Patent Description:
A conventional surveying system comprises a measuring unit generating a beam of measuring light which can be directed to a point on an object. The object reflects or scatters the incident measuring light such that the measuring unit receives some of the light back from the object. The measuring unit may then determine the distance of the object from the measuring unit based on a time of flight analysis, for example.

The surveying system further comprises a rotating mirror, wherein the measuring unit directs the generated beam of measuring light onto the rotating mirror from which the beam is reflected to positions on the object depending on the rotational position of the mirror. The mirror can be driven at high speeds so that the beam is scanned across objects located around the surveying system in order to perform a high number of distance measurements or other measurements.

Moreover, since the rotation of the rotating mirror is a controlled rotation, the direction of the beam of measuring light emitted from the surveying system is known at each instance of time. When the position and orientation of the surveying system is known in a given coordinate system, it is possible to associate the measuring results with coordinates in the coordinate system. It is in particular possible to determine the coordinates of the points where the light beam is incident on the objects around the surveying system in this coordinate system.

It is apparent that the accuracy of these determinations depends on the accuracy of the information relating to the direction at which the beam of measuring light is emitted from the surveying system at the time when the measurement is made.

Accordingly, it is an object of the present invention to provide a surveying system having a rotating mirror providing improved information relating to the directions of the emitted beam of measuring light at various rotational positions of the rotating mirror. Moreover, it is an object of the present invention to expand the usability of a surveying system having a rotating mirror.

The document <CIT> discloses a scanning-type distance measuring device comprising a light projection-reception unit provided with at least a pair of a light projector for emitting measurement light scanned along a prescribed light axis in a target space, a light receiver for receiving reflected light that is from the target space and is incident along the light axis, a first scanning mechanism provided with a first deflection member that deflects measurement light towards the target space, a first driving mechanism that rotates the first deflection member around a first axis inclined with respect to the deflection surface of the deflection member, and a second scanning mechanism that guides measurement light emitted from the light projection-reception unit to the first deflection member along a light path inclined with respect to the first axis, and that rotates the light path around the first axis.

According to the invention, a surveying system is provided as set forth in the appended independent claim <NUM>.

According to embodiments of the present invention, a surveying system comprises a mounting structure for mounting various optical and electronic components of the surveying system. In particular, a first mirror is mounted on the mounting structure, wherein the first mirror is rotatable relative to the mounting structure about an axis. A motor is provided to rotate the mirror relative to the mounting structure. A first light source is configured to direct a light beam onto the first mirror.

According to some embodiments, the first light source is mounted on the mounting structure.

According to exemplary embodiments, the surveying system further comprises a support, wherein the mounting structure is mounted on the support to be rotatable about an axis. A motor is provided to rotate the mounting structure relative to the support.

According to some embodiments, the first light source is mounted on the support.

The axis of rotation of the first mirror relative to the mounting structure may substantially coincide with the axis of rotation of the mounting structure relative to the support. A direction of incidence of the light beam on the first mirror can be substantially parallel to one of the axis of rotation of the first mirror relative to the mounting structure and of the axis of rotation of the mounting structure relative to the support. An angle between the axis of rotation of the mirror and a surface normal of a mirror surface of the first mirror can be about <NUM> degrees.

The surveying system according to the invention further comprises a first detector configured to detect light having travelled a beam path extending from the first light source via the first mirror to an object and back from the object via the first mirror to the first detector. For example, the first light source may generate a pulse of light which is directed onto the rotating mirror and reflected towards an object. A corresponding pulse of light received back from the object is detected by the first detector, and the time difference between the emission of the light pulse and the receipt of the light from the object is indicative of the distance of the object from the surveying system. This procedure can be repeated for a plurality of rotational positions of the rotating mirror relative to the mounting structure so that distances of various objects arranged around the surveying system can be measured in a plane defined by the light beam reflected from the rotating mirror.

