GEODETIC INSTRUMENT COMPRISING A BASE AND A GEODETIC SURVEYING AND/OR PROJECTION MODULE

Abstract

A geodetic instrument with a base module and a surveying or projection module. A processor for control of the instrument is situated in the base module. The surveying or projection module is rotatable about two axes by a drive unit of the base. The instrument comprises a mechanical interface connecting the surveying or projection module to the base module and an optical or electrical contact interface between the base module and the geodetic surveying or projection module. The interfaces are designed such that the surveying or projection module is mountable to the base module and dismountable from the base module by a user, whereby the geodetic instrument is designed for mounting of various surveying or projection modules of different geodetic type and execution of accordingly different geodetic surveying or projection functions.

Claims

1. A geodetic instrument comprising: a surveying or projection module supported by a base module, wherein the surveying or projection module comprises at least one sensor or projector for acquisition or projection of object data and the base module comprises: an electrical power unit for powering the geodetic instrument; a first processor, powered by the electrical power unit, for processing of geodetic data and control of the geodetic instrument; a drive, powered by the electrical power unit, adapted for driving the geodetic surveying or projection module about two rotational axes; at least one angle encoder for measuring the rotational position of the surveying or projection module with respect to the two rotational axes, wherein the geodetic instrument comprises: an optical or electrical contact interface adapted for transmission of data or energy between the base module and the surveying or projection module, and a mechanical interface adapted for mechanical connection of the surveying or projection module to the base module, whereby the interfaces are designed such that the surveying or projection module is mountable to the base module and dismountable from the base module by a user, and the geodetic instrument is designed for mounting of various surveying or projection modules of different geodetic type to the base module and execution of accordingly different geodetic surveying and/or projection functions.

2. The geodetic instrument according to claim 1, wherein the geodetic instrument is configured such that all of the mountable various surveying or projection modules are referenced to one and the same origin of coordinates.

3. The geodetic instrument according to claim 1, wherein the surveying or projection module is designed as a portable stand-alone surveying or projection module with a battery, a data storage, and a second processor such that temporarily, surveying or projection with the surveying or projection module dismounted from the base module is enabled.

4. The geodetic instrument according to claim 1, wherein the interfaces are designed such that an operable mounting of dismounted surveying or projection module to the base module and analogically dismounting of mounted surveying and projection module is effectable by a single manual action of the user.

5. The geodetic instrument according to claim 1, wherein the mechanical interface is designed such that a mechanically stable mounting of the surveying or projection module to the base module is secured by at least one of: a magnet, one screw, one spring-loaded claw, one twistable claw, a bayonet fastening, and one ball lock pin.

6. The geodetic instrument according to claim 1, wherein the mechanical interface is designed in such a way that the mounting position of a respective surveying or projection module is precisely reproducible and thermally stable.

7. The geodetic instrument according to claim 6, wherein the mechanical interface comprises at least three guidance elements with equal angular spacing to each other whereby each guidance element comprises a ball or spherical calotte and a two-point support as a receiving counterpart.

8. A geodetic instrument base module comprising: an electrical power unit; a processor powered by the electrical power unit, for processing of geodetic data and control of the base module, a mechanical interface, and an optical or electrical contact interface, wherein the interfaces are designed for mounting and dismounting of various surveying or projection modules of different geodetic type by a user, and wherein the processor is adapted for control of a respective surveying or projection module, wherein the base module further comprises: a drive, powered by the electrical power unit, adapted for driving the mechanical interface or the base module about two rotational axes, and at least one angle encoder for measuring the respective rotational position.

9. The geodetic instrument base module according to claim 8, wherein the base module comprises: a power unit part comprising the power unit; and a main part, whereby the drive comprises: a first drive unit for rotation of the main part relative to the power unit part about a first axis, and a second drive unit for rotation of the interface relative to the main part about a second axis.

10. The geodetic instrument base according to claim 8, wherein the base module is asymmetric with respect to a vertical axis.

11. The geodetic instrument base according to claim 9, wherein the mechanical interface and the optical or electrical contact interface are integrated in the second drive unit.

12. A surveying or projection module comprising: a mechanical interface designed for connecting the surveying or projection module to a base module according to claim 8, and an optical or electrical contact interface adapted for transmission of data or energy between the base module and the surveying or projection module.

