Devices and methods for improving survey accuracy

Abstract

Survey apparatus comprising: a measurement device including a plurality of motion sensors and a first locating feature; and a landing plate including a fixing configured to fix a position and / or orien

Description

Technical field The invention relates to improving the accuracy of surveys. In exemplary arrangements, the invention relates to improving the accuracy of surveys of landscaping or construction projects, or of the built environment. Background In many applications, it is desirable to survey a location to understand one or more dimensions and / or the location of features within a survey area. Such applications may include, for example, when preparing for and undertaking work onsite by landscapers or other construction professionals, when surveying the internal or external aspects of a building or other built feature, and when determining topography and features of a land area. Traditional techniques for conducting such surveys include the use of tape measures to determine a 2-dimensional (e.g. X and Y coordinate) survey of a survey area. A level may be used in conjunction with tape measures in order to measure relative elevation. However, these methods are time consuming, require two or more construction professionals to carry out and can suffer from significant inaccuracies. Greater Accuracy can be obtained using a total station to measure relative elevation of the ground at a number of points within the area. However, a total station is an expensive piece of surveying equipment requiring significant skill and experience to operate and is not suitable for the majority of applications, including smaller construction or landscaping projects. In addition, it is possible to use an inertial based measurement tool that can be placed on at a plurality of points in the survey area. Such tools may rely solely on inertial measurement data to determine position and orientation of the tool. The inertial sensors forming part of such devices record data allowing the relative position and elevation of each of the plurality of points to be measured. Such systems work well but can be limited in accuracy, for example due to the motion sensors they use and a dead reckoning approach to positioning. It is desirable to have techniques and systems for mitigating such errors. There is a need for an accurate, efficient and cost effective method for surveying an area that can be implemented in any application without significant training or experience. Summary Methods and apparatus disclosed herein are directed to solving one or more problems in the prior art, including those disclosed herein. According to the invention in a first aspect, there is provided an apparatus for improving accuracy of a survey, the apparatus comprising: a measurement device including: a plurality of motion sensors configured to sense linear and / or rotational movement of the measurement device for determining position and / or orientation of the measurement device; and a first locating feature coupled to the measurement device and having a known alignment with respect to the measurement device; the apparatus further comprising a landing plate including: a fixing configured to fix a position and / or orientation of the landing plate with respect to a region to be surveyed; and a second locating feature configured to engage with the first locating feature such that the measurement device is in a known position and / or orientation with respect to the landing plate, wherein the measurement device further comprises a computer processor configured to: determine an initial position and / or orientation of the measurement device based on initial motion data received from the motion sensors when the first locating feature is engaged with the second locating feature; determine a plurality of survey positions and / or orientations of the measurement device based on survey motion sensor data received from the motion sensors when the measurement device is positioned at a plurality of survey locations in the region to be surveyed; determine a closing position and / or orientation of the measurement device based on closing motion data received from the motion sensors when the first locating feature is engaged with the second locating feature; and determine an error in one or more of the plurality of survey positions and / or orientations based on the initial position and / or orientation, and the closing position and / or orientation. Optionally, the computer processor is configured to determine position and / or orientation based on a dead reckoning approach. Optionally, the motion sensors comprise inertial sensors and optionally comprise an inertial measurement unit. Optionally, the computer processor is configured to determine one or more of the initial position and / or orientation, the plurality of survey positions and / or orientations and the closing position and / or orientation using only the motion sensor data. Optionally, the landing plate comprises a locating plate, and optionally wherein the fixing is configured to fix the locating plate to a surface. Optionally, first locating feature comprises a male portion, and the second locating feature comprises a female portion configured to receive the male portion. Optionally, the male portion comprises an external corner portion, and wherein the female portion comprises an internal corner. Optionally, the landing plate further comprises a guide configured to direct the first locating feature into engagement with the second locating feature. Optionally, the guide comprises a ramp configured to urge the first locating feature down the ramp towards the second locating feature. Optionally, the measurement device comprises a sensor configured to determine whether the first locating feature is engaged with the second locating feature. Optionally, the landing plate further comprises an identifier configured to transmit identification data to the sensor notifying the measurement unit that the first locating feature is engaged with the second locating feature.. Optionally, the sensor is configured to transmit an interrogation signal to the identifier, and wherein the identifier is configured to respond to the interrogation signal with the identification data. Optionally, the apparatus comprises at least one further landing plate, wherein the identification data of each of the landing plate and further landing plate comprises a unique identifier. Optionally, the landing plate further comprises a Globa Navigation Satellite System (GNSS) receiver for determining a geolocation of the landing plate, and wherein the computer processor is further configured to determine a geolocation for one or more of the plurality of survey positions based on the geolocation of the landing plate and the survey motion sensor data. Optionally, the computer processor is further configured to mitigate errors in the survey positions and / or orientations based on the determined error. According to the invention in an aspect, there is provided a method for improving accuracy of a survey conducted using a measurement device that includes a plurality of motion sensors configured to sense linear and / or rotational movement of the measurement device for determining position and / or orientation of the measurement device, and that is connected to a first locating feature having a known