Method for the optical design of a head-up display, and associated head-up display

Abstract

The present invention relates to a method for the optical design of a head-up display using an existing visor (52) of a helmet (50) to form a virtual image in an observation window of a wearer of the helmet (50), the method being computer-implemented and comprising the following phases: - a. a phase of determining a position, in the helmet (50), of an image projection assembly (60) comprising an image generation unit and an optical projection unit, such that the light beam originating from the image projection assembly (60) forms a virtual image that can be seen by a wearer of the helmet (50) after reflection on the visor (52) of the helmet (50); and - b. a phase of optimising the optical projection unit so as to improve the quality of the virtual image.

Description

[0001] DESCRIPTION

[0002] TITLE: Optical design process for a head-up display and associated head-up display

[0003] The present invention relates to a method for optically designing a head-up display using an existing visor of a helmet. The present invention also relates to an associated integration method. The present invention also relates to an associated head-up display.

[0004] Head-up displays are a known method of making driving safer. These displays project a useful image directly into a driver's eyebox, without the driver having to take their eyes off the road.

[0005] However, in the case of certain vehicles, such as motorcycles or scooters, the driver is required to wear a helmet, which reduces their field of vision and can complicate the use of a head-up display.

[0006] Helmets incorporating a head-up display function were then developed, with the helmet visor acting as a semi-reflective support for the head-up display.

[0007] However, the visor of these helmets is a visor specifically designed (position, orientation, shape) for this head-up display function. These solutions are therefore not compatible for the integration of a head-up display in a helmet including an existing visor.

[0008] There is therefore a need for a solution that allows a head-up display to be integrated into any type of helmet with a visor, without modifying the characteristics of the visor (position, orientation, shape).

[0009] For this purpose, the present description relates to a method for optical design of a head-up display using an existing visor of a helmet to form a virtual image in an observation window of a wearer of the helmet, the method being implemented by computer and comprising the following phases: a. an input data reception phase comprising: i. a geometric model of the helmet and the visor, ii. optical parameters defining constraints so that the virtual image is visible to a wearer of the helmet, the optical parameters comprising at least one position of the eyes of a typical wearer, a field of vision for the typical wearer, an observation window for the typical wearer, a vertical projection angle of the virtual image for the typical wearer, a horizontal projection angle of the virtual image for the typical wearer, and a desired distance between the position of an eye of the typical wearer and the virtual image, b.a phase of determining a position, in the helmet, of an image projection assembly comprising an image generation unit and an optical projection unit, such that the light beam coming from the image projection assembly forms a virtual image visible to a wearer of the helmet after reflection on the visor of the helmet, the position of the image projection assembly being determined as a function of the geometric model and the optical parameters, c. a phase of optimizing the optical projection unit so as to improve the quality of the virtual image, the optimization phase comprising the steps of: i. determining, as a function of the determined position of the image projection assembly, the area of ​​the visor, called the local area, receiving a light beam, ii.determining the shape of the determined local area, the local area being locally deformed relative to the overall shape of the visor taken over the entire field of vision of the typical wearer, and iii. determining a modification of the optical surface of the or an optic of the optical unit so as to compensate for the local deformation of the local area, making it possible to reduce the optical aberrations of the virtual image.

[0010] According to other advantageous aspects, the optical design method comprises one or more of the following features, taken individually or in all technically possible combinations:

[0011] - the phase of determining the position of the image projection assembly comprises the following steps: a. determining a set of possible directions between the eyes of the typical wearer and the virtual image as a function of the geometric model, the position of the eyes of the typical wearer, the field of vision of the typical wearer, the observation window of the typical wearer, the vertical projection angle of the typical wearer, and the horizontal projection angle of the typical wearer, b. determining a set of possible positions for the object of the virtual image as a function of the geometric model, the set of possible directions and the desired distance between the position of the eye of the typical wearer and the virtual image, and c. determining a position for each of the image generation unit and the projection optical block of the image projection assembly, as a function of the geometric model and the set of possible positions for the object;

[0012] - the position of each of the image generation unit and the projection optical unit is determined so as to minimize the size of the optical unit in the helmet;