If the direction of incidence of the light beam onto the mirror exactly coincides with the axis of rotation of the mirror relative to the mounting structure and if the angle between the surface normal of the first mirror and the direction of the incident light beam is exactly <NUM> degrees, the light beam reflected from the mirror coincides with a plane orthogonal to the axis of rotation of the mirror about the mounting structure. In practice, this ideal situation is not fulfilled, however. For example, if the light beam directed onto the rotating mirror is parallel to the axis of rotation of the rotational mirror but arranged at a small distance from the axis of rotation, the light beam reflected from the rotating mirror is always parallel to the plane orthogonal to the axis of rotation of the rotating mirror but arranged at varying distances from that plane. The distance from the plane depends on the rotational position of the mirror. If the direction of incidence of the light beam onto the rotating mirror is oriented at a small angle relative to the axis of rotation of the rotating mirror, the light beam reflected from the rotating mirror follows a conical shape. Other deviations from the ideal case are possible and result in more complicated deviations of the emitted light beam from the plane orthogonal to the axis of rotation.

According to some embodiments, the surveying system comprises a second detector mounted on the support and configured to detect light having travelled a beam path extending from the first light source via the first mirror to the second detector.

The second detector has a small extension in the circumferential direction about the axis of rotation of the rotating mirror. The second detector receives light reflected from the rotating mirror within a small range of rotational positions of the rotating mirror, accordingly. When the rotating mirror is oriented within this small range of rotations, the second detector can determine a position at which the light beam reflected from the rotating mirror is incident on the second detector. This position is indicative of the angle between the direction of the light beam reflected from the rotating mirror and the axis of rotation of the rotating mirror. This angle represents important information for associating measurement results, such as distances, with coordinates in a coordinate system of the surveying system. However, this information is obtained at rotational positions of the rotating mirror where the beam of measuring light is incident on the second detector and not on objects to be measured and located around the surveying system. Now, the controller may actuate the first motor in order to rotate the mounting structure relative to the support by some amount and to repeat the measurement of the position of incidence of the beam reflected from the rotating mirror on the second detector. Again, this position is indicative only for a small angular range of rotational positions of the rotating mirror relative to the mounting structure, but this range of rotational positions is different from the range explored in the previous measurement. This procedure can be repeated for a sufficient number of rotational positions of the mounting structure relative to the support until a full circle is reached, resulting in plural measurements of the positions of incidence of the light beam reflected from the rotating mirror on the second detector for substantially all rotational positions of the rotating mirror about the axis of rotation of the rotating mirror relative to the mounting structure. It follows, that this method allows to determine the direction of the emission of the measuring light beam from the rotating mirror for all rotational positions of the rotating mirror about its axis of rotation.

According to further exemplary embodiments, the surveying system further comprises a base, wherein the support is mounted on the base to be rotatable about an axis oriented transverse to the axis of rotation of the mounting structure relative to the support. According to particular embodiments herein, the axis of rotation of the support relative to the base is oriented substantially orthogonal to the axis of rotation of the mounting structure relative to the support. According to further embodiments herein, the surveying system further comprises a third motor controlled by the controller and configured to rotate the support relative to the base.

According to further exemplary embodiments, the surveying system comprises a tripod, wherein the base is mounted on the tripod.

Using a tripod, the surveying system can be readily mounted at nearly any desired location, typically such that the axis of rotation of the support relative to the base is aligned with the gravity vector at the chosen location. The component of the surveying system providing the base is often referred to as an alidade in the art.

The surveying system can he operated such that the support is rotated about its axis of rotation relative to the base by <NUM> degrees at a low rotational speed. While performing this rotation, the rotating mirror is rotated about its axis of rotation relative to the mounting structure at a high speed, while distance measurements are continuously recorded. With such procedure, distances of substantially all objects positioned around the surveying system can be determined. However, if the axis of rotation of the rotating mirror relative to the mounting structure is not oriented orthogonal to the axis of rotation of the support relative to the base, it is not possible to direct beams of measuring light to objects located at positions located on the axis of rotation of the support relative to the base. Therefore, it is desirable to have the axis of rotation of the rotational mirror oriented exactly orthogonal to the axis of rotation of the support relative to the base, or, it is at least desirable to exactly know an amount of deviation of this angle from <NUM> degrees.

According to some exemplary embodiments, the surveying system further comprises a third detector mounted on the base and configured to detect light having travelled a beam path extending from the first light source via the first mirror to the third detector. This third detector may have a function as illustrated above with respect to the second detector mounted on the support.