alignment with respect to the measurement device, the method comprising: determining an initial position and / or orientation of the measurement device based on initial motion data received from the motion sensors when the first locating feature is engaged with a second locating feature forming part of a landing plate, such that the measurement device is in a fixed position and / or orientation with respect to the region to be surveyed; determining a plurality of survey positions and / or orientations of the measurement device based on survey motion sensor data received from the motion sensors when the measurement device is positioned at a plurality of survey locations in a region to be surveyed; determining a closing position and / or orientation of the measurement device based on closing motion data received from the motion sensors when the first locating feature is engaged with the second locating feature; and determining an error in one or more of the plurality of survey positions and / or orientations based on the initial position and / or orientation, and the closing position and / or orientation. According to the invention in an aspect, there is provided a computer program product comprising computer program code that, when executed on a processor, causes the processor to undertake the steps of any method or part of a method disclosed herein. According to the invention in an aspect, there is provided a landing plate for improving accuracy of a survey conducted using a measurement device that includes a plurality of motion sensors configured to sense linear and / or rotational movement of the measurement device for determining position and / or orientation of the measurement device, and that is coupled to a first locating feature having a known alignment with respect to the measurement device, the landing plate comprising: a fixing configured to fix a position and / or orientation of the landing plate with respect to a region to be surveyed; and a second locating feature configured to engage with the first locating feature such that the measurement device is in a fixed alignment with respect to the region to be surveyed. Optionally, the landing plate further comprising a GNSS receiver for determining a geolocation of the landing plate. According to the invention in an aspect, there is provided a landing plate for improving accuracy of a survey conducted using a measurement device that includes a plurality of motion sensors configured to sense linear and / or rotational movement of the measurement device for determining position and / or orientation of the measurement device, and that is coupled to a first locating feature having a known alignment with respect to the measurement device, the landing plate comprising: a fixing configured to fix a position and / or orientation of the landing plate with respect to a region to be surveyed; a second locating feature configured to engage with the first locating feature such that the measurement device is in a known alignment with respect to the region to be surveyed; a GNSS receiver configured to receive GNSS signals to determine a geolocated position of the landing plate. The landing plate may be configured to transmit data indicative of the geolocation of the landing plate to a processing device. The processing device may be configured to receive motion data from the measurement device. The processing device may be configured to determine apposition and / or orientation of the measurement device based on the motion data. The processing device may be configured to process the motion data and / or the data indicative of the geolocation of the landing plate such that the position and / or orientation of the measurement device is geolocated. It will be appreciated that some or all of the abovementioned functions and / or processing may be undertaken at the measurement device and / or the processing device. According to the invention in an aspect, there is provided a method for improving accuracy of a survey conducted using a measurement device that includes a plurality of motion sensors configured to sense linear and / or rotational movement of the measurement device for determining position and / or orientation of the measurement device, and that is connected to a first locating feature having a known alignment with respect to the measurement device, the method comprising: determining an initial position and / or orientation of the measurement device based on initial motion data received from the motion sensors when the first locating feature is engaged with a second locating feature forming part of a landing plate, such that the measurement device is in a fixed position and / or orientation with respect to the region to be surveyed; receiving, by a GNSS receiver of the landing plate, GNSS data; determining a landing plate geolocation based on the received GNSS data; determining a measurement device geolocation based on the initial position and / or orientation and the landing plate geolocation; determining a plurality of survey positions and / or orientations of the measurement device based on survey motion sensor data received from the motion sensors when the measurement device is positioned at a plurality of survey locations in a region to be surveyed; determining a closing position and / or orientation of the measurement device based on closing motion data received from the motion sensors when the first locating feature is engaged with the second locating feature; and determining an error in one or more of the plurality of survey positions and / or orientations based on the initial position and / or orientation, and the closing position and / or orientation. Brief description of the drawings Embodiments of the disclosed methods and apparatus will be described in detail below, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a system for collecting survey data; Figure 2 is a schematic representation of a measurement device; Figure 3 is a schematic representation of a processing device; Figure 4a is a perspective view of an exemplary landing plate; Figure 4b is a schematic representation of an exemplary landing plate; Figure 5 is an image of a foot that may be coupled to a measurement device; Figure 6 is an image of a housing of a measurement device; Figure 7 is a flow diagram of an exemplary method of improving accuracy of surveys; and Figure 8 is a flow diagram of an exemplary method of improving accuracy of surveys. Detailed Description Generally, disclosed herein are apparatus and methods for surveying an area. The apparatus and methods disclosed improve the accuracy of a survey by determining a closing error. In specific arrangements, the apparatus and methods disclosed may improve the accuracy of measurement devices for surveying an area that make use of a dead reckoning method. For example, measurement devices using inertial sensors. Exemplary apparatus include a landing plate that is configured to receive a measurement device in a fixed position and orientation. The absolute position and orientation of the landing plate within a coordinate system may be known. The landing plate may provide a poka-yoke arrangement that allows a user of a measurement device to begin and end a plurality of survey measurements with the measurement device in the same position and / or orientation. The measurement device is therefore able to determine a closing error, which can be