[0013] - the step of determining the position of each of the image generation unit and the projection optical block comprises: a. determining a position for the image generation unit as a function of the geometric model and the set of possible positions for the object, b. optimizing the emitting surface of the image generation unit in order to minimize the size of the optical block in the headset, while respecting resolution and brightness constraints for the virtual image, and c. determining a position for the optical block as a function of the geometric model, the position of the image generation unit and the optimized emitting surface of the image generation unit so as to minimize the size of the optical block in the headset;

[0014] - the step of determining the position of each of the image generation unit and the optical unit comprises optimizing the number and / or nature of the elements of the optical unit so as to minimize the size of the optical unit in the helmet, preferably the optical unit comprising at most two elements;

[0015] - the step of determining the shape of the local area comprises: i. carrying out a ray tracing, on the basis of the geometric model, from the position of the eyes of the typical wearer to the local area making it possible to obtain the shape of the local area, ii. mathematical modelling of the shape of the determined local area, iii. determining a recoded model of the visor based on the mathematical modelling, and iv. validating the recoded model by comparing the recoded model with the geometric model of the visor, the step of determining the modification of the optical surface being carried out based on the recoded model;

[0016] - when the local area has a toric shape, the modified optical surface being such that the corresponding optic is an aspherical biconical optic;

[0017] - the method comprises a phase of global optimization of the image projection assembly during which the inclination and the centering of the elements of the image projection assembly are optimized so as to reduce the optical aberrations of the virtual image generated by the head-up display formed of the image projection assembly and the helmet visor, the global optimization phase being carried out as a function of the geometric model, the determined position of the image projection assembly, and the optimized projection block.

[0018] The present description also relates to a method for integrating a head-up display into a helmet comprising a visor, the head-up display using the existing visor of the helmet to form a virtual image in an observation window of a wearer of the helmet, the integration method comprising: a. optical design of the head-up display in accordance with an optical design method as described previously, b. production of an image projection assembly conforming to that obtained at the end of the optical design method, and c. integration of the image projection assembly into the helmet, in accordance with the integration obtained at the end of the optical design method, so as to form the head-up display.

[0019] The present description also relates to a head-up display using an existing visor of a helmet to form a virtual image in a viewing window of a wearer of the helmet, the head-up display comprising: a. the visor of the helmet, b. an image projection assembly comprising an image generation unit and a projection optical block positioned in the helmet so that the light beam coming from the image projection assembly forms a virtual image visible to a wearer of the helmet after reflection on the visor of the helmet, the head-up display having been designed and integrated into the helmet according to the existing visor in accordance with an integration method as described previously.

[0020] Other features and advantages of the invention will become apparent upon reading the following description of embodiments of the invention, given by way of example only, and with reference to the drawings which are:

[0021] - figure 1, a schematic representation of an example of a computer configured to implement a method of optical design of a head-up display in a helmet according to the invention,

[0022] - figure 2, a flowchart of the different phases of a method of optical design and integration of a head-up display in a helmet according to the invention,

[0023] - figure 3, a schematic representation of an example aiming to determine a set of possible directions between the eyes of a typical wearer and a virtual image by varying a vertical projection angle of a typical wearer, - figure 4, a schematic representation of an example aiming to determine a set of possible directions between the eyes of a typical wearer and a virtual image by varying a horizontal projection angle of a typical wearer, and

[0024] - figure 5, a schematic representation of an example of a portion of a head-up display obtained following an optical design method according to the invention.

[0025] A calculator 10 and a computer program product 12 are illustrated in Figure 1.

[0026] The calculator 10 is preferably a computer.

[0027] More generally, the computer 10 is an electronic computer capable of manipulating and / or transforming data represented as electronic or physical quantities in computer 10 registers and / or memories into other similar data corresponding to physical data in memories, registers or other types of display, transmission or storage devices.

[0028] The calculator 10 interacts with the computer program product 12.

[0029] As illustrated in FIG. 1, the computer 10 comprises a processor 14 comprising a data processing unit 16, memories 18 and an information medium reader 20. In the example illustrated in FIG. 1, the computer 10 comprises a keyboard 22 and a display unit 24.

[0030] The computer program product 12 comprises an information medium 26.

[0031] The information medium 26 is a medium readable by the computer 10, usually by the data processing unit 16. The readable information medium 26 is a medium suitable for storing electronic instructions and capable of being coupled to a bus of a computer system.

