Method and apparatus for determining the refractive power of an optically transparent object

Abstract

The invention relates to a method and an apparatus for determining the refractive power of an optically transparent object (2) and to preferred applications thereof. The refractive power in a measured region (MB) of the object (2) in a first direction of deflection (AH) and at least one further direction of deflection (AV) is measured by means of an optical measuring device (4), and an orientation and position of the object (2), of a view point (42, 52) and of a viewing direction (BR) are defined. The point of intersection of the defined viewing direction (BR) and precisely one local measuring area (MF[i]) on the object (2), and the angle of view (ε) included by the viewing direction (BR) and a measuring direction (MR) in the identified local measuring area (MF[i]) are determined. An amplification factor is determined for the refractive power on the basis of the angle of view (ε) determined and an index of refraction (n) of the object (2), and the refractive power in the viewing direction (BR) is determined by applying the amplification factor to the local refractive-power value B[i] of the local measuring area (MF[i]).

Description

[0001] Method and device for determining the refractive power of an optically transparent object

[0002] The invention relates to a method and a device for determining the refractive power of an optically transparent object, in particular a disc-shaped object such as a glass pane, wherein the disc-shaped object can be flat or preferably curved according to claims 1 and 10. Furthermore, the invention relates to a preferred use of the method and / or the device for determining the refractive power of a windshield from any viewing angle according to claim 16.

[0003] When an optical ray passes through an optically transparent object with a refractive index different from that of its surroundings, this optical ray is refracted and usually deflected according to the laws of optics. For a homogeneous, disc-shaped, transparent object with parallel surfaces, a ray directed perpendicular to the disc passes through the disc unrefracted. A ray directed at the disc from a viewing angle other than 90° is shifted parallel to the ray's direction, causing the image to appear laterally offset.

[0004] Inhomogeneities in the lens, curvatures in the lens, and / or (even locally) non-parallel surfaces of the lens cause incident parallel lines of vision to be refracted differently, resulting in distortion in the image, similar to the effect of a lens. The strength of the distortion is described by the refractive power B in a deflection direction, usually measured in dioptrins (dpt). The refractive power ("strength of distortion") also changes with the viewing direction from which the line of vision strikes the optical object.The optical effect of flat glass with an uneven surface was described in Kerkhof, "Optical Effects of Flat Glass with Uneven Surfaces," Glastechnische Berichte, Volume 25, pages 71 to 83, published by the German Glass Technical Society, Frankfurt (Main), 1952, based on refractive geometry. The glass plate is assumed to be composed of many glass prisms with very small wedge angles of the refraction plane for various angles of incidence of the visual ray. The refraction plane is the plane in which the incident visual ray and the refracted visual ray lie.

[0005] If the local surface shape of the transparent object on both sides of the pane is known, the plane of refraction can be estimated for a given viewing direction of the transparent object and the refractive power can be determined. However, this can take into account inhomogeneities within the transparent object, which can also lead to optical refraction independent of the local surface shape of the entrance and exit surfaces of the transparent object. Furthermore, determining the surface shape of the transparent object, e.g., a pane of glass, especially a curved pane like a car windshield, is very complex and time-consuming.

[0006] A possible iterative method for determining the surface shape of a plate-like or layer-like object is described in WO 2022 / 189327 A1. An assumed surface shape is provided as the initial shape, and a plurality of measurement points are defined on the initial shape. The spatial position of the measurement points is determined optically by irradiating the surface and detecting the reflected radiation. From deviations of the detected radiation at a measurement point from the radiation expected from the initial shape, an adapted surface shape is iteratively determined until the measurements agree with the expectations within a certain accuracy value. The determined surface shape is then used to simulate a refractive power distribution. Due to the known surface shape, the refractive power can then, in principle, also be determined from defined viewing directions.Such methods are not suitable for optical quality control of optically transparent objects in an industrial production line due to the effort involved in the measurement method and the evaluation effort.

[0007] Furthermore, methods for measuring refractive power are known in which a known pattern is projected through the transparent object, and any distortion of the pattern caused by the object is quantitatively evaluated in the image. The pattern can, for example, be a pattern of parallel lines with a defined line spacing. The refractive power in this deflection direction can then be determined from the variation in the line spacing in a specific deflection direction, as described, for example, in DIN 52305 (Determination of the deflection angle and refractive index of safety glass for vehicle glazing). The pattern can also consist of a regular arrangement of circles of known diameter, with a variation in the circle diameter being evaluated in at least one deflection direction (cf. ECE R43, Agreement concerning the Adoption of Uniform Conditions of Approval of Motor Vehicle Equipment and Parts, in this case relating to Safety Glazing Materials).The problem with the measurements described is that the measurement is taken from a defined viewing direction. If the refractive power of the object is to be determined from different viewing directions relative to the object, for example, from a defined viewing point (such as the driver's position) in different viewing directions through the windshield, a large number of measurements are necessary. The advantage of measurements, however, is that the actual refractive power of the object is determined, which, in addition to the surface shape and orientation, also captures inhomogeneities within the object itself, such as inclusions or defects, and is largely free of theoretical models.

[0008] Against this background, the object of the invention is to propose a possibility for the most accurate determination possible of the actual refractive power of an optically transparent object, for example a glass pane such as a curved windshield of a motor vehicle, under any viewing direction through the object, wherein the determination of the refractive power should be possible by a measurement in particular at the speed of a conventional production line for a transported object.

[0009] For this purpose, the method proposed according to the invention comprises in particular the following steps, which may also be carried out in another technically reasonable manner or sequence.

[0010] (a) Measuring the refractive power in a measuring area of ​​the transparent object in a first deflection direction and at least one further deflection direction by means of an optical measuring device in a predetermined measuring direction, wherein the measuring area of ​​the object is divided into several measuring areas and for each of the measuring areas (also referred to as local measuring area MF[i]) a local refractive power value (also referred to as local refractive power value B[i]) is determined from the totality of the / all measuring areas. All local refractive power values ​​B[i] together form a refractive power map of the object, i.e. a local refractive power value B[i] for each measuring area MF[i],

[0011] The refractive power map with the local refractive power values ​​B[i] thus describes the refractive power for the entire measurement range of the object, with each refractive power value B[i] containing a value for the refractive power B(AH) in the first deflection direction and a value for the refractive power B(AV) for each additional measured deflection direction. When measuring the refractive power B for a first and a second deflection direction, a local refractive power value B[i] can be described or formed as a 2-tuple of the form [B[i](AH), B[i](AV)]. With more than two deflection directions, a corresponding n-tuple results for n deflection directions.

