GB2419759A

GB2419759A - Laser scanning surveying and measuring system

Info

Publication number: GB2419759A
Application number: GB0524185A
Authority: GB
Inventors: Paul Ian Harkness; Stirling Anthony Kimkeran
Original assignee: Omnicom Engineering Ltd
Current assignee: Balfour Beatty Engineering Ltd
Priority date: 2003-07-11
Filing date: 2003-07-11
Publication date: 2006-05-03
Anticipated expiration: 2023-07-11
Also published as: GB2403861A; GB0316242D0; GB2419759B; GB0524185D0; GB2403861B

Abstract

A surveying system 10 is disclosed for surveying and measuring the position of objects along a surveyed route. The system 10 comprises a laser scanner 20 and a data analyser 5. The data analyser 5 analyses data signals 102/108 from the scanner 20 to determine distance, and presence of an object A from the scanner 20. The system 10 further comprises navigational position finding units 35 such as a GPS unit 16 and an IMU 17 which determine position data, and a clock 200 which provides a common clock signal to the scanner 20, navigational position finding units 35 and data analyser 5. The data analyser uses the common clock signal from the clock 200 to correlate the determined data relating to the distance of detected objects A from the scanner 20 with the positional information from the navigational position finding units 35. The system may be used to measure and survey a railway track and trackside objects such as bridges, platforms, signals and tunnel walls.

Description

1 P351515A

A METHOD AND SYSTEM OF SURVEYING AND MEASUREMENT

The present invention relates to a method and system for surveying and measurement, and in particular to a laser scanning surveying and measurement system used to measure and survey a railway track and trackside objects, tunnels and/or platforms. The system may also be applicable to road surveys, and to surveying using other similar scanning and surveying techniques for example radar or ultrasonic, although laser surveying techniques are preferred.

Along the length of a railway track or line (an indeed along the length of a road), there are numerous trackside objects, for example, bridges, platforms, signals, and tunnel walls etc. It is generally required and desirable to : ** know the general position and location of these objects. In S...

particular it is required to know the distance of these objects from the centerline of the railway line for gauging purposes to ensure that the respective vehicle can adequately pass along the railway line clear of such trackside objects. The positions of such trackside objects along the line are also generally required to be known and monitored to both identify that such objects exist, and/or check that they are still in the correct place along the railway line.

Conventional manual surveying of the railway line involves sending personnel onto the railway line to make physical measurements, and surveys, of the railway line and trackside objects measuring the respective positions using tape measures or similar and carefully plotting the positions from datum and/or known reference points. Such an operation is time consuming and labourious, and may also be dangerous if the railway line is in use. If the railway line is taken out of use during such surveying this causes undesirable disruption to the use of the railway. This all gives rise to high and increased surveying costs. As result 2 P351515A such surveys are only infrequently carried out and so there is only a poor, and possibly out of date, knowledge of the railway and trackside objects. In addition such manual surveys are prone to errors and the amount of information that can be readily measured and recorded is limited.

More automated measurement and survey systems have accordingly been proposed. In one proposed system rotating laser range finding/scanning or profiling equipment is mounted upon a survey vehicle which travels along the rail line. Such laser profiling equipment is known for surveying in other applications for example the internal shape of offshore pipelines. The laser profiling equipment includes a laser beam that is rotated and scanned in a circle about a horizontal axis aligned with and along the rail track. A : ** 15 reflected laser signal, reflected from any object in the I...

path of the scanning laser beam, is then detected and used to determine the distance of the object from the profiling equipment. These laser profiling systems can, and are configured to produce very accurate and detailed measurements of the distance of objects.

Whilst these laser surveying systems produce more accurate and detailed information than manual surveys, and require less manual input, surveying speed is still very slow with the survey vehicle having to travel at slow speed along the rail line during such surveying. This disrupts normal use and operation of the rail line during such surveying. Furthermore conventionally such prior laser surveying systems have inherent limitations of their operation and configuration, with such systems being based upon systems conventionally used for very detailed small scale measurement surveys. For example these systems simply provide lateral distance information of objects from which the laser signal is reflected. This can allow for general gauging determinations to be made to check the maximum sizing for rail vehicles, but is from a practical 3 P351515A perspective quite limited. These systems are also limited in terms of performance with either slow speed, limited angular scanning over only for example 2700, or limited analysis and differentiation of the returned signals in order to accommodate and handle the data volume produced. Overall these prior laser profiling systems are not really adapted and tailored for extended and large scale surveying operations required for rail surveys, nor for the specific requirements of rail surveying with its particular considerations and requirements.

