Abstract: A laser scanner has multiple measuring beams for optical surveying of an environment. The laser scanner is configured to provide scanning with at least two different multi-beam scan patterns. Each multi-beam scan pattern is individually activatable by a computing unit of the laser scanner.

Abstract: In a method for selecting pictures from a sequence of pictures of an object in motion, a computerized user device determines, for each picture in the sequence of pictures, a value of a motion feature of the object. Based on analyzing the values of the motion feature of the pictures in the sequence, the device identifies a first subset of pictures from the pictures in the sequence. The device then selects, based on a second selection criterion, a second subset of pictures from the first subset of pictures. The pictures in the second subset are displayed to a user for further selection.

Abstract: Systems, methods, and computer-readable media are disclosed for a systems and methods for intra-shot dynamic LIDAR detector gain. One example method my include emitting, by an optical ranging system at a first time, a first light pulse. The example method may also include increasing, after the first time, a sensitivity of a photodetector of the optical ranging system from a first sensitivity at the first time to a second sensitivity at a second time. The example method may also include decreasing the sensitivity of the photodetector of the optical ranging system from the second sensitivity at third time to the first sensitivity at a fourth time, wherein the fourth time is after the photodetector receives return light based on the first light pulse. The example method may also include emitting, by the optical ranging system at the fourth time, a second light pulse.

Abstract: The present disclosure relates to systems and methods that facilitate a scanning light detection and ranging (LIDAR) device configured to provide an asymmetric illumination pattern. An example system includes a rotatable base configured to rotate about a first axis and a mirror assembly. The mirror assembly is configured to rotate about a second axis, which is substantially perpendicular to the first axis. The system also includes an optical cavity coupled to the rotatable base. The optical cavity includes a photodetector and a photodetector lens arranged so as to define a light-receiving axis. The optical cavity also includes a light-emitter device and a light-emitter lens arranged so as to define a light-emission axis. At least one of the light-receiving axis or the light-emission axis forms a tilt angle with respect to the first axis.

Abstract: In an exemplary embodiment, a LiDAR is provided that is configured for installation in a mobile platform. The LiDAR includes a scanner and a light-intensity receiver. The scanner includes a light source configured to direct illumination in an illuminating direction. The light-intensity receiver includes one or more light-intensity sensors; and one or more lens assemblies configured with respect to the one or more light-intensity sensors, such that that at least one sensor plane from the one or more light-intensity sensors is tilted to form a non-zero angle with at least one equivalent lens plane from the one or more lens assemblies, transferring the sensor focal plane to be align with the main light illumination direction and be consistent with the direction of movement of a mobile platform.

Abstract: A LIDAR system for ranging an object using primary and secondary light reflected at the object, includes a laser, arranged to emit the primary light along a transmit beam towards a scanning element of the system, wherein at least a part of the transmit beam adjacent to the scanning element defines a center line, a detector, arranged to detect the secondary light along a receive beam, wherein the receive beam includes a first part aligned with the center line and a second part having an inclination with respect to the center line, wherein the second part of the receive beam is in-between the first part and the detector, and a segmented lens, positioned on the center line in-between the first part of the receive beam and the second part of the receive beam, wherein the receive lens segment is designed to focus the receive beam onto the detector.

Abstract: A transmitting device, preferably containing at least two laser diodes and a scanning mirror, which is deflectable about its center (MP) and is arranged in a housing with a transparent cover element. The cover element is formed, at least in a coupling-out region, by a section of a monocentric hemispherical shell (HK) with a center of curvature (K) and is arranged to cover the scanning mirror in such a way that the center of curvature (K) of the hemispherical shell (HK) and the center (MP) of the scanning mirror coincide, and is formed in a coupling-in region by an optical block, comprising a toroidal entrance surface, in the special form of a cylindrical surface, at least one toroidal exit surface and at least two first mirror surfaces arranged between them, for deflecting and pre-collimating the laser beams.

Abstract: A handheld distance measuring instrument includes a first emission device, a first reception device and a second reception device. The first emission device is configured to emit an optical measurement radiation onto a target object. The first reception device is configured to detect the radiation returning from the target object. The second reception device is configured in order to detect a reference radiation internal to the instrument. The reception devices respectively include a first detector unit, a second detector unit, a first time measurement unit, and a second time measurement unit. The first time measurement unit is configured to be connected selectively to the first detector unit and to the second detector unit. The second time measurement unit is configured to be connected selectively to the first detector unit and to the second detector unit.

