Method for determining and visualizing an accuracy map

Abstract

A computer-implemented method for determining for a working area at a worksite, in which a surveying instrument is deployed at a station, an accuracy map, which shows for the working area at least one accuracy that can be achieved during operating the surveying instrument, the method being performed by a computer system and comprising the steps: - Dividing the working area in a grid pattern of surface elements, - Computing for the station of the surveying instrument, a pose vector, and corresponding variances and covariances for the pose elements of the pose vector, - Computing for the surface elements accuracies that can be achieved during operating the surveying instrument based on the pose vector, the variances and covariances of the pose elements, on measuring accuracies of the surveying instrument, and on representative coordinates of the surface elements, - Computing the accuracy map based on the accuracies computed for the surface elements, - Instructing a display to visualize a graphical representation of the accuracy map.

Description

[0001]HILTI Aktiengesellschaft in SchaanPrincipality of Liechtenstein Method for determining and visualizing an accuracy map.The present invention relates to a method for determining in a worksite an accuracy map ac-cording to the definition of claim 1, to a computer program according to the definition of claim8, and to an apparatus according to the definition of claim 9.Background of the inventionSurveying instruments, such as total stations, are used in construction industries to take indi-vidual, highly accurate measurements within a worksite, using a precise electronic distancemeasuring device, accurate motors to rotate this electronic distance measuring device, andangle measuring devices to measure the orientation of the electronic distance measuring de-vice. Centered within a total station is its coordinate frame and the orientation of the coordi-nate frame is usually such that the total station's x-axis pointing towards right, y-axis pointingtowards the floor, and z-axis pointing into forward direction.Known workflows to determine the pose (position and orientation) of a total station are based on manually or automatically taking measurement samples of distance and angle data in the worksite. Based on a scalable mathematical equation system, the pose can be calculated with a varying degree of precision, depending on the amount of sampling information consid-ered and their geometrical distribution. To solve the pose calculation, a minimum number ofmeasurement samples needs to be taken, while an increasing number of measurement sam- ples usually leads to the formation of an overdetermined mathematical equation system and an overall improved accuracy of the pose calculation. The basic concept of surveying using a total station is that at an initial phase, a number ofcontrol points are positioned at scattered locations at the worksite to be surveyed. Typically,control points are materialized by prisms, cat-eyes, reflective foils, or other forms of reflectivetargets for returning the laser beam from the total station. The exact location of each controlpoint is determined and logged in terms of coordinates on a specified coordinate frame, typi-cally the coordinate frame of a floorplan of the worksite. A total station can then sight a num-ber of these control points to determine its absolute position on that X, Y, Z coordinate frame using standard triangulation techniques.In operation, the operator determines the distance and angle data successively for each con-trol point. These data are stored in the total station's computer system together with the ab-solute position data for the respective control points, the latter position data being pre-loaded into the total station. The total station then implements an algorithm, generally known as afree-stationing algorithm, to determine its pose from the sightings of those control points. Thepositioning accuracy of a total station is inversely proportional to the square root of the num-ber of control points it can exploit from its location, the angular distribution of those controlpoints, as well as the stability of the worksite at which the control points and the total stationare deployed. Typically, the pose and its standard deviation are shown to the operator as numerical values and the interpretation of the quality is left to the operator and depends on his experience. To support the operator in the interpretation of the pose and its quality, Leica has released in November 2022 a new version v7.5 of their iCON Field software and included a functionality that shows to the operator a recommended working area that is a polygon created by the control points used for computing the pose. The disadvantage of the known functionality is that the working area is not evaluated based on an accuracy threshold that can be achievedduring measuring and / or layouting with the total station and the pose is not used for deter-mining the working area. Summary of the inventionTherefore, what is desired is a method for determining for a working area at a worksite an ac-curacy map which shows the accuracy that can be achieved during measuring and / or layout-ing with a surveying instrument. An operator of the surveying instrument should be supportedin the interpretation of the quality of the pose and in the accuracy, he can achieve during measuring and / or layouting with the surveying instrument.These objectives are achieved by realizing the features of the independent claims. Featureswhich further develop the invention in an advantageous manner are described in the depend- ent claims.According to an aspect of the present invention, there is provided a computer-implementedmethod for determining for a working area at a worksite, in which a surveying instrument isdeployed at a station, an accuracy map, which shows for the working area at least one accu-racy that can be achieved during operating the surveying instrument, the method being per-formed by a computer system and comprising the steps: ^Dividing the working area in a grid pattern of surface elements,^ Computing for the station of the surveying instrument, a pose vector, and corre-sponding variances and covariances for the pose elements of the pose vector,^ Computing for the surface elements, the accuracy that can be achieved during op-erating the surveying instrument based on the pose vector, the variances and co-variances of the pose elements, on measuring accuracies of the surveying instru-ment, and on representative coordinates of the surface elements,^ Computing the accuracy map based on the accuracies computed for the surfaceelements, and^ Instructing a display to visualize a graphical representation of the accuracy map.According to the method for determining an accuracy map, a working area is defined and for that working area, a grid pattern of surface elements is defined. For the station, at which thesurveying instrument is deployed, the pose vector (position and orientation) and correspond-ing variances and covariances of the pose elements are computed by means of a well-knownmethod for stationing a surveying instrument; methods for stationing are free-stationing pro-cesses, model-based stationing processes, and automatic stationing processes, but anyother stationing process can be used.The worksite defines the three-dimensional