[0012] An important aspect of the local refractive power values ​​B[i] is that they indicate the actual real refractive power for a line of sight in the measurement direction, namely in a first and at least one second (different from the first) deflection direction. The local refractive power values ​​B[i] thus describe a deflection in three-dimensional space and are not limited to a model-determined refractive plane. Furthermore, the measured refractive power is free of assumptions and models regarding the surface shape of the entrance and exit planes of the transparent object. This is valid for any (local) surface shape of the object.

[0013] (b) Determining the orientation and position of the object (), a visual point () and at least one viewing direction (BR) from the visual point () through the measuring range of the object () in a common coordinate system. This clearly defines the viewing direction of the line of sight through the object. Determining a visual point relative to the object also makes it possible to define different (at least two or more) viewing directions through an object, which correspond to a typical application in which a user looks from one visual point in different directions through a fixed object, e.g. the windshield of a motor vehicle. In this common coordinate system, the measuring direction (specified in relation to the object) relative to the viewing direction is then also known. This makes it possible to define any viewing direction from the visual point through the object and to determine the refractive power in this viewing direction.(c) Determining the intersection point of the specified viewing direction with exactly one local measuring surface MF[i] and determining the viewing angle s between the viewing direction and the measuring direction in the determined local measuring surface (MF[i]);.

[0014] (d) determining an amplification factor D for the refractive power as a function of the determined viewing angle s and a refractive index n of the object, wherein the amplification factor D comprises a factor value DH for the refractive power in the first deflection direction B(AH) and a factor value DV for each further deflection direction B(AV);

[0015] The refractive index n is the refractive index of the object against air, which is known, for example, from tabular overviews or can be measured using measuring methods known to those skilled in the art and customary in the field. “Air” represents the environment in which the measurement takes place. This can in principle be any environment, particularly gaseous or liquid. For many typical applications, normal ambient air will be used. The amplification factor D can therefore also be described or formed as an n-tuple, corresponding to the local refractive power value B[i]. For a 2-tuple, the notation [DH, DV] results for the amplification factor D. The amplification factor formed as an n-tuple therefore describes the refractive power from one viewing direction in each of the deflection directions. If, for example,the refractive power B is measured in two deflection directions AH, AV and the viewing angle s lies in the plane defined by the measuring direction MR and the deflection direction AH, the amplification factor D comprises a value DH for the deflection in the deflection direction AH and a value DV for the deflection in the deflection direction DV. If there are several deflection directions AVi, several amplification factors DVi can be applied accordingly for several or all of the deflection directions AVi in order to determine the refractive power or deflection in each of the deflection directions AVi. In this way, the refractive power for different deflection directions in three-dimensional space is determined. (e) Determination of the refractive power in the viewing direction by applying the amplification factor D to the local refractive power value B[i] of the determined local measuring surface MF[i], i.e. the one measuring surface at the intersection point with the specified viewing direction BR.

[0016] By determining amplification factors D for refractive power B for both a first deflection direction AH and at least one second deflection direction AV that is different from the first deflection direction AH, the refractive power B through the object can be determined and / or evaluated in any viewing direction BR (relative to the object), regardless of the measuring direction MR (relative to the object) in which the local refractive power values ​​B[i] were determined. This not only determines a two-dimensional deflection of a visual ray in a plane (the refraction plane) spanned by the direction of the visual ray and the deflection direction, but also a three-dimensional deflection of a visual ray incident on the object at any angle.This requires only one measurement of the refractive power from one direction, which measures or determines the object's refractive power in several different deflection directions, at least in two deflection directions: AH and AV. This allows an optical assessment of an object's refractive power in different viewing directions from a single measurement in one direction. Previous assessments required separate measurements of the object in each viewing direction.

[0017] Thus, the method proposed by the invention is not only simpler and faster to implement, but also enables a comprehensive optical evaluation of an object during production in a production line. The object is transported through an optical measuring device, the entire measuring range of the object is scanned, and the refractive power is determined from a single measuring direction. Measurements from different directions cannot be performed in a single production line. After the measurement has been performed, the optical evaluation can be performed in a computing unit, and the evaluation result can be output and / or saved.

[0018] The measuring area for which the refractive power is measured can be the entire object or a part of the object.

[0019] Each measuring surface is a sub-area of ​​the object (in the sense of a local sub-area of ​​the entire measuring range). For each local measuring surface, a value of the refractive power is determined by measurement in at least two deflection directions. Preferably, the individual local measuring surfaces together form exactly the entire measuring range. In other words, the measuring range is divided into local measuring surfaces, with the totality of all local measuring surfaces forming the measuring range of the object. The local measuring surface can be located at the position where the measuring direction intersects with the object, i.e., where the object is arranged in the optical measuring device.

[0020] A single local measuring surface MF[i] can preferably be defined by a value of the refractive power B[i] in the at least one deflection direction (or several different deflection directions). A measuring surface is therefore the surface area for which exactly one value of the refractive power in the at least one deflection direction (or several deflection directions) is determined by the optical measuring device and spatially assigned to this. By determining a value of the refractive power for a measuring surface, the refractive power B for the entire measuring range MB is determined as a refractive power map BK with a value of the refractive power B[i], where [i] is the index of exactly one defined individual measuring surface MF[i]. The optical measuring device can scan the measuring range MB of the optical object () in order to create the refractive power map BK.Preferably, the measuring surface is defined as a surface that is perpendicular to the measuring direction, regardless of the actual orientation of the surface of the optically transparent object whose refractive power is being determined. The measuring surface can be understood or used as the focal plane of a lens in which the deflection of the measuring beam occurs. Preferably, the measuring direction can coincide with the optical axis of an objective of the measuring device, typically an optical camera. This case is easy to describe. However, it is purely a question of definition how the measuring direction is defined and whether the measuring direction and the first deflection direction lie in a distinguished (i.e. specially designated) common plane and / or whether the measuring direction actually coincides with the optical axis of a camera objective.It will be clear to those skilled in the art that other mathematical descriptions are also possible, which can be converted into one another using optical trigonometric considerations. Such descriptions are also encompassed by the subject matter of the invention. However, for the sake of clarity, the description is limited to this nomenclature.

[0021] In principle, any optical measuring device capable of determining the refractive power of an optically transparent object at a measuring point in a spatial direction can be used for this purpose. Such optical measuring devices are known. Preferred examples of particularly advantageous measuring devices that allow rapid measurement of a large-area object, e.g., a glass pane, such as a curved glass pane, are described below. These are particularly suitable for measuring and inspecting glass panes online in a production line.