Abstract: A laser scanner comprises a light projecting optical system for projecting a distance measuring light, a deflecting optical member for deflecting and projecting the distance measuring light to a measurement area, a distance measuring unit for carrying out measurement based on a reflection light and for acquiring distance data of the measurement area, a second image pickup unit capable of continuously acquiring image data including the measurement area, and a control unit. The control unit has a first image processing unit for acquiring a three-dimensional image based on the image data and on the distance data, and also has a second image processing unit for detecting a mobile object by comparing image data being adjacent to each other in terms of time. The control unit controls the distance measuring unit so that measurement of the mobile object detected in the measurement area is restricted by the second image processing unit.

Abstract: A distance detecting induction device includes a casing, a circuit board within the casing, and a pair of focusing lenses provided at respective openings in the casing. The distance detecting induction device further includes an emitting device including an infrared light emitting diode for emitting infrared light rays to the emitting lens and a receiving device including a distance detection induction module for inducing reflected light rays focused by the receiving lens. The distance detecting induction device further includes an emitting light ray guiding device arranged between the emitting lens and the emitting device. The guiding device includes a small circular hole provided at a position of the emitting device and a big circular hole provided at a position of the emitting lens.

Abstract: Optical range finders are configured to transmit optical bursts toward a target and detect a corresponding received burst. DC offset in the received burst due to square law detection can be offset based on a difference between high pass and low pass filtered portions of the received burst. Edge records associated with bursts can be obtained, and correlated with a reference signal or waveform to obtain a range estimate.

Abstract: Using a hand-held range finding device to range an object in a field of view is difficult due to user-induced jitter. In particular, user-induced jitter introduces uncertainty as to which object in a field of view is actually ranged. Current approaches attempt to mitigate user-induced jitter by requiring a user to mount the hand-held range finding device onto a stabilizing device (e.g., a tripod). However, such approaches require the user to carry additional equipment. Embodiments of the present disclosure enable the user to visually confirm which object in a field of view is actually ranged during a range finding event by generating a composite image that includes a visual representation of a laser pulse emitted by the range finding device reflecting off an object in the field of view. Advantageously, disclosed embodiments provide true hand-held range finding capabilities without requiring the use of stabilization assistance techniques.

Abstract: In some embodiments, distances associated with a surface may be calculated using time-of-flight (ToF) of a plurality of pulses of light occurring at a predetermined frequency. Reflected light from a light emitter may be captured by two or more light sensors. At least one light sensor may be located in a sensor pod that is separate from the light emitter, which may be housed in an emitter pod with or without a light sensor. The sensor pod may be synchronized with the emitter pod to enable ToF of light distance calculations. The calculated distance may be used to determine movement of a surface and/or one or more pixels of a surface. In some instances, the calculated distance may be used to identify a profile of a surface, which may then be used associate the profile with an object, a command, or another association.

Abstract: A system for landing or docking a mobile platform is enabled by a flash LADAR sensor having an adaptive controller with Automatic Gain Control (AGC). Range gating in the LADAR sensor penetrates through diffuse reflectors. The LADAR sensor adapted for landing/approach comprises a system controller, pulsed laser transmitter, transmit optics, receive optics, a focal plane array of detectors, a readout integrated circuit, camera support electronics and image processor, an image analysis and bias calculation processor, and a detector array bias control circuit. The system is capable of developing a complete 3-D scene from a single point of view.

Abstract: A fast spatial light modulator based on a linear MEMS ribbon array enables a depth capture system to operate in structured light and time-of-flight modes. Time-of-flight depth information may be used to phase unwrap structured light depth information. Combined structured light and time-of-flight systems offer precise depth resolution over a wide range of distances.

Abstract: A triangulation light sensor includes at least one light transmitter for transmitting a light signal into a detection zone, a light receiver having a plurality of receiver elements for receiving light from the detection zone reflected diffusely and/or specularly, and a reception optics arranged between the detection zone and the light receiver in the beam path, with the position of a light spot produced on the light receiver in a triangulation direction by the reflected light resulting in dependence on the distance of the object. The reception optics includes at least one multisegmented lens element having a plurality of lens segments with mutually spaced apart optical axes in the triangulation direction and at least one freeform lens element or one diffractive-optical element having a multisegmented lens element having a plurality of lens segments with optical axes spaced apart from one another in the triangulation direction.

