the virtual image 300 is set by adjusting a display position of the image 700 on the windscreen 101 in accordance with a tilt angle of the main unit 1. For this reason, the image display system 10 can, for example, even if the vehicle 100 is in a forward-tilting or a backward-tilting position, display the first virtual image 301 at the specific position where the first virtual image 301 was originally intended to be displayed in the real scene as seen by the user 200. (Configuration of the embodiment) As shown in Fig. 1, the image display system 10 according to the present embodiment comprises the image projection unit 30 and a processing unit 50. The present embodiment describes an example in which a component other than the image projection unit 30 (the processing unit 50) is mounted (housed) in the main unit 1, but the present disclosure is not limited thereto. The processing unit 50 need not be contained within the main unit 1. The main unit 1 is mounted in the dashboard 102 of the vehicle 100. The processing unit 50 can be configured separately from the image projection unit 30 and can be configured as a separate housing device that is not mounted on the main unit 1. The main unit 1 can comprise a plurality of housings. The image generation unit 2 of the image projection unit 30 comprises, for example, a liquid crystal display 21 (LCD) and a light source device 22. The liquid crystal display 21 is arranged on a front side of the light source device 22. A front surface (a surface on one side opposite the light source device 22) of the liquid crystal display 21 forms the display area 20 on which the image 700 is generated. The light source device 22 is used as a backlight for the liquid crystal display 21. The light from the light source device 22 penetrates the liquid crystal display 21 from a rear side and is emitted by the image generation unit 2.The light source device 22 is a surface light source that irradiates substantially the entire area of ​​a back side of the liquid crystal display 21 with light, using a light-emitting solid element such as a light-emitting diode or a laser diode. In the image-generating unit 2, when the light source device 22 emits light in a state where the image 700 is displayed on the liquid crystal display 21, the light emitted towards the front of the light source device 22 passes through the liquid crystal display 21 and is emitted towards the front from the front surface (the display surface 20) of the liquid crystal display 21. At this point, the light emitted from the display surface 20 towards the front of the display surface 20 is light (image light) that reflects the image 700 displayed on the liquid crystal display 21. Therefore, when the display surface 20 is viewed from the front, the image 700 appears to be displayed on the display surface 20, and the image 700 is formed on the display surface 20. Although an example configuration is shown in which the image generation unit 2 contains the liquid crystal display 21, the image generation unit 2 is not limited to such a configuration. For example, the image generation unit 2 can be configured to generate the image 700 by scanning with laser light from a rear side of the display area 20 of the image generation unit 2. The projection unit 3 of the image projection unit 30 comprises a first mirror 31 and a second mirror 32. The first mirror 31 and the second mirror 32 are arranged in sequence along an optical path of the output light from the image generation unit 2. The first mirror 31 reflects the output light from the image generation unit 2 towards the second mirror 32. The second mirror 32 reflects the output light from the image generation unit 2, reflected by the first mirror 31, towards a top surface (i.e., towards the front disk 101). In this configuration, the projection unit 3 enlarges or reduces the image 700 displayed on the display surface 20 of the image generation unit 2 to a suitable size and projects the enlarged or reduced image 700 as a projection image onto the windshield 101. As a result, the virtual image 300 is displayed in the target space 400. That is, in the field of vision of the user 200 driving the vehicle 100, the virtual image 300 of the image 700 projected by the image display system 10 is displayed in such a way that it is superimposed on a real scene extending in front of the vehicle 100. The processing unit 50 comprises a position correction unit 4 and a display control unit 51. The processing unit 50 is configured with a computer or similar device containing a processor and memory, and implements various functions, for example, by having the processor execute a predetermined program stored in memory. The processor may be a microprocessor (MPU), a central processing unit (CPU), a digital signal processor (DSP), a graphics processing unit (GPU), and the like. The memory may be random access memory (RAM), read-only memory (ROM), and the like.Although this describes a case in which the program is pre-recorded in the memory of the processing unit 50, the program can be provided via a telecommunications line such as the internet or by recording it on a recording medium such as a memory card. The processing unit 50 can be housed in a control unit such as an electronic control unit (ECU), which controls each unit of the vehicle. The position correction unit 4 and the display control unit 51 can be equipped with separate processors, or at least some of the functions of the position correction unit 4 and the display control unit 51 can be shared by a single processor. The position correction unit 4 calculates a position of the main unit 1 (more precisely, an inclination angle of the vehicle 100) based on a detection value of an acceleration sensor 52, calculates a correction amount to change the display position of the image 700 on the display surface 20 based on the calculated inclination angle and outputs the correction amount to the display control unit 51. The display control unit 51 controls the image generation unit 2 to generate any image 700 on the display surface 20. Furthermore, the display control unit 51 controls the display position of the image 700 on the display surface 20. Specifically, the display control unit 51 adjusts the display position of the image 700 on the display surface 20 based on the correction amount from the position correction unit 4 and changes the display position in accordance with the tilt angle. Accordingly, the display control unit 51 controls the display position of the image 700 on the windscreen 101. As a result, the position of the virtual image 300, projected onto a display area of ​​the target space 400, is controlled. The accelerometer 52 detects an acceleration acting on the vehicle 100 (gravitational acceleration and motional acceleration). The accelerometer 52 comprises, for example, a triaxial accelerometer with an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other. The accelerometer 52 is mounted on the vehicle 100 in an arbitrary position and detects an acceleration vector generated in the vehicle 100. Motional acceleration is an acceleration generated in the vehicle 100 by acceleration or deceleration due to the vehicle 100's movement. That is, motional acceleration is the acceleration obtained by subtracting the gravitational acceleration from the acceleration acting on the vehicle 100. Motional acceleration is generated, for example, in a direction opposite to the acceleration direction of the vehicle 100.The acceleration acting on the vehicle 100 and the calculation of the inclination angle based on the acceleration will be described later. The position correction unit 4 comprises a correction unit 41 and a tilt angle calculation unit 43. The tilt angle calculation unit 43 calculates the tilt angle of the main unit 1 based on time-series data from the accelerometer 52 by means of software processing. More precisely, the tilt angle calculation unit 43 calculates the tilt angle of the vehicle 100 based on the time-series data from the accelerometer 52 and sets the calculated tilt angle as the tilt angle of the main unit 1. The correction unit 41 calculates a correction value to change the display position of image 700 on the display area 20 based on the tilt angle calculated by software processing by the tilt angle calculation unit 43 (i.e., the tilt angle of the main unit 1) and corrects the display position control performed by the display control unit 51. For at least the first virtual image 301, the correction unit 41 controls the display control