[0022] The smallest possible measuring area is predetermined by the maximum resolution of the optical measuring device. A larger measuring area can be defined, for example, as a multiple of the smallest possible measuring area. According to a preferred embodiment of the method, the viewing direction can be selected according to the invention such that the viewing angle s lies in the plane spanned by the measuring direction and the first deflection direction. The amplification factor D can therefore be used to determine the refractive power B in precisely this deflection direction. This achieves particularly high accuracy because the viewing direction lies precisely in the deflection plane of the first deflection direction for which the amplification factor DH is determined. The at least one other amplification factor DV for the at least one other deflection direction has also been determined precisely for a viewing direction in this plane.

[0023] When applying the method according to the invention, it is also possible for the viewing angle s to lie in a projection of the viewing direction (BR) into the plane spanned by the measuring direction and the first deflection direction and / or the further or several or each of the further deflection directions.

[0024] Alternatively, the viewing angle s can also be determined according to the invention from the projection into the corresponding plane. This projection of the viewing direction is referred to as the component of the viewing direction in the (first or further) deflection direction. If the projection of the viewing direction also has components in other deflection directions for which the refractive power has been measured, the refractive power can also be determined for these components of the viewing direction by appropriately applying the amplification factor. For these other deflection directions, the refractive power can then be determined analogously to the method described above, in particular by carrying out the method multiple times, whereby in each case the deflection direction in which the observed component of the deflection direction lies is regarded as the first or main deflection direction. The different refractive indices in each of the deflection directions can then be superimposed, e.g. by a linear combination orsimple or weighted addition. A local refractive power value B[i] can optionally be determined from a linear combination of local refractive power values ​​in the direction of the first and second, or more generally of the multiple deflection directions from a function F of the various local refractive power values ​​in the respective deflection directions F(B[i](AH),B[i](AV)), e.g. a linear combination of B[i](AH) and B[i](AV) with predetermined factors f(AH) and f(AV), i.e. a function F = f AH) ■ B[i](AH + f AV ■ B[i](AV)' .

[0025] The factors f(AH) and f(AV) can be fixed. This assigns different levels of importance or significance to the various deflection directions, for example, for a specific application. It is also conceivable to describe the factors f(AH) and f(AV) as a weighting of the individual refraction directions AH, AV based on the relative sizes of the viewing angles s(AH,AV) in the planes spanned by projections of the viewing direction, which is spanned by the measurement direction and the respective deflection direction AH, AV. A possible formula for the calculation could be where, if necessary, several summands or factors E(A7) and B[i]( ) are provided in the formula.

[0026] This allows for cases in which the viewing direction is not exactly in the plane spanned by the measuring direction and one of the deflection directions (taking projections into account).

[0027] Another possibility for calculating the refractive power using a formula F can be to calculate the factors from a relative weighting of the local refractive power values ​​in the different deflection directions AH, AV, basically comparable to the one explained above for the projections of the viewing angle s. This can be done, for example, using the formula This also takes into account refractions in different deflection directions when the refraction occurs in different refraction directions AH, AV, for which the local refractive power values ​​B[i](AH B[i](AV) were determined, regardless of the actual viewing direction.

[0028] The functions described above are to be understood as possible concrete embodiments of the invention, without the invention being limited to these embodiments. These can also be combined or adapted accordingly by a person skilled in the art. Instead of the function described as a linear combination, other, more complex functions are also conceivable, such as constants, polynomials, or the like.

[0029] The advantage according to the invention of determining the local refractive power values ​​as a function of all or several deflection directions from a function F of the various local refractive powers in the respective deflection directions is that it also takes into account the properties of the refractive power when the viewing direction does not lie exactly in the plane spanned by the measuring direction MR and one of the deflection directions (taking into account the projections) and / or a deflection of a line of sight in different deflection directions AH, AV occurs, for example, due to a surface structure of the glass pane that cannot be described by a cylindrical lens in a defined deflection direction. The result is then a scalar local refractive power value B[i] for a measuring surface

[0030] MF[i],

[0031] Specifying such a value can be useful for certain applications, possibly in addition to specifying a refractive power map with various refractive power values ​​in the various deflection directions for a specific viewing direction. According to the invention, the refractive power values ​​for a viewing direction are obtained, as described, by applying the amplification factor D(DH,DV) to the measured refractive power values.

[0032] According to the invention, according to one embodiment of the proposed method, the value of the amplification factor D in one of the deflection directions AH, AV can be determined as a function of the viewing angle s, assuming a transparent object with a wedge angle between the entrance surface and the exit surface, where the wedge angle of the lens describes precisely the deflection in the one of the deflection directions AH, AV under consideration. This can be done for each of the deflection directions in this way in order to determine the refractive power in this direction. It has been shown that such simple optical models can describe the local refractive power of optically transparent objects quite well and reliably.

[0033] According to a preferred specific embodiment of the method according to the invention, the amplification factor D in the plane spanned by the measuring direction and deflection direction can be defined by where n is the refractive index of the transparent object relative to the air or the measurement environment. Accordingly, the amplification factor D in a plane perpendicular to the plane spanned by the measurement direction and the deflection direction can be defined by

[0034] The amplification factors DH and DV describe the refractive power of a lens as a function of the viewing angle s, as qualitatively described in Fig. 6, where DH describes the amplification factor in the direction of tilt of the lens relative to the viewing angle s, i.e. with a viewing direction in the plane spanned by the measuring direction MR and the deflection direction AH. As expected, a strong tilt between the lens and the viewing direction (i.e. a large viewing angle s) results in a high amplification factor DH of the refractive power. In a deflection direction perpendicular to the tilt, a comparatively small amplification factor DV results over the entire tilt range (angular range of the viewing angle s).

[0035] For a lens with a refractive power of 10 mDpt, a measurement at a viewing angle of s = 55° results in a refractive power of approximately 41 mDpt. This corresponds to a magnification factor of 4.1. Figure 8 shows a magnification factor of approximately 4.2. This results in a good accuracy estimate of the magnification factor, especially in a medium angle range relevant for practical use.