13. The surveying or projection module according to claim 12, wherein the surveying or projection module is designed as a portable stand-alone geodetic surveying or projection module with a battery, a data storage and a processor such that temporarily geodetic surveying or projection with the surveying or projection module dismounted from the base module is enabled.

14. The surveying or projection module according to claim 12, wherein the surveying or projection module is embodied as a laser scanning head, an opto-electronic surveying head, a camera head, or a point or line laser projector, whereby the emission plane of each of the two line lasers is oriented orthogonal to each other and to emission direction of the point laser.

15. The surveying or projection module according to claim 13, wherein the surveying or projection module is embodied as a laser scanning head, an opto-electronic surveying head, a camera head, or a point or line laser projector, whereby the emission plane of each of the two line lasers is oriented orthogonal to each other and to emission direction of the point laser.

16. The surveying or projection module according to claim 12, wherein the surveying and/or projection module comprises: a telescope, or a panorama or wide angle objective, and an illumination light for illumination of the field of view of the telescope or the objective.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Specifically,

[0044] FIG. 1 illustrates a first example of a geodetic instrument;

[0045] FIGS. 2a,b show an exemplary embodiment of a geodetic instrument in more detail;

[0046] FIG. 3 shows examples for various surveying and/or projection modules;

[0047] FIG. 4 depicts an example of a tool-freely mountable and dismountable surveying and projection module;

[0048] FIGS. 5a,b illustrate an inside view of an exemplary geodetic instrument;

[0049] FIG. 6 illustrates another inside view of an exemplary geodetic instrument;

[0050] FIG. 7a,b show examples of a simplified mechanical interface of the geodetic instrument; and

[0051] FIGS. 8a-f show examples for means for fastening a surveying and/or projection module to the base module by the mechanical interface.

DETAILED DESCRIPTION

[0052] FIG. 1 illustrates a first example of a geodetic instrument 1 according to the invention and its utilisation by a user 3.

[0053] FIG. 1 shows on its left side the geodetic instrument 1 having a base module 2 and a surveying and/or projection module 4 connected to the base 2 by an interface 5. The geodetic instrument 1 is positioned on a tripod 7 as support structure by a release interface (not shown). In this setup, the geodetic instrument 1 can be used in principle as a portable geodetic device known in the art like a total station or theodolite, laser templator or laser scanner, which is positioned at a station for example for surveying or measuring purposes in indoor or outdoor construction works, if the surveying and/or projection module 4 is embodied as an opto-electronic surveying head, multi-photo measuring head or laser scanner head. As a further example, having a projection module 4, the instrument 1 can be used as a point and/or line laser projector, e.g. in form of a laser level or rotary laser. Further, a projection module 4 can be used for position true projection of a point, line or geometric shape on an object's surface according to a construction plan or CAD-data or the like, enabling a visual marking of a nominal position such that for instance a construction work can be performed at or according to that nominal position. For example, the instrument 1 provides by module 4 a 780 nm EDM (electronic distance measuring) laser for surveying and a 532 nm laser for pointing.

[0054] Further, as also known in principle by the skilled person, the instrument 1 can comprise an automatic target recognition (ATR)-unit (not shown) in the geodetic module 4 for locking onto a geodetic target such as a surveying pole respectively for target tracking. In addition, a far field ATR is optionally present.

[0055] For whatever surveying or construction task, the user 3 can command or operate the geodetic instrument 1 by a user interface (not shown) situated at the base 2. For example, a measuring of 3D coordinates of object points (single point measurement or scanning) can be started by pushing a button at the instrument or a remote control or running on a tablet/smartphone/control unit once the instrument 1 is stationed in a room as indicated in the figure (reference number 6).

[0056] According to the invention, the surveying and/or projection module 4 of the geodetic instrument 1 is also easily dismountable, e.g. tool-freely, from the base 2 (indicated by arrow 8) and exchangeable by another surveying and/or projection module by the user 3. That is the “sensitive” main component 4 of instrument 1 can be connected to the base main component 2 and disconnected from it in the field conveniently by user 3. Further, the geodetic instrument 1 is designed such that surveying and/or projection modules 4 of different type are supported by base module 2 and operable with their varying functionalities. For example, a laser scan module 4 for scanning an environment can be exchanged by a laser projection module for visually marking planned position or object points in the environment.