In an alternative automated surveying system, which has been used for surveying railways, a number of video cameras are mounted upon a survey vehicle to view the surveyed area and surrounding objects as the survey vehicle travels along : .. 15 the survey route. The survey vehicle also includes S...

navigational/positional finding equipment, in particular a S.'. Global Positioning System (GPS) by which the absolute position of the survey vehicle can be accurately determined.

Both the video images taken and positional information calculated during the survey are combined and stored during the surveying. By careful post processing and correlation between the images and positional information determined from the navigational/position finding equipment during the survey, and corresponding to when the image was recorded, the objects in the field of view at a particular position can be inferred, and so the position of identified objects recorded in the video images can be obtained.

Whilst this system provides some identification of the position of trackside objects the accuracy is limited.

Furthermore there is no direct measurement, in particular of the distance of the objects from the rail centre line as required for gauging purposes. Also in order to determine the position of objects from the video images the particular objects need to be specifically identified from the video images by an operator and separate processing then carried 4 P351515A out. This can be time consuming and requires the expertise of an experienced operator. These systems relying upon GPS for positional determination are also of limited use in railway applications since they require a line of sight with the satellites from which they determine their positions.

This is often not possible along significant parts of a railway line for example in tunnels, or in railway cuttings where the surveying measurements are also generally most required and critical, and are also often the most difficult sections of the railway line to readily and safely access.

It is therefore desirable to provide an improved surveying system and method of surveying which addresses the above described problems and/or which offers improvements : *s 15 generally. S... * SIS

According to a principal aspect of the present invention there is provided a system for surveying and measuring the position of objects along a surveyed route, and a method of surveying and measuring the position of objects along a surveyed route, as described in the accompanying claims.

In an embodiment of the invention there is provided a surveying system for surveying and measuring the position of objects along a surveyed route. The system is mounted upon a survey vehicle adapted to travel along a survey route. The system comprises a scanner and a data analyser. The scanner emits repeated incident energy pulses and detects corresponding returned energy pulses reflected from an object at a distance from the scanner. The scanner transmits data signals relating to the emitted and detected reflected returned pulses. The data analyser analyses the data signals received from the scanner and compares data signals of the detected returned energy beam pulses against data signals of P351515A the incident energy pulses to determine distance of the object from the scanner and generate data relating to the distance of detected objects from the scanner. The system further comprises a data gate operatively disposed between the scanner and data analyser. The data gate is adapted to enable registration in the data analyser of the data signals from the scanner relating to reflected pulses from objects within a predetermined distance range, such that only data signals relating to reflected pulses from objects within a predetermined distance range of interest are registered in, and analysed by the data analyser.

Preferably at the same time as the scanner emits a incident energy pulse, a synchronisatjo signal is sent to the data gate. The synchronisation pulse controls the : .. 15 operation of the data gate to selectively enable the S...

registration in the data analyser of the data signals from S...

the scanner.

Furthermore the data gate is adapted to selectively allow registration of data signals which are received by the data gate a predetermined minimum time (tmin) after the synchronisatjo pulse. The data gate may also be adapted to disable registration of the data signals which are received by the data gate a predetermined maximum time (tmjn) after the synchronisaj pulse.

The system may further comprise a timing unit associated with the data gate which is triggered by the synchronisajo pulse to after a predetermined time period selectively control the operation of the data gate.

There may also be provided a delay cable through which the synchronisatj0 pulse is transmitted from the scanner to the data gate. The delay cable has an extended length such that transmission of the synchronisation pulse along the length of the delay cable to the data gate is delayed by a period corresponding to the period for a data signal relating to a reflected light pulse from an object at the 6 P351515A limit of the predetermined distance range to be received at the data gate.

The scanner preferably comprises a laser scanner which emits a repetitive series of laser light pulses. The scanner also preferably emits a series of radially directed energy pulses which are rotated around a 3600 arc to define a rotating scanning beam. The rotating scanning beam may rotate at between 60,000 to 100,000 rpm. The scanner preferably emits repeated energy pulses at a frequency of nominally 1 MHz.

With this survey system the survey vehicle may travel at a surveying speed of 4 to 60 mph along the survey route.

