Method for optimizing and visualizing a layout area

Abstract

A computer-implemented method for optimizing for a worksite, in which a surveying instrument is deployed at a station, a layout area, in which accuracies not larger than a predefined accuracy threshold can be achieved during operating the surveying instrument, the method being performed by a computer system and comprising the steps: - Defining a plurality of groups of at least two control points from a set of control points, wherein the control points having known first coordinates in a first coordinate frame of the worksite and known second coordinates in a second coordinate frame of the surveying instrument, - Computing for the plurality of groups of control points a pose vector and corresponding variances and covariances for the pose elements of the pose vector, - Computing a layout area for each group of the plurality of groups of control points based on the pose, the variances and covariances, on measuring accuracies of the surveying instrument, and the accuracy threshold, - Computing an evaluation parameter for each group of the plurality of groups of control points, wherein the evaluation parameter is at least one of a surface area of a full circle and an intersecting area of the full circle and a predefined working area of the worksite, - Comparing the layout areas of the plurality of groups of control points based on the evaluation parameter and a predefined evaluation criterion, - Selecting as best layout area the layout area of that group of control points that fulfills the evaluation criterion best, and - Instructing a display to visualize a graphical representation of the best layout area (LAY).

Description

[0001]HILTI Aktiengesellschaft in SchaanPrincipality of Liechtenstein Method for optimizing and visualizing a layout area.The present invention relates to a method for optimizing in a worksite a layout area accordingto the definition of claim 1, to a computer program according to the definition of claim 7, andto an apparatus according to the definition of claim 8. 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 highly precise electronic dis-tance measuring device and accurate motors to rotate this electronic distance measuring de-vice, and angle measuring devices. Centered within a total station is its coordinate frame andthe orientation of the coordinate frame is usually such that the stations x-axis pointing to-wards right, y-axis pointing towards 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 geometric 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 retro-re-flective targets for returning the laser beam to the total station. The exact location of eachcontrol point is determined and logged in terms of coordinates on a specified coordinateframe, typically the coordinate frame of a floorplan of the worksite. A total station can thensight a number of these control points to determine its absolute position on that X, Y, Z coor-dinate frame using standard triangulation techniques.In operation, the operator determines the distance and angle data successively for eachcontrol point. These data are stored in the total station's computer system together with theabsolute 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 knownas a free-stationing algorithm, to determine its pose from the sightings of those controlpoints. The positioning accuracy of a total station is inversely proportional to the square rootof the number of control points it can exploit from its location, the angular distribution of thosecontrol points, as well as the stability of the worksite at which the control points and the totalstation are 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 functionalitythat shows to the operator a recommended working area that is a polygon created by thecontrol 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 achieved duringmeasuring and / or layouting with the total station and the pose is not used for determining theworking area. Summary of the inventionTherefore, what is desired is a method for optimizing a layout area, in which accuracies notlarger than a predefined accuracy threshold can be achieved during measuring and / or lay-outing with a surveying instrument. An operator of the surveying instrument should be sup-ported in the interpretation of the quality of the pose and in the accuracy, he can achieve dur- ing 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-implemented method for optimizing for a worksite, in which a surveying instrument is deployed at a station, a layout area, in which accuracies not larger than an accuracy threshold can be achievedduring operating the surveying instrument, the method being performed by a computer sys-tem and comprising the steps: ^Defining a plurality of groups of at least two control points from a set of controlpoints, wherein the control points having known first coordinates in a first coordinate frame of the worksite and known second coordinates in a second coor- dinate frame of the surveying instrument, ^Computing for the plurality of groups of control points a pose vector and corre-sponding variances and covariances for the pose elements of the pose vector,^ Computing a layout area for each group of the plurality of groups of control pointsbased on the pose vector, the