used to mitigate errors in the plurality of survey measurements. It will be appreciated that the above is only one exemplary arrangement intended to aid the reader in understanding the invention and need not be limiting on the scope of the invention. Other arrangements, including those discussed herein, are covered by the scope of the invention, which is defined by the claims. As used herein, the term ‘landing plate, may encompass any apparatus for receiving the measurement device (or something coupled to the measurement device) in a known alignment. In specific arrangements, the landing plate need not have a plate like structure, although that is the embodiment described herein. Figure 1 shows a schematic representation of an exemplary system 100 for collecting survey data. The system 100 comprises a measurement device 102 and a processing device 104. Detailed descriptions of exemplary measurement and processing devices 102, 104 are given below. Broadly, the measurement device 102 comprises one or more sensors arranged to obtain measured data representing the measurement device’s position and / or orientation. For example, the one or more sensors may be motion sensors configured to record linear accelerations and / or rotational velocities. The measurement device 102 is configured to transmit to the processing device 104 measured data representing its position and / or orientation. The processing device 104 includes a processor for determining survey data based on the measured data. The processing device 104 may be configured to present an indication of the survey data to a user. In some exemplary arrangements, the processing device 104 may be configured to export data representing at least part of the determined survey data. The exported data may, for example, be suitable for representation in CAD software, or the like. It will be appreciated that at least part of the processing of the measured motion and distance data may be undertaken at the measurement device 102 before transmission to the processing device 104. It will also be appreciated that the processing device 104 may form part of the measurement device 102 and they may be housed within a single unit. In exemplary arrangements, the measurement device 102 may be a hand-held or otherwise portable unit suitable for being carried in a user’s hand. In exemplary arrangements, the processing device 104 may be a portable processing device, such as a mobile phone, tablet or laptop computer. The transmission of measured data from the measurement device 102 to the processing device 104 is shown in Figure 1 as a wireless transmission 106. The wireless transmission may be a radio frequency transmission using known hardware and communications protocols, such as Bluetooth (RTM), near field communication (NFC), Wi-Fi (RTM), network based communications (e.g. the internet) or mobile telecommunications protocols. The wireless transmission 106 may also use optical transmission hardware and protocols. The transmission may be at least partially wired and, in some arrangements, could be fully wired. The processing device 104 may also transmit data to the measurement device 102 via the same, or a different, communications medium and / or protocol. The transmission of measured motion data may be substantially in real time. For example, measurements may be recorded and data representing those measurements transmitted as soon as possible thereafter, e.g. on an open communications link. In some arrangements, the transmission of data may be intermittent and / or from time-to-time. For example, the measuring device may record a plurality of measurements and store data representing the plurality of measurements for transmission at a later time. In such arrangements, the transmission may be triggered manually, e.g. after all measured data has been collected, or may be triggered by the measurement device 102 detecting an open communication channel (either direct or indirect) to the processing device 104. Figure 2 shows a schematic representation of a measurement device 102, which may be the measurement device 102 in Figure 1. The measurement device 102 comprises a transmitter 202 and, optionally, a receiver 204. The transmitter 202 and receiver 204 may be in data communication with other entities, such as the processing device 104 or servers and / or functions in a telecommunications network, and are configured to transmit and receive data accordingly. The measurement device 102 further comprises a memory 206 and a processor 208. The memory 206 may comprise a non-volatile memory and / or a volatile memory. The memory 206 may have a computer program 210 stored therein. The computer program 210 may be configured to undertake all or part of methods disclosed herein. The computer program 210 may be loaded in the memory 206 from a non-transitory computer readable medium 212, on which the computer program is stored. The measurement device 102 may also comprise motion sensors 214 (e.g. inertial sensors). In specific arrangements, the motion sensors 214 may consist of only inertial sensors. The inertial sensors may consist of MEMs sensors. The processor 208 is configured to undertake one or more of the functions necessary for operation of one or more of the elements of the measurement device 102. The inertial sensors 214 may comprise accelerometers and / or rate gyros. The inertial sensors 214 may be arranged to measure acceleration and rotational velocity of the measurement device 102 in three orthogonal axes, typically identified as x-axis, y-axis and z-axis. The accelerations and rotational velocities may be recorded in a body frame (i.e., a frame fixed in relation to the measurement device 102 and defined by the x, y and z axes) and converted to any other reference frame (e.g. a local reference frame based on the land area or a construction site) using well known techniques. The inertial sensors 214 may form part of an Inertial Measurement Unit (IMU) housed within the measurement device 102. The inertial sensors 214 may incorporate micro-electro-mechanical systems (MEMS) technology. Throughout this document, inertial sensors are referred to, although it should be understood that other motion and / or positioning sensors might be employed as an alternative or in addition to the inertial sensors in some embodiments. Such motion and / or positioning sensors might include any sensor that is able to detect rotational and / or linear movement of the measurement device 102. These may include, as examples only, sensors using technology relating to GNSS, doppler, cellular positioning, wi-fi positioning, cameras, LiDAR etc. However, in a specific arrangement, the measurement device may determine position and / or orientation using only inertial sensors. The measurement device 102 may also include a landing plate sensor 216 configured to sense that a measurement device 102 is located on a landing plate 400. The landing plate sensor 216 may comprise a short range communication device, such as an NFC transmitter of tag, or an RFID transmitter or tag. The short range communication device may be configured to communicate with a corresponding short range communication device located in the landing plate 400. The skilled person will be able to envisage other means for achieving the same purpose, which may include physical features, such as microswitches and / or electronics such as transmitters / receivers