Devices and methods for determining survey elevation

Abstract

A system for determining an elevation of a survey location comprises: a barometric reference device including: a reference barometric sensor 216 configured to measure reference barometric pressure whi

Description

Technical field The invention relates to methods and apparatus for determining an elevation (or height) of a survey measurement. In particular, the invention may relate to, but need not be limited to, the use of barometric sensors to determine elevation of a survey measurement. Background For many applications, it is necessary to have accurate survey data relating to the built and / or natural environments. Such applications include construction and landscaping projects. In order to produce such survey data, the positions and / or dimensions of a number of features of the built and / or natural environments must be measured in relation to other features within a survey area. The survey area may include one or more buildings or structures and / or an area of land. In many applications, it is desirable forthose positions to be measured in three dimensions, including horizontal and vertical dimensions. Known techniques for determining elevation (also known as height) of features in a survey include the use of spirit levels and tape measures, or other linear distance measuring means. However, methods using these apparatus are time consuming, can often require the involvement of two construction professionals and are prone to significant error. It is also known to use survey equipment, such as a surveying level and / or a total station, to provide a survey of, for example, a land area. A total station allows the positions of a number of features of a survey area to be measured in three dimensions. A surveying level allows the accurate measurement of the elevation of a feature. However, for many applications, a surveying level and / or a total station are not appropriate tools to conduct a survey. These tools are expensive and require skilled operation. For many smaller construction and / or landscaping projects, this might be described as overkill. It is known to use Global Navigation Satellite Systems (GNSS) to determine elevation in a survey. As with the survey tools mentioned above, this solution is expensive and suffers from significant inaccuracies, particularly in elevation, if the GNSS data is not augmented by some other data, such as atmospheric correction data. This solution also requires the survey to be conducted in an open area where satellite signals can be received and accurately isolated. There is a need for an accurate, efficient and cost effective method for surveying features of the built and natural environments and determining their elevation. 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 an aspect, there is provided a system fordetermining an elevation of a survey location, the system comprising: a barometric reference device including: a reference barometric sensor configured to measure reference barometric pressure while the reference barometric sensor is at a fixed elevation; and a transmitter configured to transmit data indicative of the measured reference barometric pressure, the system further comprising a measuring device including: a plurality of motion sensors configured to obtain motion data representing position and orientation of the measuring device based on rotational and linear movement of the measuring device in a body frame comprising orthogonal x, y and z axes; a survey barometric pressure sensor configured to measure survey barometric pressure at a plurality of survey locations, and a transmitter configured to transmit the measured survey barometric pressure and the motion data; the system further comprising a processing device including: a receiver configured to receive the data indicative of the measured reference barometric pressure, the measured survey barometric pressure and the motion data, and a first computer processor configured to: determine a corrected barometric pressure based on the data indicative of the measured reference barometric pressure and the measured survey barometric pressure; determine an elevation of the plurality of survey locations based on the corrected barometric pressure and the motion data. Optionally, the data indicative of the measured reference barometric pressure includes one or more of: the measured reference barometric pressure; and barometric error. Optionally, the barometric reference device includes a second computer processor configured to determine an initial barometric pressure, and wherein the transmitter is configured to transmit the initial barometric pressure. Optionally, the initial barometric pressure comprises an average of a plurality of reference barometric pressures measured overtime. Optionally, the measuring device comprises a third computer processor configured to calibrate the survey barometric pressure sensor based on the initial barometric pressure. Optionally, the first computer processor is configured to determine a horizontal position of the plurality of survey locations based on the motion data. Optionally, the first computer processor is configured to determine elevation and / or horizontal position of the plurality of survey locations based on an algorithm having inputs comprising: the data indicative of the measured reference barometric pressure; the motion data; and the measured survey barometric pressure. Optionally, the algorithm comprises a Kalman filter. According to the invention in an aspect, there is provided a method of determining an elevation of a survey location, the method comprising: measuring, by a reference barometric sensor of a barometric