According to further exemplary embodiments, the surveying system further comprises a second mirror mounted on the mounting structure, a second light source mounted on the base and configured to direct a light beam onto the second mirror when the mounting structure is arranged in a first rotational position about the axis of rotation of the mounting structure relative to the support, and when the mounting structure is in a second rotational position about this axis of rotation. A third detector is mounted on the base and configured to detect light having travelled a beam path extending from the second light source via the second mirror to the third detector. The first and second rotational positions of the mounting structure relative to the support may differ by more than <NUM> degrees or more than <NUM> degrees. According to particular embodiments, these two rotational positions differ by substantially <NUM> degrees. Using such system, it is possible to perform a set of measurements in which the mounting structure is in the first and second rotational positions, and wherein the support is in plural different positions about the axis of rotation of the support relative to the base. In each measurement, the location of incidence of the light emitted from the second light source and received by the detector via the second mirror is recorded.

Based on such measurements, it is possible to determine the angle between the axis of rotation of the support relative to the base and the axis of rotation of the mounting structure relative to the support. Moreover, it is possible to determine the angle between the axis of rotation of the rotating mirror relative to the mounting structure and the axis of rotation of the mounting structure relative to the support as illustrated above. It is apparent that such procedure allows to exactly determine the direction of the beam of measuring light reflected from the rotating mirror for all rotational positions of the rotating mirror about its axis of rotation and for all rotational positions of the support relative to the base. Therefore, it is possible to calibrate the surveying system with respect to the angles between its rotational axes without using external measuring tools.

According to further exemplary embodiments, the surveying system comprises at least one camera mounted on the mounting structure, wherein the at least one camera includes an objective lens having a main axis and a position sensitive detector. Using the camera, it is possible to record visible light images of the surroundings of the surveying system while measurements are recorded using the measuring light beam and the rotating mirror. The visible light images provide an alternative source of information which can be useful for interpreting the measuring results obtained using the measuring light beam and rotating mirror.

According to further exemplary embodiments, the surveying system comprises first and second cameras mounted on the mounting structure, wherein the main axes of the first and second cameras are oriented in different circumferential directions and/or different azimuthal directions relative to the axis of rotation of the mounting structure relative to the support. Using plural cameras oriented at different angles relative to the mounting structure allows to obtain panoramic images while operating the surveying system to record measurements using the measuring light beam and rotating mirror.

According to further exemplary embodiments, the surveying system comprises an optical instrument, such as a laser pointer and an electronic distance measuring instrument (EDM), mounted on the mounting structure, wherein the optical instrument is configured to direct a beam of light in a direction substantially coinciding with a direction of the light beam reflected from the first mirror when the first mirror is in a predetermined rotational position about the second axis. The mounting structure can be rotated relative to the support to emit the visible light beam in a selected direction for visibly marking a location on an object.

Embodiments of the invention to be illustrated with reference to the drawing below.

An exemplary surveying system will be illustrated with reference to <FIG> below. Herein, <FIG> is a simplified sectional view schematically illustrating details of a surveying system. The surveying system <NUM> comprises a base <NUM> mounted on a tripod <NUM>, and an alidade <NUM>. The alidade <NUM> is mounted on the base <NUM> and can be rotated relative to the base <NUM> about an axis <NUM> as indicated by an arrow <NUM> in <FIG>. The tripod <NUM> can be adjusted such that the axis <NUM> is oriented in the vertical direction when the surveying system <NUM> is used. A motor <NUM> is provided to rotate the alidade <NUM> relative to the base <NUM>. The motor <NUM> is controlled by a controller <NUM> mounted within the base <NUM>, or on any other suitable component of the surveying system <NUM>. The surveying system <NUM> may further comprise a rotational encoder (not shown in <FIG>) connected to the controller <NUM> so that the controller <NUM> can measure the current rotational position of the alidade <NUM> relative to the base <NUM>.

The surveying system <NUM> further comprises a measuring unit <NUM> mounted on a mounting structure <NUM>. The mounting structure <NUM> is mounted on the alidade <NUM> and rotatable relative to the alidade <NUM> about an axis <NUM> as indicated by an arrow <NUM> in <FIG>. The axis <NUM> is substantially orthogonal to the axis <NUM> of rotation of the alidade <NUM> relative to the base <NUM>. A motor <NUM> is provided to rotate the mounting structure <NUM> relative to the alidade <NUM>. The motor <NUM> is controlled by the controller <NUM>. Moreover, the surveying system <NUM> may comprise a rotational encoder (not shown in <FIG>) connected to the controller <NUM> so that the controller <NUM> can measure the current rotational position of the mounting structure <NUM> relative to the alidade <NUM>.