[0032] For example, the information medium 26 is a USB key, a floppy disk or floppy disk, an optical disk, a CD-ROM, a magneto-optical disk, a ROM memory, a RAM memory, an EPROM memory, an EEPROM memory, a magnetic card or an optical card.

[0033] The computer program 12 comprising program instructions is stored on the information medium 26.

[0034] The computer program 12 is loadable onto the data processing unit 16 and is adapted to cause the implementation of an optical design method for a head-up display, when the computer program 12 is implemented on the processing unit 16 of the computer 10.

[0035] The operation of the computer 10 will now be described with reference to figure 2, which schematically illustrates an example of implementation of a method for optical design of a head-up display, and to figures 3 to 5 which are examples allowing a better understanding of certain of the phases of the method.

[0036] The flowchart in Figure 2 includes a sequence of several phases, themselves composed of steps.

[0037] Phases 100, 200, 300 and 400 relate to a method of optically designing a head-up display using an existing visor 52 of a helmet 50 to form a virtual image in a viewing window of a wearer of the helmet 50.

[0038] The virtual image is formed by the reflection of a light beam from an image projection assembly 60 onto the visor 52 of the helmet 50. It is understood that the visor 52 of the helmet 50 is deployed so that the reflection can take place.

[0039] The 50 helmet is typically intended to be worn by a driver of a vehicle. The vehicle is, for example, a motorcycle, a scooter, a quad bike, a sidecar, a Segway, a moped, a motorcycle, or even a bicycle, a tricycle, or a three-wheeled vehicle. More generally, the vehicle is any type of land, air, or sea vehicle.

[0040] The virtual image to be generated is, for example, an image comprising vehicle control information for the driver while the driver is driving the vehicle. Such control information is, for example, navigation, safety or communication information from an on-board system in the vehicle or from an electronic device of the driver, such as a smartphone.

[0041] Phase 500 involves the production of an image projection assembly 60 for this display, in accordance with the optical design process.

[0042] Phase 600 concerns the integration of such an image projection assembly 60 into a helmet 50 having an existing visor 52 to form a head-up display.

[0043] The optical design method comprises a phase 100 of receiving input data. The phase 100 is, for example, implemented by the computer 10 in interaction with the computer program, i.e. is implemented by computer.

[0044] The input data includes at least a geometric model of the helmet 50 and the visor 52, and optical parameters.

[0045] The geometric model is a model specific to an existing helmet 50 having a visor 52 integrated into the helmet 50. The geometric model is a three-dimensional model. The geometric model is, for example, provided in a CAD (computer-aided design) file or in any other type of file. For example, the geometric model is provided by the manufacturer of the helmet 50. The optical parameters define constraints so that the virtual image generated by the head-up display is visible to a wearer of the helmet 50. The optical parameters comprise at least the following optical parameters:

[0046] - a position of the eyes 56 of a typical wearer of the helmet 50. The position of the eyes 56 is relative to the helmet 50.

[0047] - a field of vision for the typical wearer. For example, the field of vision is greater than 20 degrees (°) for good visual comfort.

[0048] - an eyebox for the typical wearer. The eyebox is the volume in which the wearer's eye sees the entire image and the field of vision along and around the line of sight in which the entire image can be seen completely. For example, the eyebox is larger than 15 mm, ideally 20 mm to cover most interpupillary distances.

[0049] - a vertical projection angle (LUA) defining the vertical projection axis of the virtual image for the typical wearer. The vertical projection angle LUA is an angle centered on the vision axis, indicating the vertical projection axis of the virtual image. For example, the vertical projection angle LUA ranges from -30° to +30°.

[0050] - a horizontal projection angle (LOA) defining the horizontal projection axis of the virtual image for the typical wearer. The horizontal projection angle LOA is an angle centered on the vision axis, indicating the horizontal projection axis of the virtual image. For example, the horizontal projection angle LOA is between 0° and 70°, preferably between 0° and 45°, advantageously between 0° and 25°. The horizontal projection angle LOA is 0° for an image centered on the eye.

[0051] - a desired distance between the position of an eye 56 (for the typical wearer) and the virtual image, called distance VI D. For example, the desired distance VI D is between 2 meters (m) and 5 m, typically greater than 7.5 m for augmented reality.

[0052] The typical carrier is, for example, a carrier corresponding to 85 ème percentile of the population.