environment, in which the surveying instrument is deployed at a station, and the working area is that part of the worksite, in which the surveyinginstrument is operating, and the operator is interested in during operating the surveying in-strument, wherein the working area is typically a two-dimensional area.For the surface elements, the accuracies that can be achieved during operating the survey-ing instrument, for example layouting or measuring, are computed based on the pose vector,the variances and covariances of the pose elements, on measuring accuracies of the survey-ing instrument, and on representative coordinates of the surface elements; representative co-ordinates of the surface elements can be a center point or any other point of the surface ele-ments. The accuracy map, which shows the accuracies that can be achieved during operat-ing the surveying instrument, is computed based on the accuracies computed for the surfaceelements. Finally, a display is instructed to visualize a graphical representation of the accu-racy map on the display.The method for determining an accuracy map according to the present invention supportsthe operator of the surveying instrument in understanding the results he achieved during sta-tioning of the surveying instrument. The operator is supported by the graphical representa-tion of the accuracy map. The values represented by the accuracy map would normally bemuch harder for the operator to understand if presented numerically in a spreadsheet, espe-cially if the data set is large or complex. The accuracy map enables operators to visualizedata and understand it easily. The operator can easily check via the graphical representationif he can achieve the required accuracy during operating the surveying instrument at theworksite.In a preferred embodiment, the working area is computed by the computer system based ona set of control points. The definition of the working area is necessary to define that area of the worksite the operator is interested in during operating the surveying instrument.In an alternative preferred embodiment, the working area is computed by the computer sys-tem based on a polygon or a polyline or a set of corner points defined by an operator. Thedefinition of the working area is necessary to define that area of the worksite the operator isinterested in during operating the surveying instrument. If the operator defines the workingarea, the computation of the accuracy map can be restricted to that area of the worksite the operator is really interested in.Preferably, the accuracy map is stored in the computer system and / or stored to a memoryconnected to the computer system and the accuracy map is provided for use in operating thesurveying instrument. By providing the accuracy map for use in operating the surveying in-strument, the operator is supported in the interpretation of the data, he can easily check viathe graphical representation of the accuracy map, if he can achieve the required accuracy.Preferably, the accuracy map is provided for use in searching for a layout point and upon se-lecting the layout point and defining an accuracy threshold, it is checked by the computersystem if the accuracy threshold can be achieved, wherein:^ upon verification that the accuracy threshold can be achieved for the layout point, apredefined action is performed, the predefined action comprising generating a mes- sage stating that the accuracy threshold can be achieved for the layout point, and^ upon verification that the accuracy threshold cannot be achieved for the layout point,a predefined action is performed, the predefined action comprising generating a mes- sage stating that the accuracy threshold cannot be achieved for the layout point.By checking via the computer system whether a predefined accuracy threshold can beachieved for a layout point, the operator is supported in achieving the required accuracy.In a preferred embodiment, the pose vector, and the corresponding variances and covari-ances for the pose elements of the pose vector are computed by a free-stationing algorithm based on a set of control points having known first coordinates in a first coordinate frame of the worksite and at least a sub-set of the set of control points having known second coordi- nates in a second coordinate frame of the surveying instrument.Free-stationing algorithms are typically used to determine the pose vector, and correspond-ing variances and covariances of a surveying instrument in the first coordinate frame of theworksite. To compute the pose vector, at least two control points are required, the pose vec-tor is computed from the first coordinates of the control points in the first coordinate frameand from the second coordinates in the second coordinate frame. The quality of the posevector is proportional to the number of control points, the angular distribution of those controlpoints, and the stability of the worksite, at which the control points and the surveying instru-ment are deployed. The graphical representation of the layout area can support the operatorin finding an appropriate selection of control points to determine the pose vector of the sur-veying instrument via a free-stationing algorithm.Preferably, from the set of control points at least one further control point being different fromthe sub-set of control points is selected, second coordinates are determined for the at least one further control point by the surveying instrument in the second coordinate frame, and a new sub-set of control points containing the sub-set of control points and the at least one fur- ther control point is defined, the method further comprising: ^Computing for the station of the surveying instrument, a new pose vector and cor-responding variances and covariances for the pose elements of the new posevector, ^Computing for the surface elements, the accuracies that can be achieved duringoperating the surveying instrument based on the new pose vector, the variancesand covariances of the new pose elements, on the measuring accuracies of thesurveying instrument, and on the representative coordinates of the surface ele-ments, ^Computing a new accuracy map based on the accuracies computed for the sur-face elements, and^ Instructing the display to visualize a graphical representation of the new accuracymap.By computing accuracy maps for different sub-sets of control points and visualizing those ac-curacy maps, the operator is supported in the interpretation of the data and the accuracy he can achieve during operating the surveying instrument. It is easy for the operator to identifythe influence of a further control point on the accuracy map, and to compare accuracy mapsfor different sub-sets of control points.According to a further aspect of the present invention, there is provided a computer program comprising instructions, which, when executed by a computer system, cause the computersystem to carry out the method according to the present invention. The computer program may be stored on the computer system or on a computer-readable medium communicativelyconnected to the computer system. The term "computer-readable medium" includes, but isnot limited to, portable or non-portable storage devices, optical storage devices, and various other mediums capable of storing, containing, or carrying instruction(s) and / or data.According to a further aspect of the present invention, there is provided an apparatus com-prising