The survey system preferably further comprises a navigational position finding unit which determines and : *.. 15 generates positional information which is sent to the data *sS.

analyser and is correlated with the determined data relating to the distance of detected objects from the scanner. A clock may provide a common clock signal to the scanner, navigational position finding units, and data analyser to correlate the data signals from the scanner, navigational position finding units. The navigational position finding unit preferably comprise one or more of a Global Positioning System, an Inertial Measurement Unit, a tachometer, and an altimeter. Further the navigational position finding unit comprises at least two of a Global Positioning System, an Inertial Measurement Unit, a tachometer, and an altimeter.

The data analyser compares and correlates the positional signals from the least two of a Global Positioning System, an Inertial Measurement Unit, a tachometer, and an altimeter to determine an aggregate corrected positional information.

The system may further comprise at least one video camera which generates video image data which is sent to the data analyser and correlated with the data relating to the distance of detected objects from the scanner.

In another aspect of an embodiment of the invention 7 P351515A there is provided a method of surveying and measuring the position of objects along a surveyed route. In this method a scanner emits repeated incident energy pulses and detects corresponding returned energy pulses reflected from an object at a distance from the scanner, and transmits data signals relating to the emitted and reflected pulses. A data analyser analyses the data signals received from the scanner and compares details of the detected returned energy beam pulses against details of the incident energy pulses to determine distance of the object from the scanner and generates data relating to the distance of detected objects from the scanner. The method further comprises selectively registering in the data analyser only the data signals from the scanner relating to reflected pulses from objects within : .. 15 a predetermined distance range, such that only data signals S...

relating to reflected pulses from objects within a *SSS predetermined distance range or interest are registered in, and analysed by the data analyser.

Other aspects of the invention and surveying systems and methods will also be apparent from the following

description of an embodiment of the invention.

The present invention will now be described by way of example only with reference to the following figures in which: Figure 1 is a schematic illustration of a rail survey vehicle including a surveying system of an embodiment of the present invention; Figure 2 is a more detailed schematic illustration of the main elements of the survey system shown in figure 1 illustrating the main functional interconnections between the elements; Figures 3a, 3b, and 3c are schematic illustrations illustrating the scanning of the laser beam in the surveying 8 P351515A systems of figures 1 and 2; and Figure 4 is a more detailed schematic illustration of the laser scanning unit of the surveying system shown in figures 1 and 2.

Referring to figure 1 the survey or measurement system of an embodiment of the invention is schematically illustrated as fitted to a survey vehicle 2 which travels along a survey route. In this particular and preferred embodiment the survey vehicle 2 comprises a railway vehicle which travels along a railway track 4 making a survey of the railway line and any tracksjde objects. The system 10 can though in other embodiments be fitted to any other appropriate survey vehicle 2, for example a road vehicle, : * 15 and can be used to carry out a survey along other I...

infrastructure along a predetermined survey route, for example along a road.

The survey or measurement system 10 comprises a scanner 20, in this case a laser scanner, operatively connected by a network 21 to a computer 5 which comprises a data analyser to analyse the data from the scanner 20 and other systems.

A navigational/position finding unit 35, comprising a differential Global Positioning System (DGPS) 16, an inertial measurement system 17 (to determine vehicle vibration and attitude), and a tachometer, an altimeter, and/or other similar navigationa1/posjtjo finding systems (not all shown in figure 1), are also connected to and transmit data to the computer 5 via the network. The DGPS 16 system determines the global absolute position of the survey vehicle 2 from signals received from a constellation of satellites orbiting the globe. In this embodiment video cameras 18 are also mounted on the survey vehicle 2 at various positions to provide and capture various different views of the track and surrounding area as the survey vehicle 2 travels along the survey route. The video cameras 9 P351515A 18 are linked to suitable video recording equipment to record the frame- by-frame images of the track and surrounding area as provided by the video cameras 18. The video equipment is also interconnected and linked via the network to the computer 5.

Suitable power supplies and other operating and control systems (not shown) for the operation of the various elements of the survey system 10, as would be readily understood by those skilled in the art are also connect and provided as required.

The scanner 20, as described preferably comprises a laser scanner. The scanner 20 transmits a beam comprising a repetitive series of laser light pulses in a direction perpendicular to the direction of travel of the survey vehicle 2. The laser beam 22 is further continuously rotated sill 3600 and scanned about an axis 1 centred on the scanner 20 and aligned and parallel with the direction of travel.