[0036] The method according to the invention was also tested for a particularly preferred application, determining the refractive power of a motor vehicle windshield. For this purpose, the local refractive power value B[i] was measured in a selected measuring area MF[i] of the windshield, which was (vertically) vertical relative to the measuring direction MR (tilt angle 0° around a horizontal axis of rotation), in the vertical deflection direction AH using an optical measuring device. The windshield was also symmetrically aligned relative to the measuring direction MR such that the windshield was (horizontally) vertical relative to the measuring direction MR (yaw angle 0° around a vertical axis of rotation). The terms "horizontal" and "vertical" are fundamentally arbitrary and, in this text, refer to a normal installation position in a motor vehicle parked on a level road.In a vertical plane running in the measuring direction MR, the amplification factors D were determined according to the method proposed according to the invention in different viewing directions (all of which also lie in this vertical plane) for different viewing angles s by applying the formulas for amplification factors DH and DV defined above.

[0037] To verify these formulas, the windshield was rotated around a horizontal axis of rotation, which is perpendicular to the vertical plane running in the measurement direction MR, through the selected measuring surface MF[i] by the respective viewing angle s in accordance with the application of the inventive method (rotation by the tilt angle), and the local refractive power value B[i] in the selected measuring surface MF[i] was measured by the optical measuring arrangement. The amplification factors D(exp) were determined experimentally from the quotient of the local refractive power value B[i](s) measured under the respective viewing angle s and the original local refractive power value B[i](s = 0°) without rotation by the tilt angle.

[0038] Fig. 9 shows the course of the gain factors DH(theo) determined (theoretically) according to the proposed method in comparison to gain factors DH(exp) derived from the measurement.

[0039] For the viewing angles s of interest in realistic installation positions of up to approximately 55° or 60°, it can be seen that the values ​​determined according to the method according to the invention correspond to the actually measured values ​​with great accuracy. This opens up a wide range of possibilities for the application of the method according to the invention in the optical quality control of transparent objects, in particular large-area objects, where optical properties, in particular the refractive power, must be evaluated from different viewing directions. An important application of the method proposed according to the invention and of an optical measuring device configured to carry out the method is the measurement of glass panes, in particular glass panes for use in motor vehicles, such as windshields, with specifications for the refractive power.

[0040] According to the invention, the measuring direction can preferably correspond to a preferred viewing direction through the optically transparent object. A preferred viewing direction can be predetermined, for example, by a typical installation situation of the object. In a particularly preferred application of the method, a windshield of a motor vehicle can be used as the optically transparent object, which is rotated from a vertical orientation about a horizontal axis of rotation (along the longer side of the side of the windshield) by a tilt angle in the range between 40° and 75°, in particular between 55° and 60°. This tilt angle can be measured or defined as the angle between a windshield normal in the center of the windshield and the measuring direction MR.The advantage of such an arrangement of the transparent object in the optical measuring device when implementing the method according to the invention is that the viewing angle s between the measuring direction MR and the viewing direction BR is minimized for a practically relevant application. Typically, the smaller the viewing angle s, the smaller the error in determining the amplification factors D when applying the proposed method. This preferred arrangement of the optically transparent object according to the invention thus improves the accuracy of the proposed method.

[0041] In a particularly preferred embodiment of the method, a curved windshield can be transported as an optically transparent object through the optical measuring device in an orientation predetermined by a transport device, and the optical measuring device can be positioned such that the measuring direction of the optical measuring device, relative to an installation position of the windshield in a motor vehicle, lies in a horizontal vehicle plane and is directed in the direction of a vehicle traveling straight ahead. By configuring the method in this way, the refractive power is measured in a way that comes very close to the subsequent usage situation and / or quality control specifications. In a motor vehicle, a driver usually looks through the windshield in the direction of travel of the vehicle, or in a direction of view rotated by a viewing angle s in the horizontal plane.In the vertical direction, the (safety-relevant) viewing angle changes very little, at least in the typical user situation.

[0042] Therefore, a preferred embodiment or application of the method according to the invention provides for the viewing direction relative to the measuring direction to lie in a plane that is parallel to the plane spanned by the measuring direction MR and one of the deflection directions AH, AV, preferably the first deflection direction AH. This plane is preferably parallel to the horizontal vehicle plane. According to the invention, the refractive power is measured in a measuring direction that is as close as possible to the viewing direction BR for which the refractive power is determined using the method according to the invention.

[0043] According to the invention, the optical refractive power can preferably be measured by the optical measuring device (at least) in a horizontal deflection direction as the first deflection direction (AH) and in a vertical deflection direction as the second deflection direction (AV) relative to the installation position of the windshield in the motor vehicle. These are particularly important deflection directions for the qualitative assessment of the windshield with regard to its refractive power. If necessary, further deflection directions AV can also be taken into account according to the invention, so that the angle of rotation of the deflection directions relative to one another around the measuring direction is not 90°, but, for example, 45° or 30°. This results in a more precise description of the refractive power and the optical refractive behavior of the object, in particular a windshield.

[0044] The invention also relates to a device for determining the refractive power (B) of an optically transparent object with the features of claim 10 with an optical measuring device having a camera and an illumination, wherein the camera records the illumination through the transparent object, with a holding and transport device for fixing the optically transparent object in the optical measuring device, wherein the holding and transport device is set up to move the optically transparent object through the optical measuring device for scanning the entire measuring area, and with a computing unit which is set up to carry out the measurement of the refractive power and to carry out the method according to the invention according to one of claims 1 to 9.According to the invention, the computing unit is configured to control the optical measuring device and to carry out the method described above or parts thereof by means of suitable data processing programs which are installed on the computing unit in an executable manner.

[0045] Designs of the optical measuring device are possible in which the illumination device generates a collimated light beam (e.g. a laser beam) which is refracted in the object and recorded by the camera. The refraction of the object can be calculated from the deflection of the light beam recorded by the camera. To generate a refractive power map, the light beam can scan the entire measuring range MB of the object. Another alternative is to shine a light through the pane (object) from or with a point light source and to observe the (areal) intensity distribution on a screen behind the pane (object). From the area-wide distribution, the deflection or refraction can be determined in basically any direction. A camera can record the screen or serve directly as a screen and record the intensity in the individual pixels of the camera.

[0046] According to a preferred embodiment of the invention, a faster scanning of the measurement area of ​​the object is possible. In this preferred embodiment, the optical measuring device has a slit camera as the camera and a pattern of a known structure as the illumination, wherein the slit camera records the pattern through the optically transparent object in such a way that the pattern is imaged in the slit camera in a slit longitudinal direction such that it is visible in the slit longitudinal direction across the entire measurement area of ​​the object, and wherein the holding and transport device moves the object perpendicular to the slit longitudinal direction through the optical measuring device. In this embodiment, the refractive power map can be generated with a single measurement in which the object is continuously moved through the optical measuring device. This is particularly efficient and advantageous for use in a production line.