The measuring unit <NUM> comprises a rotating mirror <NUM> carried by a motor <NUM> mounted on the mounting structure <NUM>. The motor <NUM> is controlled by the controller <NUM> and rotates the rotating mirror <NUM> about an axis <NUM> of rotation as indicated by an arrow <NUM> in <FIG>. The axis <NUM> of rotation of the mirror substantially coincides with the axis <NUM> of rotation of the mounting structure <NUM> relative to the alidade <NUM>. The rotating mirror <NUM> has a substantially flat mirror surface <NUM> having a surface normal oriented at an angle of <NUM> degrees relative to the axis <NUM> of rotation of the rotating mirror <NUM>.

The measuring unit <NUM> further comprises a light source <NUM>, such as a laser source, pulsed laser source and/or a fiber laser, for example. The light source <NUM> is mounted on the mounting structure <NUM> and configured to generate light pulses which are supplied to an emitting element <NUM>, such as a collimation lens, via a fiber <NUM>. A thin beam <NUM> of measuring light is emitted from the emitting element <NUM>, enters a glass prism <NUM> and is reflected from an internal surface <NUM> of the prism <NUM> such that it substantially coincides with the axis <NUM> of rotation of the rotating mirror <NUM>. The beam <NUM> of measuring light leaves the prism <NUM> through a glass plate <NUM>. The glass plate <NUM> has a mirror surface <NUM> having a surface normal which can be oriented relative to the axis <NUM> of rotation of the rotating mirror <NUM> at an angle of <NUM> degrees, for example. The mirror surface <NUM> has a central portion <NUM> traversed by the beam <NUM> of measuring light. The central portion <NUM> may carry an antireflective coating such that a low amount of the measuring light is reflected from the mirror surface <NUM> while the main portion of the beam <NUM> of measuring light is incident on the mirror surface <NUM> at an angle of <NUM> degrees. When the rotating mirror <NUM> is oriented as shown in <FIG>, the beam <NUM> of measuring light is reflected from the mirror surface <NUM> such that the thin beam <NUM> of measuring light is emitted from the surveying system <NUM> in the vertical direction as indicated by an arrow <NUM> in <FIG>. This measuring light will be incident on an object, and a portion of that light is scattered by the object or reflected from the object such that it travels back to the surveying system <NUM> as a broader beam <NUM> as indicated by arrows <NUM> in <FIG>.

The mounting structure <NUM> comprises one or more windows <NUM> allowing the beam <NUM> of measuring light to leave the measuring unit <NUM> and to allow the light <NUM> received back from the object to enter the measuring unit <NUM>. The window <NUM> can be a single ring-shaped window extending around the axis <NUM> of rotation of the rotating mirror <NUM>.

The light received back from the object is incident on the mirror surface <NUM> of the rotating mirror <NUM>, and is reflected from the mirror surface <NUM> to be incident on the mirror <NUM>. Apart from its central portion <NUM>, the mirror surface <NUM> carries a reflective coating such that most of the light received back from the object is directed towards a focusing lens <NUM> concentrating the light received back from the object onto a detector <NUM>. Detection signals produced by the detector <NUM> are supplied to the controller <NUM>. The controller <NUM> may measure differences between times when light pulses are generated by the light source <NUM> and corresponding times when these light pulses are detected by the detector <NUM>. These time differences represent the time of flight of a light pulse from the measuring unit to the object and from the object back to the measuring unit <NUM>. This measured time of flight is indicative of the distance of the object from the surveying system <NUM>.

The controller <NUM> may control the motor <NUM> to rotate the mirror <NUM> about the axis <NUM>. This results in the light beam <NUM> emitted from the surveying system <NUM> to rotate about the axis <NUM> in a plane orthogonal to the axis <NUM>. By operating the motor <NUM> in order to rotate the alidade <NUM> about the axis <NUM>, the controller <NUM> may direct the measuring light beam <NUM> emitted from the serving system <NUM> in any direction.