unit 51 to change the position of image 700 on the display area 20 in order to compensate for (reduce) a change in the position of virtual image 300 in the target space 400 due to a change in the tilt angle of the main unit 1. The display control unit 51 displays (renders) arbitrary video content on the liquid crystal display 21 while controlling the display position of the image 700 on the display area 20 by software processing. Accordingly, an arbitrary image 700 is generated at a predetermined position on the display area 20. The position correction unit 4 and the display control unit 51 control the display position of the image to change the position of the image 700 on the display area 20, thereby changing the position of the image 700 projected onto the front window 101, and as a consequence, also changing the position of the virtual image 300 projected onto the display area of ​​the target space 400. As described above, if the position of the main unit 1 changes, the image display system 10 can control the position at which the virtual image 300 is formed by changing the display position of the image 700 on the display surface 20 according to the change in position. For example, the first virtual image 301 can be corrected to the specific position at which the first virtual image 301 was originally intended to be displayed in the real scene as seen by the user 200, and the user 200 can visually perceive the first virtual image 301. (Measurement of the tilt angle) Next, an acceleration acting on the vehicle 100 and the measurement of an inclination angle calculated from the acceleration are described. Fig. 3A is a graphical diagram illustrating the gravitational acceleration that acts when the vehicle is not tilted at the time of stopping. Fig. 3B is a graphical diagram illustrating the gravitational acceleration that acts when the vehicle is tilted at the time of stopping. The tilt angle calculation unit 43 of the position correction unit 4 calculates a tilt angle based on a detected value from the acceleration sensor 52, thereby performing a tilt angle measurement. In the present embodiment, an up-down axis Az direction (up-down direction), a front-back axis Ax direction (front-back direction), and a left-right axis Ay direction (left-right direction) are defined as a coordinate system (vehicle coordinate system) in the vehicle 100. The three-axis vehicle coordinate system is a virtual axis that is fixed to the vehicle 100.Although the left-right axis Ay is not shown in the drawing in a direction perpendicular to a paper surface, an acceleration component is also generated in the left-right axis Ay direction when the vehicle 100 is tilted in the left-right direction with respect to a direction of travel of the vehicle 100. The acceleration sensor 52 detects accelerations in the direction of the up-down axis Az, in the direction of the front-back axis Ax, and in the direction of the left-right axis Ay. In the present embodiment, a calculated value (measured value) of the tilt angle is zero if an Ax-Ay plane, comprising the front-back axis Ax and the left-right axis Ay, is a reference plane of the vehicle 100 and the reference plane is parallel to the road surface 600. The tilt angle is calculated as the inclination of the reference plane of the vehicle 100 with respect to the road surface 600 or as the inclination of the top-down axis Az of the vehicle 100 relative to a perpendicular in the direction of gravity. It should be noted that the tilt angle can be calculated using acceleration components in two directions: the Az direction of the top-down axis and the Ax direction of the front-back axis, i.e., the top-down direction and an orthogonal direction perpendicular to the top-down direction, without using an acceleration component in the Ay direction of the left-right axis. When vehicle 100 is stopped, as shown in Figures 3A and 3B, the tilt angle is calculated in accordance with a ratio of the gravitational acceleration in three axes: the up-down axis (Az direction), the front-back axis (Ax direction), and the left-right axis (Ay direction) of vehicle 100 during the stop. An algorithm for calculating the tilt angle when vehicle 100 stops is referred to below as the "stop algorithm". If the position of the vehicle 100 during the stop is not inclined in the front-back direction with respect to the road surface 600, the gravitational acceleration acting on the vehicle 100 acts only in the direction of the up-down axis Az of the vehicle 100. Therefore, a value of the acceleration detection G of the acceleration sensor 52 (i.e., a detection value of the gravitational acceleration) includes only an acceleration component Gz in the direction of the up-down axis Az (see Fig. 3A). On the other hand, if the vehicle 100 is tilted while stationary, for example in a front-to-back direction with respect to the road surface 600, the gravitational acceleration acting on the vehicle 100 acts both in the direction of the up-down axis Az and in the direction of the front-to-back axis Ax of the vehicle 100. Fig. 3B shows a condition in which the vehicle 100 is tilted backward (the front part of the vehicle is angled upwards), e.g., when luggage is loaded in a rear luggage compartment. Therefore, the acceleration reading G of the accelerometer 52 has an acceleration component Gz in the direction of the up-down axis Az and an acceleration component Gx in the direction of the front-to-back axis Ax (see Fig. 3B). In the tilt angle calculation unit 43, a tilt angle β, calculated using the stopping algorithm, is obtained by the following equation (1). [Formula 1] According to the stopping algorithm described above, it is possible to calculate and monitor the measured inclination angle and the rate of change of this measurement in real time while the vehicle is stopped. In practice, for example, an average value of the inclination angle measurements is determined over a specified period, e.g., several seconds to several minutes, and the rate of change is calculated based on this time-averaged inclination angle value. In a case where the road surface is inclined, e.g., when the vehicle is stopped on an incline, the vehicle's inclination angle cannot be measured accurately while stopped. In such a case, the inclination angle measurement can be appropriately corrected so that it does not include the inclination angle of the road surface. This can be done, for example, by determining the difference between inclination angle measurements at predetermined time intervals and calculating an inclination angle from which a component of the road surface inclination angle is removed. Figure 4A is a graphical diagram illustrating the acceleration of motion that occurs when a vehicle is not tilted while moving. Figure 4B is a graphical diagram illustrating the acceleration of motion that occurs when the vehicle is tilted while moving. When the vehicle 100 is moving, as shown in Figures 4A and 4B, the tilt angle is calculated according to a ratio of the magnitudes of change of the acceleration of motion in the three axes of the vehicle 100: the up-down axis (Az direction), the front-back axis (Ax direction), and the left-right axis (Ay direction). Hereinafter, an algorithm for calculating the tilt angle while the vehicle 100 is moving is referred to as the "driving algorithm".If the position of the forward-moving vehicle 100 relative to the road surface 600 is not inclined in the front-to-back direction, the acceleration acting on the vehicle 100 acts only in the direction of the front-to-back axis Ax of the vehicle 100. Therefore, a value of the acceleration detection ΔG of the acceleration sensor 52 (i.e., a detection value of the acceleration) has only an acceleration component ΔGx in the direction of the front-to-back axis Ax (see Fig. 4A). Since the acceleration in the driving algorithm is calculated based on a difference between the acceleration detection values ​​at predetermined time intervals, the magnitudes of the changes in acceleration are represented as ΔG, ΔGx, and the like. On the other hand, the acceleration of motion acting on the vehicle 100 acts both in the direction of the up-down axis Az and in the direction of the front-back axis Ax of the vehicle 100 when the position of the forward-moving vehicle 100 relative to the road surface 600 is inclined, for example, in the direction of the front-back axis. Fig. 4B shows a condition in which the vehicle 100 is inclined backward (the front part of the vehicle is angled upwards), e.g., when