variances and covariances of the pose elements ofthe pose vector, on measuring accuracies of the surveying instrument, and the ac-curacy threshold, ^Computing an evaluation parameter for each group of the plurality of groups ofcontrol points, wherein the evaluation parameter is at least one of a surface area of a full circle and an intersecting area of the full circle and a predefined workingarea of the worksite, ^Comparing the layout areas of the plurality of groups of control points based onthe evaluation parameter and a predefined evaluation criterion, ^Selecting as best layout area the layout area of that group of control points thatfulfills the evaluation criterion best, and ^Instructing a display to visualize a graphical representation of the best layout area.The method for optimizing a layout area according to the present invention supports the op- erator of the surveying instrument in understanding the results he achieved during stationing of the surveying instrument. The layout area is computed by the computer system based onthe pose, the variances and covariances for the station, based on measuring accuracies, andthe predefined accuracy threshold. The operator is supported by a graphical representation of the layout area. The values represented by the layout area would normally be muchharder for the operator to understand if presented numerically in a spreadsheet, especially ifthe data set is large or complex. The layout area enables operators to visualize data and un-derstand it easily. The operator can easily check via the graphical representation if he canachieve the required accuracy during layouting or measuring with the surveying instrument atthe worksite.Preferably, the layout area is defined by a circular contour line having a center defined by(ES,  NS) +^ ^ ^Q^S,ori, − Q^S,ori^ and a radius defined by2 ^ ^S S^^S S^^^ ^^^ ,or^^ ^ u^ ,^ ^ ,^ ^^ S i ^S,ori^ − ^ + ^^, with c = Qori,ori + σ ^^^ . The curves of equal accuracyare concentric circles having the same center, wherein the radius of the circles increases with increasing accuracy threshold.The layout area can be defined as full circle, in which accuracies not larger than the accuracythreshold can be achieved during operating the surveying instrument, or the layout area canbe an intersecting area of the full circle and a predefined working area, in which the survey- ing instrument is deployed. The inside of the contour line corresponds to the layout area, inwhich accuracies not larger than the accuracy threshold can be achieved, whereas at theoutside of the contour line accuracies not larger than the accuracy threshold cannot beachieved.Preferably, the layout area is related to the worksite and stored in the computer systemand / or stored to a memory connected to the computer system and the layout area is pro-vided for use in operating the surveying instrument. By providing the layout area for use inoperating the surveying instrument, the operator is supported in the interpretation of the data, he can easily check via the graphical representation of the layout area if he can achieve the required accuracy.Preferably, the layout area is provided for use in layouting a point of interest and upon select-ing the point of interest, it is checked by the computer system whether the point of interest is located inside of the layout area or outside of the layout area, wherein: ^upon verification that the point of interest is located inside of the layout area, a prede-fined action is performed, the predefined action comprising generating a message stating that the point of interest is located inside of the layout area and / or that the ac- curacy threshold can be achieved, and^ upon verification that the point of interest is located outside of the layout area, a pre-defined action is performed, the predefined action comprising generating a message stating that the point of interest is not located inside of the layout area and / or that the accuracy threshold cannot be achieved.By checking via the computer system whether a point of interest selected for layouting is lo-cated inside or outside of the layout area, the operator is supported in achieving the required accuracy.In a preferred embodiment, the at least one accuracy threshold comprises at least a first ac-curacy threshold and a second accuracy threshold different from the first accuracy thresholdand in the step of computing the layout area, a first layout area is computed by the computersystem for the first accuracy threshold and a second layout area is computed for the secondaccuracy threshold. By using a first accuracy threshold to compute a first layout area and asecond accuracy threshold to compute a second layout area, the operator can be supportedin the interpretation of different accuracies he can achieve during layouting and / or measuring with the surveying instrument.Preferably, a first graphical representation of the first layout area is displayed, a secondgraphical representation of the second layout area is displayed, or the first graphical repre-sentation of the first layout area and the second graphical representation of the second lay-out area are displayed. During layouting with a surveying instrument at a worksite, at whichthe surveying instrument is deployed, different accuracies can be required.