Accordingly as the survey vehicle 2 travels along the railway line the scanner 20 and laser beam 22 scans in a helical manner such that a point along the beam 22 describes a spiral helix 24 of a radius R from the scanner 20 and axis 1 as illustrated schematically in figures 3a,3b,3c. The pitch or spacing between successive complete 360 rotations of the scanned beam 22 is dependent upon the speed of rotation of the beam 22 in relation to the forward speed of the survey vehicle 2. As shown in figure 3b a larger pitch and scan spacing is generated if the survey vehicle 2 travels at a higher speed or if the beam 22 is rotated more slowly. As is mentioned in further detail below in the preferred arrangement the beam 22 is scanned at between 60,000 and 100,000 rpm such that in relation to a typical survey forward speed, at line operating speeds of up to 60mph a very small pitch is produced and in effect the laser beam 22 effectively scans the same point repeatedly as the survey vehicle moves forward. The laser beam 22 is also P351515A pulsed and sampled at a nominal frequency of 1 MHz such that in effect as the beam 22 is rotated the beam 22 is directed at and scanned over a continuum of points, corresponding to the pulses, about and around the path of the rotated beam 22. The scanning frequency, and frequency of repetitive laser light pulses, may be variable, but known and tightly controlled within a particular range for example 10%. The scanning frequency may be set, controlled and monitored by the computer 5.

The rotated beam 22 of repetitive laser light pulses is directed radially outwards perpendicular to the axis 1 and direction of travel. As this beam 22 is rotated it accordingly strikes any object A, spaced along the radial line of the beam 22 from the scanner 20. Such objects A : * 15 comprise for example the walls of tunnels, bridges, a * a embankment sides, overhead lines and gantries, signals and other track side objects, the rail track and rails themselves. In other words the beam 22 and pulses will be reflected from any object A in the vicinity and in a line of sight from the survey vehicle scanner 20. A portion of the incident light pulse striking the object A will be reflected back towards the scanner 20 as a reflected return beam 28 of the light pulses. This reflected return beam 28 of the light pulses is collected and detected in the scanner 20. As is known in the art, and as is conventional with laser scanning apparatus 20, a comparison of the time difference between the transmitted incident laser beam pulse 22 and the respective corresponding reflected laser beam pulse 28 received and/or of the phase shift between the incident 22 and reflected pulses 28, provides a measurement of optical path length that the incident 22 and reflected beams 28 have travelled and so of the radial distance R of the object A struck by the laser beam pulse 22 from the scanner 20.

The laser scanner 20 is shown in more detail in figure 4. As shown the scanner 20 comprises, in this embodiment, a 11 P351515A class III B laser transmitter 12 that directs a repetitive stream of laser light pulses at a small fixed mirror 9 at an angle of 450 to the laser beam pulses 22. This mirror 9 is located on the axis 1 at one end of a hollow shaft 13 and is also at 450 to the axis 1 of the shaft 13. The laser light pulses 22 are reflected axially into and down the centre of the hollow shaft 13 set with its axis corresponding to the axis 1 of the scanner 20. At the opposite end of the hollow shaft 13 there is a further larger rotating mirror 14 again set at an angle of 450 to the axis 1 of the hollow shaft 13 and located within and mounted to the hollow shaft 13. This deflects the laser beam pulses at an angle of 90 to the axis 1 of the scanner 20 and out through an opening 26 in the side of the hollow tube 13 and perpendicular to the : *, 15 direction of travel of the survey vehicle 2. The opening 26 I...

and end of the shaft 13 are arranged and mounted such that they project clear of the survey vehicle 2 such that the laser beam 22 has a clear 360 line of sight from and normal to the survey vehicle 2. The hollow tube 13, and also the large mirror 14 located therein, are accurately and precisely rotatably located within air bearing and motor unit 10 such that it is rotated about the central axis 1.

The air bearing and motor unit 10 rotates the hollow shaft 13 at precisely controlled rotational speeds c typically in the range of 60,000 to 100,000 rpm, with the rotational speeds c carefully and precisely controlled by a speed controller within the motor unit 10 which also measures and transmits the actual rotational speed via the network to the computer 5. The air bearings minimise the friction at such high rotational speeds, whilst the air bearing and motor unit 10 are both water cooled to dissipate any heat which may also effect the measurements and cause distortion of the measurement equipment. The rotation of the hollow shaft 13 and mirror 14 rotates the laser beam pulses 22 emitted from the scanner 20 through the window 26 creating 12 P351515A a rotating beam 22 which is rotated and scans around 360 at the controlled measured rotational speed of the hollow shaft 13 and which pulsed at a laser pulse rate set by the laser generator 12.