reference device, a reference barometric pressure, wherein the reference barometric pressure has been measured while the reference barometric sensor is at a fixed elevation; transmitting, by a transmitter of the barometric reference device, data indicative of the measured reference barometric pressure; obtaining, from a plurality of motion sensors forming part of a measuring device, motion data representing position and orientation of the measuring device based on rotational and linear movement of the measuring device in a body frame comprising orthogonal x, y and z axes; measuring, by a survey barometric pressure sensor of the measuring device, survey barometric pressure at a plurality of survey locations; transmitting, by a transmitter of the measuring device, the motion data and the measured survey barometric pressure; receiving, by a receiver of a processing device, the measured reference barometric pressure, the measured survey barometric pressure and the motion data; determining, by a first computer processor of the processing device, a corrected barometric pressure based on the data indicative of the measured reference barometric pressure and the measured survey barometric pressure; and determining, by the first computer processor, an elevation of the plurality of survey locations based on the corrected barometric pressure and the motion data. According to the invention in an aspect, there is provided a processing device for determining an elevation of a survey location, the processing device comprising: a receiver configured to: receive, from a barometric reference device, data indicative of a reference barometric pressure, wherein the reference barometric pressure has been measured while the reference barometric sensor is at a fixed elevation; receive, from a measuring device, survey barometric pressure measured at a plurality of survey locations, and motion data obtained from a plurality of motion sensors forming part of the measuring device, the motion data representing position and orientation of the measuring device based on rotational and linear movement of the measuring device in a body frame comprising orthogonal x, y and z axes; and a first computer processor configured to: determine a corrected barometric pressure based on the data indicative of the measured reference barometric pressure and the measured survey barometric pressure; determine an elevation of the plurality of survey locations based on the corrected barometric pressure and the motion data. According to the invention in an aspect, there is provided a method of determining an elevation of a survey location, the method comprising: receiving, from a barometric reference device, data indicative of a reference barometric pressure, wherein the reference barometric pressure has been measured while the reference barometric sensor is at a fixed elevation; receiving, from a measuring device, survey barometric pressure measured at a plurality of survey locations, and motion data obtained from a plurality of motion sensors forming part of the measuring device, the motion data representing position and orientation of the measuring device based on rotational and linear movement of the measuring device in a body frame comprising orthogonal x, y and z axes; determining, by a first computer processor, a corrected barometric pressure based on the data indicative of the measured reference barometric pressure and the measured survey barometric pressure; determining, by the first computer processor, an elevation of the plurality of survey locations based on the corrected barometric pressure and the motion data. According to the invention in an aspect, there are provided computer program products configured, when executed on a computer processor, to control a processing device to undertake one or more of the steps of any of the methods disclosed herein. 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 determining elevation of a survey location; Figure 2 is a schematic representation of a measuring device; Figure 3 is a schematic representation of a processing device; Figure 4 is a schematic representation of a barometric reference device; Figure 5A is Detailed Description Generally, disclosed in this specification are methods and apparatus for determining an elevation of a feature of the natural or built environment during a survey using barometric pressure. In described arrangements, the elevation of a feature is determined using differential barometric pressure data. As used in this specification, the term “differential barometric pressure data” encompasses barometric pressure data recorded by a reference barometric sensor positioned at a known or fixed elevation. A measurement device includes a barometric pressure sensor arranged to determine an elevation of the device (and thereby the feature). A reference barometric pressure sensor may be placed at a reference location having a known or fixed elevation. The reference location may be within a particular range of the feature. Changes in barometric pressure sensed by the reference barometric pressure sensor are due to barometric pressure errors and may be used to correct the barometric pressure sensed by the measuring device. As used in this specification, barometric pressure errors encompass factors that cause a change in barometric pressure without a change in elevation. These factors may include wind speed and temperature. In the arrangements discussed in this specification, a topographical survey is used as an exemplary application. It will be understood that the methods and apparatus disclosed may be used in other applications and / or environments. Figure 1 shows a schematic representation of an exemplary system 100. The