[0047] Preferably, the illumination pattern can be a periodic line pattern whose structure is known. The refractive power can be determined by the deviation in the periodic structure of the line pattern in the recorded image. Methods for this are known to those skilled in the art.

[0048] According to one embodiment of the invention, the line pattern can be formed from two line pairs that are aligned perpendicular to one another, each line pair being constructed from periodically arranged parallel lines. The lines are preferably aligned obliquely to the longitudinal direction of the column of the column camera, preferably at an angle of 45°. This enables particularly precise determination of the refractive power of the object in the longitudinal direction of the column and perpendicular to the longitudinal direction of the column, i.e. in the first deflection direction and a second deflection direction perpendicular to the first deflection direction, in a simple manner. In principle, other patterns, e.g. circular patterns, can also be used. Line pairs that are not perpendicular to one another can also be used, as long as the lines run in two different directions.

[0049] In a preferred embodiment, the column camera can be formed by light-sensitive pixels arranged side by side in the column's longitudinal direction. One or more pixels can be arranged transversely to the column's longitudinal direction. With only one pixel (transversely to the column's longitudinal direction), the column camera is also referred to as a line scan camera. Such a line scan camera has the advantage that the minimum possible number of pixels needs to be processed per image acquisition. The same applies, of course, when combining several of the camera's hardware pixels into one effective pixel during analysis.

[0050] This minimizes the processing time when measuring the refractive power. However, the pattern is only imaged one-dimensionally in the longitudinal direction of the column. Depending on the number of pixels arranged next to each other, multiple pixels arranged transversely to the longitudinal direction of the column multiply the evaluation effort and lead to a longer processing time. This may not be available in a production line or may limit the production speed. Therefore, a line scan camera is often a preferred solution according to the invention in practice. The advantage of multiple pixels arranged transversely to the longitudinal direction of the column is that a two-dimensional section of the periodic pattern is recorded, which enables simple evaluation in many different deflection directions of the refraction. This can be advantageous for applications with high demands on the accuracy of determining the refractive power.In this context, the invention can provide for images to be recorded by a column camera with multiple pixels arranged transversely to the column's longitudinal direction. However, for online evaluation in the production line, only the images of one of the pixels are evaluated, i.e., the image from a line scan camera. For offline evaluation, the two-dimensional image can then be used in addition. This can be the case, for example, if refraction effects for different viewing angles are to be evaluated and corrected when evaluating an image from an assistant camera looking through the window. Possible applications will be explained below.

[0051] In a particularly preferred embodiment according to the invention, the periodic line pattern of the illumination and an image recording structure of the slit camera can have different (spatial) periodicity. Due to the different spatial periodicity of pattern and image recording structure, an optical effect is created in the image recorded through the transparent object through the moiré effect (known per se and calculable by a person skilled in the art), in which the superposition of the regular patterns creates a separate periodic grid that has a special structure that is not present in any of the individual patterns and is also dependent on the type of superposition. Since the periodic line pattern and the image recording structure are known, the accuracy in determining the refractive power can be further increased by calculating the separate periodic grid according to the moiré effect.

[0052] The invention also relates to a particularly advantageous use of the above-described method, in particular according to one of claims 1 to 9 and / or the above-described device, in particular according to one of claims 10 to 15, for determining the refractive power of a windshield at a (non-zero) viewing angle s between a viewing direction and a measuring direction under which the refractive power for the windshield is measured, for at least one of the following applications:

[0053] Determining the refractive power of the windshield from the driver's point of view in different viewing directions through the windshield;

[0054] Determining the refractive power of the windshield from the viewing point of an assistant camera arranged on the windshield and recording through the windshield for different viewing directions within a recording angle covered by a lens of the assistant camera.

[0055] Such assistance cameras can be used, among other things, to measure the distance to vehicles ahead or as a lane departure warning system. To prevent excessive distortion in the images, which could lead to incorrect image interpretation, it is generally necessary for the refractive power of the windshield to be within a tolerance range for different viewing directions within the recording angle. This can be determined using the method and / or device according to the invention without having to perform measurements in different measuring directions. The same applies to different viewing directions of the driver.

[0056] In the described application for an assistance camera, the determination of the refractive power with the method and / or device according to the invention can also be used as a basis for correcting the images of the assistance camera, for example when determining the distance or a lane keeping assistant.

[0057] Further advantages, features, and possible applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features, together or in any combination deemed reasonable by a person skilled in the art, are part of the subject matter of the invention, regardless of their combination in the described or illustrated exemplary embodiments or in the claims.

[0058] They show:

[0059] Fig. 1 schematically shows a three-dimensional view of a device for determining the refractive power of an optically transparent object according to an embodiment of the invention;

[0060] Fig. 2 is a schematic side view of the device according to the invention shown in Fig. 1;

[0061] Fig. 3 schematically shows a windshield as an optically transparent object with measuring surfaces of the measuring range according to a preferred use of the invention in a plan view from the measuring direction:

[0062] Fig. 4a schematically shows a pattern of illumination of the measuring device three-dimensionally according to an embodiment of the invention;

[0063] Fig. 4b schematically shows an image of the pattern according to Fig. 4a in a view through the object with refraction effects;

[0064] Fig. 5a schematically shows a pattern of the illumination of the measuring device three-dimensionally according to another embodiment of the invention;

[0065] Fig. 5b schematically shows an image of the pattern according to Fig. 5a in a view through the object with refraction effects; and Fig. 6 schematically shows a common coordinate system of the measuring and evaluation arrangement for carrying out the method according to the invention for determining the refractive power in any viewing direction according to one embodiment;

[0066] Fig. 7 schematically shows a common coordinate system of the measuring and evaluation arrangement for carrying out the method according to the invention for determining the refractive power in any viewing direction according to a further embodiment;

[0067] Fig. 8 shows an example of the factor values ​​DH, DV of the amplification factor as a function of the viewing angle s between 0° and 80°; and

[0068] Fig. 9 shows an example of the factor value DH in the first deflection direction of the amplification factor determined theoretically according to the invention and the factor value DH in the first deflection direction measured in an experimental arrangement for different viewing angles s.

[0069] In the drawing, the invention is described using a particularly preferred embodiment in which a method and a device according to the invention are used to determine the refractive power of a transparent object designed as a windshield. However, the invention is not limited to this application and can also be used for other optically transparent objects in a corresponding manner with a suitably adapted device and a suitably adapted method. Starting from the invention, the person skilled in the art will suitably adapt the embodiments shown in the drawing and described for the specific embodiment within the scope of their specialist knowledge and the more general above description. Fig.Figure 1 schematically shows a preferred embodiment of a device 1 according to the invention for determining the refractive power of an optically transparent object 2, with which the method according to the invention can be carried out. The optically transparent object 2 is a windshield 3 of a motor vehicle. The terms "object 2" and "windshield 3" are used synonymously below.