[0053] The optical design method comprises a phase 200 of determining a position, in the helmet 50, of an image projection assembly 60 comprising an image generation unit 70 (in English PGU for “Projection Generation Unit”) and an optical projection block 72, such that the light beam coming from the image projection assembly 60 forms a virtual image visible to a wearer of the helmet 50 after reflection on the visor 52 of the helmet 50. The phase 200 is, for example, implemented by the computer 10 in interaction with the computer program, that is to say is implemented by computer.

[0054] The position of the image projection assembly 60 is determined based on the geometric model and optical parameters.

[0055] The image projection assembly 60 is typically previously defined (e.g.: number of optics and nature of the optics of the optical block 72) and can be optimized subsequently.

[0056] In an exemplary implementation, the phase 200 of determining the position of the image projection assembly 60 comprises a step 210 of determining a set 60 of possible directions between the eyes 56 of the typical wearer and the virtual image as a function of the geometric model, the position of the eyes 56 of the typical wearer, the field of vision of the typical wearer, the observation window of the typical wearer, the vertical projection angle LUA of the typical wearer, and the horizontal projection angle LOA of the typical wearer.

[0057] In one example, the geometric model is imported into an optical simulation tool in imaging or optical ray propagation mode. The tool is, for example, the Zemax software.

[0058] For example, a ray trace is carried out starting from the position of the eyes 56 of the typical wearer in the direction of the visor 52 of the helmet 50, within the limit of the field of vision and the observation window of the typical wearer, an angle scan according to the vertical projection angle LUA of the typical wearer and the horizontal projection angle LOA of the typical wearer is then carried out making it possible to determine the set of possible directions D between the eyes 56 of the typical wearer and the virtual image.

[0059] The phase of determining the position of the image projection assembly 60 then comprises a step 220 of determining a set of possible positions for the object of the virtual image as a function of the geometric model, the set of possible directions D and the desired distance between the position of the eye 56 and the virtual image. The object of the virtual image is in this case the image projection assembly 60.

[0060] Indeed, knowing the desired distance between the position of the eye 56 and the virtual image, each position is determined as being on a possible direction and located at a distance from the eye 56 equal to the desired distance.

[0061] Figures 3 and 4 illustrate an example in side view, respectively in top view, of a helmet 50 comprising a visor 52. A direction D for the virtual image is defined by its angles LUA and LOA as a function of the position of the eyes 56 of a typical wearer. For each direction D, a position in the helmet 50 is then determined for the image projection assembly 60 as a function of the desired distance between the position of the eye 56 and the virtual image.

[0062] The phase of determining the position of the image projection assembly 60 also comprises a step 230 of determining a position for each of the image generation unit 70 and the optical projection block 72 of the image projection assembly 60, as a function of the geometric model and the set of possible positions for the object.

[0063] Preferably, the position of each of the image generation unit 70 and the optical projection unit 72 is determined so as to minimize the size of the optical unit 72 in the helmet 50. Alternatively, the position of the image generation unit 70 and the optical projection unit 72 is chosen randomly from the set of possible positions.

[0064] Optionally, in an exemplary implementation, the step of determining the position of each of the image generation unit 70 and the optical projection unit 72 comprises: determining a position for the image generation unit 70 based on the geometric model and the set of possible positions for the object. optimizing the emitting surface of the image generation unit 70 in order to minimize the size of the optical unit 72 in the headset 50, while respecting resolution and brightness constraints for the virtual image. In one example, the emitting surface is chosen so that the resolution of the virtual image is sufficient so that the resolution of the virtual image projected at the desired distance is compatible with the resolving power of the eye.The image generation unit 70 is also chosen so as to satisfy luminance constraints and so that its pixel matrix is ​​compatible with the quantity of information to be displayed. determining a position for the optical block 72 as a function of the geometric model, the position of the image generation unit 70 and the optimized emitting surface of the image generation unit 70 so as to minimize the size of the optical block 72 in the headset 50.

[0065] For example, the resolution of the virtual image is:

[0066] - at least 60 pixels / 0 : this corresponds to the resolution of the eye since 1 pixel = 1 minute of arc.

[0067] - preferably at least 90 pixels / 0 .

[0068] - ideally 120 pixels / 0 . Since speed impacts visual perception, a lower resolution of the virtual image is not necessarily perceived by the wearer of the headset 50.