system 100 comprises a measuring device 102 and a processing device 104 and a barometric reference device 106. Detailed descriptions of exemplary measuring device 102, processing devices 104 and barometric reference device 106 are given below. Broadly, the measuring device 102 comprises one or more sensors arranged to obtain measured data representing position and / or orientation. For example, the one or more sensors may be configured to record linear accelerations and rotational velocities. One or more sensors may be configured to measure barometric pressure. The measuring device 102 is configured to transmit to the processing device 104 measured data representing its position and / or orientation and survey barometric pressure. The measuring device 102 may transmit raw measurement data and / or data that is at least partially processed into position and 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 construction worker. 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. The barometric reference device 106 is configured to determine barometric error data and transmit it to the processing device 104 for correcting the survey barometric data. It will be appreciated that at least part of the processing of the measured motion and pressure data may be undertaken at the measuring device 102 and / or the barometric reference device 106 before transmission to the processing device 104. It will also be appreciated that the processing device 104 may form part of the measuring device 102 and they may be housed within a single unit. In exemplary arrangements, the measuring device 102 may be a hand-held or otherwise portable unit suitable for being carried by a construction worker. 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 data between the measuring device 102, the processing device 104 and the barometric reference device 106 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, Wi-Fi, network based communications (e.g. the internet) or mobile telecommunications protocols. The wireless transmission 108 may also use optical transmission hardware and protocols. The transmission may be at least partially wired or cabled and, in some arrangements, could be fully wired. The transmission of measured motion data and barometric pressure 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 measuring device 102 upon detecting an open communication channel (either direct or indirect) to the processing device 104. Figure 2 shows a schematic representation of a measuring device 102, which may be the measuring device 102 in Figure 1. The measuring 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 measuring 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 cause the processor to undertake one or more steps 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 210 is stored. The measuring device 102 may also comprise motion sensors 214 (e.g. inertial sensors). The measuring device also comprises a survey barometric sensor 216. The processor 208 is configured to undertake one or more of the functions necessary for operation of one or more of the other elements of the measuring device 102. In one exemplary arrangement, the motion sensors are inertial sensors 214, which may comprise accelerometers and / or rate gyros. The inertial sensors 214 may be arranged to measure acceleration and rotational velocity of the measuring 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 measuring device 102 and defined by the x, y and z axes) and converted to any other reference frame (e.g. a local coordinate system or reference frame based on a land area or a construction site to be surveyed) using well known techniques. The inertial sensors 214 may form part of an Inertial Measurement Unit (IMU) housed within the measuring 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 or positioning sensors may be employed. Such motion or positioning sensors include any sensor that is able to detect rotational and / or linear movement of the measuring device 102. These may include, as examples only, sensors using technology relating to GNSS, doppler, cellular positioning, wi-fi positioning, cameras, lasers etc. Each of the transmitter 202 and receiver 204, memory 206, processor 208, inertial sensors 214 and survey barometric sensor 216 is in data communication with the other features of the measuring device 102. The measuring 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 measuring 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 cause the processor 308 to undertake one or more steps of 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 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. 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 software to undertake one or more steps of methods disclosed herein, but are not limited to such. Figure 4 shows a schematic representation of a barometric reference device 106. The barometric reference device 106 comprises a transmitter 402 and, optionally, a receiver 404. The transmitter 402 and receiver 404 may be in data communication with other entities, such as the processing device 104 and the measuring device 102 or servers and / or functions in a telecommunications network and are configured to transmit and receive data accordingly. The barometric reference device 106 further comprises a memory 406 and a processor 408. The memory 406 may comprise a non-volatile memory and / or a volatile memory. The memory 406 may have a computer program 410 stored therein. The computer program 410 may be configured to cause the processor 408 to undertake one or more steps of methods disclosed herein. The computer program 410 may be loaded in the memory 406 from a non-transitory computer readable medium 412, on