means for carrying out the method according to the present invention.Brief Description of the drawingsThe aspects of the invention are described or explained in more detail below, purely by way of example, with reference to working examples shown schematically in the drawing. Identi- cal elements are labelled with the same reference numerals in the figures. The described embodiments are generally not shown true in scale, and they are also not to be interpreted as limiting the invention. Specifically,FIG.1 shows an operator using a surveying instrument deployed at a worksite, thesurveying instrument comprising a measuring unit mounted on a tripod and aremote controller connected via a communication link to the measuring unit,FIGS.2A, B show an exemplary version of the measuring unit used in the surveying instru-ment of FIG.1 (FIG.2A) and a block diagram of the main components of themeasuring unit as illustrated in FIG. 2A (FIG.2B),FIGS.3A, B show an exemplary version of the remote controller used in the surveying in-strument of FIG.1 (FIG.3A) and a block diagram of the main components ofthe remote controller as illustrated in FIG. 3A (FIG. 3B),FIG.4 shows a method for determining for a working area an accuracy map accord-ing to the present invention in a flow chart,FIGS. 5A, B illustrate schematically how a working area can be determined by the operatorusing the surveying instrument (FIG.5A) or by a computer system (FIG.5B),FIG.6 illustrate a graphical user interface of an exemplary implementation of themethod for determining an accuracy map according to the present invention,FIGS.7A-C illustrate the graphical user interface of FIG.6 during stationing of a total sta-tion via a free-stationing process,FIG.8 illustrates a graphical user interface of an exemplary implementation how theoperator can define an accuracy threshold for layout points, andFIGS. 9A, B illustrate the graphical user interface of FIG. 8 during layouting, wherein a pre-defined accuracy threshold can be achieved (FIG.9A) or cannot be achieved (FIG.9B). Detailed Description Reference will now be made in detail to the present preferred embodiment, an example of which is illustrated in the accompanying drawings. It is to be understood that the technology disclosed herein is not limited in its application to the details of construction and the arrange- ment of components set forth in the following description or illustrated in the drawings. The technology disclosed herein is capable of other embodiments and of being practiced or of be- ing carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the pur- pose of description and should not be regarded as limiting. All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in docu- ments incorporated by reference, and / or ordinary meanings of the defined terms.FIG.1 shows an operator using a surveying instrument 10 deployed at a worksite 11. Theworksite 11 may be a construction site, inside or outside, or a surveying site, amongst others.In addition to the surveying instrument 10, a target 12 that is remote from the surveying in-strument 10 may be deployed at the worksite 11. The target 12 may include a reflector 13,such as a prism and / or a cat-eye, that is mounted on top of a pole 14. The surveying instrument 10 is formed as a total station and comprises a measuring unit 15 that is mounted on a mounting support structure in the form of a tripod 16. The surveying in- strument 10 also comprises a removable control panel in the form of a remote controller 17 that can be used for remote control of the measuring unit 15 via a wireless connection 18. Before the operator can use the total station 10 for layouting, measuring and / or other tasks, the total station must be stationed via a stationing process to the worksite 11. From prior art, different stationing processes are known, such as free-stationing process, model-based sta- tioning process, automatic stationing process, or any other stationing process.The basic concept of free-stationing processes is that at an initial phase, a number of controlpoints, here control points CP-1, CP-2, CP-3, CP-4, CP-5, CP-6, are positioned at scatteredlocations at the worksite 11. The control points are materialized by prisms, cat-eyes, reflec-tive foils, or other forms of reflective targets for returning the laser beam from the total sta-tion. The exact location of the control points is determined and logged in terms of coordinateson a specified coordinate frame, here the coordinate frame of the worksite 11.To determine the pose (position and orientation) of the total station 10 in the coordinateframe of the worksite 11, the total station 10 sights a number of the control points and takesmeasurement samples of distance and angle data in its coordinate frame. To differ betweenthe coordinate frames, the coordinate frame of the worksite 11 is called "first coordinateframe" CF-1 and the coordinate frame of the total station 10 is called "second coordinateframe" CF-2. The coordinates in the first coordinate frame CF-1 are called "first coordinates" and the coordinates in the second coordinate frame CF-2 are called "second coordinates". Based on a mathematical equation system, the pose of the total station can be calculated from the first coordinates of the control points in the first coordinate frame CF-1 and from the second coordinates of the control points in the second coordinate frame CF-2. With increas- ing number of measurement samples and a good angular distribution of the control points at the worksite 11 the position accuracy of the pose can increase.FIGS.2A, B show an exemplary version of the measuring unit 15 used in the surveying in-strument 10 of FIG.1 in a perspective view (FIG.2A) and a block diagram of the main com-ponents of the measuring unit 15 as illustrated in FIG. 2A (FIG.2B).The surveying instrument 10 is designed as robotic total station and the measuring unit 15comprises a base 21, a support 22, and a measuring head 23. The measuring head 23 is en-closed by a housing 24, which includes an exit window 25. In the housing 24, a distancemeasuring device that can emit a distance measuring beam and a tracking device that canemit a radiation are arranged. The distance measuring beam and the radiation are emittedthrough the exit window 25 to leave the housing 24.In the exemplary version of FIG.2A, the support 22 is U-formed and includes a bottom por-tion 27, a first side portion 28, and a second side portion 29. The support 22 can rotate com-pletely around its circumference at a full 360° angle with respect to the base 21 about a firstaxis of rotation 31. The measuring head 23 is pivotably mounted to the support 22 about asecond axis of rotation 32 and is arranged between the first side portion 28 and the secondside portion 29 of the support. Usually, the first axis of rotation 31 is aligned parallel to a localdirection of gravitation 33, and the second axis of rotation 32 is aligned perpendicular to the local direction of gravitation 33.An azimuth motor device and a first angle encoder may be located in the bottom portion 27of the support 22 and allow to rotate the measuring unit 15 about the first axis of rotation 31and to determine the direction of the distance measuring beam in a first plane perpendicularto the first axis of rotation 31. An elevation motor device and a second angle encoder may belocated in the first side portion 28 of the support 22 and allow the measuring