[0069] Preferably, in the preceding example, the step of determining the position of each of the image generation unit 70 and the optical block 72 comprises the optimization of the number and / or the nature of the elements of the optical block 72 so as to minimize the size of the optical block 72 in the helmet 50. Such an optimization is for example carried out between the optimization of the emitting surface and the determination of the position of the optical block 72.

[0070] The optical unit 72 is, for example, based on a folding system, for example based on lens(es) and / or mirror(s). The optical unit 72 may optionally be folded using mirrors or total internal reflection to minimize its size. Preferably, the optical unit 72 comprises at most two elements, or even a single element.

[0071] The optical design method comprises a phase 300 of optimizing the optical projection block 72 so as to improve the quality of the virtual image. Phase 300 is, for example, implemented by the computer 10 in interaction with the computer program, that is to say is implemented by computer.

[0072] The optimization phase 300 comprises a step 310 of determining, as a function of the determined position of the image generation assembly 60, the area of ​​the visor 52, called the local area, receiving a light beam coming from the image generation assembly 60.

[0073] The optimization phase 300 comprises a step 320 of determining the shape of the determined local zone, the local zone being deformed locally relative to the overall shape of the visor 52 taken over the entire field of vision of the typical wearer.

[0074] In an exemplary implementation, the step 320 of determining the shape of the local area comprises: performing a ray tracing, based on the geometric model, from the position of the eyes 56 of the typical wearer to the local area making it possible to obtain the shape of the local area (the impact of the rays on the local area models the shape of the local area), mathematical modeling of the shape of the determined local area, determining a recoded model of the visor 52 based on the mathematical modeling. validating the recoded model by comparing the recoded model with the geometric model of the visor 52. For example, the recoded model is superimposed on the geometric model and the difference between the two models is evaluated. The recoded model is validated if the determined difference is less than a predetermined threshold.

[0075] The recoded model allows the optical block 72 to be optimized in the optical simulation tool (Zemax) in imaging mode. The mathematical modeling of the shape of the local area is, for example, chosen from one of the surface types available in the optical simulation software (spherical, toric, biconical, aspherical, freeform, etc.).

[0076] The optimization phase 300 comprises a step 330 of determining a modification of the optical surface of the or one optic of the optical block 72 so as to compensate for the local deformation of the local zone, making it possible to reduce the optical aberrations of the virtual image.

[0077] In the previous example, the step of determining the modification of the optical surface is carried out based on the recoded model.

[0078] In an exemplary implementation, the analysis of the local area used of the visor 52 shows that its shape differs from the general shape of the visor 52 taken over the entire field of vision. It is therefore appropriate for the optics considered of the optical block 72 to have a specific surface to compensate for the local deformation induced by the visor 52. This specific surface will then be modified and optimized to compensate for all the optical aberrations. This surface can be a diopter or a mirror. Its equation can be of the following form (aspherical and biconical shape):

[0079] Or :

[0080] • C x = 1 / R X with R x the horizontal radius of curvature of the local visor,

[0081] • C y = 1 / R y with R y the vertical radius of curvature of the local visor,

[0082] • The Z terms L are the standard coefficients of the Zernike polynomials,

[0083] • k x is the coefficient of taper in x,

[0084] • k y is the coefficient of taper in y,

[0085] • a; are the coefficients of the polynomial in x,

[0086] • Pi are the coefficients of the polynomial in y,

[0087] • Ai are the coefficients of the Zernike polynomials,

[0088] • p etcp are the polar coordinates of the point (x,y) considered, and

[0089] • N is the number of Zernike polynomials used. Preferably, when the local area has a toric shape, the modified optical surface is such that the corresponding optic is an aspherical biconical optic.

[0090] In an exemplary implementation, the power of the visor 52 being quite significant, the optical block 72 can be limited to a single optical focusing element, plus a folding mirror to limit the distance of the optics to the edge of the helmet 50. The chromatic aberrations will be of little importance due to the low power of the focusing optics. The optical elements used make it possible to correct the geometric aberrations introduced by the visor 52 in order to satisfy the constraints on the required resolution and the distortion limit.

[0091] Optionally, the optical design method comprises a phase 400 of global optimization of the image projection assembly 60. The phase 400 is, for example, implemented by the computer 10 in interaction with the computer program, that is to say is implemented by computer.