or a combination thereof. In specific arrangements, the landing plate sensor 216 may receive a unique identifier from the landing plate, such that the measurement device 102 can determine which of a plurality of landing plates 400 it is positioned on. The measurement device 102 may be a portable and in some cases handheld device. In exemplary arrangements, the measurement device 102 and the processing device 104 may be combined and may together be portable and / or handheld. In specific arrangements, the measurement device 102 and / or the processing device 104 may be a handheld tool suitable for use by a construction worker. The handheld tool may be carried from a first position to a second position for measuring relative location of the first and second positions. Each of the transmitter 202 and receiver 204, memory 206, processor 208, and inertial sensors 214 is in data communication with the other features of the measurement device 102. The measurement device 102 can be implemented as a combination of hardware and software. In particular, software may be configured to run on the processor 208. The memory 206 stores the various programs / executable files that are implemented by the processor 208, and also provides a storage unit for any required data. Figure 3 shows a schematic representation of a processing device 104, which may be the processing device 104 in Figure 1. The processing device 104 comprises a receiver 304 and optionally a transmitter 302. The transmitter 302 and receiver 304 may be in data communication with other entities, such as measurement device 102 or servers and / or functions in a telecommunications network, and are configured to transmit and receive data accordingly. The processing device 104 further comprises a memory 306 and a processor 308. The memory 306 may comprise a non-volatile memory and / or a volatile memory. The memory 306 may have a computer program 310 stored therein. The computer program 310 may be configured to undertake the methods disclosed herein. The computer program 310 may be loaded in the memory 306 from a non-transitory computer readable medium 312, on which the computer program 310 is stored. The processor 308 is configured to undertake the functions of a position and orientation determiner 314 and an error mitigator 316. The processing device 104 also optionally comprises a display 322 and a user interface 324. Each of the transmitter 302 and receiver 304, memory 306, processor 308, display 322 and user interface 324 is in data communication with the other features of the processing device 104. The processing device 104 can be implemented as a combination of hardware and software. In particular, the position and orientation determiner 314 and error mitigator 316 may be implemented as software configured to run on the processor 308. The memory 306 stores various programs / executable files that are implemented by the processor 308, and also provides a storage unit for any required data. The programs / executable files stored in the memory 306, and implemented by the processor 308, can include the position and orientation determiner 314 and error mitigator 316, but are not limited to such. Figure 4a shows a perspective view of a landing plate 400. In the example shown, the landing plate 400 is a plate that may be fixed to a surface. However, it will be appreciated that the landing plate 400 may have other forms and a plate is used only as an example. Accordingly, the term ‘landing plate’ may be construed as encompassing arrangements that do not have a plate-like structure. The landing plate 400 comprises a substantially flat base plate 402. The flat base plate 402 comprises a fixing, which in the exemplary arrangement of Figure 4 comprises a plurality of through holes 404. The through holes are located at edges of the base plate 402 and are configured to receive nails, screws pegs or the like so as to secure the base plate to a surface. In other arrangements, the fixing may comprise an adhesive, Velcro (RTM) or the like for fixing to fabric based surfaces, or the landing plate 400 may comprise one or more protrusions configured to be inserted into a surface. The skilled person will be able to envisage other types of fixing. In exemplary arrangements, the fixing is configured to secure the position and orientation of the landing plate 400. That is, once the landing plate 400 is secured using the fixing, it will be held in position and be unable to rotate. The landing plate 400 further comprises a landing plate locating feature 406. The locating feature 406 is configured to engage with a corresponding locating feature coupled to the measurement device 102 (described below). In the exemplary arrangement of Figure 4, the locating feature 406 provides a female arrangement that is configured to receive a male arrangement of the measurement device locating feature. Specifically, the locating feature 406 comprises at least two walls 408a, 408b. The walls 408a, 408b are aligned transverse to one another and in the arrangement of Figure 4a are perpendicular. The transverse walls 408a, 408b provide surfaces against which corresponding surfaces of the measurement device locating feature may be retained, thereby fixing position and orientation of the measurement device 102 with respect to the landing plate 400. The transverse walls 408a, 408b form a corner even though they do not intersect or meet at a vertex. The landing plate 400 includes a guide 410 for urging the locating feature of the measurement device 102 into the locating feature 406 of the landing plate 400. In the exemplary arrangement of Figure 4a, the guide 410 comprises a ramp 412. The ramp 412 is angled such that downward force applied to the measurement device 102 is translated to lateral force on the measurement device 102, moving the locating feature of the measurement device 102 towards and into engagement with the landing plate locating feature 406. In other arrangements, other guides may be used. Further, other locating features may be used, for example the locating features may comprise elements suitable for implementing a latch fit or a snap fit. Other locating features may be used, for example the locating feature 406 may be a male arrangement and the measurement device locating feature may be a female arrangement. Figure 4b shows a schematic representation of an exemplary landing plate 400. The landing plate 400 of Figure 4b may have electronics installed therein and may therefore be considered ‘smart’. It is noted that other exemplary landing plates 400 may include some or none of the electronic components shown in Figure 4b. The landing plate 400 optionally comprises a transmitter 420 and a receiver 422. The transmitter 420 and receiver 422 may be in data communication with other entities, such as measurement device 102 or servers and / or functions in a telecommunications network, and are configured to transmit and receive data accordingly. In specific arrangements, as an alternative or in addition to the transmitter 420 and receiver 422, the landing plate 400 may comprise a landing plate identifier 434 configured to sense that a measurement device 102 is located thereon and notify the measurement device 102 that it is located on the landing plate 400. The landing plate identifier 434 may comprise a short range communication device, such as a NFC transmitter or tag, or an RFID transmitter or tag. The