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 this light back from the object. The measuring unit may then determine the distance of the object from the measuring unit based on a time flight analysis, for example.

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

The document <CIT> discloses a laser radar apparatus consisting of laser beam generation, photo detection, a mirror assembly, light deflection, and rotation driving components. The laser beam generator emits a beam with an axis, while the photo detector captures reflected beams from objects. The mirror assembly includes a through-hole for transmitting the laser beam and a reflecting surface to redirect reflected beams toward the photo detector. The light deflector, with flat and concave mirrors, guides the laser beam to the measurement range and reflects object-generated beams back to the mirror assembly.

In many fields of use of surveying systems having rotating mirrors it is desirable to perform highly accurate measurements at high frequencies. This imposes high demands on the mechanical and optical quality of the components of the surveying system. These demands result in high costs for obtaining and maintaining a surveying system.

Based on the above, it is an object of the present invention to provide a surveying system and a rotating mirror for a surveying system having simplified structures while allowing relatively high performances.

According to embodiments of the invention, a surveying system comprises a support, a rotating mirror unit mounted on the support and including a rotating mirror, a measuring unit mounted on the support and including a light source and optics configured to direct a beam of measuring light onto the rotating mirror. The support can be, for example, an alidade, which is mounted on a base to be rotatable about an axis in order to change directions of the beam reflected from the rotating mirror. The base can be mounted, for example, on a tripod or other stand for holding the surveying system in a measuring environment.

According to exemplary embodiments, the surveying system comprises a window made of a material transmitting light of the beam, wherein the window is arranged in a beam path of the beam of measuring light reflected from the rotating mirror. The window may have a function of preventing dust and other particles from entering a housing of the surveying system and deteriorating its performance. It is not required that the window is traversed by the light of the beam at all possible rotational positions of the rotating mirror. However, the window may have an extension sufficient to allow the beam to traverse the window over a sufficient range of rotational positions of the rotating mirror in order to perform desired surveying tasks.

According to some embodiments, the window extends around an axis of rotation of the rotating mirror over a range of more than <NUM>° and, in particular, a range of more than <NUM>°. According to other exemplary embodiments, the window fully surrounds the axis of rotation of the rotatable mirror such that the beam of measuring light is transmitted through the window at all possible rotational positions of the rotating mirror.

According to some embodiments, the window mechanically connects a mounting structure of the measuring unit and a mounting structure of the rotating mirror unit. The mounting structure of the rotating mirror unit provides support for a motor having a shaft rotatable about the axis of rotation of the rotating mirror, and a mirror having a mirror surface, wherein the mirror is mounted on the shaft of the motor. The mounting structure of the measuring unit provides support for a light source and optics configured to generate a beam of measuring light and to direct the beam of measuring light onto the mirror surface.

The mechanical connection between the mounting structure of the measuring unit and the mounting structure of the rotating mirror unit can be provided such that, if one of the units is fixed to the support, the other unit does not require to be supported separately since the other unit is mounted on and carried by the window which, in turn, is mounted on and carried by the unit mounted on the support.

According to particular embodiments, the surveying system comprises a support, wherein the mounting structure of the measuring unit is mounted on and carried by the support, whereas the mounting structure of the rotating mirror unit is carried by the window. In particular, apart from the window, there is not provided any other means for supporting the rotating mirror unit and for carrying its weight.

According to other embodiments, the surveying system comprises a support, wherein the mounting structure of the rotating mirror is mounted on and carried by the support, whereas the mounting structure of the measuring unit is carried by the window. In particular, apart from the window, no other means are provided for supporting the measuring unit and for carrying its weight.

According to some embodiments, the light source and optics are configured to emit the beam of measuring light along an axis which substantially coincides with the axis of rotation of the rotating mirror. Such configuration is advantageous in view of a measurement accuracy which can be achieved with the surveying system. In embodiments using the window for supporting one of the rotating mirror unit and the measuring unit, a required alignment of the axis of the beam of measuring light and the rotation axis can be achieved at lower efforts as compared to embodiments providing separate supports for the rotating mirror unit and the measuring unit.

According to some embodiments, the window extends around the axis of rotation of the rotating mirror over a range of more than <NUM>° at a constant distance from the axis of rotation. In particular, at least one surface of the window may extend along a circle having its center on the axis of rotation.