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 programmay 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 optimizing a layout area according to the present inven-tion in a flow chart,FIGS. 5A, B illustrate a graphical user interface showing a first type of layout area formedas a full circle (FIG.5A) and a second type of layout area formed as an inter- secting area (FIG.5B),FIGS. 6A, B illustrate an exemplary version of a layout area formed as full circle in a firstgraphical representation (FIG.6A) and in a second graphical representation(FIG.6B),FIGS. 7A, B illustrate a graphical user interface of an exemplary implementation of themethod for optimizing a layout area according to the present invention,FIGS. 8A, B illustrate the graphical user interface of FIG.7 during stationing of a total sta-tion via a free-stationing process, andFIGS. 9A-C illustrate schematically a first graphical representation (FIG.9A), a secondgraphical representation (FIG.9B), and a first and second graphical represen-tation (FIG. 9C).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.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 andprocessing, 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 to be 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 worksite, at which a surveying in-strument is deployed, a layout area, in which accuracies not larger than a predefined accu-racy threshold can be achieved during operating the surveying instrument.The method for determining a layout area is performed by a computer system. The term"computer system" is defined as a device or collection of devices, including input and output support 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 is not 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 type of 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 optimizing for a worksite, in which a surveying instrument is de-ployed at a station, a layout area according to the present invention in a flow chart. The sur-veying instrument 10 deployed at the worksite 11 and the computer system 94 can be usedto perform the method according to the present invention. The worksite defines the three-dimensional environment, in which the surveying instrument 10 is deployed at a station, and the layout area defines at the worksite 11 an area, in whichaccuracies not larger than a predefined accuracy threshold u can be achieved during operat-ing the surveying instrument 10. The term "station" is used to clarify that the surveying instru-ment 10 is arranged at a fixed position and not moved in the worksite. At its station, the posi- tion of the surveying instrument 10 is fixed, but the head of the surveying instrument 10 can rotate about its axes of rotation 31, 32.Measurements with the surveying instrument 10 are usually described by a well-establishederror model, where angle and distance measurements are treated as independent randomvariables with measuring accuracies σHA for the horizontal angle HA and σHD for the hori-zontal distance HD. The method for optimizing a layout area according to the present invention is performed by the computer system 94 and comprises the following steps: ^Defining a plurality of groups of at least two control points from a set of controlpoints, wherein the control points having known first coordinates in the first coordi-nate frame CF-1 of the worksite 11 and known second coordinates in the secondcoordinate frame CF-2 of the surveying instrument 10 (step S10),^ Computing for each group of the plurality of groups of control points a pose vector(ES,  NS,  ori) and corresponding variances (Q^S,^S , Q^S,^S , Qori, ori) and covari-ances (Q^S,^^^, Q^S,^^^) for the pose elements of the pose vector (step S20), ^Computing a layout area for each group of the plurality of groups of control pointsbased on the pose vector (ES,  NS,  ori), the variances (Q^S,^S , Q^S,^S , Qori, ori) andcovariances (Q^S,^^^, Q^S,^^^) of the pose elements of the pose vector, the meas-uring accuracies (σHA,  σHD) of the surveying instruments, and the accuracythreshold u (step S30),^ Computing an evaluation parameter for each group of the plurality of groups ofcontrol points, wherein the evaluation parameter is at least one of a surface areaof a full circle and an intersecting area of the full circle and a predefined workingarea of the worksite, (step S40),^ Comparing the layout areas of all groups of the plurality of groups of control pointsbased on the evaluation parameter and a predefined evaluation criterion (stepS50), ^Selecting as best layout area the layout area of that group of the plurality ofgroups of control points that fulfills the evaluation criterion best (step S60), and^ Instructing a display (101) to visualize a graphical representation of the best lay-out area (step S70).