luggage is being loaded into the rear trunk. Therefore, the value of the acceleration measurement ΔG of the acceleration sensor 52 has the acceleration component ΔGx in the direction of the front-back axis Ax and an acceleration component ΔGz in the direction of the up-down axis Az (see Fig. 4B). In the tilt angle calculation unit 43, a tilt angle β calculated with the driving algorithm is obtained by the following equation (2). [Formula 2] According to the driving algorithm described above, it is possible to calculate the measured value of the tilt angle during the journey of vehicle 100 and the amount of change in the measured value. At this point, for example, an average value of the tilt angle measurements is determined over a predetermined period, such as several seconds to several minutes, and the amount of change is calculated based on this time-averaged value of the tilt angle. (Control of the display position) Next, the control of the display position for image 700 is described, which is carried out by the processing unit 50 including the position correction unit 4 and the display control unit 51. Fig. 5A is a schematic diagram of a vehicle that is not inclined with respect to a road surface (in a state where it is parallel to the road surface), viewed from one side. Fig. 5B is a conceptual diagram showing the field of vision of a user driving the vehicle in the state shown in Fig. 5A. The image generation unit 2 and the projection unit 3 project and display the image 700 generated on the display surface 20 onto the windshield 101, thereby projecting the corresponding virtual image 300 into the target space 400. In the example shown, the first virtual image 301, e.g., navigation information, shows an arrow indicating a "left turn" at an intersection (T-shaped road) ahead of the vehicle 100 in virtual image 300. Furthermore, the second virtual image 302, e.g.,The instrument information shows a driving speed of "50 km / h" as the current vehicle speed information of vehicle 100. If the virtual image 300 (the first virtual image 301 and the second virtual image 302) is to be projected onto the target space 400 as in the example shown, the display control unit 51 determines the content of the first virtual image 301 (orientation, position, and the like of the arrow) and the content of the second virtual image 302 (vehicle speed and the like). Furthermore, the display control unit 51 also determines the position of the image 700 on the display area 20 of the liquid crystal display 21. If the position of the image 700 on the display area 20 changes, the position of the virtual image 300, which is projected onto a display area 401 of the target space 400, also changes. The correction unit 41 of the position correction unit 4 generates a correction amount to change the display position of image 700 on the display area 20, based on a tilt angle calculated by the tilt angle calculation unit 43 (i.e., the tilt angle of the main unit 1), and outputs the correction amount to the display control unit 51. The display control unit 51 controls the position at which image 700 is to be displayed, based on the correction amount of the display position detected by the correction unit 41. This control corrects the position of the virtual image 300, which is projected onto the display area 401 of the target space 400, in accordance with the tilt angle of the main unit 1.The processing unit 50, which includes the position correction unit 4 and the display control unit 51, calculates a correction amount for the display position, at least for the first virtual image 301, in order to compensate for (reduce) a change in the position of the virtual image 300 in the target space 400 due to a change in the tilt angle of the main unit 1. The processing unit 50 then controls the display position in accordance with the correction amount. Accordingly, the position of image 700 on the display surface 20 is changed. More precisely, as shown in Figures 5A and 5B, in a state where the tilt angle of the vehicle 100 is a reference angle (e.g., 0 degrees), the processing unit 50 displays the virtual image 300 at a standard display position without changing the position of the virtual image 300 (the first virtual image 301) projected onto the display area 401 of the target space 400. Here, the standard display position of the first virtual image 301 is an essentially central part of the display area 401, i.e., a position through which the optical axis 500 (see Figure 5A) passes. In the illustrated example, an area in the target space 400 into which the virtual image 300 can be projected is represented as the display area 401. Here, the first virtual image 301 represents an arrow indicating a left turn on a T-shaped road in front of the vehicle 100.This means that the first virtual image 301 is displayed in the user's field of view 200 such that it overlays the T-shaped road in the real scene within the display area 401. Furthermore, the second virtual image 302 is displayed in a position that is the lower left corner of the display area 401 (see Fig. 5B). Fig. 6A is a schematic diagram of a vehicle tilted upwards with respect to a road surface, viewed from one side. Fig. 6B is a conceptual diagram showing the field of view of a user driving the vehicle in the state shown in Fig. 6A. When the tilt angle of the vehicle 100 deviates from the reference angle and the vehicle 100 is tilted, the processing unit 50 changes the position of the virtual image 300 (the first virtual image 301) projected onto the display area 401 of the target space 400 from its standard display position. As shown in Fig. 6A and Fig. 6B, for example, when the vehicle 100 is in a backward tilted position, the display area 401 and the first virtual image 301 move upwards in the user's field of view 200. That is, as shown in Fig.As shown in Figure 6B, a display area 401 (Y) is formed at a position that is shifted upwards relative to a display area 401 (X) in a standard state. Accordingly, in the standard display position, a first virtual image 301 (X) is displayed essentially in a central area of ​​the display area 401 (Y). Therefore, the first virtual image 301 (X) is displayed in the user's field of view 200 such that it is superimposed at a position shifted forward (towards the rear) from the T-shaped road in the real scene. Here, the display area 401 and the first virtual image 301 before the movement have reference numbers marked with an "X", and the display area 401 and the first virtual image 301 after the movement have reference numbers marked with a "Y", so that those before the movement and those after the movement are distinguished from each other. In the case of the backward tilted state, the processing unit 50 changes the position of image 700 on the display area 20, so that the display position of the virtual image 300 is shifted downwards. Accordingly, as shown in Fig. 6A, the position of the first virtual image 301, which is projected onto the target space 400, moves downwards, and in the display area 401(Y), the first virtual image 301(Y) is displayed in a position that is shifted downwards relative to the first virtual image 301(X) in the standard state. As a result, the first virtual image 301(Y) is displayed in the user's field of vision 200, as shown in Fig. 6B, such that it overlays the T-shaped road in the real scene in the display area 401(Y). Furthermore, the second virtual image 302 is displayed at a position which is a lower left corner of the display area 401 (Y) (see Fig. 6B). Fig. 7A is a schematic diagram of a vehicle tilted downwards with respect to a road surface, viewed from one side. Fig. 7B is a conceptual diagram showing the field of vision of a user driving the vehicle in the state shown in Fig. 7A. As illustrated in Figs. 7A and 7B, for example, when the vehicle 100 is in a forward-tilting position, the display area 401 and the first virtual image 301 move downwards in the user's field of vision 200. That is, as shown in Fig. 7B, the display area 401(Y) is formed at a position that is shifted downwards with respect to the display area 401(X) in the standard state. Accordingly, in the standard display position, the first virtual image 301(X) is displayed substantially in the central area of ​​the display area 401(Y).Therefore, the first virtual image 301 (X) in the user's field of view 200 is displayed in such a way that it is superimposed at a position that is shifted backward (towards a near side) from the T-shaped road in the real scene. In the