short range communication device may be configured to communicate with a corresponding short range communication device located in the measurement device 102. The skilled person will be able to envisage other means for achieving the same purpose. In specific arrangements, the landing plate identifier 434 may provide a unique identifier to the measurement device 102 such that the measurement device 102 knows which of a plurality of landing plates 400 it is positioned on. The landing plate 400 may optionally further comprise a memory 424 and a processor 426. The memory 424 may comprise a non-volatile memory and / or a volatile memory. The memory 426 may have a computer program 428 stored therein. The computer program 428 may be configured to undertake methods disclosed herein. The computer program 428 may be loaded in the memory 424 from a non-transitory computer readable medium 430, on which the computer program 428 is stored. The landing plate 400 may optionally include a GNSS receiver configured to determine the position of the landing plate 400, such that it may be geolocated. The landing plate 400 can be implemented as a combination of hardware and software configured to run on the processor 426. The memory 424 stores various programs / executable files that are implemented by the processor 426, and also provides a storage unit for any required data. The programs / executable files are stored in the memory 424, and implemented by the processor 426. Figure 5 shows a foot 500 that may be coupled to a measurement device 102. In exemplary arrangements, the foot 500 may be coupled to the measurement device 102. In some arrangements, the foot 500 is configured to receive the measurement device 102 and, in the case of the exemplary arrangement of Figure 5, the foot 500 includes a slot 501 into which the measurement device 102 is received. Alternatively, the foot 500 may be coupled to the measurement device 102 via an elongate member or support, such as a pole. In such arrangements, the measurement device 102 may be located at a proximal end of the elongate member, which is uppermost in use. The foot may be located at a distal end. The foot may be positioned at various locations in the survey area in order to determine position and / or orientation at those locations. The relative position and / or orientation of the measurement device 102 to the foot 500 may be known. The foot 500 comprises a plate 502 having a flat bottom surface 504. The plate 502 includes a foot (or measurement device) locating feature 506 that is configured to engage with the landing plate locating feature 406. In the exemplary arrangement shown in Figure 5, the foot locating feature 506 comprises first and second straight edges 508a, 508b that are arranged to abut the walls 408a, 408b of the landing plate 400. Accordingly, the angle between the straight edges 508a, 508b may correspond to the angle between the walls 408a, 408b. When the straight edges 508a, 508b abut the walls 408a, 408b the horizontal position of the foot 500 is known relative to the landing plate 400. Further, because two edges abut two walls, the orientation of the foot 500 with respect to the landing plate 400 is also known. If vertical positioning is required then the vertical position of the foot 500 is known relative to the landing plate 400 as the base of the foot 500 abuts the surface of the landing plate 400. It will be apparent to the skilled person that other locating features may be used on the landing plate 400 and the plate 500. For example, the foot locating feature may be configured to fit within an aperture forming at least part of the landing plate locating feature and retaining the foot in both position and orientation. The locating features may have any poka-yoke arrangement that results in the foot locating feature engaging with the landing plate locating feature to result in a known relative position and orientation between the two. The foot 500 comprises a straight rear edge 510 that is configured to align with the guide 412, and specifically in this exemplary arrangement, to align with the surface of the ramp 412. A distance from the bottom of the ramp 412 to a point on the walls 408a, 408b is the same or greater than the corresponding distance from the straight rear edge 510 to a corresponding point on the straight edges 508a, 508b. This arrangement allows a user to more easily engage the foot locating feature 506 with the landing plate locating feature 406. The straight rear edge 510 contacts the ramp 412 and downward force is translated into lateral force urging the foot locating feature 506 into engagement with the landing plate locating feature 406. Figure 6 shows an exemplary measurement device 102. The measurement device 102 may comprise a measurement device locating feature 600 that is configured to engage with the landing plate locating feature 406 in ways similar to those discussed above. Accordingly, the description of the foot 500 may apply equally to the measurement device 102 and is not repeated here. In one specific arrangement, the measurement device 102 may include straight edges 602a, 602b that are configured to abut the walls 408a, 408b. Figure 7 is a flow diagram showing an exemplary method for improving accuracy of surveys. The steps identified in Figure 7 use the foot 500 as an example, although the same steps may be used with the measurement device 102 alone. The foot locating feature 506 is engaged 700 with the landing plate locating feature 406. In the exemplary arrangements shown in the drawings, this may be done by engaging the straight rear edge 510 of the foot 500 with the ramp 412. The straight rear edge 510 slides down the ramp 412 urging the straight edges 508a, 508b of the foot locating feature 506 into engagement with the walls 408a, 408b. At step 702, an initial position and orientation of the measurement device 102 is determined. This is done by the position and orientation determiner 314 of the processor 308 of the processing device. Specifically, the processing device 104 receives motion data recorded by the motion sensors 214 of the measurement device 102 and determines the initial position and orientation of the measurement device 102 based on the motion data. In exemplary arrangements, the initial position and orientation may be determined based solely on the motion data. At step 704, the measurement device is placed at one or more survey locations within a survey area. The survey locations may, for example, identify the location of a feature, such as a building, a driveway, a pool or a lawn. Alternatively, the survey locations may be indoors and identify rooms of a building or fixed features such as kitchen islands. At each survey location, the position and / or orientation of the measurement device 102 is determined 706 by the position and orientation determiner 314 of the processor 308 of the processing device 104. Specifically, the processing device 104 receives motion data recorded by the motion sensors 214 of the measurement device 102 while the measurement device 102 is travelling to and stationary at a survey location and determines the position and / or orientation of the measurement device 102 based on the motion data. In exemplary arrangements, the position and / or orientation may be determined based solely on the motion data. At step 708, it is determined whether more survey locations are to be surveyed. If