According to particular embodiments herein, the mirror surface is a curved surface having a surface curvature selected such that an astigmatism induced on the beam of measuring light when traversing the window is compensated to at least some extent.

According to some embodiments herein, the mirror surface has a curvature such that a smallest osculating circle at a point where the axis of rotation of the rotational mirror intersects the mirror surface is contained in a plane which substantially coincides with the axis of rotation. According to other embodiments, the mirror surface has a curvature such that a smallest osculating circle at a point where the axis of rotation of the rotating mirror intersects the mirror surface is contained in a plane substantially orthogonal to a plane containing the axis of rotation and a center of the osculating circle. With such curvature, the astigmatism induced on the beam of measuring light when traversing the window can be compensated when the beam incident on the mirror surface is a parallel beam. Other curvatures can be used when the beam of measuring light incident on the mirror surface is a convergent or divergent beam.

There is an infinite number of osculating circles at the point of intersection of the axis of rotation and the mirror surface. Planes containing the osculating circles differ in their orientations about a surface normal of the mirror surface at the point of intersection. These osculating circles also have different radii. The osculating circle having the smallest radius defines the plane in which the mirror surface has its strongest curvature.

According to some embodiments, the rotating mirror is a lightweight rotating mirror having a mirror body, wherein the mirror body includes a base portion configured to be mounted on a carrier rotatable about an axis of rotation. The carrier can be a shaft of a motor, for example.

The mirror body includes a mirror portion providing a mirror surface. The mirror body may comprise plural spaced apart ribs extending between the mirror portion and the base portion.

According to some embodiments, the base portion, the mirror portion and the plural ribs are integrally made of plastic.

According to some embodiments, the mirror body is formed by injection molding.

The mirror surface provided by the mirror portion may have a shape resulting from the manufacturing process for the integrally forming of the mirror body. If the mirror body is formed by injection molding, the shape of the mirror surface is determined by the shape of the mold used for the molding process. Subsequent to the forming of the mirror body, the metal layer can be applied to the mirror surface in order to improve the reflectivity of the mirror. The metal layer can be applied by evaporation, for example. The metal layer can be provided by an aluminum layer, for example.

According to other embodiments, a process of shaping the mirror surface can be applied to the mirror portion subsequent to the integrally forming of the mirror body, and prior to applying of the metal layer. Such shaping process may include grinding or polishing, for example.

It is desirable that the total mass of the rotating mirror is low. A low mass of the rotating mirror reduces the demands on bearings used in the motor for rotating mirror, for example. Moreover, when the mass of the mirror is sufficiently low, it might not be required to perform a separate process of balancing the rotating unit formed by the shaft of the motor and the mirror body. According to some embodiments, a motor having a fluid bearing is used for driving and carrying the rotating mirror. For example, the mirror may rotate at speeds of <NUM> · <NUM>/s to <NUM> · <NUM>/s.

A low mass of the mirror body can be achieved by providing spaces not filled with plastic material within the volume occupied by the mirror portion. Such spaces are provided between the adjacent ribs extending between the mirror portion and the base portion.

It is, however, advantageous to maintain at least some of the ribs extending between the mirror portion and the base portion instead of removing those ribs in order to provide further spaces in view of an even more reduced weight of the rotating mirror. The mirror surface is typically oriented under an angle of <NUM>° relative to the axis of rotation. Therefore, the mirror portion has a proximal section located closer to the base portion than an opposite distal section of the mirror portion. Moreover, centrifugal forces acting on the mirror portion when it is rotated tend to change the angle of inclination of the mirror portion relative to the axis of rotation, resulting in a deformation of the rotating mirror and loss of measuring accuracy, accordingly. The ribs extending between the mirror portion and the base portion support the mirror portion relative to the base portion and help to maintain the orientation of the mirror portion relative to the axis of rotation during high speed rotation of the rotating mirror.

According to some embodiments, the ribs have main surfaces having surface portions extending substantially orthogonally to the mirror surface. Such arrangement may further increase the rigidity of the mirror body and may reduce deformation of the mirror body during rotation at high speeds.