which the computer program 410 is stored. The barometric reference device 106 also comprises a reference barometric sensor 414. Each of the transmitter 402 and receiver 404, memory 406, processor 408 and reference barometric sensor 414 is in data communication with the other features of the processing device 104. The barometric reference device 106 can be implemented as a combination of hardware and software. The memory 406 stores various programs / executable files that are implemented by the processor 408, and also provides a storage unit for any required data. The programs / executable files stored in the memory 406, and implemented by the processor 408, can include software to undertake one or more steps of methods disclosed herein, but are not limited to such. Figures 5A and 5B show an exemplary arrangement for conducting a survey relating to a topographical survey for a landscaping project. It will be understood that the methods and apparatus disclosed in this specification may be applied to other survey types. Figure 5A shows a plan view of a plot of a domestic dwelling. The plot includes a house 500 and a garage 502. A rear garden 504 is enclosed by a rear fence 506. A front garden 508 is enclosed by a front fence 510. The plot also includes a driveway 512 leading up to the garage 502. Figure 5B shows a section A-A through the plot shown in Figure 5A. As can be seen in Figure 5B, the rear garden 504 includes a slope that rises towards the rear fence 506. If a construction professional is to undertake a landscaping project in the rear garden 504 then they should first conduct a survey of the topography of the rear garden 504. This might include measuring the location of the boundary of the rear garden 504 and measuring an elevation of a number of positions within the rear garden 504 so that the relief of the ground can be estimated. A barometric reference device 106 is positioned in proximity to a survey area, which in this case is the rear garden 504. In the exemplary arrangement shown in Figures 5A and 5B, the barometric reference device 106 is positioned within the survey area and is mounted on a tripod. However, it will be appreciated that the barometric reference device 106 may be positioned elsewhere and may be differently mounted. For example, the barometric reference device 106 may be positioned at an edge of the survey area or may be positioned outside the survey area. The barometric reference device 106 may also be placed on a surface where its elevation, and optionally horizontal position, will be stable over the duration of the survey, e.g. placed on a wall, on a paved area or a flat surface. The barometric reference device 106 is for providing data indicating changes in barometric pressure caused by factors other than elevation, such as wind and temperature. This may be termed barometric error data. The barometric error data may be used to correct barometric pressure data recorded by the measuring device 102. The closer the barometric reference device 106 is to an elevation measurement recorded by the measuring device 102 then the more accurate the correction will be. Accordingly, the barometric reference device 106 may be positioned in proximity to the survey area and, in some arrangements, at a distance from the survey area that is based on a desired accuracy of the elevation measurements and / or a local variability of barometric pressure over the time period for the survey. For example, if wind conditions or temperature are highly variable during the survey then the barometric reference device 106 may be positioned closer to the features to be surveyed (the survey locations). Figure 6 is a flow diagram showing an exemplary method of determining an elevation of a feature during a survey. The barometric reference device 106 is positioned (step 600) so as to provide barometric variability data for the survey area 504. The location of the barometric reference device 106 relative to the survey area 504 may be determined based on a desired accuracy for barometric pressure measured during the survey and / or on the local variability of barometric pressure errors caused by factors other than elevation. In the example shown in Figures 5A and 5B, the barometric reference device 106 is broadly positioned in the centre of the survey area 504, although other positions are possible. The vertical position (elevation) of the barometric reference device 106 is fixed during the survey. The reference barometric sensor 414 of the barometric reference device 106 measures barometric pressure and transmits reference barometric pressure representing the measured barometric pressure. This may be done repeatedly (and optionally periodically) during the time that the survey is being conducted. The transmitted reference barometric pressure may be received by the measuring device 102 and / or the processing device 104. In exemplary arrangements, an initial barometric pressure may be determined and optionally transmitted. The initial barometric pressure may be the barometric pressure at start up of the barometric reference device 106. Alternatively, the initial barometric pressure may be determined based on a plurality of temporally spaced barometric pressure measurements recorded by the reference barometric sensor 414. For example, the initial barometric pressure may comprise an average of a plurality of barometric pressure measurements. The initial barometric pressure may provide a reference point for the barometric error data in that deviations of measured barometric pressure from the initial barometric pressure indicate barometric error data. The measuring device 102 may then be calibrated (step 602), although this step is not essential. Calibration