[0070] The device 1 has an optical measuring device 4 with a camera 5 and an illumination 6, wherein the camera 5 records the illumination 6 through the transparent object 2. The recording area 7 shows that the camera 5 is designed as a line or column camera, which records a pattern 20, 30 of the illumination 6 (as shown by way of example in Figs. 4a, 5a) through the windshield 3 such that the pattern 20, 30 is imaged in the camera 5 in a column longitudinal direction such that it is visible in a column longitudinal direction 11 over the entire measuring range MB of the object 2, in the example shown therefore extending from an upper horizontal edge of the windshield 3 to a lower horizontal edge of the windshield 3 and covering the entire height of the windshield 3. The object 2 is transported transversely to the column longitudinal direction 11 in a transport direction 10 through the optical measuring device 4.

[0071] Fig. 2 shows the device 1 in a sectional side view. The device 1 is mounted on feet 8. In a downwardly open space of the device 1 between the camera 5 and the lighting 6, the windshield 3 is arranged such that the measuring direction MR corresponds to a preferred viewing direction BR of a user through the optically transparent object 2. In the case of a windshield 3, the measuring direction MR preferably corresponds to a horizontal viewing direction of a driver of the vehicle in the direction of travel when driving straight ahead. As indicated in Figs. 1 and 2, the windshield is usually installed tilted by a tilt angle compared to a vertical orientation. In addition, windshields 3 are usually curved, as also schematically indicated in Figs. 1 and 2.For the application of the device and method according to the invention, neither the shape nor the orientation of the optically transparent object 2 are important. These do not need to be known. This also applies to the surface shape and orientation of the entry and exit surfaces relative to the line of sight, which are generally considered in ray optics, because the optical measuring device determines the actual refractive properties of an arbitrarily shaped object 2, specifically in the measuring direction MR specified by the measuring device.

[0072] The object 2, or rather the windshield 3, is fixed on a holding and transport device 9 of the device 1 in the desired orientation relative to the optical measuring device 4. The holding and transport device 9 is configured to move the optically transparent object 2 through the optical measuring device 4 for scanning the entire measuring area. For this purpose, the holding and transport device 9 moves the windshield 3 in the transport direction 10 through the optical measuring device 4, which is preferably oriented perpendicular to the column longitudinal direction 11 of the camera 5.

[0073] The device 1 further comprises a computing unit (not shown in the drawing) which, according to the invention, is used to carry out the measurement of the refractive power in the measuring direction MR by means of the optical measuring direction 4 and to carry out the method for determining the refractive power in a viewing direction BR through the object 2 which is different (in particular from the measuring direction MR). This procedure is explained in more detail below.

[0074] To measure the refractive power with the measuring device 4, a measuring area MB is defined on the object 2, which is represented in Fig. 3 by the set of squares. In the example shown, the measuring area MB covers only a portion of the entire object 2. The edge areas of the windshield 3 are excluded from the refractive power measurement in the example shown. In other applications, however, the measuring area MB can also cover the entire object.

[0075] Each of the squares in the measuring range MB represents a measuring surface MF. The measuring range MB is thus divided into several measuring surfaces MF, with the totality of all measuring surfaces MF (or in other words: all measuring surfaces MF together) preferably forming the measuring range MB. The shape of the measuring surfaces MF is not limited to the squares shown in the drawing, but can be suitably selected by a person skilled in the art according to the application. The size and number of measuring surfaces MF relative to the object 2 are also to be understood as examples (qualitative) in the drawing. In realistic applications, the number of measuring surfaces MF is typically larger and the size of the measuring surfaces MF relative to the object 2 is typically smaller. A minimum size of the measuring surfaces MF results from the resolution of the optical measuring device 4.For the sake of clarity, only two measuring surfaces are designated with the reference symbol MF in the drawing, although each of the squares shown indicates a measuring surface MF.

[0076] For each of the measuring surfaces MF[i], a local refractive power value B[i] is determined in a measuring direction MR specified relative to the object, whereby all local refractive power values ​​B[i] together form a refractive power map for the object 2, the resolution of which is specified by the size and arrangement of the measuring surfaces MF. The index [i] denotes a defined measuring surface [i]. In the example shown here, the measuring direction MR should be perpendicular to the plane of the drawing, regardless of any curvature or tilt of the object 2 relative to the plane of the drawing. According to the invention, the refractive power is determined in a first deflection direction AH and at least one further deflection direction AV. The deflection directions AH, AV describe an actual refraction of a line of sight in the direction shown.

[0077] For the preferred embodiment illustrated here, the first deflection direction AH describes a deflection by refraction in a horizontal direction (relative to a typical installation position of the windshield 3 in a motor vehicle). The further (second) deflection direction AV describes a deflection by refraction in a vertical direction (relative to a typical installation position of the windshield 3 in a motor vehicle). The measuring direction MR is orthogonal to the plane spanned by the deflection directions AH, AV and is indicated in Fig. 3 by a point in the measuring surface MF[i].

[0078] The measuring method for determining the refractive power in a deflection direction, as carried out by the optical measuring device 4, is generally known to those skilled in the art. It consists of recording a known pattern 20, 30 with the camera 5 through the object 2. With a line-scan camera, as described in this embodiment, an image of the pattern is obtained by temporally successive images as the object 20 is progressively transported through the measuring device 4.

[0079] Examples of possible patterns 20, 30 are shown qualitatively in Figs. 4a and 5a, once as a dot pattern and once as a line pattern, each in their relative orientation to the deflection directions AH, AV. Figs. 4b and 5b show images of the patterns 20, 30 taken by the camera through the object 2, which reveal distortions due to optical refraction in the object 2 or the windshield 3 in the specific example at the points marked by ellipses. Due to the known geometric arrangement of patterns 20, 30 in the illumination 6, object 2 and camera 3 as well as the geometric dimensions of the patterns 20, 30, the refractive power of the object 2 in each measuring surface MF[i] for the measuring direction MR determined by the viewing direction of the camera 5 can be determined according to known ray optics.The refractive power is measured and recorded as an n-tuple of the refractive power for each of the measuring surfaces MF[i] in each of the deflection directions AH, AV. In the diagram shown with the two deflection directions AH, AV, a 2-tuple of the form B[i]=[B[i](AH), B[i](AV)] results for the local refractive power values ​​B[i] of each of the measuring surfaces MF[i]. For all measuring surfaces MF of the measuring range MB together, the refractive power map of object 2 is thus formed.