forward-tilted state, the processing unit 50 changes the position of image 700 on the display area 20, shifting the display position of virtual image 300 upwards. Accordingly, as shown in Fig. 7A, the position of the first virtual image 301 projected onto the target space 400 moves forwards, and in the display area 401(Y), the first virtual image 301(Y) is displayed at a position shifted upwards relative to the first virtual image 301(X) in the standard state. Consequently, in the user's field of vision 200, as shown in Fig. 6B, the first virtual image 301(Y) is displayed superimposed on the T-shaped road in the real scene within the display area 401(Y). Furthermore, the second virtual image 302 is displayed at a position which is a lower left corner of the display area 401 (Y) (see Fig. 7B). Since the virtual image 300 is projected onto and superimposed on the road surface 600, an image displayed on the upper side of the display area 401 in a head-up display device mounted on the vehicle 100 will be projected far, and an image displayed on the lower side of the display area 401 will be projected near. Therefore, when changing the display position of an image to be superimposed on it, it is advantageous to define a correction amount of the display position by angle corresponding to a change in the angle of inclination. For example, if a portion of the display area 401 is approximately 3 degrees in the up-down direction, the position of the virtual image 300 superimposed on the road surface 600 will change significantly even with a small angular change in the display position. In the present embodiment, for example, during a stop, the vehicle 100 detects an inclination angle at the moment of stopping using the stopping algorithm to calculate the magnitude of the change in the inclination angle, and a display position correction is performed so that the change in the inclination angle is reflected in the display position of a projection image. Then, when the vehicle 100 is moving, an inclination angle at the moment of moving is detected using the driving algorithm to calculate the magnitude of the change in the inclination angle, and the display position of the projection image is corrected according to the change in the inclination angle. (Details of the display position control processing) When the display position control for the virtual image 300 is carried out in accordance with the tilt angle of the vehicle 100 by the processing unit 50, the user experiences a feeling of discomfort in visually perceiving the image if the change in tilt angle is large and a position correction equal to or greater than a predetermined value is required, and a sudden movement of the image is caused by a change in its display position at any given time. Therefore, in the present embodiment, a correction amount of the display position per predetermined unit of time is set in accordance with a change in the tilt angle within a predetermined period, so that the display position within the user's field of vision does not change drastically all at once.In particular, if the change in the tilt angle is equal to or greater than a predetermined value, the correction amount used per unit of time to correct the display position is adjusted, and the correction amount per instance (per unit of time) is made smaller than the total correction amount up to a target control value, for example, by performing the display position correction a large number of times. Accordingly, the discomfort experienced by the user in their field of vision is reduced. [First example of adjusting the correction amount] A first example illustrates a process where a display position is changed multiple times when the change in a tilt angle relative to a calculated value from a previous measurement is large (e.g., 0.3 degrees or more) and the correction amount for display positions before and after the update is equal to or greater than a predefined value. In this case, processing unit 50 divides the display position correction amount into predefined values ​​and continuously changes the display position at a multitude of times. As described above, in the first example, a display position correction amount is set per time unit by evenly dividing the total correction amount up to the control target value.With regard to the correction amount per unit of time, it is not limited to setting the correction amount the same in each of several periods into which a period for correcting the display position is divided, and any value can be set in each of the divided periods. Regarding the correction amount of the display position, various operating modes are possible, such as setting the correction amount used each time to correct the display position to a predetermined fixed value that is smaller than the total correction amount, setting the number of divisions relative to the total correction amount to a fixed value, and varying the correction amount per instance and / or the number of divisions according to a size of the total correction amount. For example, if the change in the tilt angle is 0.5 degrees, the display position will be shifted 10 times in a 10-second period by 0.05 degrees per second. Here, the total correction amount of the display position is a total movement amount of the display position that is changed in accordance with the change in the tilt angle, and normally corresponds to a movement amount from a current position to a control target position to counteract the change in the tilt angle with respect to the road surface. In a head-up display device, a correction amount of a display position is represented by a change in the angle of incidence of light for the projection of a virtual image, and a displacement (the number of pixels, the number of lines, or the like) on a display screen of an image generation unit, corresponding to an angle, is given as a control value from the processing unit 50 to the image projection unit 30.Since a user-visually perceived image is formed in a three-dimensional space, when controlling the display position, the displacement amount on the display screen of the image generation unit can differ depending on a position in a display area of ​​a target space, even if a correction amount is used for the same angle. In the first example, if the change in the vehicle's tilt angle is equal to or greater than a predetermined value and the position changes significantly, the display position control reduces the correction amount used each time to adjust the display position, and the correction to the target value is not performed all at once. Accordingly, a mode is implemented in which the image projected by the image projection unit moves gradually. This prevents the image from moving drastically all at once and reduces the discomfort experienced by the user in their field of vision. [Second example of adjusting the correction amount] A second example is a modification of the first and illustrates a process of gradually changing a display position, such that a correction amount is large at the initial stage and then steadily decreases as a target control position is approached. This occurs in cases where the display position is corrected multiple times. That is, when the display position is changed several times, it is continuously modified with a predetermined time constant. In this case, processing unit 50 divides a correction amount of the display position, for example, using a logarithmic function, and continuously changes the display position at multiple time intervals.As described above, in the second example, a correction amount for the display position per unit of time is set so that it decreases over time with respect to a total correction amount up to a target tax value. Regarding the correction amount of the display position, various operating modes are possible, such as setting the correction amount to decrease continuously from a large state to a small state by each predetermined time unit, or continuously extending the correction time from a short state to a long state by the correction amount each time as a predetermined fixed or variable value. For example, if the change in the tilt angle is 0.5 degrees, the correction amount per second is continuously reduced to 0.1 degrees, 0.05 degrees, 0.025 degrees, 0.0125 degrees, ... and the display position is shifted such that the display position changes sharply (quickly) in the initial phase and then gradually (slowly). In the second example, if the change in a vehicle's tilt angle is equal