head 23 to pivot about the second axis of rotation 32 and to determine the direction of the distance measuringbeam in a second plane perpendicular to the second axis of rotation 32. To make the instru-ment 12 fully automatic, a self-leveling device, which may be arranged in the bottom portion27 of the support 22, can be included.FIG.2B shows a block diagram of the main components of the measuring unit 15 of the sur-veying instrument 10. The measuring unit 15 includes a first electronic device 41, a distancemeasuring device 42, a first angle encoder 43, an azimuth motor device 44, a second angleencoder 45, and an elevation motor device 46. Optionally, the measuring unit 15 can addi-tionally include one or more cameras, such as a tracking camera configured to track a reflec- tor target, or an aiming camera configured to let the user aim to a point of interest. The first electronic device 41 comprises a first processing circuit (µP) 50, a first memory cir- cuit 51 that may include associated random-access memory (RAM) and read only memory (ROM), a first communications circuit 52, and a first input / output (I / O) interface circuit 53. Thefirst processing circuit 50, also called device control unit, may communicate with the firstmemory circuit 51 and first communications circuit 52 and is configured to control the laserinstrument 12. The first communications circuit 52 includes a first transmitter circuit 54 and afirst receiver circuit 55 and is configured to be connected to a communications circuit of theremote controller via the communication link. The first input / output interface circuit 53 is aninterface between the first processing circuit 50 and the various types of motor driver circuits and sensor circuits of the measuring unit 15.The distance measuring device 42 includes a laser transmitter 56, a laser driver circuit 57, aphotosensor 58, and a laser receiver interface circuit 59. The laser driver circuit 57 provides current for the laser transmitter 56 which emits a distance measuring beam. The photosensor 58 receives at least a part of the distance measuring beam reflected at a target or a surface of the worksite, and the current signal that is outputted by the photosensor 58 is directed tothe laser receiver interface circuit 59. After appropriate amplification, demodulation and pro-cessing, distance data are sent via the first input / output interface circuit 53 to the first pro-cessing circuit 50. The first angle encoder 43 provides input signals to the first processing circuit 50, so that it knows exactly in which horizontal angle the laser transmitter 56 is arranged in the horizontal plane; the output signal of the first angle encoder 43 is directed to the first input / output inter-face circuit 53. The azimuth motor device 44 includes an azimuth motor 62, which is the mo-tive force to rotate the main housing 22 of the measuring unit 15 about the first axis of rota-tion 31, and an azimuth motor driver circuit 63, which will provide the proper current and volt-age to drive the azimuth motor 62. The second angle encoder 45 provides input signals to the first processing circuit 50, so that it knows exactly in which second angle the laser transmitter 56 is arranged in the second plane; the output signal of the second angle encoder 45 is directed to the first input / outputinterface circuit 53. The elevation motor device 46 includes an elevation motor 65, which isthe motive force to pivot the measuring head 23 about the second axis of rotation 32, and anelevation motor driver circuit 66, which will provide the proper current and voltage to drive theelevation motor 65.FIGS.3A, B show an exemplary version of the remote controller 17 used in the surveying in-strument 10 of FIG.1 in a front view (FIG.3A) and a block diagram of the main componentsof the remote controller 17 as illustrated in FIG. 3A (FIG.3B).The remote controller 17 is designed as tablet computer and includes a housing 81, a touch screen display 82, a battery 83, a set of buttons 84, e.g., volume control button, power on / off button, and display control button, a set of indicators 85, e.g., for operating status, data stor-age status, and battery status, a set of connectors 86, e.g., for docking, data storage, andUSB, and a card slot 87.FIG.3B shows a block diagram of the main components of the remote controller 17. The re-mote controller 17 may include a second electronic device 91, a display device 92, and aninput device 93. The second electronic device 91 comprises a second processing circuit (µP) 94, a secondmemory circuit 95 that may include associated random-access memory (RAM), read onlymemory (ROM), and some type of bulk memory (BULK), a second communications circuit 96, and a second input / output (I / O) interface circuit 97. The second processing circuit 94 may communicate with the second memory circuit 95 and second communications circuit 96 andis configured to control the remote controller 17. The second communications circuit 96 in-cludes a second transmitter circuit 98 and a second receiver circuit 99 and is configured tobe connected to the first communications circuit 52 of the measuring unit 15 via the wirelesscommunication 18. The second input / output interface circuit 97 is an interface between thesecond processing circuit 94 and the various driver circuits of the remote controller 17. In the second memory circuit 95 several program codes having computer-executable instruc- tions for performing a method may be stored. The stored program codes may include a pro-gram code for performing a method for determining for a working area at a worksite, in whicha surveying instrument is deployed, an accuracy map, which shows for the working area atleast one accuracy that can be achieved during operating the surveying instrument. The method for determining an accuracy map is performed by a computer system. The term"computer system" is defined as a device or collection of devices, including input and outputsupport devices, and excluding calculators which are not programmable and capable of be-ing used in conjunction with external files, which contain computer programs, electronic in- structions, input data and output data, that performs logic, arithmetic, data storage and re-trieval, communication control and other functions. The computer system may include, but isnot limited to, processing units, microprocessors, controlling units, microcontrollers, and vari- ous other units capable of processing and / or controlling.In the exemplary version of the surveying instrument 10, the computer system is integratedinto the second processing circuit 94 of the second electronic device 91 of the remote con- troller 17. Alternatively, the computer system may be integrated into the first processing cir- cuit 50, or into the first and second processing circuits 50, 94, or in any other type of suitable processing circuit.The display device 92 includes a display 101 and a display driver circuit 102. The displaydriver circuit will be in communication with the second I / O interface circuit 97 and providesthe correct interface and data signals for the display 101. If the remote controller 17 is a lap-top computer, for example, then this would be the standard display seen in most laptop com-puters. Or, if the remote controller 17 is a tablet computer or a smart phone, in which casethe display device is a much smaller physical device, the display device 101 could be a