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 S20, S30 and S40 can be executed for each group of the plurality of groups ofcontrol points separately or each of the steps S20, S30 and S40 is executed for all groups ofthe plurality of groups of control points.In step S40, an evaluation parameter is computed for each group of the plurality of groups of control points, wherein the evaluation parameter is at least one of a surface area of a full cir-cle and an intersecting area of the full circle and a predefined working area of the worksite. Instep S50, the layout areas of the plurality of groups of control points are compared based onthe evaluation parameter and a predefined evaluation criterion; the evaluation criterion canbe the largest surface area of the full circle or the largest intersecting area of the full circleand the working area. In step S60, the layout area of that group of control points that fulfillsthe evaluation criterion best is selected as best layout area.The pose of the total station can be calculated by a free-stationing process, a model-based stationing process, an automatic stationing process, or any other stationing process. For thefree-stationing process that is used according to the present invention, at least two controlpoints are used, the control points having known first coordinates in the first coordinate frame CF-1 of the worksite 11 and known second coordinates in the second coordinate frame CF-2of the surveying instrument 10.In statistics, a covariance matrix is a square matrix giving the covariance values between each pair of elements of a given random 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^^^,^SQori, oriThe diagonal elements (Q^S,^S , Q^S,^S, Qori, ori) of the covariance matrix represent the vari-ances of the variables ES and NS, i.e., covariances of an element with itself, and the off-diag-onal elements (Q^S,^S = Q^S,^S, Q^S,^^^ = Q^^^,^S, Q^S,^^^ = Q^^^,^S) of the covariance matrixrepresent the covariances between pairs of the pose elements ES,  NS,  ori.An observation point OP can be denoted by variables HD and HA with HD being a horizontaldistance and HA being a horizontal angle. With the pose (ES,  NS,  ori), the coordinates E andN of the observation point OP can be computed by:−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 H sin(HA + ori)cos(HA + ori)^The accuracy u(OP) that can be achieved at the observation point OP can be denoted by Curves of equal accuracy u can be denoted byu = ^^^^^^ Σ^, ^ = const.The curves of equal accuracy u = const. take the form of concentric circles and can be trans-formed to equations for the center and the radius. The center is defined in the first coordinateframe CF-1 of the worksite 11 by:  −The radius is defined by: 2 ^ ^S S^^S S^^^ ^^^ ,or^^ ^ u^ ,^ ^ ,^ ^^ S i ^S,ori. As discussed with reference to FIG.4, the layout area, in which accuracies not larger thanthe accuracy threshold u can be achieved during operating the surveying instrument 10,takes the form of a circle. FIGS.5A, B illustrate a graphical user interface showing a firsttype of layout area formed as a full circle (FIG.5A) and a second type of layout area formed as an intersecting area (FIG.5B). FIG.5A illustrates the graphical user interface showing the first type of layout area. The lay- out area is formed as a full circle that is projected onto a two-dimensional plan of the worksite. FIG.5B illustrates the graphical user interface showing the second type of layout area. The layout area is formed as intersecting area of the full circle and a predefined work- ing area at the worksite. In practice, the operator is interested in that section of the working area, in which he can achieve accuracies smaller than the predefined accuracy threshold.The intersecting area visualizes that section of the working area. The working area can bedefined by the operator as polygon, or the computer system can define the working area aspolygon that is defined by the set of control points that is used for the stationing process of the total station 10. Both types of layout area allow an operator to easily check if he can achieve the required ac-curacy during layouting or measuring with the surveying instrument at the worksite. The firstand second type of layout area enable the operator to visualize data and understand it easily.FIGS. 6A, B illustrate an exemplary version of a layout area formed as full circle in a firstgraphical representation (FIG.6A) and in a second graphical representation (FIG.6B).FIG.6A shows the first graphical representation that contains a contour line 111 of equal ac-curacy, wherein the inside of the contour line is filled. The first graphical representation of thelayout area is called "full circle (positive)" and refers to the feature "graphical representation" of the present invention.FIG.6B shows the second graphical representation that contains the contour line 111 ofequal accuracy, wherein the outside of the contour line is filled. The second graphical repre-sentation of the layout area is called "full circle (negative)" and refers to the feature "graphicalrepresentation" of the present invention.FIGS. 7A, B illustrate a graphical user interface of an exemplary implementation of themethod for optimizing a layout area according to the present invention. Before an operator can use the total station 10 for layouting, measuring and / or other tasks at the worksite, the total station 10 must be stationed via a stationing process to the worksite 11. In the exemplary version shown in FIG.7A, the stationing process is a free-stationing pro- cess using a set of control points. At an initial phase, the operator has loaded a floorplan ofthe worksite and a set of control points CP-1 to CP-13 to the computer system 94. The con-trol points have known first 