[0092] The global optimization phase 400 aims to optimize the inclination and centering of the elements of the image projection assembly 60 so as to reduce the optical aberrations of the virtual image generated by the head-up display formed of the image projection assembly 60 and the visor 52 of the helmet 50. The global optimization phase is carried out as a function of the geometric model, the determined position of the image projection assembly 60, and the optimized projection block.

[0093] Figure 5 shows an example of design obtained for a field of vision of 20°, a distance VI D of 5 m and an eyebox of width 20 mm. The image projection assembly 60 comprises an image generation unit 70 whose output is illustrated by the reference 71, and an optical block 72. The optical block 72 comprises a single focusing optic consisting of a single prism, which facilitates integration into the helmet 50. The material of the prism also makes it possible to push back the focal plane, making it possible to fold the optical path. This makes it possible to maximize the distance between the prism and the driver's head for safety reasons. Over the entire field of vision of the visor 52 of the helmet 50, the shape can be assimilated as a first approximation to a spherical surface. Over the local area of ​​the visor 52 used to project the virtual image, the shape is similar to a torus. A toric compensation surface is then introduced into the focusing system.To achieve the desired optical performance, the addition of asphericity coefficients transforms this toric surface into an aspherized biconical surface. The desired performance of the system is obtained thanks to the input face of the prism which is of aspherical and biconical shape (see previous equation). In particular, the prism has a flat surface 80, a reflective flat surface 82 and an aspherical biconical surface 84. The phase 500 of the integration method is a phase of producing an image projection assembly 60 conforming to that obtained at the end of the optical design method. For this, in particular, an optical block 72 is produced conforming to the number of optics / type of optics / correction surface of the optical block 72 of the optical design.

[0094] Phase 600 of the integration method is a phase of integrating the image projection assembly 60 into the helmet 50, in accordance with the integration obtained at the end of the optical design method, so as to form the head-up display.

[0095] At the end of the integration process, a head-up display is obtained using an existing visor 52 of a helmet 50 to form a virtual image in an observation window of a wearer of the helmet 50. The head-up display comprises the visor 52 of the helmet 50 and an image projection assembly 60 comprising an image generation unit 70 and an optical projection block 72 positioned in the helmet 50 so that the light beam coming from the image projection assembly 60 forms a virtual image visible to a wearer of the helmet 50 after reflection on the visor 52 of the helmet 50.

[0096] Thus, the optical design method makes it possible to design a head-up display for any type of helmet 50 having a visor 52, without modifying the characteristics of the visor 52 (position, orientation, shape).

[0097] The process also allows for the design of a HUD that is fully integrated into the helmet shell without any external elements. This design process also avoids the integration of any optical or optomechanical adjustment system that would make integration into the helmet difficult, if not impossible. Finally, this method allows for the wearing of vision prescriptions to be taken into account.

[0098] Those skilled in the art will understand that the embodiments described above are capable of being combined with each other when such combinations are compatible.

Claims

CLAIMS 1. A method for optically designing a head-up display using an existing visor (52) of a helmet (50) to form a virtual image in a viewing window of a wearer of the helmet (50), the method being computer-implemented and comprising the following phases: a. an input data receiving phase comprising: i. a geometric model of the helmet (50) and the visor (52), ii. optical parameters defining constraints for the virtual image to be visible to a wearer of the helmet (50), the optical parameters comprising at least one eye position (56) of a typical wearer, a field of view for the typical wearer, a viewing window for the typical wearer, a vertical projection angle of the virtual image for the typical wearer, a horizontal projection angle of the virtual image for the typical wearer, and a desired distance between the position of an eye (56) of the typical wearer and the virtual image, b.a phase of determining a position, in the helmet (50), of an image projection assembly (60) comprising an image generation unit (70) and an optical projection block (72), such that the light beam coming from the image projection assembly (60) forms a virtual image visible to a wearer of the helmet (50) after reflection on the visor (52) of the helmet (50), the position of the image projection assembly (60) being determined as a function of the geometric model and the optical parameters, c. a phase of optimizing the optical projection block (72) so as to improve the quality of the virtual image, the optimization phase comprising the steps of: i. determining, as a function of the determined position of the image projection assembly (60), the area of the visor (52), called the local area, receiving a light beam, ii.determining the shape of the determined local area, the local area being locally deformed relative to the overall shape of the visor (52) taken over the entire field of vision of the typical wearer, and iii. determining a modification of the optical surface of the or an optic of the optical block (72) so as to compensate for the local deformation of the local area, making it possible to reduce the optical aberrations of the virtual image.