According to some embodiments, there are two ribs which are, among the plural spaced apart ribs, arranged closest to a center of the mirror surface but at a distance from the center of the mirror surface. Specifically, the center of the mirror surface can be located at an intersection of the axis of rotation of the mirror with the mirror surface. A surface normal of the mirror surface at the mirror center extends between these two ribs extending from the backside of the mirror portion mentioned above. A distance between this surface normal and the surfaces of these ribs is greater than <NUM> or greater than <NUM>. This may have an advantage in that a quality of the shape of the mirror surface can be improved. When the mirror body is integrally formed by injection molding, some shrinking of material occurs upon solidification of the molded material. Such shrinking can be higher in those regions of the mirror portion where the ribs meet with the mirror portion. By spacing these regions apart from the center of the mirror, shrinking during solidification will less likely deform the mirror surface at the center of the mirror surface where the beam of measuring light is incident on the mirror surface.

According to some embodiments, the number of the plural ribs extending between the mirror portion and the base portion is an even number.

According to some exemplary embodiments, the mass of the mirror body is <NUM> or less.

According to some embodiments, the rotating mirror comprises an encoder ring mounted to the base portion. The encoder ring may carry a plurality of marks which can be optically detected in order to determine the rotational positions of the rotating mirror during rotation.

Embodiments of the invention will be illustrated with reference to the drawings below.

An exemplary surveying system will be illustrated with reference to <FIG> and <FIG> below. Herein, <FIG> is a simplified sectional view schematically illustrating details of a surveying system, and <FIG> is a simplified sectional view of the surveying system along a line II-II shown in <FIG>.

The surveying system <NUM> comprises a base <NUM> supported by a tripod <NUM>, and an alidade <NUM>. The alidade <NUM> is mounted on and carried by the base <NUM>. Moreover, the alidade <NUM> can be rotated relative to the base 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 is used.

The surveying system further comprises a measuring unit <NUM> having a mounting structure <NUM> for carrying various components of the measuring unit <NUM>. In the illustrated example, the mounting structure <NUM> is mounted on and carried by the alidade <NUM>. In other examples, the alidade may also house and carry some components of the measuring unit such that the alidade performs some functions of the mounting structure of the illustrated example.

The measuring unit <NUM> further comprises a light source <NUM>, such as a laser source, pulsed laser source and a fiber laser, for example. The light generated by the light source <NUM> is supplied to a collimator <NUM> in the illustrated example.

A thin beam <NUM> of measuring light is emitted from the collimator <NUM>, enters a glass prism <NUM> and is reflected from an internal surface <NUM> of the prism <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> 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 high amount of the measuring light is emitted as the beam <NUM> of measuring light from the prism <NUM>. The beam <NUM> of measuring light is emitted in a direction orthogonal to the axis of rotation <NUM> of the alidade <NUM> relative to the base <NUM>.

The surveying system further comprises a rotating mirror unit <NUM> including a mounting structure <NUM>, a motor <NUM> and a rotating mirror <NUM>. The motor <NUM> is mounted on and carried by the mounting structure <NUM>. The motor <NUM> has a shaft <NUM> which rotates about an axis of rotation <NUM> when the motor <NUM> is operated. The rotating mirror <NUM> is mounted on the shaft <NUM> of the motor <NUM> and has a mirror surface <NUM> which rotates about the axis of rotation <NUM> when the motor <NUM> is operated. The mirror surface <NUM> is oriented under an angle of <NUM>° relative to the axis of rotation <NUM>.

The rotating mirror unit <NUM> is mounted relative to the measuring unit <NUM> such that the axis of rotation <NUM> is aligned parallel with the beam <NUM> of measuring light emitted from the measuring unit such that the beam <NUM> is incident on the mirror surface <NUM> at a location which is also intersected by the axis of rotation <NUM> of the rotating mirror <NUM>. For this purpose, the rotating mirror <NUM> can be mounted on the shaft <NUM> of the motor <NUM> such that the orientation of the rotating mirror <NUM> relative to the shaft <NUM> can be adjusted within a suitable rage. Moreover, the motor <NUM> can be mounted on the mounting structure <NUM> such that the orientation of the motor <NUM> relative to the mounting structure <NUM> can be adjusted within a suitable range.