Abstract: Coordinate measurement device configured to send a first beam of light to a target includes first and second light sources configured to emit first and second lights having differing first and second wavelengths; fiber-optic coupler that includes three ports, a first port configured to accept a first portion of the first light, a second port configured to accept a second portion of the second light, a third port configured to transmit a third light which includes a portion of the first and second portions; first and second angle measuring devices configured to measure first and second angles of rotation; distance meter configured to measure a first distance from the device to the target based at least in part on a third portion of the second beam received by an optical detector; and a processor configured to provide 3D coordinates of the target.

Abstract: A method for measuring three-dimensional coordinates of a probe center includes: providing a spherically mounted retroreflector; providing a probe assembly; providing an orientation sensor; providing a coordinate measurement device; placing the spherically mounted retroreflector on the probe head; directing the first beam of light from the coordinate measurement device to the spherically mounted retroreflector; measuring the first distance; measuring the first angle of rotation; measuring the second angle of rotation; measuring the three orientational degrees of freedom based at least in part on information provided by the orientation sensor; calculating the three-dimensional coordinates of the probe center based at least in part on the first distance, the first angle of rotation, the second angle of rotation, and the three orientational degrees of freedom; and storing the three-dimensional coordinates of the probe center.

Abstract: In the method for geo-referencing of optical remote sensing images of an area of the earth's surface, the geo-referencing is corrected based on an SAR image which is geo-referenced.

Abstract: A method and apparatus for defining, from a first periodic signal, a second signal of same period, including the steps of: generating a third signal exhibiting detectable events; and synchronizing the second signal for each event.

Abstract: A method of categorizing the reliability of measurement data in a chromatic range sensor (e.g., an optical pen) which uses chromatically dispersed light to measure the distance to a surface. In one embodiment, the system performs a number of predetermined reliability checks which determine the reliability categories for the sets of measurement data. The reliability categories may be stored as metadata with the respective workpiece height measurements that are determined from the associated measurement data. The reliability categories may be reported to the user (e.g., as graphical reliability category indicators that accompany a graphical display of the measurement data). With these reliability categories, the user may make informed decisions regarding the measurement data (e.g., deciding to filter out data that is associated with certain reliability categories, making adjustments to the setup to achieve improved measurements, etc.).

Abstract: A handheld measuring device for optical distance measurement includes a transmitting device, a receiving device, an evaluation device, and a homogenizing device. The transmitting device is configured to transmit periodically modulated optical measurement radiation toward a target object. The receiving device is configured to detect optical measurement radiation returning from the target object. The evaluation device is configured to receive and evaluate detection signals of the receiving device. The evaluation device comprises a plurality of accumulation devices configured to accumulate detection signals. The evaluation device conducts detection signals during a sampling time window from a plurality of sampling time windows temporally schematically changeably to an assigned accumulation device from the plurality of accumulation devices, such that the accumulation device accumulates the detection signals during the sampling time window.

Abstract: An optical proximity sensor includes a driver, light detector and offset signal generator. The driver selectively drives a light source. The light detector produces an analog detection signal indicative of an intensity of light detected by the light detector. The detected light can include light transmitted by the light source that reflected off an object within the sense region of the optical sensor, interference light and ambient light. The interference light includes light transmitted by the light source, and detected by the light detector, that was not reflected off an object within the sense region of the optical sensor. The offset signal generator selectively produces an analog offset signal that is combined with the analog detection signal produced by the photodetector to produce an analog compensated detection signal. The analog offset signal compensates for at least a portion of the interference light included in the light detected by the photodetector.

Abstract: A laser distance measuring device comprising a transmitter channel (1), a receiver channel (2) and a dimensionally stable multilayer base printed circuit board (3), with the transmitter channel (1) and the receiver channel (2) being mounted and symmetrically disposed one on each side of the base printed circuit board (3), with the base printed circuit board (3) serving as a mechanical foundation, as an optical and electrical shield, as a carrier of electrical and optical connections and, optionally, as a heat conductor.