touchscreen display.The user-operated input device 93 includes a keypad 103 and a keypad driver circuit 104.The keypad driver circuit will be in communication with the second I / O interface circuit 97 andcontrols the signals that interface to the keypad 103. If the display device 101 is a touchscreen display, then there may not be a separate keypad on the remote controller 17, be- cause most of the command or data to input functions will be available by touching the dis-play itself and the keypad is integrated in the touch screen display. There may be some typeof power on / off button, but that would not necessarily be considered a true keypad and typi- cally would not be used for entering data.FIG.4 shows a method for determining for a working area of a worksite, in which a surveyinginstrument is deployed at a station, an accuracy map according to the present invention in aflow chart. The method is performed by the computer system 94.The worksite defines the three-dimensional environment, in which the surveying instrument10 is deployed at a station, and the working area is that part of the worksite, in which the sur-veying instrument 10 is operating, wherein the working area is typically a two-dimensionalarea. The term "station" is used to clarify that the surveying instrument 10 is arranged at afixed position and not moved in the worksite. At its station, the position of the surveying in-strument 10 is fixed, but the head of the surveying instrument 10 can rotate about its axes ofrotation 31, 32.The method for determining an accuracy map for a working area comprises the following steps: ^Dividing the working area in a grid pattern of surface elements (step S10),^ Computing for the station of the surveying instrument 10, a pose vector(ES,  NS,  ori) and corresponding variances (Q^S,^S , Q^S,^S , Qori, ori) and covari-ances (Q^S,^S , Q^S,^^^, Q^S,^^^) for the pose elements of the pose vector(ES,  NS,  ori) (step S20),^ Computing for the surface elements accuracies that can be achieved during oper-ating the surveying instrument 10 based on the pose vector (ES,  NS,  ori), the vari-ances (Q^S,^S , Q^S,^S , Qori, ori) and covariances (Q^S,^S , Q^S,^^^, Q^S,^^^) of the poseelements, on measuring accuracies (^HD, ^HA) of the surveying instrument 10, and on representative coordinates of the surface elements (step S30),^ Computing the accuracy map based on the accuracies computed for the surfaceelements (step S40), and^ Instructing a display 101 to visualize a graphical representation of the accuracymap (step S50).Although the steps of the method are illustrated in a particular order, in some embodiments, one or more steps may be executed in a different order than illustrated in FIG.4. For exam- ple, the steps S10 and S20 can be executed in a different order, but the steps S10 and S20 must be executed before step S30 and the steps S30 to S50 must be executed in that order shown in FIG.4.In step S10, the grid pattern of surface elements is created for the working area. The resolu-tion of the grid pattern and the form the surface elements will adapted to the working area.FIGS. 5A, B show a worksite that is an inside construction worksite limited by walls. Theworking area is that area of the worksite, the operator is interested in and in which the sur-veying instrument 10 is planned to be operated.FIG. 5A shows a first working area WA-1 that is defined by an operator. To define the firstworking area WA-1, the operator can define corner points, here P-1, P-2, P-3, and P-4, and the computer system 94 creates a polygon based on the corner points, or the operatordefines the polygon. For the first working area WA-1, a 11 x 10 grid pattern GP-1 of rectan-gular surface elements is created.FIG. 5B shows a second working area WA-2 that is defined by the computer system 94based on a set of control points, here CP-1, CP-2, …, CP-10, and CP-11, which can be used for stationing processes using control points. For the second working area WA-2, a 55 x 20 grid pattern GP-2 of rectangular surface elements is created.In step S20 of the method shown in FIG.4, the pose vector (ES,  NS,  ori) and correspondingvariances and covariances of the pose elements are computed for the station, at which thesurveying instrument 10 is deployed, by means of well-known methods for stationing a sur-veying instrument. Well-known methods for stationing are free-stationing processes, model-based stationing processes, and automatic stationing processes, but any other stationing process can also be used. With respect to FIG.7, one option how to calculate a pose vectorwill be explained in more detail. In the patent applications WO 2024 / 141424 A1 and WO2024 / 141425 A1, model-based stationing processes for determining a pose for a surveyinginstrument without using a set of control points having known coordinates in the first coordi-nate frame of the worksite are disclosed. In statistics, a covariance matrix is a square matrix giving the covariance values betweeneach pair of elements of a vector. The well-known covariance matrix Qxx of the pose vector(ES,  NS,  ori) can be written as:Q^S,^SQ^S,^SQ^S,^^^Qxx = ^Q^S,^SQ^S,^SQ^S,^^^ ^Q^^^,^SQ^^^,^S oriThe diagonal elements (Q^S,^S , Q^S,^S, Qori, ori) of the covariance matrix represent the vari-ances of the pose elements ES, NS, ori, i.e., covariances of an element with itself, and theoff-diagonal elements (Q^S,^S = Q^S,^S , Q^S,^^^ = Q^^^,^S, Q^S,^^^ = Q^^^,^S) of the covariancematrix represent the covariances between pairs of the pose elements ES,  NS,  ori.In step S30, the accuracies that can be achieved during operating the surveying instrument10 are computed for the surface elements based on the pose vector (ES,  NS,  ori), the vari-ances (Q^S,^S , Q^S,^S , Qori, ori) and covariances (Q^S,^S , Q^S,^^^, Q^S,^^^) of the pose elements,on measuring accuracies of the surveying instrument 10, and on representative coordinatesof the surface elements. Representative coordinates of the surface elements can be a centerpoint or any other point of the surface elements.The accuracy for a surface element can be computed as follows: An arbitrary point OP, thatcorresponds to the representative coordinates of the surface element in the first coordinateframe CF-1 of the worksite, can be denoted by Euclidian coordinates E and N. With the posevector (ES,  NS,  ori), the angle and distance values HA and HD of the arbitrary point OP in thesecond coordinate frame CF-2 of the surveying instrument 10 can be computed by:HA = arctan ori HD = ^(ES − E)^ + (NS − N)^The covariance matrix Σ^, ^ of E and N can be computed through well-known variance propa-gation by: sin(HA + ori)cos(HA + ori)^The accuracy u(OP) that can be achieved at the arbitrary point OP can be denoted byu(OP) = ^^^^^^ Σ^, ^For the surface elements of the grid pattern, the formula u(OP) = ^^^^^^ Σ^, ^ is used tocompute the accuracy that can be achieved during operating the surveying instrument 10.In step S40, the accuracy map, which shows the accuracies that can be achieved during op-erating the surveying instrument 10, is computed based on the accuracies u(OP) computedfor the surface elements in step S30. In step S50, a display is instructed to visualize a graph-ical representation of the accuracy map on the display.The graphical representation of the accuracy map can be a heatmap that depicts values forthe accuracy across two axis as a grid pattern of colored squares, or any other