The beam <NUM> is incident on the mirror surface <NUM> and reflected from the mirror surface <NUM> as the beam of measuring light carrying reference numeral <NUM> in <FIG>. The beam <NUM> of measuring light travels in a direction orthogonal to the axis of rotation <NUM> downstream of the rotating mirror <NUM>. The beam <NUM> reflected from the mirror surface <NUM> traverses a window <NUM> arranged downstream of the rotating mirror <NUM> in the beam path of the measuring light. The beam <NUM> having traversed the window <NUM>, may then be incident on an object located near the measuring system <NUM>. Light scattered or reflected from the object travels back to the measuring system <NUM> as a broader beam <NUM>, is incident on the rotating mirror <NUM> and directed by the rotating mirror <NUM> back to the measuring unit <NUM> where it is 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>.

The measuring unit <NUM> may include a processor (not shown in <FIG>) for analyzing the signals detected by the detector <NUM>. For example, a distance of the object from the measuring unit <NUM> may be determined by such analysis.

It is apparent from <FIG> that the window <NUM> fully surrounds the axis of rotation <NUM>. An inner surface <NUM> of the window <NUM> has a constant distance R from the axis of rotation <NUM>. The inner surface <NUM> of the window <NUM> is arranged on a circle about the axis of rotation <NUM>, accordingly.

Since the window <NUM> fully surrounds the axis of rotation <NUM>, the beam <NUM> of measuring light may traverse the window <NUM> at each rotational position of the rotating mirror <NUM>. <FIG> shows an angular range <NUM> of about <NUM>° in which the beam <NUM> of measuring light is incident on the alidade <NUM>. This angular range can be greater or smaller than the exemplary value of <NUM>° depending on the configuration of the alidade <NUM> and base <NUM> and other components capable of obstructing the beam <NUM> of measuring light. It is not possible to measure objects located within this angular range <NUM> relative to the surveying system <NUM>. Objects located outside of this angular range <NUM> relative to the surveying system <NUM> can be measured using the beam <NUM> of measuring light.

The window <NUM> has a function of protecting the rotating mirror <NUM> and the measuring unit <NUM> from dust, particles and humidity which might otherwise deteriorate the function of these components.

Moreover, in the illustrated example, the window <NUM> carries the weight of the rotating mirror unit <NUM>. For this purpose, the window <NUM> is mechanically connected to the mounting structure <NUM> of the measuring unit <NUM>, and the window <NUM> is mechanically connected to the mounting structure <NUM> of the rotating mirror unit <NUM>. The surveying system <NUM> does not include any other means for carrying the weight of the rotating mirror unit <NUM>.

In other examples, the rotating mirror unit is mounted on and carried by the alidade, while the measuring unit is carried by the rotating mirror unit.

The surveying system <NUM> includes conventional means (not shown in the figures) for adjusting the light source <NUM>, optics <NUM>, <NUM>, <NUM> and motor <NUM> such that the direction of the beam <NUM> and the axis of rotation <NUM> are substantially coincide. It has been found that the arrangement of these components relative to each other is maintained relatively stable and that, for example, changes in temperature have a relatively small influence on the alignment of the axis of rotation <NUM> with the beam <NUM>. This allows for a stable operation and high achievable accuracy of the surveying system <NUM>.

It can be seen from the section in <FIG> that an outer surface <NUM> of the window <NUM> is substantially parallel to the inner surface <NUM> of the window <NUM>. A line <NUM> in <FIG> indicates a surface normal of the outer surface <NUM> of the mirror <NUM> at a location where the beam <NUM> traverses the window <NUM>. Since the inner and outer surfaces <NUM>, <NUM> of the window <NUM> are substantially parallel in the section shown in <FIG>, the surface normal of the inner surface <NUM> substantially coincides with the surface normal <NUM> of the outer surface <NUM>. A smallest angle α between the surface normal <NUM> and the direction of the beam <NUM> is different from zero. In the illustrated example, the angle α is <NUM>°. The angle α different from zero has an advantage in that light of the measuring light beam <NUM> reflected from the inner and outer surfaces <NUM>, <NUM> of the window <NUM> may not reach the detector of the measuring system <NUM> and contribute to background noise in the detected light. According to some examples, the surfaces <NUM> and <NUM> of the window <NUM> are not provided with an anti-reflective coating since an increase of detected background light is avoided by the angle α being greater than zero. Avoiding the antireflective coating allows to reduce the manufacturing costs of the surveying system. According to some examples, the outer surface <NUM> of the window <NUM> is provided with an anti-scratch coating.