to or greater than a predetermined value, and the position is significantly altered, the display position control reduces the correction amount used each time to adjust the display position over time, without performing the correction all at once to the target value. Accordingly, a mode is implemented in which an image projected by a projection unit moves rapidly in the initial phase and then gradually slows down as it approaches a target position. This prevents the image from moving sharply at any one moment and avoids any visual discomfort for the user. It should be noted that the first and second examples can be combined. For instance, a period in which a display item is corrected can be subdivided into multiple periods, and a correction amount per unit of time can be evenly distributed across each of the periods after subdivision, set to any desired value, or the correction amount per unit of time can be set to decrease over time within an entire correction period. As described above, various modifications can be made to the display item correction amount, as long as a procedure is used that ensures the correction amount used each time to correct the display item is less than the total correction amount up to the tax target value. [Third example of adjusting the correction amount] A third example illustrates a process for changing a display position at a specific time when performing a display position correction, such as when the image display of a virtual image, like navigation information, is switched off for a predetermined time or longer. For instance, if navigation information is projected and displayed in an image display system to appear as an overlay on a road surface, the navigation information is not always displayed, but rather intermittently at appropriate times depending on the vehicle's position, such as at an intersection.In this case, even amidst the continuous changes to the display position in the first or second example, processing unit 50 switches to a display position correction mode and immediately changes the display position to a target control position if there is a period in which the virtual image is not rendered for a predetermined time or longer. That is, if the image display is stopped for a predetermined time or longer, the display position correction mode switches from a gradual display position correction to an immediate display position correction. As described above, in the third example, if there is a period in which an image is not rendered for a predetermined time or longer, the display position correction is switched to an immediate correction to a target control value. In the third example, if the display of a projection image is switched off, the display position is corrected all at once to the control target position, regardless of the amount of change in the tilt angle, so that it is possible to control the display position quickly and appropriately. [Tax procedure of the display position] As an example of controlling a display position according to the present embodiment, an example of controlling the display position in a stopped state and in a moving state is described here. Fig. 8 is a flowchart illustrating the operation of the display position control at the time of stopping in the display control device according to the embodiment. When the vehicle 100 is in a stopped state, the processing unit 50 measures a tilt angle of the vehicle 100 during stopping based on a detected value of gravitational acceleration using the stopping algorithm described above (S11). If, at this time, a load change occurs due to an increase or decrease in luggage, an increase or decrease in the number of occupants, or similar (S12), a measured value of the tilt angle changes according to the tilt angle calculation unit 43 (S13). The processing unit 50 calculates a change in the tilt angle of the vehicle 100 at this time (S14).When determining the amount of change in the tilt angle, the processing unit 50 calculates the amount of change, for example, in accordance with an average value of tilt angle measurements in units of several minutes, taking into account various influences such as disturbances, noise, and measurement errors, and updates the tilt angle measurement. The processing unit 50 then controls the image generation unit 2 to perform the display position control processing, while setting a correction amount corresponding to the amount of change in the tilt angle as described above, and changes a display position of a projection image by the projection unit 3 (S15). Fig. 9 is a flowchart illustrating the operation of the display position control during driving in the display control device according to the embodiment. When the vehicle 100 is in a driving state, the processing unit 50 measures a tilt angle of the vehicle 100 during driving based on a detected value of motion acceleration using the driving algorithm described above (S21). At this point, when a load change occurs due to a decrease in fuel, such as gasoline, or movement of an occupant during driving (S22), a measured value of the tilt angle changes according to the tilt angle calculation unit 43 (S23). The processing unit 50 calculates a change in the tilt angle of the vehicle 100 at this point (S24).When determining the amount of change in the tilt angle, the processing unit 50 calculates the amount of change, for example, in accordance with an average value of tilt angle measurements in units of several minutes, taking into account various influences such as disturbances, noise, and measurement errors, and updates the tilt angle measurement. The processing unit 50 then controls the image generation unit 2 to perform the display position control processing, adjusting a correction amount in accordance with the amount of change in the tilt angle as described above, and changes a display position of a projection image by the projection unit 3 (S25). Fig. 10 is a flowchart showing the operation of the display position control in the display control device according to the embodiment in a case of switching from stop to drive. The operating example in Fig. 10 illustrates a case in which a change in position occurs while the vehicle is stopped and the vehicle transitions to driving mode within a short time interval. This corresponds, for example, to a case in which a person enters and exits the vehicle while it is stationary, and the vehicle immediately begins to move. In a state where the vehicle 100 is stopped, the processing unit 50 measures a tilt angle of the vehicle 100 during the stop based on a detected value of gravitational acceleration using the stop algorithm (S31).At this point, a load change occurs due to an increase or decrease in the number of occupants (S32), and vehicle 100 begins to move before processing unit 50 updates the tilt angle measurement (S33). When vehicle 100 enters a driving state, processing unit 50 measures a tilt angle of vehicle 100 while moving based on a detected value of motion acceleration using the driving algorithm (S34). In this case, since the vehicle is moving after the load change at the time of stopping, the tilt angle measurement changes due to the tilt angle calculation unit 43 (S35). Processing unit 50 calculates a change in the tilt angle of vehicle 100 at this point (S36).When determining the amount of change in the tilt angle, the processing unit 50 calculates the amount of change, for example, in accordance with an average value of tilt angle measurements in units of several minutes, taking into account various influences such as disturbances, noise, and measurement errors, and updates the tilt angle measurement. The processing unit 50 then controls the image generation unit 2 to perform the display position control processing, adjusting a correction amount in accordance with the amount of change in the tilt angle as described above, and changes a display position of a projection image by the projection unit 3 (S37). According to the procedures of the operating examples described above, in each of the cases where the vehicle is stopped, in the case where the vehicle is moving, and in the case where the vehicle is immediately moved from stopping to moving, the amount of change is calculated by measuring the tilt angle of the vehicle, and the correction amount is set in accordance with the amount of change of the tilt angle, thereby enabling the control of the display position of the projected image. [Fourth example of adjusting the correction amount] As a fourth example of