The scanner 20 also includes a detector 15 positioned optically behind a lens arrangement ii at the laser generator 12 end of the hollow shaft 13 and coaxially aligned with the central axis 1 of the scanner 20 and hollow shaft 13. The detector comprises 1 GHz sensitive photodiode detector generally known in the art. As the hollow shaft 13 rotates the reflected laser beam pulses 26, reflected and returned from an object A are received through the opening 26. They are similarly reflected by the rotating mirror 14 axially back through the hollow shaft 13 through the lens 11 : ** 15 where they are concentrated and focussed on the detector 15 where the returned reflected beam 28 is detected and a return detected data signal 100 is then generated from the detector 15.

The laser scanner 20, as shown, is mounted upon an anti-vibration platform 29 via suitable dampers 30 and springs 32 to reduce vibration and is mounted upon a rigid support arm 34 on the survey vehicle 2 at a known fixed determined position from the respective navigational/positjoj finding units 35. The datum position of the scanner 20 from which the laser measurements are made is thereby provided and determined by the positional data provided by the navigational/positi0n determining units 35.

Referring now to figure 4, the laser scanner 20 also includes data gate 36 which controls and gates the reflected data signal 100 sent from the detector 15 to the computer 5.

A delay circuit 38 controls the operation of the data gate 36. It is this data gate 36 and delay circuit 38 and their operation that form a key part of an aspect of the present invention. Specifically it has been recognised and 13 P351515A appreciated according to the invention that when surveying a railway, or road way, that the scanner 20 does not need to detect any objects A within an minimum predetermined radial distance Rm, for example closer than the rails (about lm) or reflected signals corresponding to reflections from objects A at such a distance Rmi. These detected signals are either false or due noise or may be from the survey vehicle 2 itself and do not correspond to objects A of interest.

Similarly objects beyond a prescribed maximum radial distance Rr,a, for example 5m from the surveying centerline.

In particular current requirements specify that objects and infrastructure greater than 6m from the track 4 and track centreline are not of general interest and do not need to be measured being well outside of any gauging considerations.

: .**. 15 Most of the objects A of interest, for example signals, I...

tunnel walls, gantries are located relatively close to the track 4 and within this maximum distance. This requirement can be met by mounting the scanner 20 say im above the rails and using a maximum radial distance Rma of 5m.

Accordingly the data gate 36 is configured eliminate return detected data signals 100 corresponding to reflected signals detected from below or above these predetermined distances Rma., Rmin. In other words the gate 36 only selectively transmits a return detected data signal 102 to the computer 5. The transmitted return detected data signal 102 from the data gate 36 corresponds to only return detected data signals 100 corresponding to objects A at radial distances RA within the predetermined range of interest Rmn to Rmd(1 to 5m) . This advantageously has the effect of significantly and dramatically reducing the volume and quantity of data signals 102 and data received by the computer 5 for processing. it also eliminates or at least reduces unwanted signal noise and erroneous detected signals/ref1ecio5 substantially at source and prior to significant processing and analysis. In this way only 14 P351515A detected data signals 100 from objects A of interest located within the predetermined distances (between Rmi and Rma:) are sent as data signals 102 to the computer 5 for data analysis and subsequent processing.

The significant reduction in data and removal of noise and unwanted data at source prior to subsequent substantive processing and analysis provided by the data gate 36 allows more rapid and efficient processing of the data captured during the surveying, and for the actual data captured and transmitted to be more easily and efficiently handled. This allows the survey vehicle 2 to be able to travel at faster speeds, approaching line operating speeds (for example 60mph), without the data analysis systems and computer 5 becoming overloaded with excessive data. It also allows the : *. 15 high rotational speeds o and high pulse rates of the laser S...

beam 22 to be used which improves accuracy and also again allows more rapid surveying to be carried out.

The reduction in detected reflected signals from the laser measurement systems to only signals corresponding to objects A of genuine interest within the specified predetermined limits Rna, to Rmin also allows the laser measurement data derived therefrom to be more easily and readily correlated and integrated with other data, for example the navigational/postj0 information and also video information. Previously due in particular to the volume of data generated by laser measurement systems it has been impossible to practically integrate such laser measurements with such additional survey information.