of the measuring device 102 includes calibrating the survey barometric sensor 216 of the measuring device to the reference barometric sensor 414 of the barometric reference device. In exemplary arrangements, the measuring device 102 may be placed in calibration mode. This may be done by a user through the measuring device 102 itself (e.g., by depressing a button orthe like) orthroughthe processing device 104 (e.g. through the user interface 324 and transmitting a signal to the measuring device 102). When in calibration mode, the measuring device 102 may be placed next to the barometric reference device 106, or otherwise positioned to be at the same elevation as the barometric reference device 106. The measuring device 102 may receive the initial barometric pressure transmitted by the barometric reference device 106 and calibrate to that initial barometric pressure. In some examples, calibration of the survey barometric sensor 216 of the measuring device 102 may include setting the measured barometric pressure to be the same as the initial barometric pressure. The initial barometric pressure may be received from the barometric reference device 106 and / or the processing device 104. Also, it is noted that the calibration may be done in post processing at the processing device 104. In this way, the elevation of the barometric reference device 106 may provide a reference elevation, i.e. the initial barometric pressure, forthe survey. All elevation measurements taken by the measuring device 102 will then be determined relative to the reference elevation. The measuring device 102 is placed at a survey location 516 within the survey area 504 (step 604). In some examples, the survey locations may be predetermined, for example using a grid 514, each measurement being taken at a grid intersection 516 (four grid intersections 516A-D have been specifically identified and will be used below to aid description). The grid may be formally laid out or may be approximated by a construction professional when walking around the survey area. Alternatively, the survey locations 516 may be decided in an ad hoc fashion by the construction professional based on the requirements of the survey and the conditions of the survey area 504. In some arrangements, the two-dimensional position of each survey location 516 is determined along with elevation. This allows a surface showing the topography of the survey area 504 to be determined without the need for predetermined survey locations 516. Motion data is recorded by the motion sensors 214 and survey barometric pressure is recorded by the survey barometric sensor 216 (step 606). In exemplary arrangements, the measuring device 102 may transmit the motion data and the survey barometric pressure to the processing device 104. The processing device 104 may also receive the reference barometric pressure from the barometric reference device 106. The survey barometric pressure is corrected based on the reference barometric pressure (step 608). The processor 308 of the processing device 104 may correct the survey barometric pressure based on the reference barometric pressure, thereby generating corrected barometric pressure. Because the barometric reference device 106 is at a fixed elevation, any changes in barometric pressure measured by the reference barometric sensor 414 of the barometric reference device 106 will be caused by barometric error, such as changes in temperature or wind, ratherthan changes in elevation. Within the proximity of the barometric reference device 106, other barometric sensors, e.g. the survey barometric sensor 216 of the measuring device 102, may be considered to experience the same, or highly correlated, barometric error. Therefore, the barometric error measured by the barometric reference device may be used to correct the survey barometric pressure measured by the measuring device. 5 To illustrate, and referring to Figure 5B, the barometric reference device 106 is positioned at a constant elevation, in this case on a tripod. At the start of the survey, the initial barometric pressure at the barometric reference device 106 is, for example, 100760 Pa. 10 The measuring device 102 may be calibrated to the initial barometric pressure. The measuring device 102 is placed at survey location 516A some time later (t1) and records a barometric pressure of 100802.5 Pa. At the same time (t1) the barometric pressure reading at the barometric reference device 106 is 100762.3 Pa, which is a change of+2.3 Pa. The difference in barometric pressure at the barometric reference device 106 is not caused by a change in 15 elevation as the elevation of the barometric reference device 106 is fixed. Therefore, the difference is a result of barometric error. This is shown for survey locations 516A-D in the table below. Survey location Time Reference baro (Pa) Survey baro (Pa) Error (Pa) 516A t1 100762.3 100802.5 +2.3 516B t2 100755.4 100791.2 -4.6 516C t3 100754.8 100782.0 -5.2 516D t4 100758.7 100777.4 -1.3 The barometric errors experienced at the barometric reference device 106 are considered to be the same, or highly correlated with barometric errors experienced at the measuring device 102. Accordingly, the processor 308 may correct the survey barometric pressure based on one or more of: the absolute reference barometric pressure; a change in reference barometric pressure over time; and a rate of change in reference barometric pressure. In one implementation, the corrected barometric pressure may comprise the survey barometric pressure plus the barometric error. Returning to Fig. 6, it is determined whether more survey locations 516 remain (step 610). If so, the method returns to step 604 and the measuring device 102 is