It is apparent that plural factors generate deviations from the ideal situation illustrated above, in which the light beam <NUM> emitted from the surveying system <NUM> coincides with a mathematical plane orthogonal to the axis <NUM> of rotation of the rotating mirror <NUM>. These factors include deviations of the angle of incidence of the measuring light beam <NUM> on the mirror surface <NUM> from <NUM>°, displacements of the location of incidence of the beam <NUM> on the mirror surface <NUM> from the point where the axis <NUM> of rotation of the rotating mirror <NUM> intersects the mirror surface <NUM>, and deviations of the angle between the axis <NUM> of rotation of the rotating mirror <NUM> and the axis <NUM> of rotation of the alidade <NUM> relative to the base <NUM> from <NUM>°.

The surveying system <NUM> comprises a calibration unit <NUM> configured to determine at least some of these deviations. The calibration unit <NUM> comprises a position sensitive detector <NUM> mounted on the base <NUM> and configured to receive measuring light <NUM> emitted from the measuring unit <NUM> at at least some rotational positions of the rotating mirror <NUM> about the axis <NUM>. For this purpose, the alidade <NUM> comprises a window <NUM> transmitting measuring light having traversed the window <NUM> of the mounting structure <NUM> when the rotating mirror <NUM> is in a rotational position opposite to that shown in <FIG> such that it reflects the beam <NUM> of measuring light in the downward direction in <FIG>.

The support of the alidade <NUM> on the base <NUM> is provided by a hollow shaft <NUM> such that this measuring light is incident on a reflecting surface <NUM>. The light is reflected from this reflecting surface <NUM> towards a focusing lens <NUM>. The lens <NUM> focuses the light reflected from the rotating mirror <NUM> on a detection surface of the detector <NUM>, subsequent to a reflection from a semitransparent surface <NUM> of a beam splitter <NUM>.

Based on detection signals supplied by the detector <NUM> to the controller <NUM>, the controller <NUM> may determine the locations of incidence of the light beam <NUM> emitted from the measuring unit <NUM> on the detection surface of the detector <NUM>. This position is indicative of the direction into which the beam <NUM> of measuring light is emitted from the measuring unit <NUM> at a given rotational position of the rotating mirror <NUM> about its axis <NUM> of rotation. However, this position of incidence of the light on the detector <NUM> can only be determined for a small range of orientations of the rotating mirror <NUM> about its axis <NUM> rotation. In order to expand this range, the controller <NUM> is configured to operate the motor <NUM> in order to rotate the mounting structure <NUM> about the axis <NUM> relative to the alidade <NUM>. After such rotation, the detector <NUM> will detect the light emitted from the measuring unit <NUM> at other rotational positions of the rotating mirror <NUM> about its axis <NUM> of rotation. Based on this method, the direction of the emission of the measuring light from the measuring unit <NUM> can be determined for many or all rotational positions of the rotating mirror <NUM> about its axis <NUM> of rotation.

The calibration system <NUM> further comprises a light source <NUM> illuminating a pinhole <NUM>. The light emitted from the pinhole <NUM> traverses the beam splitter <NUM> and is collimated by the focusing lens <NUM>. According to other examples, this light beam can be generated by a point source LED. The light having traversed the focusing lens <NUM> is reflected from the mirror <NUM> and travels in the vertical direction in <FIG> and enters the mounting structure <NUM> through the window <NUM>. A glass plate <NUM> is arranged in a beam path of this light. The glass plate <NUM> carries an anti-reflective coating on its main flat surface <NUM>, and a coating having a high reflectivity on its other main flat surface <NUM>. A portion of the light emitted by the light source <NUM> is reflected from the surface <NUM> of the glass plate <NUM> and travels back to the mirror <NUM>, where it is reflected and focused on the detector <NUM>. The controller <NUM> determines the location of incidence of this light for plural different rotational positions of the alidade <NUM> relative to the base <NUM>. Thereafter, the mounting structure <NUM> is rotated about the axis <NUM> by <NUM>°, such that the glass plate <NUM> is located at a position indicated with dotted lines in <FIG>. Also in this position, some of the light emitted by the light source <NUM> is reflected from the surface <NUM> of the glass plate <NUM> such that it is detected by the detector <NUM>. Again, plural measurements are performed for different rotational positions of alidade <NUM> about the axis <NUM>.