<FIG> and <FIG> illustrate a configuration of the rotating mirror <NUM> in more detail. Herein, <FIG> is a sectional view of the rotating mirror, <FIG> is a perspective view of the rotating mirror, and <FIG> is an elevational rear review of the rotating mirror <NUM>.

The rotating mirror <NUM> comprises a mirror body <NUM> made of plastic by injection molding. The total mass of the mirror body is about <NUM> grams. The mirror body <NUM> comprises a base portion <NUM> configured to be mounted on a carrier which can be rotated about an axis of rotation <NUM>. In the present example, the carrier is the shaft <NUM> of the motor <NUM>.

The mirror body <NUM> further comprises a mirror portion <NUM> providing a mirror surface <NUM>. The mirror surface <NUM> is inclined relative to the axis of rotation <NUM>. The mirror portion <NUM> has a proximal section <NUM> closer to the base portion <NUM> and a distal portion <NUM> farther away from the base portion <NUM>. When the mirror body <NUM> is rotated about the axis of rotation <NUM>, centrifugal forces tend to deform the mirror body <NUM>. Specifically, a force indicated by an arrow <NUM> in <FIG> tries to orient the mirror portion <NUM> such that the mirror surface <NUM> is oriented orthogonal to the axis of rotation <NUM>. Such deformation of the mirror portion <NUM> will deteriorate the optical properties of the surveying system <NUM> using the rotating mirror <NUM>. In order to support the mirror portion <NUM> relative to the base portion which is mounted on the carrier <NUM> and in order to prevent deformation of the mirror body <NUM>, the mirror body <NUM> comprises plural spaced apart ribs <NUM> extending between the mirror portion <NUM> and the base portion <NUM>. The ribs <NUM> have main surfaces <NUM> extending substantially orthogonally to the mirror surface. The ribs <NUM> are connected to the mirror portion <NUM> at a rear surface <NUM> of the mirror portion <NUM>.

The mirror surface <NUM> has a center <NUM> where the axis of rotation <NUM> intersects the mirror surface <NUM>. The mirror surface <NUM> has a surface normal <NUM> at its center <NUM>. The main surfaces <NUM> of the ribs <NUM> are nearly parallel to the surface normal <NUM>. Specifically, the main surfaces <NUM> of the ribs <NUM> are not exactly parallel to the surface normal <NUM> since the ribs <NUM> are slightly wedge shaped to allow removal of the mirror body <NUM> from a mold in its manufacturing process. Moreover, the main surfaces <NUM> closest to the surface normal <NUM> have a distance d from the surface normal <NUM> of <NUM>. This distance d has an effect in that a region close to the center <NUM> of the mirror surface <NUM> is not affected by deformations resulting from shrinking of the material of the mirror body <NUM> upon solidification during manufacture.

The illustrated example of the mirror body <NUM> includes two ribs <NUM>. However, only one rib or a higher number of ribs can be provided. If the number of ribs is an even number, the distance d between the surface normal <NUM> and the main surface of the two ribs closest to the surface normal <NUM> can be maintained.

The mirror body <NUM> further comprises a portion <NUM> provided as a counterbalance. Material can be removed from the counterbalance <NUM> in order to achieve a precise balancing of the mirror body <NUM> about the axis of rotation <NUM>. It is further possible to add material, such as an adhesive, to various surface portions of the mirror body for achieving precise balancing of the mirror body <NUM> about the axis of rotation <NUM>.

An encoder ring <NUM> is mounted on the base portion <NUM>. The encoder ring <NUM> carries a plurality of optical marks which can be detected by a sensor mounted on the mounting structure <NUM> of the measuring unit <NUM> for determining the rotational position of the rotating mirror <NUM>.