moved to another survey location 516. When motion data and corrected barometric pressure have been obtained for all survey locations 516, the topography of the survey area 504 may be determined (step 612). As will be understood by the skilled person, barometric pressure and elevation are negatively correlated - barometric pressure reduces as elevation increases. Accordingly, the elevation of each location 516 may be determined based on the barometric pressure recorded at that location 516. The processor 308 of the processing device 104 may determine the topography based on the measured motion data and the corrected barometric pressure. In exemplary arrangements, the processor may determine a two-dimensional (or horizontal) position for each survey location 516 based on the motion data. The processor 308 may determine the elevation of each survey location 516 based on the corrected barometric pressure. In some exemplary arrangements, the processor 308 may determine the elevation of each survey location 516 based on a combination of the motion data and the corrected barometric pressure. Such a combination may be undertaken using methods including a weighted average algorithm, a least squares algorithm and a Kalman filter algorithm. In some exemplary arrangements, the processor 308 may determine two-dimensional position and elevation of each survey location based on a combination of the motion data, the survey barometric pressure and the reference barometric pressure. Other data may also be incorporated, such as quality of the reference barometric pressure. The quality of the reference barometric pressure may be based on a distance between the survey location 516 (and therefore the measured barometric pressure) and the barometric reference device 106. The two-dimensional position and elevation of each survey location 516 may be determined using a single algorithm such that determination of the corrected barometric data is incorporated into the algorithm and is not a separate step. Such a combination may be undertaken using methods including a weighted average algorithm, a least squares algorithm and a Kalman filter algorithm. For example, a Kalman filter may take inputs including motion data in all three axes, survey barometric pressure, reference barometric pressure, initial barometric pressure and reference barometric pressure quality. The Kalman filter may provide an output including horizontal position and elevation of a survey point 516, optionally in a local coordinate system. It will be appreciated, therefore, that generation of the corrected barometric pressure need not be explicit and may be implicitly undertaken within an algorithm for determining position and / or elevation of each survey location 516. It is noted that where one or more survey locations 516 are predetermined, e.g. in grid 514, two-dimensional position of those survey locations need not be determined. In such arrangements, the motion data, survey barometric pressure and reference barometric pressure may be used in ways similar to those discussed above to determine only the elevation of each survey location 516. It is noted that, although the exemplary arrangement describes the processor 308 of the processing device 104 undertaking the determination of the corrected barometric pressure and topography, some or all of the steps for this may be undertaken in the measuring device 102. In some arrangements, calibration of the measuring device 102 to the initial barometric pressure of the barometric reference device 106 at step 602 is not necessary. In such arrangements, the error in reference barometric pressure determined at the barometric reference device 106 may be used to determine the corrected barometric pressure. In some exemplary arrangements a plurality of barometric reference devices 106 may be used. This may provide increased accuracy of the barometric error, for example when the survey area 504 is large. In such cases, the corrected barometric pressure may be determined based on a plurality of reference barometric pressures, each from a different barometric reference device 106. Some arrangements may determine the corrected barometric pressure based on a combination of reference barometric pressures in an algorithm including a weighted average, a least squares or a Kalman filter. In such algorithms, a weight may be applied to each reference barometric pressure based on a quality of the reference barometric pressure. As stated above, the quality may be determined based on a distance between the corresponding barometric reference device 106 and the survey location 516. In exemplary arrangements, an algorithm operating on the processor 408 of the processing device may detect that measurements at a survey location 516 have been completed and / or that measurements at a further survey location 516 have begun. Such algorithms are not explained in detail herein. Alternatively, the construction professional may indicate through the user interface 322 or the like that measurements at one survey location 516 have been completed and / or that measurements of a further survey location 516 have begun. In exemplary arrangements, the measuring device 102 may include a reference point. The reference point may be a location or surface on the measuring device 102 at which the position and / or orientation of the measuring device 102 is to be calculated. 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 between the blocks that are illustrated. 5 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 and methods. It is intended that the specification and examples be considered as exemplary 10 only, with a true scope being indicated by the following claims and their equivalents.