correction amount adjustment, a process for performing the correction amount adjustment in accordance with a deviation in a tilt angle measurement using the driving algorithm is described. Fig. 11 is a table illustrating an example of a correction amount for a display position corresponding to a deviation in a tilt angle measurement during driving and a change in the tilt angle according to the embodiment. The processing unit 50 changes the correction amount of the display position in accordance with the deviation of the tilt angle measurement during driving. Furthermore, the processing unit 50 initiates an adjustment process of the correction amount corresponding to the change in the tilt angle. When calculating the change in the vehicle's tilt angle during travel, as described above, the change is calculated by determining an average value of the tilt angle measurements over a predetermined period, e.g., several seconds to several minutes. If, at this time, the deviation of the tilt angle measurement during travel is large and the variation in the detected tilt angle is significant, it is assumed that the influence of disturbances or similar factors is substantial, and the reliability of the tilt angle measurement is considered low. Conversely, if the deviation of the tilt angle measurement is small, it is assumed that the sensor output for the tilt angle measurement is stable and the reliability of the tilt angle measurement is high. The processing unit 50 sets a predetermined first threshold TH1 and a predetermined second threshold TH2 (TH1 < TH2) as deviation thresholds to determine the magnitude of the tilt angle measurement deviation. In accordance with the tilt angle measurement deviation during driving, if the deviation during driving is less than the first threshold TH1, the reliability of the tilt angle measurement is high, and thus the processing unit 50 adjusts the correction amount according to a value of the tilt angle after the change to compensate for the change in the tilt angle and changes the display position.If the deviation of the tilt angle measurement during driving is equal to or greater than the first threshold TH1 and less than the second threshold TH2 (between TH1 and TH2), the reliability of the tilt angle measurement is at an average degree. Therefore, the processing unit 50 sets the correction amount by using an intermediate value of the tilt angles before and after the change as the control target value and changes the display position. In this case, the "intermediate value" set as the control target value can be any value greater than zero and up to the value (corresponding to the amount of change in the tilt angle) of the tilt angle after the change, and the value is not limited. Preferably, the intermediate value can be a value (median value) that lies midway between the tilt angles before and after the change.Then, a total correction amount is calculated, corresponding to the control target value of the set intermediate value, and the display position is corrected. The deviation threshold is not limited to the two examples described above; one, three, or more thresholds can be set. Furthermore, the number of possible intermediate values ​​and their associated deviation thresholds is not limited to one; multiple values ​​are permitted. Additionally, the deviation amount of the tilt angle measurement and the control target value can be interlocked. For example, based on a predefined function such as Control Target Value = Change in Tilt Angle × A / Deviation Amount (where A is a weighting coefficient), the control target value can be set to large when the deviation amount is small, and the control target value can be set to small when the deviation amount is large. If the deviation of the tilt angle measurement during driving is equal to or greater than the second threshold TH2, the reliability of the tilt angle measurement is low, and therefore the processing unit 50 sets the correction amount to zero and does not correct the display position. A deviation threshold at which the tilt angle deviation is large and the display position is not corrected can be set separately as a third threshold TH3. The third threshold TH3 is set, for example, to a value that is greater than the first threshold TH1 and equal to or less than the second threshold TH2. In the case of the example shown in Fig. 11, the second threshold TH2 is equal to the third threshold TH3. At this point, the processing unit 50 switches to a display position control mode in accordance with the amount of change in the tilt angle, with respect to setting the correction amount of the display position. For example, if the amount of change in the tilt angle is equal to or greater than a predetermined value and equal to or greater than a predetermined change amount threshold, the display position must be changed significantly, and accordingly, the processing unit 50 performs such display position control processing as in the second example described above, in which the display position is changed significantly in an initial phase and then gradually.If the change in the tilt angle is equal to or greater than the predetermined value and less than the predetermined change threshold, the total correction amount of the display position is small, and accordingly, the processing unit 50 performs such display position control processing as in the first example described above, in which the display position is changed linearly incrementally. In the fourth example, if the deviation of the tilt angle measurement is large, the total correction amount for the tilt angle change is set to an intermediate value before and after the change, and the change in the display image due to the display position correction is reduced. If the deviation of the tilt angle measurement is large, the correction amount is set to zero, so no display position correction is performed. Accordingly, it is possible to correct the display position based on the variation of the tilt angle measurement, according to the system's reliability. In this case, if the reliability of the tilt angle measurement is not very high (medium degree), the correction amount is reduced to an intermediate value, and excessive correction of the display position can be prevented.Furthermore, the display position is not corrected if the reliability of the tilt angle measurement is low, and failure of the display position correction due to external noise or similar can be prevented. If the change in tilt angle is relatively small, display position correction is performed, in which the position is changed continuously at a constant rate, according to the procedure described in the first example above. If the change in tilt angle is relatively large, display position correction is performed, in which the position is changed continuously with a time constant, according to the procedure described in the second example above. Accordingly, if the change in tilt angle is relatively large, the display position can be controlled so that it moves quickly in an initial phase and then approaches the target position steadily and slowly, and it appears to the user as if the image is changing smoothly.Furthermore, the display position can be controlled to gradually approach the target position at a constant speed when the change in the tilt angle is relatively small, making the image appear to the user to change quickly and smoothly. In this way, the display position can be controlled smoothly in accordance with the magnitude of the change in the tilt angle without causing the user any visual discomfort. As described above, in the present embodiment, the display control device controls the display position of an image in the image projection unit 30, which projects the image onto a display object such as the windshield 101 of the vehicle 100, which serves as an example of a mobile body. The display control device comprises the processing unit 50, which performs processing related to correcting the display position. The processing unit 50 includes the position correction unit 4, which sets a correction amount used for correcting the display position, and the display control unit 51, which controls the display position of the image based on the correction amount set by the position correction unit 4.The position correction unit 4 receives a reading of the acceleration acting on the vehicle 100 from the acceleration sensor 52 and calculates a tilt angle of the vehicle 100 based on this reading. The position correction unit 