yes then the method returns to step 704. If not then the method continues to step 710, where the foot 500 is engaged with the landing plate 400 in the same way as discussed above. At step 712, a closing position and / or orientation of the measurement device 102 is determined. This is done by the position and orientation determiner 314 of the processor 308 of the processing device 104. Specifically, the processing device 104 receives motion data recorded by the motion sensors 214 of the measurement device 102 while the foot 500 is engaged with the landing plate 400 and determines the closing position and / or orientation of the measurement device based on the motion data. In exemplary arrangements, the closing position and / or orientation may be determined based solely on the motion data. At step 714, an error between the initial position and / or orientation and the closing position and / or orientation is determined by the error mitigator 316. The error mitigator 316 may then use the determined error to update 716 the position and / or orientation of the survey locations, thereby improving the accuracy of the survey. In exemplary arrangements, a user may notify the measurement device 102 and / or the processing device 104 when they have placed the measurement device 102 on a landing plate 400. This may allow the processing device 104 to correctly identify landing plate locations and process motion data accordingly. In other arrangements, the processing device 104 may be configured to determine when the measurement device 102 is located on a landing plate 400 based on the motion data recorded by the motion sensors 214. In yet further arrangements, the landing plate sensor 216 of the measurement device 102 may be configured to determine when the measurement device is positioned on a landing plate 400. For example, the landing plate sensor 216 may comprise a communications device, such as an NFC or RFID device. Accordingly, the landing plate sensor 216 may comprise an NFC or RFID transmitter arranged to receive a response from an NFC or RFID tag located in the landing plate 400. The reverse configuration is also possible. Other short range communications protocols and apparatus may also be used. In this way, the measurement device 102 may determine whether it is positioned at a landing plate 400 without input from the user or more complicated and less robust methods incorporating inertial sensor data processing. In some use cases it may be beneficial to position a plurality of landing plates 400 in a survey area. Each of the plurality of landing plates 400 may have a unique identifier. The unique identifier may be transmitted from each landing plate 400 to the measurement device 102 by the landing plate identifier 434. The unique identifier may be embedded within an NFC or RFID tag and form part of the response received by the measurement device 102. Alternatively, the unique ID may be transmitted by the transmitter 420. A user may distribute a plurality of landing plates 400 in an area to be surveyed. The measurement device 102 (e.g. using the foot 500) may then be positioned at a first landing plate 400, followed by each of the further landing plates 400 in turn. The measurement device 102 may then be positioned again at the first (or any other) landing plate 400 such that errors can be determined and compensated for. This provides the location of each landing plate 400. The locations can be associated with the corresponding landing plate’s unique identifier. After the locations of the landing plates 400 have been determined, the user may position the measurement device 102 at the first landing plate 400 (or any other of the landing plates) before being positioned at a plurality of survey locations. At any time during the survey, the user may place the measurement device 102 at any of the landing plates 400. This allows errors in the survey measurements to be determined and compensated for during the survey, rather than waiting until the end of the survey and placing the measurement device at the first landing plate 400 again to determine any closing errors. This provides advantages when a survey is conducted over a large area and some survey locations are a long distance from the first landing plate 400. As discussed with reference to Figure 4b, the landing plate may include a GNSS receiver 436. The GNSS receiver 436 may be configured to record GNSS data and transmit it to the processing device 104, such that a geolocation of the landing plate 400 may be determined. Alternatively, the processor 426 of the landing plate 400 may be configured to undertake all or part of the processing of the GNSS data. Figure 8 shows a further method. The landing plate 400 is positioned at a suitable location. In this example, the landing plate 400 includes the GNSS receiver 436. Accordingly, the landing plate is preferably positioned with a clear view of the sky. The fixing is used to secure the landing plate 400 in position. At step 802, the GNSS receiver 436 collects GNSS data that is then processed to provide a geolocation for the landing plate 400. The GNSS data may be processed by the processor 426 of the landing plate 400. In some arrangements, the GNSS data may be transmitted to the processing device 104 and processed by the processing device 104. The GNSS data may be processed using techniques that improve the accuracy of the determined geolocation, for example carrier phase or real time kinematic GNSS. It is noted that the GNSS data need not be processed in the order shown in Figure 8 and can instead be processed later, possibly after the survey is complete. The foot locating feature 506 is engaged 804 with the landing plate locating feature 406. In the exemplary arrangements shown in the drawings, this may be done by engaging the straight rear edge 510 of the foot 500 with the ramp 412. The straight rear edge 510 slides down the ramp 412 urging the straight edges 508a, 508b of the foot locating feature 506 into engagement with the walls 408a, 408b. At step 806, an initial position and / or orientation of the measurement device 102 is determined. This is done by the position and orientation determiner 314 of the processor 308 of the processing device 104. Specifically, the processing device 104 receives motion data recorded by the motion sensors 214 of the measurement device 102 and determines the initial position and orientation of the measurement device 102 based on the motion data. In exemplary arrangements, the initial position and / or orientation may be determined based solely on the motion data. The initial position and / or orientation is determined relative to the landing plate 400 and may therefore be geolocated based on the geolocation of the landing plate 400. Accordingly, the landing plate 400 may be configured to transmit data to the processing device 104 that is indicative of the geolocated position of the landing plate 400. The transmitted data may be raw GNSS data, partially processed GNSS data and / or a geolocation determined based on the GNSS data. The processing device 104 may therefore process the motion data to determine the initial position relative to the geolocation of the landing plate 400. At step 808, the measurement device is placed at one or more survey locations within a survey area. The survey locations may, for example, identify the location of a feature, such as a building, a