two-dimen-sional representation of data sets. Heatmaps use different colors or different shades of thesame color to represent different data values and to communicate relationships that may ex- ist between the values plotted on the two axes; the two most common schemes are gray-scale and rainbow. In grayscale heatmaps, lighter shades of gray are usually used to repre-sent lower values in the data set, while darker shades, including black, indicate higher datavalues, and rainbow-schemed heatmaps use more colors to indicate the various data values,warmer tones like red and orange indicate higher data values, while cooler tomes like blue and green represent lower data values.The concept of the present invention can be used in combination with any type of workingarea, any type and any resolution of the grid pattern, any form of the surface elements, and any type of graphical representation of the accuracy map.FIG.6 illustrates a graphical user interface of an exemplary implementation of the method fordetermining an accuracy map according to the present invention. The graphical user inter-face allows the operator to define the accuracy map.In the exemplary version, the operator can select the type of graphical representation that isused for visualization and how the working area is defined. The definition of the workingarea, the graphical representation of the accuracy map, and the resolution of the grid patterncan be selected from a menu. In FIG. 6, all three menus are opened for illustration; in prac-tice, only one menu can be open.The working area can be defined by the computer system based on a set of control points ina first coordinate frame of the worksite or the working area can be defined by the operator aspolygon or polyline or corner points. The graphical representation of the accuracy map is agrayscale heatmap or a rainbow-schemed heatmap.FIGS. 7A-C illustrate the graphical user interface of FIG.6 during stationing of the total sta-tion 10. Before an operator can use the total station 10 for layouting, measuring and / or other tasks at the worksite 11, the total station 10 must be stationed via a stationing process to the worksite 11. In the exemplary version, the stationing process is a free-stationing process using a set of control points. At an initial phase, the operator has loaded a floorplan of the worksite and aset of control points CP-1 to CP-13 to the computer system. The control points have knownfirst coordinates in the first coordinate frame CF-1 of the worksite. To determine the pose of the total station 10 in the first coordinate frame CF-1, the total station 10 will sight a number of the control points and take measurement samples of distance and angle data in the sec- ond coordinate frame CF-2 of the total station 10. The measurements can be performed manually by the operator, semi-automatically or full- automatically by the total station 10. In the exemplary version shown in FIG.7A, the control points are materialized by reflector foils (CP-1, CP-11, and CP-12), by two-dimensional cat- eyes (CP2 to CP-10), and by a glass prism (CP-13), and the measurements are performed semi-automatically by the total station 10.For stationing the total station 10, the operator selects a first control point, here control pointCP-2, from the set of control points. Upon the operator`s selection of CP-2 and confirming hisselection by clicking the measurement button 122, the total station 10 is instructed by thecomputer system 94 to measure angle and distance data to the control point CP-2. Once theangle and distance data for the control point CP-2 have been measured, the measurement to CP-2 can be shown by highlighting the control point CP-2 in the floorplan. Then, the operator selects a second control point from the set of control points, here controlpoint CP-13. Upon the operator`s selection of CP-13 and clicking the measurement button122, the total station 10 is instructed by the computer system 94 to measure distance andangle data to the control point CP-13. Once the distance and angle data for CP-13 have been measured, the measurement to CP-13 can be shown by highlighting the control point CP-13 in the floorplan. Since for at least two control points second coordinates are available in the second coordi-nate frame CF-2 of the total station 10, a pose vector, and corresponding variances and co-variances for the pose elements can be computed by the computer system 94 from the firstcoordinates and second coordinates of the control points CP-2 and CP-13 (step S20).The control points CP-2 and CP-13 have known Euclidean coordinates E2, N2 respectivelyE13, N13 in the first coordinate frame CF-1 of the worksite and the angle and distance dataHA2, HD2 respectively HA13 , HD13 have been measured by means of the surveying instru-ment 10.With the assumption that the orientation of the surveying instrument 10 is zero, the Euclideancoordinates E`^ , N^`respectively E`^^ , N `^^ in the second coordinate frame CF-2 can be writtenfor the control points CP-2 and CP-13 as: The Euclidean coordinates can be transformed by means of a rotation matrix R = with rotation angles c, s and a translation vector T = ^t^t^ ^ from the second coordinate frameCF-2 to the first coordinate frame CF-1: Defining the quantities we get for the rotation angles c, s and the value θ:c =^ ^ ^ ^^^^^, s =^^^^^, θ = arctan (^).The translation vector T = ^t^t^ ^ is given by: The pose vector (ES,  NS,  ori) is defined by:E^ = t^, N^ = t^, ori = θAs discussed with respect to FIG. 4, the covariance matrix of the pose vector (ES,  NS,  ori) isa square matrix giving the covariance values between each pair of pose elements of thepose vector (ES,  NS,  ori). The covariance matrix of the pose vector (ES,  NS,  ori) can be esti-mated by means of well-known mathematical methods, such as least-squares formulation. The least-squares method finds the parameters by L+ v = f (X) with arg m^^inv vThe model equation is linearized around an estimated parameter vector X^ with X = X^ +ΔX: L- f (X^)+ v = A(X^)*ΔXFrom the definition of the Jacobian, we have for the components of A: A^^(X^)=∂ / ∂X^f^(X)|^^ ^^The covariance matrix Qxx is computed asQxx = (^^^)^^For the free-stationing method shown in FIG.7B, the model equations for the control pointsCP-2 and CP-13 can be written as follows:HA^ + v^^^ = arctan HD^ + v^^^ = ^(E^ − E^)^ + (N^ − N^)^HA + v^^ = arctan Once the pose vector (ES,  NS,  ori) and the corresponding variances and covariances for thepose elements are computed, the accuracy u(OP) = ^^^^^^ Σ^, ^ that can be achieved fora surface element during operating the total station 10 is computed based on the pose vec-tor, the variances and covariances of the pose elements, on the measurement accuracies^HD, ^HA of the surveying instrument 10, and on representative coordinates of the surface ele-ments (step S30). The details about the formula u(OP) = ^^^^^^ Σ^, ^ are disclosed withrespect to FIG.4, particularly with respect to step S30 of the method shown in FIG.4.Based on the accuracies computed for the surface elements, an accuracy map AM is com-puted by the computer system 94 (step S40). Finally, the display 101 is instructed to visual-ize a graphical representation of the accuracy map AM (step S50).In the exemplary version, the accuracy map AM is a rainbow-schemed heatmap. The accu- racy map AM shows that the accuracies computed based on the pose vector are very inac- curate for a huge part