Based on these measurements, it is possible to determine the angle between the axis <NUM> of rotation of the alidade <NUM> relative to the base <NUM> and the axis <NUM> of rotation of the mounting structure <NUM> relative to the alidade <NUM>. In particular, it is possible to determine deviations of this angle from <NUM>°. Additional information relating to this method of determination of the angle between the axis of rotation of the alidade relative to the base and the axis of rotation of the mounting structure relative to the alidade can be found in the co-pending patent application of the present applicant titled "SURVEYING INSTRUMENT AND METHOD OF CALIBRATING A SURVEY INSTRUMENT" which is filed on the same day as the present application.

According to some examples, the measuring light emitted by the light source <NUM> has a wavelength different from a wavelength of the light emitted from the light source <NUM>, and the reflective coating on the surface <NUM> is designed such that it is substantially transparent for the light of the measuring light source <NUM>.

The surveying system <NUM> further comprises plural cameras <NUM> mounted on the mounting structure <NUM>. Each camera <NUM> comprises an objective lens <NUM> and a position sensitive detector <NUM> and is configured to record visual images of the surroundings of the surveying system <NUM>. Each camera <NUM> has a main axis <NUM> defined by the optical axis of the objective lens <NUM>. The plural cameras <NUM> differ with respect to the orientations of their main axes <NUM> relative to the mounting structure <NUM>. The main axes <NUM> of the plural cameras <NUM> differ with respect to their orientation in the circumferential direction about the axis <NUM> and with respect to the azimuthal direction with respect to the axis <NUM>. The cameras <NUM> can be used to record visual light images of the surroundings of the surveying system simultaneously with the recording of distance measurements using the measuring light beam <NUM> reflected from the rotating mirror <NUM>, for example.

The measuring unit can be operated in two modes of operation, for example. In a first mode, the first light source <NUM> emits a continuous train of light pulses at a given frequency such that the light pulses are directed in plural discrete circumferential directions about the axis <NUM> of rotation of the rotating mirror <NUM>. These circumferential directions depend on the speed and phase of the rotation of the rotating mirror about the axis <NUM>. In a second mode, the first light source <NUM> is operated such that single pulses of light are triggered at selected times when the rotating mirror <NUM> is in a given rotational position in order to perform measurements in desired selected directions about the axis <NUM> of rotation of the mirror <NUM>, wherein the selected directions can be determined independently of the frequency of the light pulses used in in the first mode.

In the above illustrated embodiment, the light source <NUM> of the measuring unit <NUM> is mounted on the mounting structure <NUM> which is rotatable relative to the alidade <NUM> about the axis <NUM>. According to other embodiments, the light source generating the measuring light for performing measurements, such as distance measurements, is mounted on the alidade <NUM>. In such embodiments, a shaft supporting the mounting structure <NUM> on the alidade can be formed as a hollow shaft such that the measuring light generated by the light source outside of the mounting structure may enter the mounting structures by traversing the hollow shaft such that it is incident on the mirror surface <NUM> of the rotating mirror <NUM> along the axis <NUM> of rotation of the rotating mirror <NUM>.

In the embodiment illustrated above, the mounting structure is rotatably mounted on the alidade <NUM> which is again rotatably mounted on the base <NUM>, wherein the base <NUM> can be mounted on a tripod <NUM>, for example. According to other embodiments, the mounting structure supporting the rotating mirror <NUM> is rotatably mounted on supports which do not form an alidade which is rotatable relative to a base about an axis substantially orthogonal to the axis of rotation of the rotating mirror. It is, for example possible to mount such support on a vehicle, such as car, a train or an aircraft, such that the axis of rotation of the rotating mirror is aligned with the moving direction of the vehicle. Other orientations relative to the moving direction of the vehicle are possible, as long as the axis of rotation of the rotating mirror is not orthogonal to the moving direction of the vehicle. It is then possible to scan the surroundings of a route, such as a street, a train track or flight path, respectively, along which the vehicle is traveling. It is, for example, possible to record shapes of the walls of a tunnel traversed by the vehicle with high accuracy. In such embodiments, it is advantageous to mount components of the calibration unit in the mounting structure rather than the base for achieving the advantage of being able to determine the directions of emissions of the measuring light for all rotational positions of the rotating mirror about its axis of rotation.