2. Method according to claim 1, in which the phase of determining the position of the image projection assembly (60) comprises the following steps: a. determining a set of possible directions (D) between the eyes (56) of the typical wearer and the virtual image as a function of the geometric model, the position of the eyes (56) of the typical wearer, the field of vision of the typical wearer, the observation window of the typical wearer, the vertical projection angle of the typical wearer, and the horizontal projection angle of the typical wearer, b. determining a set of possible positions for the object of the virtual image as a function of the geometric model, the set of possible directions (D) and the desired distance between the position of the eye (56) of the typical wearer and the virtual image, and c. determining a position for each of the image generation unit (70) and the optical projection block (72) of the image projection assembly (60), as a function of the geometric model and the set of possible positions for the object.

3. Method according to claim 2, in which the position of each of the image generation unit (70) and the optical projection unit (72) is determined so as to minimize the size of the optical unit (72) in the helmet (50).

4. The method of claim 2, wherein the step of determining the position of each of the image generation unit (70) and the optical projection unit (72) comprises: a. determining a position for the image generation unit (70) based on the geometric model and the set of possible positions for the object, b. optimizing the emitting surface of the image generation unit (70) to minimize the size of the optical unit (72) in the headset (50), while respecting resolution and brightness constraints for the virtual image, and c. determining a position for the optical unit (72) based on the geometric model, the position of the image generation unit (70) and the optimized emitting surface of the image generation unit (70) so as to minimize the size of the optical unit (72) in the headset (50).

5. Method according to claim 4, in which the step of determining the position of each of the image generation unit (70) and the optical block (72) comprises optimizing the number and / or the nature of the elements of the optical block (72) so as to minimize the size of the optical block (72) in the helmet (50), preferably the optical block (72) comprising at most two elements.

6. A method according to any one of claims 1 to 5, wherein the step of determining the shape of the local area comprises: i. performing a ray tracing, based on the geometric model, from the position of the eyes (56) of the typical wearer to the local area to obtain the shape of the local area, ii. mathematical modeling of the shape of the determined local area, iii. determining a recoded model of the visor (52) based on the mathematical modeling, and iv. validating the recoded model by comparing the recoded model with the geometric model of the visor (52), the step of determining the modification of the optical surface being performed based on the recoded model.

7. A method according to any one of claims 1 to 6, wherein when the local area has a toric shape, the modified optical surface being such that the corresponding optic is an aspherical biconical optic.

8. Method according to any one of claims 1 to 7, wherein the method comprises a phase of global optimization of the image projection assembly (60) during which the inclination and the centering of the elements of the image projection assembly (60) are optimized so as to reduce the optical aberrations of the virtual image generated by the head-up display formed of the image projection assembly (60) and the visor (52) of the helmet (50), the global optimization phase being carried out as a function of the geometric model, the determined position of the image projection assembly (60), and the optimized projection block.

9. A method of integrating a head-up display into a helmet (50) comprising a visor (52), the head-up display using the existing visor (52) of the helmet (50) to form a virtual image in a viewing window of a wearer of the helmet (50), the integration method comprising: a. optically designing the head-up display in accordance with an optical design method according to any one of claims 1 to 8, b. producing an image projection assembly (60) in accordance with that obtained at the end of the optical design method, and c. integrating the image projection assembly (60) into the helmet (50), in accordance with the integration obtained at the end of the optical design process, so as to form the head-up display.

10. A head-up display using an existing visor (52) of a helmet (50) to form a virtual image in a viewing window of a wearer of the helmet (50), the head-up display comprising: a. the visor (52) of the helmet (50), b. an image projection assembly (60) comprising an image generation unit (70) and an optical projection block (72) positioned in the helmet (50) such that the light beam from the image projection assembly (60) forms a virtual image visible to a wearer of the helmet (50) after reflection on the visor (52) of the helmet (50), the head-up display having been designed and integrated into the helmet (50) as a function of the existing visor (52) in accordance with an integration method according to claim 9.

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