of the working area, the accuracies that can be achieved for the work- ing area during operating the total station 10 vary between 20 mm and 220 mm. For mostlayouting applications, accuracies above 50 mm are not sufficient.Upon visualizing the accuracy map AM corresponding to the control points CP-2 and CP-13,the operator can decide whether a further measurement should be performed, or the station- ing process is over. By clicking the confirm button 122, the stationing process is over and the current values for the pose vector, the corresponding variances and covariances of the poseelements, and the accuracy map AM are used for operating the total station 10.To continue the stationing process, the operator selects as shown in FIG.7C a third controlpoint from the set of control points, here control point CP-10. Upon the operator`s selectionof CP-10 and clicking the measurement button 121, the total station 10 is instructed by thecomputer system 94 to measure angle and distance data to the control point CP-10. Oncethe angle and distance data for CP-10 have been measured, the measurement to CP-10 canbe shown by highlighting the control point CP-10 in the floorplan.Once the second coordinates for control point CP-10 are available, the steps S20, S30, S40and S50 are repeated for the sub-set of the control points CP-2, CP-13, and CP-10. A newpose vector and corresponding variances and covariances for the new pose elements (poseelements of the new pose vector) are computed by the computer system 94 from the first co-ordinates and second coordinates of the control points CP-2, CP-13, and CP-10 (step S20);the new pose vector is a feature that corresponds to the terms "pose vector" and "new posevector" in the present invention. The computation of the pose vector as presented for the control points CP-2 and CP-13(FIG.7B) is only applicable for stationing processes using two control points. A method forcomputing a pose vector based on three or more control points is known as least-square es-timation of Euclidian transformation between two different point patterns. Details about least-square estimation can be found in "Least-squares estimation of transformation parametersbetween two point patterns." Umeyama, Shinji. IEEE Transactions on Pattern Analysis & Ma-chine Intelligence 13.04 (1991): 376-380.Once the new pose vector and the corresponding variances and covariances of the newpose elements are computed, the accuracy u(OP) = ^^^^^^ Σ^, ^ that can be achieved at asurface element during operating the total station 10 is computed based on the new posevector, the corresponding variances and covariances of the new pose elements, on themeasurement accuracies ^HD, ^HA of the surveying instrument 10, and on the representativecoordinates of the surface elements (step S30). The details about the formula u(OP) =^^^^^^ Σ^, ^ are disclosed with respect to FIG.4, particularly with respect to step S30 of themethod shown in FIG.4.Based on the accuracies computed for the surface elements, a new accuracy map AMnew iscomputed by the computer system 94 (step S40); the new accuracy map is a feature thatcorresponds to the terms "accuracy map" and "new accuracy map" in the present invention.Finally, the display 101 is instructed to visualize a rainbow-schemed heatmap as graphicalrepresentation of the new accuracy map AMnew (step S50) as shown in FIG. 7C.The new accuracy map AMnew shows that the accuracies computed based on the new posevector are more accurate than the accuracies computed based on the pose vector. The ac-curacy maps AM and AMnew can support the operator in understanding the quality of the pose vector he achieved during stationing of the total station 10. According to the accuracy map AM shown in FIG.7B, the accuracies that can be achieved at the worksite vary between 20 mm and 220 mm, and, according to the new accuracy map AMnewshown in FIG.7C, the accuracies that can be achieved at the worksite vary between 7 mm and 17 mm. Searching for a layout point, also known as layouting, is a well-known application of a sur- veying instrument at a worksite. The layout point has known coordinates in the first coordi-nate frame of the worksite, and the operator is supported by the surveying instrument insearching for the layout point at the worksite. Upon selecting a layout point and defining anaccuracy threshold that must be achieved during layouting, it is checked by the computersystem 94 if the accuracy threshold can be achieved.Usually, an operator has to search for more than one layout point at the worksite. The layoutpoints may be known from a floorplan of the worksite, and a list of layout points is uploadedto the computer system 94. In many cases, the required accuracy that must be achieved dur- ing layouting is identical.FIG.8 illustrates a graphical user interface of an exemplary implementation how the operatorcan define an accuracy threshold for layout points. The graphical user interface allows theoperator to define the accuracy threshold. In the exemplary version, the operator can selectthe accuracy threshold from a menu of predefined accuracy thresholds, such as 2 mm, 4 mm, 8 mm, or 16 mm, or he can select the option "Other value" and insert any other value for the accuracy threshold.Alternatively, instead of using a fixed accuracy threshold for several layout points, individualaccuracy thresholds can be uploaded together with the list of layout points, or the operatorcan define individual accuracy thresholds for each layout point he is searching for at the worksite.FIGS. 9A, B illustrate the graphical user interface of FIG. 8 during layouting, wherein a pre-defined accuracy threshold can be achieved (FIG.9A) or cannot be achieved (FIG.9B).In FIG.9A, a first layout point, here LP-2, is selected by the operator from a list of layoutpoints that have been uploaded to the computer system 94, the first layout point LP-2 beinglocated in the upper right area of the worksite. The new accuracy map AMnew of FIG.7Cshows that in that upper right area of the worksite, accuracies of 7 mm can be achieved dur-ing operating the total station 10.The accuracy that can be achieved for the first layout point LP-2 is compared by the com-puter system 94 with the defined accuracy threshold of 8 mm, and the operator is informedabout the result of the comparison. Upon verification that the accuracy threshold of 8 mm canbe achieved for the first layout point LP-2, a predefined action is performed, the predefinedaction comprising generating a message stating that the accuracy threshold of 8 mmm canbe achieved for the layout point LP-2.In FIG.9B, a second layout point, here LP-8, is selected by the operator from the list of lay-out points, the second layout point LP-8 being located in the lower right area of the worksite. The new accuracy map AMnewof FIG.7C shows that in that lower right area of the worksite,accuracies of 16 mm can be achieved during operating the total station 10.The accuracy that can be achieved for the second layout point LP-8 is compared by the com-puter system 94 with the defined accuracy threshold of 8 mm, and the operator is informedabout the result of the comparison. Upon verification that the accuracy threshold of 8 mmcannot be achieved for the second layout point LP-8, a predefined action is performed, thepredefined action comprising generating a message stating that the accuracy threshold of 8mm cannot be achieved for the layout point LP-8.