[0057] All mountable modules 4 thereby relate to one and the same origin of coordinates. Hence for instance, a surrounding first can be scanned by a scanning module 4, then referenced or compared to a stored digital map of the surrounding, the map comprising target positions, and then these target positions can be visibly marked position-true in the surrounding by a projection module 4 mounted by the user 3 instead of the scanning module 4 in the meantime, based on the scan data and reference data. Thereby, due to the same coordinate origin, no parallax has to be taken into account and no computational correction of coordinates is needed.

[0058] In the example, surveying and/or projection module 4 is in addition not only operational in connection to the base module 2, but temporarily usable as stand-alone geodetic device. As indicated in exemplary FIG. 1, the user 3 can use the module 4 for free-hand geodetic tasks, controlling it by a human-machine-interface (HMI) at the module 4 (indicated by reference number 9).

[0059] For example, often not all 3D coordinates of a room can be measured from a station but some points are hidden or occluded. The user 3 then can quickly disconnect the geodetic module 4 wherefore conveniently no tools are necessary, go to a position wherefrom the missing points are visible and measure these points. Measuring can be done e.g. using a measuring beam L as shown in the figure and using measuring methods such as time-of-flight, phase, wave form, photogrammetric or interferometric evaluation.

[0060] Preferably, the interface 5 comprises an electrical contact such that the battery of the surveying and/or projection module 4 can be loaded from the power unit of the base 2 through this electrical interface, thus providing an easy and self-reliant way of charging surveying and/or projection module 4.

[0061] For referencing of free-hand measurements with dismounted surveying and/or projection module 4 to the same reference or coordinate system of the stationary measurements, the module 4 comprises for instance positional sensors such as an inertial measurement unit (IMU), gyroscope and/or inclinometer or GNSS-receivers in case of outdoor activities (not shown). Additionally or alternatively, a referencing such as registration of 3D point clouds can be effected by measuring a number of reference points from both the stationary position as well as from the free-hand position and/or by 2D- or 3D-image based path derivation using image processing techniques such as feature matching with algorithms such as SIFT—(Scale Invariant Feature Transformation), SURF—(Speeded Up Robust Features), FAST—(Features from Accelerated Segment Test), BRIEF—(Robust Independent Elementary Features) or ORB—(Oriented FAST and Rotated BRIEF).

[0062] As another example, the autonomy of the surveying and/or projection module 4 and its relatively small size can be used to position it at nearly every position, in particular positions which are not accessible with the relatively large or bulky geodetic device 1 as a whole. Thus, e.g. a level laser can be emitted from nearly everywhere in a room. For this purpose, the geodetic module 4 may have attaching means such as magnet or clamp (not shown) for attaching it onto a wall or ceiling or the like.

[0063] As still another example, the possibility of independent operation of the geodetic module 4 enables the user 3 to perform quick data acquisition such as a rough scanning of a room. Hence, for instance a 3D-overview of a surrounding can be gathered just by the user 3 holding the module 4 and turning around himself. When more reliability resp. more precise measurement is needed, e.g. a specific section of the surrounding determined or selected based on the rough overview surveying, the geodetic module 4 is then mounted to the base 2—which is easily done due to the tool-free handling enabled by interface 5—for improved measurement capabilities.

[0064] Improved surveying capabilities of the complete geodetic device 1 as a whole—compared to the geodetic module 4 on its own—are provided by the stable holding and automatic positioning of the geodetic module 4 when mounted to the base 2. For precise positioning and thus measuring or projecting, the base 2 comprises a drive (not shown in FIG. 1), powered by an electrical power unit (not shown) of the base module 2, for driving the surveying and/or projection module 4 about a first axis H and a second axis V. The respective actual rotational position about each axis H, V is determined with respective angle encoder (not shown).

[0065] In addition, the power unit of the base 2 possesses a relatively large capacity, allowing for power intensive computations with a processor built into the base 2, power intensive surveying operations such as measuring points in the far field with a measuring beam and long operating duration. Compared with, the geodetic module 4 when used as a temporarily stand-alone device is of limited operational and computational power.