driveway, a pool or a lawn. Alternatively, the survey locations may be indoors and identify rooms of a building or fixed features such as kitchen islands. At each survey location, the position and / or orientation of the measurement device 102 is determined 810 by the position and orientation determiner 314 of the processor 308 of the processing device 104. Specifically, the processing device 104 receives motion data recorded by the motion sensors 214 of the measurement device 102 while the measurement device 102 is travelling to and stationary at a survey location and determines the position and / or orientation of the measurement device 102 based on the motion data. In exemplary arrangements, the position and / or orientation may be determined based solely on the motion data. As mentioned above, the position and / or orientation is determined relative to the landing plate 400 and may therefore be geolocated based on the geolocation of the landing plate 400. At step 812, it is determined whether more survey locations are to be surveyed. If yes then the method returns to step 704. If not then the method continues to step 814, where the foot 500 is engaged with the landing plate 400 in the same way as discussed above. At step 816, a closing position and / or orientation of the measurement device 102 is determined. This is done by the position and orientation determiner 314 of the processor 308 of the processing device 104. Specifically, the processing device 104 receives motion data recorded by the motion sensors 214 of the measurement device 102 while the foot 500 is engaged with the landing plate 400 and determines the closing position and / or orientation of the measurement device based on the motion data. In exemplary arrangements, the closing position and / or orientation may be determined based solely on the motion data. At step 818, an error between the initial position and / or orientation and the closing position and / or orientation is determined by the error mitigator 316. The error mitigator 316 may then use the determined error to update 820 the position and / or orientation of the survey locations, thereby improving the accuracy of the survey. In a similar way to that described above, a plurality of landing plates 400 may be used. At least one of the landing plates 400 may include the GNSS receiver 436. In such configurations, the user may position the measurement device 102 (e.g. using the foot 500) at a first landing plate 400, followed by each of the further landing plates 400 in turn. The measurement device 102 is then positioned again at the first (or any other) landing plate 400 such that errors can be determined and compensated for. This provides the location of each landing plate 400 and because at least one of the landing plates 400 includes the GNSS receiver 436, each of the landing plates may be geolocated based on their relative positions. The locations can be associated with the corresponding landing plate’s unique identifier. After the locations of the landing plates 400 have been determined, the user may position the measurement device 102 at the first landing plate 400 (or any other of the landing plates) before being positioned at a plurality of survey locations. At any time during the survey, the user may place the measurement device 102 at any of the landing plates 400. Alternatively, each of the plurality of landing plates 400 may include the GNSS receiver 436. In such configurations, each of the landing plates 400 may determine its own geolocation. A computer program may be configured to provide any of the above described methods. The computer program may be provided on a computer readable medium. The computer program may be a computer program product. The product may comprise a non-transitory computer usable storage medium. The computer program product may have computer-readable program code embodied in the medium configured to perform the method. The computer program product may be configured to cause at least one processor to perform some or all of the method. Various methods and apparatus are described herein with reference to block diagrams or flowchart illustrations of computer-implemented methods, apparatus (systems and / or devices) and / or computer program products. It is understood that a block of the block diagrams and / or flowchart illustrations, and combinations of blocks in the block diagrams and / or flowchart illustrations, can be implemented by computer program instructions that are performed by one or more computer circuits. These computer program instructions may be provided to a processor circuit of a general purpose computer circuit, special purpose computer circuit, and / or other programmable data processing circuit to produce a machine, such that the instructions, which execute via the processor of the computer and / or other programmable data processing apparatus, transform and control transistors, values stored in memory locations, and other hardware components within such circuitry to implement the functions / acts specified in the block diagrams and / or flowchart block or blocks, and thereby create means (functionality) and / or structure for implementing the functions / acts specified in the block diagrams and / or flowchart block(s). Computer program instructions may also be stored in a computer-readable medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable medium produce an article of manufacture including instructions which implement the functions / acts specified in the block diagrams and / or flowchart block or blocks. A tangible, non-transitory computer-readable medium may include an electronic, magnetic, optical, electromagnetic, or semiconductor data storage system, apparatus, or device. More specific examples of the computer-readable medium would include the following: a portable computer diskette, a random access memory (RAM) circuit, a read-only memory (ROM) circuit, an erasable programmable read-only memory (EPROM or Flash memory) circuit, a portable compact disc read-only memory (CD-ROM), and a portable digital video disc readonly memory (DVD / Blu-ray). The computer program instructions may also be loaded onto a computer and / or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer and / or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions / acts specified in the block diagrams and / or flowchart block or blocks. Accordingly, the invention may be embodied in hardware and / or in software (including firmware, resident software, micro-code, etc.) that runs on a processor, which may collectively be referred to as “circuitry,” “a module” or variants thereof. It should also be noted that in some alternate implementations, the functions / acts noted in the blocks may occur out of the order noted in the flowcharts. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality / acts involved. Moreover, the functionality of a given block of the flowcharts and / or block diagrams may be separated into multiple blocks and / or the functionality of two or more blocks of the flowcharts and / or block diagrams may be at least partially integrated. Finally, other blocks may be added / inserted 5 between the blocks that are illustrated. It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed systems and methods. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed systems 10 and methods. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.