[0080] For the application of the method according to the invention, as shown in Fig. 6, a common coordinate system 40 is used for the measuring and evaluation arrangement. In a preferred arrangement of the coordinate system 40, in particular when using the device and the method for determining the refractive power of a windshield 3, orthogonal axes of the coordinate system 40 can be through the first deflection direction AH, the measuring direction MR of the optical measuring device 4, and the further (second) deflection direction AV, thus forming a typical xyz coordinate system. In such a coordinate system 40, the application of the proposed method according to the invention is particularly easy to implement. In principle, however, the person skilled in the art is free to use any coordinate system to describe the method and the refractive power. The person skilled in the art can make such adaptations within the scope of their specialist knowledge.

[0081] In this illustrated coordinate system 40, a coordinate plane 41 is spanned by the measuring direction MR and the first deflection direction AH, which is aligned parallel to the horizontal edges of the windshield 3 (as object 2). When carrying out the method according to the invention, the orientation and position of object 2, a viewing point 42 and a viewing direction BR from the viewing point 42 through the measuring range MB of object 2 are determined. The viewing direction BR can in principle be selected arbitrarily. The measuring direction MR is defined by the measuring device 4 relative to the object 2 and, in the embodiment described with reference to Fig. 6, also determines the position of the coordinate system 40. In principle, however, the coordinate system can be freely selected in space and the measuring direction MR can also be described in coordinates of the coordinate system.

[0082] Subsequently, the intersection point of the specified viewing direction BR with exactly one local measuring surface MF[i] is determined in the coordinate system 40, and the viewing angle s between the viewing direction BR and the measuring direction MR in the determined local measuring surface MF[i] is determined. By determining the local measuring surface MF[i], the local refractive power values ​​B[i](AH) and B[i](AV) can also be determined from the refractive power map, which were previously measured as described above.

[0083] In the measuring and evaluation arrangement, an amplification factor for the refractive power is then determined as a function of the specific viewing angle s and a known refractive index n of the object 2, wherein the amplification factor comprises a factor value DH for the refractive power in the first deflection direction AH and a factor value DV for each further deflection direction AV. In the example shown here, therefore, a factor value DH and a factor value DV, matching the local refractive indices B[i](AH) and B[i](AV). For glass panes, the refractive index n against air is typically in the order of approximately n = 1.5 and is either specified by the manufacturer of the glass panes or measured in known measuring arrangements in a manner known to those skilled in the art.

[0084] The gain factors DH and DV are defined in the example as follows:

[0085] Using these amplification factors DH and DV for the different deflection directions AH, AV, the local refractive power values ​​at the viewing angle s are then calculated as B[i](AH,E or as B [i]G47, e) =

[0086] 07(e) ■ B [i]G47), as illustrated in Fig. 6.

[0087] In the example of a windshield 3 shown in Fig. 6, the viewing point 42 lies in the horizontally directed coordinate plane 41. The viewing direction BR is the viewing direction of a driver of the motor vehicle sitting at the viewing point 42, who looks laterally (at the viewing angle s) through the windshield in a horizontal plane (which, in the example shown here, coincides with the coordinate plane 41). By varying the viewing angle s, a turning of the driver's head in each of the viewing directions can be simulated. In this arrangement, the viewing angle s is also referred to as the yaw angle.

[0088] Fig. 7 shows a further example of a windshield 3 for an arrangement with a coordinate system 50, in which the viewing point 52 lies in a vertically directed coordinate plane 51. The viewing direction BR is the viewing direction of a driver of the motor vehicle sitting at the viewing point 42, who looks through the windshield in a horizontal plane (which in the example shown here is perpendicular to the coordinate plane 41) through an installation angle corresponding to the viewing angle s. By varying the viewing angle s, different installation angles can be simulated. In this arrangement, the viewing angle s is also referred to as the tilt angle. It is easily apparent that the coordinate systems 40, 50 can be converted into one another by exchanging the designations of the first and second deflection directions AH, AV. The above formulas for DH and DV apply in the same way. By implementing the methods according to the arrangements according to Fig. 6 and Fig.7 are applied one after the other (each time updating the refractive power maps), a combination of different viewing angles in different deflection directions can be observed.

[0089] For viewing points 42, 52 that do not lie in the coordinate plane 41, 51, projections of the viewing angles s into the respective coordinate plane 41, 51 can be considered in a corresponding manner.

[0090] Fig. 8 shows the course of the (dimensionless) amplification factors DH, DH for different viewing angles s, as described in the above forms for DH and DV. The viewing angle s lies, as shown in Fig. 5 or 6, in the coordinate plane 41, 51 defined by the measurement direction MR and the first deflection direction AH. As expected, the refractive power and, accordingly, the amplification factor increase significantly at large viewing angles s. In comparison, the refractive power in the second deflection direction AV, perpendicular to the first deflection direction, remains approximately constant.

[0091] Fig. 9 shows a comparison of the calculated amplification factor DH (theo) in comparison to an experimentally determined amplification factor DH (exp) for an arrangement according to Fig. 7 (various Tiit or tilt angles of the windshield 3). The reference measured values ​​for the refractive power were determined for a vertically positioned windshield 3, i.e. when the measuring direction MR and the viewing direction BR coincide in Fig. 7. The calculated values ​​for the amplification factor DH are determined as described above using the method according to the invention. For the experimental comparison, the windshield 3 was aligned in the measuring arrangement 4 such that the measuring direction MR corresponded to the viewing direction BR from the application of the method for the various viewing angles s. For viewing angles s < 40° (Tiit), a deviation is negligible.With a larger viewing angle s, the deviation between experiment and the method according to the invention increases, but up to viewing angles of about 60° (which reasonably cover a practical range), the refractive power values ​​determined with the amplification factors according to the invention can be used as a good estimate.

[0092] This enables simplified quality control for windshields 3 in the production line. For assistance cameras, refraction effects in different viewing directions along multiple deflection directions can be easily estimated by placing the viewing point at the mounting point of the assistance camera in front of windshield 3.