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 second coordinate frame CF-2 of the total station 10. The measurements can be performed manually by the operator, semi-automatically or auto- matically by the total station 10. In the exemplary version, 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 glass prisms (CP-13) and the measurements are performed semi-automatically bythe total station 10. The operator selects a control point from the set of control points by click- ing and confirms his selection by clicking a measurement button 121. FIG.7B illustrates the graphical user interface that allows the operator to define the layout area. In the exemplary version shown in FIG.7B, the operator can select the accuracy threshold that is used for computing the layout area and the type of layout area that is usedfor visualization. As discussed with reference to FIGS. 5 and 6, the layout area can be a fullcircle (positive), a full circle (negative) or an intersecting area of the full circle and the working area. The accuracy threshold and the type of layout area can be selected from a menu. In FIG.7B, both menus for the accuracy threshold and the type of layout area are shown. This is done for illustration. In practice, only one menu can be shown. Instead of using predefined values for the accuracy threshold as shown in FIG.7B, the accuracy threshold can be defined by the operator by setting a value in millimeters.FIGS.8A, B illustrate the graphical user interface of FIG. 7 during stationing of the total sta-tion 10 via a free-stationing process. As explained with respect to FIG.7, the operator hasloaded a floorplan of the worksite and the control points CP-1 to CP-13 to the computer sys-tem 94. Before an operator can start the method for optimizing a layout area, the total station 10 has to take measurement samples of distance and angle data in the second coordinate frameCF-2 of the total station 10. FIG.8A shows measurement samples for five control points, CP-7, CP-13, CP-2, CP-10, and CP-8. Since the measured distance and the CAD information derived from the floorplan do not match for the control point CP-8, this control point is excluded from computing the pose and the layout area. The control points CP-7, CP-13, CP-2, and CP-10 define the set of control points that is usedfor optimizing the layout area. If the operator defines a minimum number of three controlpoints necessary for computing the pose of the surveying instrument 10, a plurality of fivegroups of control points can be defined by the computer system 94 in order to determine alayout area, and if the operator defines a minimum number of two control points necessaryfor computing the pose of the surveying instrument 10, a plurality of eleven groups of controlpoints can be defined by the computer system 94 in order to determine a layout area.In the exemplary versions of the layout area shown in FIGS. 5 to 8, the accuracy thresholdcomprises one value. Alternatively, the accuracy threshold can comprise a first accuracythreshold u1 and a second accuracy threshold u2 different from the first accuracy threshold.In the step S20 of computing the layout area, a first layout area L-1 corresponding to the firstaccuracy threshold a second layout area L-2 corresponding to the second accuracythreshold u2 can be computed by the computer system 94. In the step S30 of visualizing agraphical representation of the layout area, a first graphical representation of the first layoutarea, a second graphical representation of the second layout area, or the first graphical rep-resentation of the first layout area and the second graphical representation of the second lay-out area can be displayed. FIGS. 9A-C illustrate the three options how to visualize the firstand second layout areas.In the exemplary version of FIG.9, the first graphical representation is a first contour line re-lated to the first accuracy threshold (FIG. 9A), and the second graphical representation isa second contour line related to the second accuracy threshold u2 (FIG. 9B). In Fig. 9C, thefirst contour line and the second contour line are displayed. The layout area that is determined during stationing of the total station 10 is provided for usein layouting a point of interest POI. Upon selecting the point of interest POI by the operator, itis checked by the computer system 94 whether the selected point of interest POI is locatedinside or outside of the layout area.As shown in FIG. 9A, the point of interest POI is located outside of the (first) layout area L-1.Upon verification that the point of interest POI is located outside of the (first) layout area L-1,a predefined action can be performed. The predefined action may comprise generating amessage stating that the point of interest POI is not located inside of the (first) layout areaand / or that the (first) accuracy threshold cannot be achieved.As shown in FIG. 9B, the point of interest POI is located inside of the (second) layout area L-2. Upon verification that the point of interest POI is located inside of the (second) layout areaL-2, a predefined action can be performed. The predefined action may comprise generating amessage stating that the point of interest POI is located inside of the (second) layout areaand / or that the (second) accuracy threshold can be achieved.