4 then adjusts the correction amount of the display position to control the position of the image projected onto the display object in accordance with the tilt angle. The correction amount in the position correction unit 4 is set by adjusting a correction amount per predetermined time unit in accordance with a change in the tilt angle over a predetermined period. This allows the display position of the image to be controlled in accordance with the change in the tilt angle, thus preventing any visual discrepancies for the user. Furthermore, in the present embodiment, when setting the correction amount of the display position, if the change in the tilt angle is equal to or greater than a predetermined value, the position correction unit 4 adjusts the correction amount used each time to correct the display position so that it is less than the total correction amount up to a target control value. Accordingly, it is possible to prevent a projected image from moving excessively at any given time and to avoid any visual discomfort for the user. Furthermore, in the present embodiment, the position correction unit 4 corrects the display position multiple times when the change in the tilt angle is equal to or greater than a predetermined value, and reduces the correction amount used each time to correct the display position. Accordingly, it is possible to prevent a projected image from moving significantly at any one time and to prevent any visual discomfort for the user. Furthermore, in the present embodiment, when setting the correction amount used each time to correct the display position, the position correction unit 4 adjusts the correction amount of the display position each time or per unit of time by evenly dividing the total correction amount up to the target control value. Accordingly, the display position can be controlled so that the image steadily approaches a target control position, and it appears to the user as if the image changes quickly and smoothly. Furthermore, in the present embodiment, when setting the correction amount used each time to correct the display position, the position correction unit 4 adjusts the correction amount of the display position per unit of time so that it decreases over time relative to the total correction amount until the target control value is reached. Accordingly, the display position can be controlled to move quickly in an initial phase and then approach the target control position steadily and slowly, and the image appears to change smoothly to the user. Furthermore, in the present embodiment, when setting the correction amount used each time to correct the display position, if the change in the tilt angle is equal to or greater than a predetermined value and equal to or greater than a predetermined change threshold, the position correction unit 4 adjusts the correction amount of the display position each time or per time unit by evenly dividing the total correction amount up to the control target value, or sets the correction amount of the display position per time unit to any desired value. Additionally, the processing unit 50 adjusts the correction amount of the display position per time unit to decrease over time if the change in the tilt angle is equal to or greater than the predetermined value and less than the change threshold.Accordingly, the display position can be smoothly controlled in accordance with the size of the change in the tilt angle, without giving the user a feeling of visual discomfort. Furthermore, in the present embodiment, the position correction unit 4 adjusts the correction amount used each time to correct the display position in accordance with a deviation of a measured inclination angle over a predetermined period. Accordingly, it is possible to appropriately correct the display position with sufficient reliability based on the variation of the inclination angle measurement. Furthermore, in the present embodiment, if the deviation of the tilt angle measurement is equal to or greater than a first threshold of a predetermined deviation threshold and less than a second threshold that is greater than the first threshold, the position correction unit 4 sets the correction amount by using an intermediate value before and after the change in the tilt angle as the control target value. Accordingly, in a condition where the reliability of the tilt angle measurement is not very high, the correction amount can be reduced to prevent excessive correction of the display position. Furthermore, in the present embodiment, the position correction unit 4 sets the correction amount of the display position to zero if the deviation of the tilt angle measurement is equal to or greater than a third threshold of the predetermined deviation threshold. Accordingly, in the event of a condition where the reliability of the tilt angle measurement is low, the display position is not corrected, and a failure of the correction due to external noise or similar factors can be prevented. Furthermore, in the present embodiment, the position correction unit 4 switches the correction amount of the display position to a correction amount for correcting to the control target value at a single point in time during a period in which an image to be projected onto a display object is not rendered for a predetermined time or longer. Accordingly, in a case where the display of the image is switched off, the display position is corrected to the control target position all at once, so that it is possible to control the display position quickly and appropriately. Furthermore, in the present embodiment, the position correction unit 4 calculates the tilt angle of the vehicle 100 when the vehicle 100 is stopped, based on acceleration components of a gravitational acceleration in at least two directions, including an up-down direction of the vehicle 100 and an orthogonal direction perpendicular to the up-down direction. Accordingly, it is possible to adequately measure a tilt angle while a mobile body is stationary. Furthermore, in the present embodiment, the position correction unit 4 calculates the tilt angle of the vehicle 100 when the vehicle 100 is moving, based on acceleration components of a motion acceleration in at least two directions, including an up-down direction of the vehicle 100 and an orthogonal direction perpendicular to the up-down direction. Accordingly, it is possible to accurately measure the tilt angle during the movement of a mobile body. Furthermore, in the present embodiment, the position correction unit 4 can be configured by the user to switch between a mode in which correction is performed stepwise up to the target control value and a mode in which correction is performed all at once. Additionally, in the mode in which the position correction unit 4 performs the correction stepwise up to the target control value, the user can set the correction amount used each time to correct the display position. Furthermore, in the present embodiment, the image display system is mounted on the vehicle 100, which serves as an example of a mobile body, and comprises the image projection unit 30, which projects an image onto a display object such as the windshield 101 of the vehicle 100, and the display control device, which includes the position correction unit 4 described above. Accordingly, it is possible to provide an image display system capable of appropriately controlling the display position of an image in accordance with a change in the angle of inclination. Furthermore, the vehicle 100, which serves as an example of a mobile body, includes the image display system described above in the present embodiment. The display object in the mobile body is a windshield, such as the windshield 101 of the vehicle 100. Accordingly, it is possible to provide a mobile body capable of appropriately controlling the display position of an image in accordance with a change in the angle of inclination. Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It will be clear to those skilled in the art that various changes, modifications, substitutions, additions, deletions, and equivalents are conceivable within the scope of the claims, and it should be clear that such changes also fall within the technical scope of the present disclosure. Components in the various embodiments described above can optionally be combined in one area without departing from the spirit of the invention. The present application is based on Japanese patent application No. 2019-120438, which was filed on June 27, 2019, and the contents of which are incorporated herein by reference. COMMERCIAL APPLICABILITY The present disclosure improves the control of a display position of an image and is useful, for example, as a display control device of a display unit that uses a head-up display device or the like, an image display system, a mobile body, a display control method and a program. REFERENCE MARK LIST 10 Image display system 30 Image projection unit 41 Correction unit 43 Tilt angle calculation unit 50 Processing unit 51 Display control unit 52 Acceleration sensor 100 Vehicle (mobile body) 101 Windscreen (display object) 300 Virtual image 301 First virtual image 302 Second virtual image 400 Target space 401 Display area 600 Road surface 700 Image Ax Front-back axis Az Up-down axis Ay Left-right axis G, ΔG Acceleration measurement value Gx, Gy, Gz, ΔGx, ΔGy, ΔGz Acceleration component β Tilt angle