<FIG> shows a detail of a configuration of the mirror surface <NUM> according to a particular illustrating example. The mirror surface <NUM> is a slightly curved surface. The curvature of the mirror surface <NUM> is exaggerated in the sectional view shown in <FIG>. The sectional view of <FIG> is taken along the same plane as the sectional view of <FIG>. Reference numeral <NUM> indicates an osculating circle of the mirror surface <NUM> at the center <NUM> of the mirror surface <NUM>, reference numeral <NUM> indicates a center of the osculating circle <NUM>, and reference numeral r indicates the radius of the osculating circle <NUM>. There is an infinite number of osculating circles differing in their orientations about the surface normal <NUM>. The osculating circle <NUM> shown in <FIG> coincides with the drawing plane of the figure. This osculating circle <NUM> is not necessarily the smallest osculating circle, i.e. the osculating circle among the possible osculating circles having the smallest radius r.

When the beam <NUM> of measuring light incident on the mirror surface <NUM> is a parallel collimated beam, it is advantageous to design the curvature of the mirror surface <NUM> such that the plane of the smallest osculating circle is oriented orthogonal to the drawing plane of <FIG>. This means that the mirror surface <NUM> has its highest curvature in the plane orthogonal to the plane of the section shown in <FIG>. The plane of the section shown in <FIG> contains the osculating circle <NUM> and the axis of rotation <NUM>. According to a particular embodiment, the plane of the smallest osculating circle is oriented orthogonal to the drawing plane of <FIG>, and the osculating circle in the drawing plane of <FIG> has an infinite radius. This means that the surface <NUM> has a cylindrical shape.

The curved shape of the mirror surface <NUM> is provided for compensating an astigmatism induced on the beam <NUM> of measuring light by the window <NUM>. The window <NUM> has flat surfaces <NUM> and <NUM> in the section shown in <FIG> and curved surfaces <NUM> and <NUM> in the section shown in <FIG>. The difference in curvatures in the two orthogonal sections of <FIG> and <FIG>, respectively, results in a change of astigmatism when the beam <NUM> traverses the window <NUM>. This change of astigmatism can be at least partially compensated by the curvature of the mirror surface <NUM> as shown in <FIG>.

According to an example, the window <NUM> is made of polycarbonate glass having an index of refraction of about <NUM>. The window may have a thickness of <NUM> to <NUM>, and the radius R (see <FIG>) of the inner surface <NUM> of the window <NUM> can be <NUM>, for example. For compensating a change of astigmatism induced by this type of window, the curvature of the mirror surface <NUM> is designed such that the smallest osculating circle at the point where the axis <NUM> of rotation intersects the mirror surface <NUM> is contained in a plane oriented orthogonal to a plane containing the axis <NUM> of rotation and the center <NUM> of the osculating circle <NUM>, wherein the osculating circle <NUM> has a radius r of about <NUM>. The section of the mirror surface <NUM> in a plane corresponding to the section shown in <FIG> will then be a straight line.

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 HAVING A ROTATING MIRROR" 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.

Claim 1:
A surveying system, comprising:
- a support (<NUM>, <NUM>);
- a rotating mirror unit (<NUM>) including
- a mounting structure (<NUM>),
- a motor (<NUM>) having a shaft (<NUM>) rotatable about a first axis (<NUM>), wherein the motor (<NUM>) is mounted on the mounting structure (<NUM>), and
- a mirror (<NUM>) having a mirror surface (<NUM>), wherein the mirror (<NUM>) is mounted on the shaft (<NUM>) of the motor (<NUM>);
- a measuring unit (<NUM>) including
- a mounting structure (<NUM>) and
- a light source (<NUM>) and optics (<NUM>, <NUM>, <NUM>) mounted on the mounting structure (<NUM>) and configured to direct a beam (<NUM>) of measuring light onto the mirror surface (<NUM>); and
- a window (<NUM>) made of a material transmitting light of the beam (<NUM>) of measuring light,
- wherein the window (<NUM>) is arranged in a beam path of the beam (<NUM>) of measuring light downstream of the mirror (<NUM>), and
- wherein the window (<NUM>) mechanically connects the mounting structure (<NUM>) of the measuring unit (<NUM>) and the mounting structure (<NUM>) of the rotating mirror unit (<NUM>),
wherein one of the mounting structure (<NUM>) of the measuring unit (<NUM>) and the mounting structure (<NUM>) of the rotating mirror unit (<NUM>) is mounted on and carried by the support (<NUM>, <NUM>)
characterized in that the other one of the mounting structure (<NUM>) of the measuring unit (<NUM>) and the mounting structure (<NUM>) of the rotating mirror unit (<NUM>) is carried by the window (<NUM>).