Claims

1. An apparatus for improving accuracy of a survey, the apparatus comprising:a measurement device including:a plurality of motion sensors configured to sense linear and / or rotational movement of the measurement device for determining position and / or orientation of the measurement device; anda first locating feature coupled to the measurement device and having a known alignment with respect to the measurement device;the apparatus further comprising a landing plate including:a fixing configured to fix a position and / or orientation of the landing plate with respect to a region to be surveyed; anda second locating feature configured to engage with the first locating feature such that the measurement device is in a known position and / or orientation with respect to the landing plate,wherein the measurement device further comprises a computer processor configured to:determine an initial position and / or orientation of the measurement device based on initial motion data received from the motion sensors when the first locating feature is engaged with the second locating feature;determine a plurality of survey positions and / or orientations of the measurement device based on survey motion sensor data received from the motion sensors when the measurement device is positioned at a plurality of survey locations in the region to be surveyed;determine a closing position and / or orientation of the measurement device based on closing motion data received from the motion sensors when the first locating feature is engaged with the second locating feature; anddetermine an error in one or more of the plurality of survey positions and / or orientations based on the initial position and / or orientation, and the closing position and / or orientation.

2. The apparatus according to claim 1, wherein the computer processor is configured to determine position and / or orientation based on a dead reckoning approach.

3. The apparatus according to claim 1 or 2, wherein the motion sensors comprise inertial sensors and optionally comprise an inertial measurement unit.

4. The apparatus according to any preceding claim, wherein the computer processor is configured to determine one or more of the initial position and / or orientation, the plurality of survey positions and / or orientations and the closing position and / or orientation using only the motion sensor data.

5. The apparatus according to any preceding claim, wherein the landing plate comprises a locating plate, and optionally wherein the fixing is configured to fix the locating plate to a surface.

6. The apparatus according to any preceding claim, wherein first locating feature comprises a male portion, and the second locating feature comprises a female portion configured to receive the male portion.

7. The apparatus according to claim 6, wherein the male portion comprises an external corner portion, and wherein the female portion comprises an internal corner.

8. The apparatus according to any preceding claim, wherein the landing plate further comprises a guide configured to direct the first locating feature into engagement with the second locating feature.

9. The apparatus according to claim 8, wherein the guide comprises a ramp configured to urge the first locating feature down the ramp towards the second locating feature.

10. The apparatus according to any preceding claim, wherein the measurement device comprises a sensor configured to determine whether the first locating feature is engaged with the second locating feature..

11. The apparatus according to claim 10, wherein the landing plate further comprises an identifier configured to transmit identification data to the sensor notifying the measurement unit that the first locating feature is engaged with the second locating feature..

12. The apparatus according to claim 11, wherein the sensor is configured to transmit an interrogation signal to the identifier, and wherein the identifier is configured to respond to the interrogation signal with the identification data.

13. The apparatus according to claim 11 or 12, comprising at least one further landing plate, wherein the identification data of each of the landing plate and further landing plate comprises a unique identifier.

14. The apparatus according to any preceding claim, wherein the landing plate further comprises a GNSS receiver for determining a geolocation of the landing plate, and wherein the computer processor is further configured to determine a geolocation for one or more of the plurality of survey positions based on the geolocation of the landing plate and the survey motion sensor data.

15. The apparatus according to any preceding claim, wherein the computer processor is further configured to mitigate errors in the survey positions and / or orientations based on the determined error.

16. A method for improving accuracy of a survey conducted using a measurement device that includes a plurality of motion sensors configured to sense linear and / or rotational movement of the measurement device for determining position and / or orientation of the measurement device, and that is connected to a first locating feature having a known alignment with respect to the measurement device, the method comprising:determining an initial position and / or orientation of the measurement device based on initial motion data received from the motion sensors when the first locating feature is engaged with a second locating feature forming part of a landing plate, such that the measurement device is in a fixed position and / or orientation with respect to the region to be surveyed;determining a plurality of survey positions and / or orientations of the measurement device based on survey motion sensor data received from the motion sensors when the measurement device is positioned at a plurality of survey locations in a region to be surveyed;determining a closing position and / or orientation of the measurement device based on closing motion data received from the motion sensors when the first locating feature is engaged with the second locating feature; anddetermining an error in one or more of the plurality of survey positions and / or orientations based on the initial position and / or orientation, and the closing position and / or orientation.

17. A computer program product comprising computer program code that, when executed on a processor, causes the processor to undertake the steps of claim 16.

18. A landing plate for improving accuracy of a survey conducted using a measurement 5 device that includes a plurality of motion sensors configured to sense linear and / or rotational movement of the measurement device for determining position and / or orientation of the measurement device, and that is coupled to a first locating feature having a known alignment with respect to the measurement device,the landing plate comprising:10 a fixing configured to fix a position and / or orientation of the landing plate withrespect to a region to be surveyed; anda second locating feature configured to engage with the first locating feature such that the measurement device is in a fixed alignment with respect to the region to be surveyed.1519. The landing plate according to claim 18 further comprising a GNSS receiver for determining a geolocation of the landing plate.s

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