Claims

1. A system for determining an elevation of a survey location, the system comprising:a barometric reference device including:a reference barometric sensor configured to measure reference barometric pressure while the reference barometric sensor is at a fixed elevation; anda transmitter configured to transmit data indicative of the measured reference barometric pressure,the system further comprising a measuring device including:a plurality of motion sensors configured to obtain motion data representing position and orientation of the measuring device based on rotational and linear movement of the measuring device in a body frame comprising orthogonal x, y and z axes;a survey barometric pressure sensor configured to measure survey barometric pressure at a plurality of survey locations, anda transmitter configured to transmit the measured survey barometric pressure and the motion data;the system further comprising a processing device including:a receiver configured to receive the data indicative of the measured reference barometric pressure, the measured survey barometric pressure and the motion data, anda first computer processor configured to:determine a corrected barometric pressure based on the data indicative of the measured reference barometric pressure and the measured survey barometric pressure;determine an elevation of the plurality of survey locations based on the corrected barometric pressure and the motion data.

2. The system according to claim 1, wherein the data indicative of the measured reference barometric pressure includes one or more of: the measured reference barometric pressure; and barometric error.

3. The system according to claim 1 or 2, wherein the barometric reference device includes a second computer processor configured to determine an initial barometric pressure, and wherein the transmitter is configured to transmit the initial barometric pressure.

4. The system according to claim 3, wherein the initial barometric pressure comprises an average of a plurality of reference barometric pressures measured overtime.

5. The system according to claim 3 or 4, wherein the measuring device comprises a third computer processor configured to calibrate the survey barometric pressure sensor based on the initial barometric pressure.

6. The system according to any preceding claim, wherein the first computer processor is configured to determine a horizontal position of the plurality of survey locations based on the motion data.

7. The system according to any preceding claim wherein the first computer processor is configured to determine elevation and / or horizontal position of the plurality of survey locations based on an algorithm having inputs comprising: the data indicative of the measured reference barometric pressure; the motion data; and the measured survey barometric pressure.

8. The system according to claim 7, wherein the algorithm comprises a Kalman filter.

9. A method of determining an elevation of a survey location, the method comprising:measuring, by a reference barometric sensor of a barometric reference device, a reference barometric pressure, wherein the reference barometric pressure has been measured while the reference barometric sensor is at a fixed elevation;transmitting, by a transmitter of the barometric reference device, data indicative of the measured reference barometric pressure;obtaining, from a plurality of motion sensors forming part of a measuring device, motion data representing position and orientation of the measuring device based on rotational and linear movement of the measuring device in a body frame comprising orthogonal x, y and z axes;measuring, by a survey barometric pressure sensor of the measuring device, survey barometric pressure at a plurality of survey locations;transmitting, by a transmitter of the measuring device, the motion data and the measured survey barometric pressure;receiving, by a receiver of a processing device, the measured reference barometric pressure, the measured survey barometric pressure and the motion data;determining, by a first computer processor of the processing device, a corrected barometric pressure based on the data indicative of the measured reference barometric pressure and the measured survey barometric pressure; anddetermining, by the first computer processor, an elevation of the plurality of survey locations based on the corrected barometric pressure and the motion data.

10. A computer program product configured, when executed on one or more computer processors, to control a system to undertake the steps of the method of claim 9.

11. A processing device for determining an elevation of a survey location, the processing device comprising:a receiver configured to:receive, from a barometric reference device, data indicative of a reference barometric pressure, wherein the reference barometric pressure has been measured while the reference barometric sensor is at a fixed elevation;receive, from a measuring device, survey barometric pressure measured at a plurality of survey locations, and motion data obtained from a plurality of motion sensors forming part of the measuring device, the motion data representing position and orientation of the measuring device based on rotational and linear movement of the measuring device in a body frame comprising orthogonal x, y and z axes; and a first computer processor configured to:determine a corrected barometric pressure based on the data indicative of the measured reference barometric pressure and the measured survey barometric pressure;determine an elevation of the plurality of survey locations based on the corrected barometric pressure and the motion data.

12. A method of determining an elevation of a survey location, the method comprising:receiving, from a barometric reference device, data indicative of a reference barometric pressure, wherein the reference barometric pressure has been measured while the reference barometric sensor is at a fixed elevation;receiving, from a measuring device, survey barometric pressure measured at a plurality of survey locations, and motion data obtained from a plurality of motion sensors forming part of the measuring device, the motion data representing position and orientation of the measuring device based on rotational and linear movement of the measuring device in a body frame comprising orthogonal x, y and z axes;determining, by a first computer processor, a corrected barometric pressure based on the data indicative of the measured reference barometric pressure and the measured survey barometric pressure;determining, by the first computer processor, an elevation of the plurality of survey locations based on the corrected barometric pressure and the motion data..

13. A computer program product configured, when executed on a computer processor, to 5 control a processing device to undertake one or more of the steps of the method of claim 12.

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