[0066] For example, data intensive measurements (e.g. a laser scan) in the autonomous, off-station modus of the surveying and/or projection module 4 are just stored on an internal data storage of the module 4 without any further data evaluation or processing. Then, after attaching the module 4 to the base 2, the stored data is transferred to the base module 2 and the computational power of the base 2 is used to process and evaluate the measurement data and e.g. to form a graphic representation or interpretation, displaying it on a display of the instrument 1 (which may also be a portable display such as a tablet or smartphone connected with the base 2 resp. instrument 1). In an analogous manner, it is possible to buffer the scan data in the module 4 and then directly transfer (when connected) to a tablet or other control unit.

[0067] Alternatively, data acquired in the stand-alone mode can be transferred wirelessly from module 4 to the base 2 for further processing there, particularly on-the-fly or already during measuring. In such embodiments with wireless data transmitters, the data storage of the mobile module 4 may be only a non-permanent storage and a permanent storage may be dispensable or optional, e.g. in form of an exchangeable storage card inserted in a card reader of module 4 or e.g. as a back-up to the already transferred data to tablet, smartphone or control unit.

[0068] Generally spoken, the geodetic measurement capabilities or range of functions of the geodetic module 4 are enhanced and extended when combined with the base 2 to form the geodetic instrument 1 compared to its stand-alone use. The capacity and functionality of the module 4 in autonomous application are limited compared to the “full” instrument 1.

[0069] The described configuration of geodetic instrument 1 enables first robust and highly reliable geodetic measurements or position true projection by the combination of surveying and/or projection module 4 and base module 2 with a high level of geodetic capability/functionality and precision.

[0070] Second, the geodetic instrument 1 is designed such that it may comprise various exchangeable geodetic survey or projection modules 4 of different type, thus providing different geodetic functionalities with only one and the same basic (infra-)structure (in form of base 2) which is described in more detail with respect to FIG. 3. In other words, the geodetic instrument 1 is configured such that not only one (generic group of) module 4 is provided but multiple sort of module 4 can be combined with base 2, thus providing a bunch of geodetic capabilities. Geodetic instrument 1 serves as a multi-purpose geodetic instrument by the possibility to easily exchange the measuring or pointing module 4 with another one. High flexibility and improved range of application is provided in that the geodetic module 4 is easily exchangeable by another geodetic module 4, i.e. base module 2 can be combined with different surveying and/or projection modules 4.

[0071] Third, high flexibility and improved range of application is further enhanced in that the geodetic module 4 is easily attachable and detachable to the base 2 and in that it can be used as a semi- or temporarily autonomous geodetic unit, e.g. for quick or supplemental measurements, fast and temporary change of location or locations not or hardly accessible with the complete instrument 1. Flexibility of module mounting and dismounting and stationed and free-hand measurement is provided.

[0072] FIGS. 2a and 2b show in a 3D-view an exemplary embodiment of a geodetic instrument 1—as for instance intended for geodetic measuring or referencing at a construction site—in more detail.

[0073] In FIG. 2a, the geodetic instrument 1 is depicted with the geodetic survey and/or projection module 4 docked to the base module 2. For attachment, the base 2 and the surveying and/or projection module 4 comprise an interface 5 or that is to say the instrument 1 comprise an interface 5 with part of it situated at base 2 and the counterpart situated at module 4. Interface 5 is shown in more detail in FIG. 2b.

[0074] The base module 2 optionally comprises on its lower side or bottom face 2s a connector (not shown) for connection of the instrument 1 to a stand, e.g. a tripod. Alternatively or additionally, the bottom face 2s is designed such, for example as a flat surface or with three contact points, that the instrument 1 can be placed stable on a surface (bottom) wherefore the instrument 1 is designed such that the centre of gravity of the instrument 1 lies securely within bottom surface 2s.

[0075] As depicted, the exemplary instrument 1 is asymmetric with respect to the vertical axis V. This facilitates a simple mounting and demounting of the surveying and/or projection module 4 by an operator.

[0076] FIG. 2b illustrates the geodetic instrument 1 with a detached surveying and/or projection module 4 such that the interface 5 is visible. Also indicated are the vertical axis V the base 2 and accordingly the module 4 attached to the base is rotatable about and the horizontal axis H as a second axis the module 4 is rotatable about by the interface 5 when attached with the help of one or more drives and angular sensors which are described in more detail in the following figures. For example, the interface 5 is integrated in a drive unit for driving the module 4 about horizontal axis H.