The surveying system <NUM> may further comprise a laser pointer <NUM> shown in dotted lines in <FIG>. The laser pointer <NUM> is mounted on the mounting structure <NUM> and configured to emit a beam of visible light indicated by an arrow <NUM> in <FIG>. The laser pointer <NUM> is positioned and oriented relative to the mounting structure <NUM> such that the beam <NUM> of visible light coincides with the direction <NUM> of the measuring light beam <NUM> reflected from the rotating mirror <NUM> when the rotating mirror <NUM> is in a predetermined rotational position about its axis <NUM> of rotation. When the rotating mirror <NUM> is in this predetermined rotational position, the laser pointer <NUM> may block the beam <NUM> of measuring light but the beam <NUM> of visible light emitted by the laser pointer <NUM> extends along a line substantially coinciding with the line along which the beam <NUM> of measuring light would extend if the laser pointer <NUM> were not present.

The beam <NUM> of visible light can be used to mark selected positions on objects such that these positions are visible to a user of the surveying system. For this purpose, the controller <NUM> may rotate the alidade <NUM> relative to the base <NUM> and the mounting structure <NUM> relative to the alidade <NUM> until the beam <NUM> is emitted in a desired direction and illuminates a location on an object. The user may then confirm this location, and the controller may rotate the mounting structure <NUM> relative to the alidade <NUM> until the laser pointer <NUM> no longer blocks the beam <NUM> of measuring light when it is reflected from the rotating mirror <NUM> in the direction previously confirmed by the user. A distance measurement may then be performed relative to the confirmed location on the object, for example.

Alternatively or in addition to the laser pointer <NUM>, the surveying system may further comprise some other an optical instrument, such as an electronic distance measuring instrument (EDM), mounted on the mounting structure <NUM> and configured to direct a beam of measuring light in a direction substantially coinciding with the direction of the light beam <NUM> reflected from the first mirror <NUM> when the first mirror <NUM> is in a predetermined rotational position about the second axis <NUM>. When the additional optical instrument is an electronic distance measuring instrument (EDM), it can be used to perform precision distance measurements in selected directions, for example.

Additional information relating to surveying instruments having rotating mirrors can be found in the co-pending patent application of the present applicant titled "SURVEYING SYSTEM AND ROTATING MIRROR FOR A SURVEYING SYSTEM" which is filed on the same day as the present application.

Some embodiments have been described in connection with the accompanying drawing. However, it should be understood that the figure is not drawn to scale. Distances, angles, etc. are merely illustrative and do not necessarily bear an exact relationship to actual dimensions and layout of the devices illustrated. Components can be added, removed, and/or rearranged. Further, the disclosure herein of any particular feature, aspect, method, property, characteristic, quality, attribute, element, or the like in connection with various embodiments can be used in all other embodiments set forth herein. Additionally, it will be recognized that any methods described herein may be practiced using any device suitable for performing the recited steps.

It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment.

Claim 1:
A surveying system, comprising:
- a controller (<NUM>);
- a support (<NUM>);
- a mounting structure (<NUM>) mounted on the support (<NUM>), wherein the mounting structure (<NUM>) is rotatable about a first axis (<NUM>) relative to the support (<NUM>);
a first motor (<NUM>) controlled by the controller (<NUM>) and configured to rotate the mounting structure (<NUM>) relative to the support (<NUM>);
a first mirror (<NUM>) mounted on the mounting structure (<NUM>), wherein the first mirror (<NUM>) is rotatable relative to the mounting structure (<NUM>) about a second axis (<NUM>), wherein the second axis (<NUM>) substantially coincides with the first axis (<NUM>);
a second motor (<NUM>) controlled by the controller (<NUM>) and configured to rotate the first mirror (<NUM>) relative to the mounting structure (<NUM>); and
a first light source (<NUM>, <NUM>) configured to direct a light beam (<NUM>) onto the first mirror (<NUM>); and
a first detector (<NUM>) configured to detect light having traveled a beam path extending from the first light source (<NUM>) via the first mirror (<NUM>) to an object and back from the object via the first mirror (<NUM>) to the first detector (<NUM>).