[0093] List of reference symbols:

[0094] 1 device for determining the refractive power

[0095] 2 optically transparent object

[0096] 3 Windshield

[0097] 4 optical measuring device

[0098] 5 Camera

[0099] 6 Lighting

[0100] 7 Recording area

[0101] 8 feet of the device

[0102] 9 Holding and transport device

[0103] 10 Transport direction

[0104] 11 Column longitudinal direction of the camera

[0105] 20 Pattern 21 Image of the pattern

[0106] 22 Distortion of the pattern due to refraction

[0107] 30 patterns

[0108] 31 Image of the pattern

[0109] 32 Distortion of the pattern due to refraction

[0110] 40 Coordinate system

[0111] 41 plane spanned by the measuring direction and the first deflection direction (coordinate plane)

[0112] 42 Viewpoint

[0113] 50 coordinate system

[0114] 51 plane spanned by the measuring direction and the first deflection direction (coordinate plane)

[0115] 52 Viewpoint

[0116] AH first deflection direction of refraction

[0117] AV second deflection direction of refraction

[0118] B[i] local refractive power value

[0119] BR Viewing direction

[0120] DH Factor value of the gain factor D

[0121] DV Factor value of the gain factor D s viewing angle

[0122] MB measuring range

[0123] MF[i]Measuring area

[0124] MR measurement direction n refractive index

Claims

Claims 1. Method for determining the refractive power of an optically transparent object (2), comprising the following steps Measuring the refractive power in a measuring area (MB) of the object (2) in a first deflection direction (AH) and at least one further deflection direction (AV) by means of an optical measuring device (4) in a measuring direction (MR) predetermined with respect to the object (2), wherein the measuring area (MB) of the object (2) is divided into several measuring areas (MF) and a local refractive power value (B[i]) is determined for each of the measuring areas (MF[i]), wherein all local refractive power values ​​(B[i]) form a refractive power map; Determining the orientation and position of the object (2), a viewing point (42, 52) and a viewing direction (BR) from the viewing point (42, 52) through the measuring range (MB) of the object (2) in a common coordinate system (40); Determining the intersection point of the specified viewing direction (BR) with exactly one local measuring surface (MF[i]) and determining the viewing angle (s) between the viewing direction (BR) and the measuring direction (MR) in the determined local measuring surface (MF[i]); Determining an amplification factor for the refractive power as a function of the determined viewing angle (s) and a refractive index (n) of the object (2), wherein the amplification factor comprises a factor value (DH) for the refractive power in the first deflection direction (AH) and a factor value (DV) for each further deflection direction (AV); Determine the refractive power in the viewing direction (BR) by applying the amplification factor to the local refractive power value B[i] of the determined local measuring area (MF[i]).

2. Method according to claim 1, characterized in that the viewing angle (s) lies in a plane (41, 51) which is spanned by the measuring direction (MR) and the first deflection directions (AH).

3. Method according to claim 1, characterized in that the viewing angle (s) lies in a projection of the viewing direction (BR) into a plane (41, 51) which is spanned by the measuring direction (MR) and the first deflection directions (AH).

4. Method according to one of the preceding claims, characterized in that the value of the amplification factor in one of the deflection directions (AH, AV) is determined as a function of the viewing angle (s) assuming a transparent object (2) with a wedge angle between the entrance surface and the exit surface.

5. Method according to one of the preceding claims, characterized in that the amplification factor in the plane (41, 51) spanned by the measuring direction (MR) and deflection direction (AH) is defined by where n is the refractive index of the transparent object (2) against air.

6. Method according to claim 5, characterized in that the amplification factor is in a plane perpendicular to the plane defined by the measuring direction (MR) and deflection direction (AH) spanned plane (41, 51), is defined by 7. Method according to one of the preceding claims, characterized in that the measuring direction (MR) corresponds to a preferred viewing direction (BR) through the optically transparent object (2).

8. Method according to one of the preceding claims, characterized in that as object (2) a curved windshield (3) is transported through the optical measuring device (4) in an orientation predetermined by a holding and transport device (9) and that the optical measuring device (4) is positioned such that the measuring direction (MR) of the optical measuring device (4) lies in a horizontal vehicle plane with respect to an installation position of the windshield (3) in a motor vehicle and is directed in the direction of a vehicle traveling straight ahead.

9. Method according to claim 8, characterized in that the optical refractive power is measured by the optical measuring device (4) in a horizontal deflection direction as a first deflection direction (AH) and in a vertical deflection direction as a second deflection direction (AV) relative to the installation position of the windshield (3) in the motor vehicle.

10. Device for determining the refractive power of an optically transparent object (2) with an optical measuring device (4) having a camera (5) and an illumination (6), wherein the camera (5) records the illumination (6) through the transparent object (2), with a holding and transport device (9) for fixing the optically transparent object (2) in the optical measuring device (4), wherein the holding and transport device (9) for moving of the optically transparent object (2) by the optical measuring device (4) is set up for scanning an entire measuring area (MB) of the object (2), and with a computing unit which is set up to carry out the measurement of the refractive power and to carry out the method according to the invention according to one of claims 1 to 9.

11. Device according to claim 10, characterized in that the optical measuring device (4) has a column camera as the camera (5) and a pattern (20, 30) of known structure as the illumination (6), wherein the column camera records the pattern (20, 30) through the optically transparent object (2) in such a way that the pattern (20, 30) is imaged in the column camera in a column longitudinal direction (11) in such a way that it is visible in the column longitudinal direction (11) over the entire measuring range (MB) of the object (2), and that the holding and transport device (4) moves the object (2) perpendicular to the column longitudinal direction (11) through the optical measuring device (4).

12. Device according to claim 11, characterized in that the pattern (30) is a periodic line pattern.

13. Device according to claim 12, characterized in that the line pattern is formed from two pairs of lines aligned perpendicular to each other, each pair of lines being constructed from periodically arranged parallel lines.

14. Device according to one of claims 11 to 13, characterized in that the column camera is formed by light-sensitive pixels arranged next to one another in the column longitudinal direction (11).

15. Device according to one of claims 12 to 14, characterized in that the periodic line pattern of the illumination (6) and an image recording structure of the column camera have a different periodicity.

16. Use of the method according to one of claims 1 to 9 and / or the device according to one of claims 10 to 15 for determining the refractive power of a windshield (3) at a viewing angle (s) between a viewing direction (BR) and a measuring direction (MR) under which the refractive power for the windshield (3) is measured, for at least one of the following Applications: Determining the refractive power of the windshield (3) from the viewing point (42, 52) of a driver in different viewing directions through the windshield (3); determining the refractive power of the windshield (3) from the viewing point of an assistant camera arranged on the windshield (3) and recording through the windshield (3) for different viewing directions (BR) within a recording angle covered by a lens of the assistant camera.

Images