[0077] As shown in the upper part of FIG. 2b, the interface 5 comprises a mechanical part 5a, an electrical connection 5b and optical connection 5c. One can also say that there are two interfaces, a mechanical interface 5a for fastening the module 4 to the base and an optical and electrical interface 5b, 5c for energy supply and data transfer, wherein the two interfaces 5a and 5b,c are embodied a joined interface 5.

[0078] As said, the interface 5 comprises a mechanical centering and fixation 5a as well as an electrical connection 5b and an optical connection 5c. The interface 5 is designed such that the module 4 can be mounted to the base 2 and demounted from the base 2 very easily, with a only one operation, for example with one translation or rotation, with or preferably without any tool. For example, the interface 5 comprises a release button for demounting the module 4 and it has just to be “clicked” onto for mounting. Alternatively, the module 4 can be slided or pressed onto and off without button release. For example, the interface comprises a single eight-pole connector connecting the geodetic module 4 with the base 2.

[0079] Thereby, though the interface 5 is designed in such a way that fast fastening of various surveying modules 4 of different type (and therewith often different geometry and mass or mass distribution) is enabled, it is also designed in such a way that a repeatedly stable connection between module 4 and its base 2 is guaranteed. That is that the mounting remains positional precise despite environmental influences such a temperature change, various dismounting and mounting procedures and despite the fact that it is embodied as receptacle for various surveying and/or projection units 4. Thus, the high precise interface 5 allows for no shift of an internal reference point of respective module 4 but any coordinative measuring or projection is precisely referenced with respect to a common reference position, no matter how often there is a module change or how long a measurement tasks takes. The interface 5 combines easy handling and flexibility with high, stable and reproducible mounting position precision.

[0080] FIG. 3 shows an example for various surveying and/or projection modules 4a-4d of different type which all can be mounted on base 2. That is the instrument 1 is designed such that exchangeability of a geodetic module 4a-4d of one type with another one of another type. Hence, the instrument 1 can advantageously be equipped with different surveying or projection heads, enabling multiple geodetic functionality with one and the same base 2 as main structure.

[0081] FIG. 3 depicts the base 2 comprising mechanical and opto-electrical interface 5 on the left side and four different exemplary geodetic modules 4a, 4b, 4c and 4d which each of them can be combined with the base 2 to form a different geodetic instrument 1. Thus, only one base 2 as basic support-, drive-, energy- and computation-unit, providing defined positioning mechanism, controlling and data evaluation means, energy supply, HMI-elements as well as additional infrastructure such as shock protection, is sufficient for enabling various geodetic measurement and construction aid functionalities. Preferably, each module 4a-4d comprises an identifier, e.g. by RFID, such that the base 2 can automatically identify which type or which individual module 4a-4d is mounted.

[0082] First exemplary geodetic module 4a is embodied as a telescope surveying head. A measurement beam, generated by a light source (not shown) such as a laser source or SLED inside module 4 is emitted through objective 10 onto an object point. The reflected beam is captured through objective 10 by an optical sensor (not shown) and from the sensor signal a distance to the object point is calculated, e.g. based on TOF or phase measurement. The measurement beam can be visible or an additional visible light beam is generated as a pointer. The module 4a can also comprise a camera (with objective 10 being part of it) such that a user can capture images or a live-stream of the environment and view them on a display of the module 4a (not shown).

[0083] When used in stand-alone modus, the module 4a can be used as an electronic distance meter or camera. In combination with base 2, there is provided a geodetic instrument 1 in form of total station- or electronic tachymeter-type or lasertracker-type.

[0084] The second example, geodetic module 4b, is designed as a point and line-laser projection module, thus providing functionality of visible marking of spatial references. The point laser 11a can for example be used for point pointing or plumbing or perpendicular marking whereas the two (or more) line lasers 11b, 11c can mark vertical or—dependent on the orientation of module 4b—horizontal reference lines. When dismounted from base 2, it can be positioned nearly everywhere whereas a construction laser level or rotary laser as geodetic instrument 1 is provided in combination with base 2. As shown, in the example the first line laser 11b is perpendicular to the second line laser 11c and the point laser 11a is perpendicular to both line lasers 11b, 11c.

[0085] Module 4c is a third example and embodied as a laser scanning head. It comprises a rotatable deflection element 23 for fast deflection of measurement beam such that a dense scan pattern of a high number of 3D coordinates of an object's surface can be acquired.