Abstract: A LIDAR device may transmit light pulses originating from one or more light sources and may receive reflected light pulses that are then detected by one or more detectors. The LIDAR device may include a lens that both (i) collimates the light from the one or more light sources to provide collimated light for transmission into an environment of the LIDAR device and (ii) focuses the reflected light onto the one or more detectors. The lens may define a curved focal surface in a transmit path of the light from the one or more light sources and a curved focal surface in a receive path of the one or more detectors. The one or more light sources may be arranged along the curved focal surface in the transmit path. The one or more detectors may be arranged along the curved focal surface in the receive path.

Abstract: Method for determining wheel alignment of a vehicle, which vehicle comprises at least one wheel axle (12, 13, 14) having an axle end with at least one wheel member (2a-b, 3a-b, 4a-b) at a respective longitudinal side of the vehicle. The method comprises steps for determining the out of square of the wheel axle in relation to the longitudinal geometric centerline of the vehicle. A system for carrying out the method is also described.

Abstract: A three dimensional imaging camera comprises a system controller, pulsed laser transmitter, receiving optics, an infrared focal plane array light detector, and an image processor. The described invention is capable of developing a complete 3-D scene from a single point of view. The 3-D imaging camera utilizes a pulsed laser transmitter capable of illuminating an entire scene with a single high power flash of light. The 3-D imaging camera employs a system controller to trigger a pulse of high intensity light from the pulsed laser transmitter, and counts the time from the start of the transmitter light pulse. The light reflected from the illuminated scene impinges on a receiving optics and is detected by a focal plane array optical detector. An image processor applies image enhancing algorithms to improve the image quality and develop object data for subjects in the field of view of the flash ladar imaging camera.

Abstract: A multifunctional detector for emitting and receiving optical signals in order to determine the presence, location, and range movement of a player within a field of regard is disclosed. The detector generally includes a laser module operable for emitting an optical signal; an optional fiber optical delay line; a microcontroller/processor; a faceted scanning mirror pattern having multiple facets with each facet being tilted downward to allow for unique depressions for reflecting and scattering optical signals emitted by the laser module; a spinner/motor for driving and rotating the faceted mirror pattern; an optional combiner for separating emitted optical signals from the laser module or combining reflected optical signals from an reflective source; and a transceiver with an integrated APD receiver for receiving reflected optical signals combined from the combiner and transmitting reflected optical signal data to a central controller or other players. A method of using the detector is also disclosed.

Abstract: A range finder adapted for finding the object distance of a subject having a specific height includes a shell unit, an objective lens assembly, a magnifying unit having multiple selectable magnification ratios, and a range finding unit. The range finding unit includes a scale, a pointer, and a mark. The object distance of the subject is known by comparing the scale and the pointer in an imaging plane when an end of an image of the specific height of the subject formed on the imaging plane is aligned with the mark.

Abstract: An optical beam scanner includes a light source, an optical scanner configured to scan a light beam irradiated from the light source, and an input optical system configured to direct the light beam irradiated from the light source to the optical scanner, wherein the optical scanner includes a rotating mirror configured to rotate around a rotational axis and reflect the light beam irradiated from the light source; the rotating mirror is rotated around the rotational axis so that the light beam is irradiated on differing positions of a mirror surface of the rotating mirror; and the mirror surface of the rotating mirror has a mirror surface inclining angle with respect to a direction parallel to the rotational axis that is arranged to gradually increase from a first side to a second side of the rotating mirror in a direction parallel to a plane perpendicular to the rotational axis.

Abstract: A LiDAR-based 3-D point cloud measuring system includes a base, a housing, a plurality of photon transmitters and photon detectors contained within the housing, a rotary motor that rotates the housing about the base, and a communication component that allows transmission of signals generated by the photon detectors to external components. In several versions of the invention, the system includes a vertically oriented motherboard, thin circuit boards such as ceramic hybrids for selectively mounting emitters and detectors, a conjoined D-shaped lens array, and preferred firing sequences.

Abstract: The present invention provides an inexpensive range image sensor and etc. A range image sensor comprises diffractive optical elements and on which are formed diffractive gratings that change a traveling direction of incident parallel light so that in a coordinate space defined by a xyz-axis, the incident parallel light is split into split beams, and angles formed by the x-axis and line segments determined by projected light spots formed by the split beams on a predetermined projection plane intersecting the z-axis become predetermined angles. Furthermore, the range image sensor is provided with a distance determining unit for determining distances to the projected light spots on the basis of the tilting with respect to the x-axis of the line segments determined by the projected light spots formed on the object by the split beams.