Claims

Claims1. A computer-implemented method for optimizing for a worksite (11), in which a surveyinginstrument (10) is deployed at a station, a layout area, in which accuracies not larger than apredefined accuracy threshold (u) can be achieved during operating the surveying in-strument (10), the method being performed by a computer system (94) and comprisingthe steps: ^Defining a plurality of groups of at least two control points from a set of controlpoints (CP-2, CP-7, CP-10, CP-13), wherein the control points having known firstcoordinates in a first coordinate frame (CF-1) of the worksite (11) and known sec- ond coordinates in a second coordinate frame (CF-2) of the surveying instrument (10), ^Computing for each group of the plurality of groups of control points a pose vector(ES,  NS,  ori) and corresponding variances (Q^S,^S , Q^S,^S , Qori, ori) and covariances(Q^S,^^^, Q^S,^^^) for the pose elements of the pose vector,^ Computing a layout area for each group of the plurality of groups of control pointsbased on the pose vector (ES,  NS,  ori), the variances (Q^S,^S , Q^S,^S , Qori, ori) andcovariances (Q^S,^^^, Q^S,^^^) of the pose elements of the pose vector, on measur-ing accuracies (σHA ,  σHD) of the surveying instrument (10), and the accuracythreshold (u),^ Computing an evaluation parameter for each group of the plurality of groups ofcontrol points, wherein the evaluation parameter is at least one of a surface areaof a full circle and an intersecting area of the full circle and a predefined workingarea of the worksite,^ Comparing the layout areas of all groups of the plurality of groups of control pointsbased on the evaluation parameter and a predefined evaluation criterion, ^Selecting as best layout area the layout area of that group of the plurality ofgroups of control points that fulfills the evaluation criterion best, and^ Instructing a display (101) to visualize a graphical representation (LAY) of the bestlayout area.

2. Method according to claim 1, wherein the layout area is defined by a circular contour line^− ^ a radius defined by^ − ^ + ^^, c = ori,ori ^^.

3. Method of any one of claims 1 to 2, wherein the layout area is related to the worksite (11)and stored in the computer system (94) and / or stored to a memory connected to the com-puter system (94) and the layout area is provided for use in operating the surveying in-strument (10).

4. Method of claim 3, wherein the layout area is provided for use in layouting a point of inter-est (POI) and upon selecting the point of interest (POI), it is checked by the computer system (94) whether the point of interest (POI) is located inside of the layout area or out- side of the layout area, wherein: ^upon verification that the point of interest (POI) is located inside of the layout area,a predefined action is performed, the predefined action comprising generating a message stating that the point of interest (POI) is located inside of the layout area and / or that the accuracy threshold can be achieved, and^ upon verification that the point of interest (POI) is located outside of the layoutarea, a predefined action is performed, the predefined action comprising generat- ing a message stating that the point of interest (POI) is not located inside of the layout area and / or that the accuracy threshold cannot be achieved.

5. Method of any one of claims 1 to 4, wherein the at least one accuracy threshold com-prises at least a first accuracy threshold (u1) and a second accuracy threshold (u2) differ-ent from the first accuracy threshold (u1) and in the step of computing the layout area, afirst layout area (L-1) corresponding to the first accuracy threshold (u1) and a second lay-out area (L-2) corresponding to the second accuracy threshold (u2) are computed by thecomputer system (94).

6. Method of the previous claim 5, wherein a first graphical representation of the first layoutarea (L-1) is displayed, a second graphical representation of the second layout area (L-2)is displayed, or the first graphical representation of the first layout area (L-1) and the sec-ond graphical representation of the second layout area (L-2) are displayed.

7. 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 6.

8. An apparatus comprising means for carrying out the method according to any one ofclaims 1 to 6.

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