[0086] The fourth example is module 4d, embodied as a multi-photo measuring head. It comprises a number of photosensors or photodetectors 24 distributed on a housing of the module 4d.

[0087] FIG. 4 illustrates another example of a tool-freely mountable and dismountable geodetic surveying and projection module 4e, providing specific geodetic functionality and being non-permanently or limitedly usable as a stand-alone geodetic unit. Module 4e comprises a surveying telescope 40 for coordinative measuring of object points using a measurement beam 41. Further, the module 4e comprises a horizontal projecting line laser 42 and a vertical projection line laser 43 as well as an orthogonal projection point laser 44. In the example as can be seen, the emission direction or plane of each of the two line lasers 42, 43 are perpendicular to each other as well as to the emission direction of point laser 44.

[0088] For capturing images of the surrounding or surveying environment, the module 4e has a panorama camera objective 46 on the top as well as a wide angle objective 47 on one side whereby both objectives can be part of a combined panorama and wide angle camera. In addition, geodetic module 4e comprises an illumination light 45 as sort of flashlight for illumination of a target object or field of view of the telescope 40 and/or camera objectives 46, 47.

[0089] FIGS. 5a and 5b illustrate some “inner” components of the geodetic instrument 1.

[0090] FIG. 5a is a cross-sectional view of the geodetic instrument 1 with the asymmetrical base part 2 to the left and bottom and the detachable module unit 4 to the upper right.

[0091] The surveying and/or projection module 4 comprises a battery 16, a data processing unit 17 with a permanent or non-permanent data storage and a surveying and/or projection unit 18.

[0092] The base module 2 comprises a lower part with a battery 14 for providing energy to the base 2, e.g. the motors for change of orientation, a processor 15, and through interface 5 to the module 4. Instead of or in addition to a battery 14, the base 2 comprises a power supply unit for connection to an external power supple. Further, an inclinometer sensor 25 is part of the base 2 for measuring a tilt of instrument 1.

[0093] The base 2 comprises above that in its lower part a first or vertical drive unit 13 for rotation of the base 2 and therewith module 4 (if attached) about the vertical axis V. In addition, the upper part comprises a second or horizontal drive unit 12 for rotation of the module 4 about horizontal axis H. In the example, the interface 5 and an angle encoder are integrated in the drive unit 12 which shown in more detail in FIG. 5b. Preferably, first and second drive unit 12 and 13 are substantially structurally identical, except for interface 5. As can be seen, base 2 is asymmetrical with respect to axis V due to the non-centric upper part, situated at one side of the lower battery part.

[0094] FIG. 5b shows the first (or similarly second) drive unit 12 in detail. The drive unit comprises a motor 19, an angular measuring system or angular sensor 20 and an axle bearing 21. Further, it shows interface 5 with mechanical centering and fixation 5a, electrical contact 5b and optical interface 5c. The presented drive unit 12 resp. 13 provides a compact and nevertheless reliable and robust mean for precise rotation of geodetic instrument 1 resp. change of its aiming or targeting direction.

[0095] FIG. 6 shows a variation of the embodiment as shown in FIG. 5a. In difference to this above described embodiment, the battery or power unit part 2b, comprising battery 14, is separated from and superimposed on the main part 2a by an interface 5′, the main part 2a comprising CPU 15, second drive 12 and first drive 13. By first drive 13, the main part 2a and thus module 4 is drivable around the vertical axis and relative to battery part 2b. Thus, the relatively heavy power unit 14 has not to be moved which saves energy.

[0096] Preferably, the power unit part 2b is detachable tool free from the main part 2a. This allows for a quick and easy exchange or replacement of battery 14, without the need for a longer interruption of the geodetic work.

[0097] In particular advantageous embodiments, the whole instrument 1 is temporarily supplied with energy through interface 5 by the module battery 16 during exchange of main battery 14 or in case of any failure in power supply by base battery 14. Thus, advantageously, there is an electrical reserve in form of module battery 16 in case of low or broken main battery 14. This allows for a limited continuation of operation (limited with respect to time and/or functionality) which is e.g. particularly advantageous in case of measurements which otherwise would have to be repeated completely from the beginning. At least, an “emergency” power reserve by module battery 16 prevents loss of data as at least it gives time to permanently store measurement data before instrument 1 is off.