Abstract: Disclosed is apparatus for distinguishing between ground and an obstacle for autonomous mobile vehicle, comprising an upper 2D laser radar 1, a lower 2D laser radar 2, and a processing unit 10, the processing unit 10 comprising a distance data receiving part 11, an inclination calculating part 12, a ground and obstacle determining part 13, and a transmitting part. Also disclosed is a method for distinguishing between ground and an obstacle for autonomous mobile vehicle by using the apparatus for distinguishing between ground and an obstacle for autonomous mobile vehicle of claim 1, in which the detected object is determined as an obstacle when the actual inclination (g) of the detected object is larger than the reference inclination, and as ground when the actual inclination (g) of the detected object is smaller than the reference inclination.

Abstract: An optical signal transmission structure of a laser distance measuring device, comprising: a laser pipe, suspended right above a center of a rotation disk, to emit laser beam downward; a light projector module, provided with at least two reflection plates, to reflect laser beam of said laser pipe onto a target; a lens, disposed on said rotation disk, to receive laser beam reflected from said target; and a circuit board, disposed on a lower side of said rotation disk, so laser beam received by said lens is transmitted onto a light sensor element on said circuit board, to produce at least a photoelectric signal, so that circuits on said circuit board determine distance to said target based on said photoelectric signal.

Abstract: A division line depicted on a road is detected. A beam-formed electromagnetic wave is repetitively at intervals transmitted toward the road viewed from a vehicle to scan in the vehicle width direction. Each beam-formed electromagnetic wave is radiated to a radiation area on the road, and the radiation areas made by transmitting the beam-formed electromagnetic wave a plurality of times virtually produces a scan area on the road. Every beam-formed electromagnetic wave, distance data indicative of a distance between a division line on the road and the vehicle is measured based on information about a reflected electromagnetic wave. The distance data measured is received to detect the division line based on characteristics of changes in a sequence of the distance data produced by mapping the received distance data in a scanning order of the beam-formed electromagnetic wave.

Abstract: An apparatus and method for recognizing presence of an object is provided, the apparatus and method are mounted on or implemented a vehicle. In the apparatus and method, by scanning a beam-shaped electromagnetic wave, data showing reflection intensities of reflected waves and distances between the vehicle and objects outside the vehicle are obtained. Based on the detected data, characteristics presented by frequency distributions of the distances and intensity frequency distributions of the refection intensities obtained in multiple rows in a field of view in the height direction of the vehicle. The characteristics depend on an angle of the electromagnetic wave to a road on which the vehicle travels. It is determined that the characteristics are obtained from the road when the characteristics meet predetermined requirements.

Abstract: The present invention provides a small diffractive optical element that emits twisted beam, a small distance measuring apparatus and a distance measuring method using a small diffractive optical element. A diffractive optical element includes a first diffractive grating that twists, in a coordinate space defined by an x-axis, a y-axis and a z-axis, parallel light forming a flat plane parallel to the x-axis and going advance in the z-axis direction so that an angle of the flat plane relative to the x-axis becomes a predetermined angle at a location where the parallel light traveling in the z-axis by a predetermined distance reaches.

Abstract: The invention provides a measuring instrument, comprising a telescope, a distance measuring unit, an image pickup unit, angle detecting units for detecting a vertical and horizontal angle in the sighting direction, an automatic sighting unit, an arithmetic unit, and a storage unit. The arithmetic unit makes the telescope rotate in horizontal and vertical direction and perform scanning over a predetermined range so that a plurality of objects to be measured are included and makes the image pickup unit acquire digital images during the scanning process. The arithmetic unit detects the objects in the digital images, calculates a vertical and horizontal angle of the objects based on the angle detector and a deviation of each of the objects from sighting axis, associates the calculated angles with each of the objects, and makes the storage unit store the vertical and horizontal angles of the objects as target values for automatic sighting.

Abstract: In one aspect, a computerized method to automatically determine thresholds includes receiving data generated from a Geiger-mode avalanche photodiode (GmAPD) laser detecting and ranging (LADAR) sensor of a scene, determining an overall threshold value for the scene using a binomial distribution and determining post threshold values for each x-y position in the scene. The computerized method also includes, for each x-y position, using a maximum value of the post threshold values and the overall threshold value to filter the data from the scene.