Claims

Claims1. A computer-implemented method for determining for a working area (WA) at a worksite(11), in which a surveying instrument (10) is deployed at a station, an accuracy map (AM,AMnew), which shows for the working area (WA-1, WA-2) at least one accuracy that can be achieved during operating the surveying instrument (10), the method being performedby a computer system (94) and comprising the steps:^ Dividing the working area (WA-1, WA-2) in a grid pattern (GP-1, GP-2) of surfaceelements, ^Computing for the station of the surveying instrument (10), a pose vector(ES,  NS,  ori) and corresponding variances (Q^S,^S , Q^S,^S , Qori, ori) and covariances(Q^S,^S , Q^S,^^^, Q^S,^^^) for the pose elements of the pose vector (ES,  NS,  ori),^ Computing for the surface elements accuracies that can be achieved during oper-ating the surveying instrument (10) based on the pose vector (ES,  NS,  ori), thevariances (Q^S,^S , Q^S,^S , Qori, ori) and covariances (Q^S,^S , Q^S,^^^, Q^S,^^^) of thepose elements, on measuring accuracies (^HD, ^HA) of the surveying instrument(10), and on representative coordinates of the surface elements,^ Computing the accuracy map (AM, AMnew) based on the accuracies computed forthe surface elements, and^ Instructing a display (101) to visualize a graphical representation of the accuracymap (AM, AMnew).

2. Method of claim 1, wherein the working area (WA-2) is computed by the computer sys-tem (94) based on a set of control points.

3. Method of claim 1, wherein the working area (WA-1) is computed by the computer sys-tem (94) based on a polygon or a polyline or a set of corner points (P-1, P-2, P-3, P-4)defined by an operator.

4. Method of any one of claims 1 to 3, wherein the accuracy map is stored in the computersystem (94) and / or stored to a memory connected to the computer system (94) and theaccuracy map is provided for use in operating the surveying instrument (10).

5. Method of claim 4, wherein the accuracy map is provided for use in searching for a layoutpoint and upon selecting the layout point and defining an accuracy threshold, it ischecked by the computer system (94) if the accuracy threshold can be achieved,wherein:^ upon verification that the accuracy threshold can be achieved for the layout point,a predefined action is performed, the predefined action comprising generating a message stating that the accuracy threshold can be achieved for the layout point,and ^upon verification that the accuracy threshold cannot be achieved for the layoutpoint, a predefined action is performed, the predefined action comprising generat- ing a message stating that the accuracy threshold cannot be achieved for the lay-out point.

6. Method of any one of claims 1 to 5, wherein the pose vector and the corresponding vari-ances and covariances for the pose elements of the pose vector are computed by a free-stationing algorithm based on a set of control points (CP-1, …, CP-13) having known first coordinates in a first coordinate frame (CF-1) of the worksite (11) and at least a sub-set(CP-2, CP-13) of the set of control points having known second coordinates in a second coordinate frame (CF-2) of the surveying instrument (10).

7. Method of the previous claim 6, wherein from the set of control points (CP-1, …, CP-13)at least one further control point (CP-10) being different from the sub-set (CP-2, CP-13)of control points is selected, second coordinates are determined for the at least one fur- ther control point (CP-10) by the surveying instrument (10) in the second coordinate frame (CF-2), and a new sub-set (CP-2, CP-13, CP-10) of control points containing thesub-set of control points and the at least one further control point is defined, the methodfurther comprising: ^Computing for the station of the surveying instrument (10), a new pose vector(ES,  NS,  ori) and corresponding variances (Q^S,^S , Q^S,^S , Qori, ori) and covariances(Q^S,^S , Q^S,^^^, Q^S,^^^) for the pose elements of the new pose vector,^ Computing for the surface elements, the accuracies that can be achieved duringoperating the surveying instrument (10) based on the new pose vector(ES,  NS,  ori), the variances (Q^S,^S , Q^S,^S , Qori, ori) and covariances(Q^S,^S , Q^S,^^^, Q^S,^^^) of the new pose elements, on the measuring accuracies(^HD, ^HA) of the surveying instrument (10), and on the representative coordinatesof the surface elements,^ Computing a new accuracy map (AMnew) based on the accuracies computed forthe surface elements, and^ Instructing the display (101) to visualize a graphical representation of the new ac-curacy map (AMnew).

8. A computer program comprising instructions, which, when executed by a computer sys-tem (94), cause the computer system (94) to carry out the method according to any oneof claims 1 to 7.

9. An apparatus comprising means for carrying out the method according to any one ofclaims 1 to 7.

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