[0098] FIGS. 7a and 7b illustrate a way of position stable fixation of two separable modules or units of the geodetic instrument with respect to each other by a mechanic interface 5a.

[0099] FIG. 7a shows in the upper part two 3D views of (part of) mechanical interface 5a as used for mounting or connection of a surveying or projection module and base module. In the lower part, there are two side and cross sectional views. On the left side, FIG. 7a depicts the reception part and the insertion part separated or dismounted (semi-exploded view) and the right side depicts the interface 5a when the modules are attached to each other.

[0100] As shown, the interface 5a comprises three balls 27 fixed in conical receptions (bores) 28, distributed equally around a center (120° angular spacing) and being part of the base module 2. The balls 27 are to be clamped by a pair of elongated cylindrical guiding elements 26 each situated in the interface's counterpart at surveying module 4. The clamping is for example effected by magnetic force. Therefore, for instance the cylinders 26 are made of steel and the balls 27 are made of steel or ceramic and a magnet either in the center of the arrangement (not shown) or located around the balls (not shown) are pulling the two parts 4 and 2 towards each other (see also FIG. 8a). This configuration results in a self-centering coupling.

[0101] A possible alternative to the configuration shown in FIG. 7a as a robust and tolerance independent interface, which can compensate for thermal expansion, too, the fixation 50 comprises three equally spaced cylinders 26 (or elongated prismatic bodies) clamped into a pair of balls 27 each. That is to say, in difference to the embodiment shown in FIG. 7a, not the balls 27 are fixed by cylinders 26 but the other way round.

[0102] FIG. 7b shows in a sketchy cross-sectional view another alternative illustrating the underlying principle of a positional stable interface. The base module 2 comprises three spherical calottes 27a distributed in an area or plane. The calottes 27a are received by a two-point reception 26a accordingly distributed at the interface at surveying module 4.

[0103] FIGS. 8a-8f show in cross sectional views examples for fastening means as an instrument's mechanical interface or part of it, e.g. for convenient and user-friendly but nevertheless position stable mounting and dismounting a surveying and/or projection module 4 to the base module 2 (each depicted in a respective figure only symbolically).

[0104] FIG. 8a shows a first example using magnetic force as already mentioned above. The instrument thereby comprises a set of magnets 29a, 29b. A first group of magnets 29a, situated at dismountable part 4 exert force on a second group of magnets 29b, situated at the static part 2. Surveying module 4 thus can be mounted by docking onto base part 2 and dismounted by pulling it away.

[0105] FIG. 8b shows another example wherein the interface is secured by a screw 30b at base part 2 going into a thread 30a at mobile part 4. The screw 30b thereby can be revolved tool-free by hand as depicted or alternatively is designed for manipulation with a specialized tool like a screwdriver or an item like a coin or key fob as a tool.

[0106] FIG. 8c shows an embodiment wherein a pin 31a is to be secured by a claw 31b at base part 2, the claw 31b being preloaded with a spring 31c (indicated by the black dots). The claw 31b and the interface at base part 2 thereby are formed in such a way that a force is exerted in the mounted state due to spring 31c.

[0107] FIG. 8d shows an embodiment having a bayonet fastening 32, whereby in the lower part of FIG. 8d in addition a birds-eye view is given. Module 4 comprises the inner part 32a of the bayonet fastening and module 2 the outer (counter-)part 32b.

[0108] FIG. 8e shows another embodiment with a claw 33b. Therein, a pin 33a is to be secured by a claw 33b at base part 2, the claw 33b being rotatable as indicated in lower part of FIG. 8e, showing a 3D-view of claw 33b.

[0109] FIG. 8f shows an example with a ball lock pin 34b at base part 2 for being secured by reception 34a at module 4 for fixation.

[0110] Preferably, the mechanical interface comprises not more than one of such a fixation means as depicted in FIGS. 8b, 8c, 8e and 8f. Thus, in all examples one movement of a user's hand is sufficient for mounting or dismounting (fix and unfix) of a separable unit of the geodetic instrument.

[0111] A skilled person is aware of the fact that details, which are here shown and explained with respect to different embodiments, can also be combined in other permutations in the sense of the invention if not indicated otherwise.