Abstract: The system includes a rotary turret platform for aiming of a high power laser beam. The system further includes a turret payload device coupled to the rotary turret platform. The system further includes an off-axis telescope coupled to the turret payload, having an articulated secondary mirror for correcting optical aberrations, and configured to reflect the high power laser beam to a target through a first of at least two conformal windows. The system further includes an illuminator beam device configured to actively illuminating the target to generate a return aberrated wavefront through the first of the at least two conformal windows. The system further includes a coarse tracker coupled to the turret payload, positioned parallel to and on an axis of revolution of the off-axis telescope, and configured to detect, acquire, and track the target through the second of the at least two conformal windows.

Abstract: A line of sight adjustment device (LSAD) employs a simple yet robust structure and method to adjust the line of sight (or boresight) of a telescope, clip-on night sight, night vision sight, day scope, or other optical sighting device. In one embodiment, the LSAD includes a single optical element adjusted to change the apparent viewing angle to a target viewed through the device without degrading the optical quality of the image.

Abstract: A Multimode Optical Sensor (MMOS) is a laser radar (ladar) that employs both coherent, or heterodyne, and noncoherent detection at long range, i.e. ranges for which the target is no more than a pixel in dimension. Coherent detection provides much higher velocity resolution while the noncoherent detection can provide better detectability.

Abstract: A Multimode Optical Sensor (MMOS) is a laser radar (ladar) that employs both coherent, or heterodyne, and noncoherent detection at long range, i.e. ranges for which the target is no more than a pixel in dimension. Coherent detection provides much higher velocity resolution while the noncoherent detection can provide better detectability.

Abstract: The present invention relates to mixtures prepared from (A) at least one linear, branched, or cyclic monomeric organosilane having at least two silicon atoms with hydrolyzable and/or condensation-crosslinking groups in which the silicon atoms are bonded to one another through at least one carbon atom in a linking unit, and (B) at least one boron- and/or aluminum-containing compound having the formula (I) RxM(OR′)3-x  (I)  wherein M is Al or B, x is 0, 1, or 2, R is C1-C6-alkyl, C6-C12-aryl, or (O)1/2, with the proviso that if R is (O)1/2, then the compound of the formula (I) is a chain when x is 1 and a cyclic or cage-form compound when x is 2, and each R′ is independently H, C1-C10-alkyl, or C6-C12-aryl. The invention further relates to hybrid materials prepared from such mixtures and to coatings produced therefrom.

Abstract: Three different color light beams which are converged to a single light spot on the surface of a circuit board at predetermined incident angles, are irradiated onto the top surface of an electronic part mounted on the circuit board, then distances between the positions of the top surface of the electronic part to which the light beams are irradiated respectively, from the single light spot on the surface of the circuit board are measured, and the height and an inclined angle of the top surface of the electronic part are computed in accordance with the relationship between the measured distances and the incident angles.

Abstract: An apparatus for detecting the distance between one's car and the car ahead, together with the angle between the axes of the two cars. The apparatus has a pair of driving optical systems disposed at a predetermined distance from each other, each driving optical system comprising an optical system having a light projector which projects pulse light having a specific code toward the car which is ahead of the one's car and a light receiver which receives the reflected pulse light from the car ahead, the light projector and receiver being disposed in so close proximity to each other that the respective optical axes can be considered to be on substantially the same axis, and a driving system for adjusting the angle of projection of the light projector on the basis of a signal from the light receiver.

Abstract: A bearing bush with a side opening is mounted within a telescope barrel. The telescope thus may be easily mounted on a tilting axis by simply inserting an axle into the bush. Mounting and adjustment of the tilting axis within its bearings and of angular measuring systems is thus independent of mounting of the telescope.

Abstract: As is known, the walls in cavity structures often become quiescent only after a prolonged period. In order to detect whether and to what extent rock displacements can occur, measuring instruments are installed at mutually opposite points (I, II) on walls (W1, W2). A pendulum (1) mounted on gimbals carries a light source (5) at the mounting point and a light receiver (3) at the pendulum mass (2). On the opposite wall (W2), a mirror (4) is arranged at an inclination .alpha. relative to the vertical. A displacement of the mirror by T.sub.x or by T.sub.Z leads to an indication T.sub.Z at the light receiver (3).