Claims

A display control device configured to control the display position of an image in an image projection unit (30) configured to project the image onto a display object (101) of a mobile body (100), the display control device comprising: a position correction unit (4) configured to set a correction amount used to correct the display position; and a display control unit (51) configured to control the display position of the image based on the correction amount set by the position correction unit.wherein the position correction unit (4) is configured to: receive a detection value of an acceleration acting on the mobile body (100) and calculate an inclination angle (β) of the mobile body (100) based on the received detection value of the acceleration; and adjust the correction amount of the display position to control the display position of the image to be projected onto the display object (101) in accordance with the inclination angle (β), wherein the adjustment of the correction amount of the display position in the position correction unit (4) is carried out by adjusting the correction amount per predetermined time unit in accordance with a change in the inclination angle (β) in a predetermined period, wherein the position correction unit (4), when adjusting the correction amount of the display position, in a case where the change in the inclination angle (β) is equal to or greater than a predetermined value,sets a correction amount used each time to correct the display position that is less than a total correction amount up to a control target value, wherein the position correction unit (4) is further configured to: set the correction amount of the display position per unit of time by evenly dividing the total correction amount up to the control target value; or set the correction amount of the display position per unit of time to any value in a case where the change in the tilt angle (β) is equal to or greater than a predetermined value and equal to or greater than a predetermined change threshold; and set the correction amount of the display position per unit of time to decrease over time.if the change in the angle of inclination (β) is equal to or greater than the predetermined value and less than the change threshold value. Display control device according to claim 1, wherein the position correction unit (4) is configured to perform the correction of the display position several times in a case where the change in the tilt angle (β) is equal to or greater than a predetermined value, in order to reduce the correction amount used each time to correct the display position. Display control device according to one of claims 1 to 2, wherein the position correction unit (4) is configured such that, when setting the correction amount used each time to correct the display position, it sets the correction amount used each time to correct the display position in accordance with a deviation of a measured value of the inclination angle (β) in the predetermined period. Display control device according to claim 3, wherein the position correction unit (4) is configured to set the correction amount using an intermediate value of values ​​before and after the change in the tilt angle (β) as the control target value in a case where the deviation of the measured value of the tilt angle (β) is equal to or greater than a first threshold of a predetermined deviation threshold and less than a second threshold which is greater than the first threshold. Display control device according to claim 3, wherein the position correction unit (4) is configured to set the correction amount of the display position to zero in a case where the deviation of the measured value of the inclination angle (β) is equal to or greater than a third threshold of the predetermined deviation threshold. Display control device according to one of claims 1 to 5, wherein the position correction unit (4) is configured to switch the correction amount of the display position to a correction amount in a case in which there is a period in which an image to be projected onto the display object (101) is not rendered for a predetermined time or longer, in order to be corrected to the control target value at once. Display control device according to one of claims 1 to 6, wherein the position correction unit (4) is configured to calculate the tilt angle (β) of the mobile body (100) on the basis of acceleration components of a gravitational acceleration in at least two directions, comprising an up-down direction of the mobile body (100) and an orthogonal direction orthogonal to the up-down direction in a case where the mobile body (100) is stopped. Display control device according to one of claims 1 to 6, wherein the position correction unit (4) is configured to calculate the tilt angle (β) of the mobile body (100) on the basis of acceleration components of a motion acceleration in at least two directions, including an up-down direction of the mobile body (100) and an orthogonal direction orthogonal to the up-down direction in a case where the mobile body (100) is moving. Image display system (10) to be attached to a mobile body (100), wherein the image display system (10) comprises: an image projection unit (30) configured to project an image onto a display object (101) of the mobile body (100); and the display control device according to any one of claims 1 to 8. Mobile body (100) comprising: the image display system (10) according to claim 9, wherein the display object (101) is a window pane of the mobile body (100). A display control method for controlling the display position of an image in an image projection unit (30) configured to project the image onto a display object (101) of a mobile body (100), the display control method comprising the following steps: in a position correction unit (4) configured to specify a correction amount used to correct the display position, acquiring a detection value of an acceleration acting on the mobile body (100) and calculating an inclination angle (β) of the mobile body (100) based on the detected acceleration value; and setting the display position correction amount to control the display position of the image to be projected onto the display object (101) in accordance with the inclination angle (β).wherein the adjustment of the display position correction amount is performed by setting the adjustment amount per predetermined time unit in accordance with a change in the tilt angle (β) in a predetermined period, when adjusting the adjustment of the display position in a case where the change in the tilt angle (β) is equal to or greater than a predetermined value, specifying a adjustment amount used each time to adjust the display position less than a total adjustment amount up to a control target value, and when adjusting the adjustment amount used each time to adjust the display position includes: adjusting the adjustment amount of the display position per time unit by evenly dividing the total adjustment amount up to the control target value, or adjusting the adjustment amount of the display position per time unit to any value in a case,in which the change in the tilt angle (β) is equal to or greater than a predetermined value and equal to or greater than a predetermined change threshold; and adjusting the correction amount of the display position per unit of time so that it decreases over time when the change in the tilt angle (β) is equal to or greater than the predetermined value and less than the change threshold. Program that causes a computer to execute each step of the display control method according to claim 11.

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