The data gate 36 in this embodiment selects the detected signals ioo from the detector 15 to be eliminated or blocked using a synchronjsaj pulse signal 108 and delay circuit 38. At the same time as a pulse of laser light is emitted by the laser generator 12 a synchronisajon pulse signal 104 is sent to the delay circuit 38. Using this synchronisation pulse 104 the delay circuit 38 transmits an P351515A open control signal 106a to the data gate 36 at a suitably delayed time period tmlfl after the synchronisation pulse 104 and so transmission of the laser pulse. This delayed time period corresponds to the time for the incident laser beam 22 to Lravej from the laser generator 12 along the optical path length to the minimum radial distance RmLfl and return from such a radial distance Rmin to be detected and generate a return detected data signal 100. The control signal 106a when sent after the delay then opens data gate 36.

Accordingly any return detected data signals 100 returned earlier than the open signal 106a transmission will not be transmitted as a detected data signal 102 through and from the data gate 36 to the computer 5 and registered therein for processing. Similarly after a further longer period tma.

: ** 15 after the synchronisation pulse 104, corresponding to the S...

time for the incident laser beam 22 to travel from the laser S..' generator 12 along the optical path length to the maximum radial distance and return from such a radial distance Rina: to be detected and generate areturn detected data signal 100, a second close control signal 106b is sent. This second closed control signal 106b closes the data gate 36.

Accordingly any return detected data signals 100 returned later than the closed signal 106b transmission will not be transmitted as a detected data signal 102 through and from the data gate 36 to the computer 5 and registered therein for processing. This is repeated and coordinated for each laser pulse sent by the laser generator 12.

The delay 38 and control signals 106a,106b may be provided by a suitable timing circuit/timing card (not shown) within the computer 5. Indeed in the preferred embodiment such a timing circuit within the computer 5 is used to generate the required open control signals lO6a to establish the initial period t1 following the transmission of each laser pulse. Alternatively, the delay 38 can be provided by means of a delay cable, and in the preferred 16 P351515A embodiment and as described below such a delay cable is used to define the second and maximum end period tma corresponding to the maximum distance of interest.

The delay cable comprises a normal coaxial cable that transmits and carries the synchronisation signal 104 from the laser generator 12 to the data gate 36. The cable has a length from the laser generator 12 to the data gate 36 which is significantly longer that of a cable from the detector 15 to the data gate 36 carrying the detected data signals 100.

The difference in length, subject to the known difference in velocity of an electric pulse along a coaxial cable length to the speed of light in air, corresponds to the total optical path length from the laser generator 12 to the maximum radial distance Rma of interest and back to the : .**. 15 detector 15. As a result of length of the delay cable the S...

delay in the transmission of the synchronisaj0 pulse 104 S." along the length of the delay cable corresponds to the time for a detected signal 100 generated from a reflection from an object A at the maximum radial distance Rma. to be received. Therefore the synchronisat0 signal 104, by the time it reaches the data gate 36 having travel along the delay cable itself provides the required close control signal 106b. The use of a delay cable provides a robust simple and accurate hardware implemented method for providing the required delay and controlling the data gate 36.

It will of course be appreciated that a shorter delay cable can be used to set the initial period tmlfl and delay from the detected signals from the minimum radial distance Riir. Similarly the simple timing circuit used to set the initial period could also be used to set the maximum period.

A timing pulse 108 is also sent to the computer 5 from the laser generator 12 for comparison with the detected data signal 102 received by the computer 5. By comparing the time 17 P351515A delay between the timing pulse 108, sent when the incident laser pulse 22 is transmitted, with the arrival time of the detected signal 102 the optical path length travelled by the laser pulse 22 from the laser generator 12 to the object A and reflected back 28 can be determined in the conventional manner using suitable timing and calculation in the computer 5. Since the optical path length within the scanner 20 is fixed and known the radial distance R of the object A can thereby be calculated.

This measured radial distance RA data for object A is also correlated within the computer 5 with the rotation of the beam 22 as determined by the motor sped controller 10 to relate the angular position of the beam 22 as it rotates with the radial distance measurements RA recorded. The : *** 15 scanner 20 accordingly generates a data set relating to the *s.S radial distance RA from the scanner 20 axis 1 of detected objects A within the predetermined maximum and minimum limits Rma. to Rmin.

The system 10 also preferably includes navigational and positional finding units 35. As mentioned above these may include for example a GPS 16 system to determine an generate absolute global latitude and longitude information of the survey vehicle 2 and generate a GPS data signal 116. An inertial measurement unit (IMU), which as described above is preferably located closely with the scanner 20, may also be provided to determine the attitude of the scanner 20 in relation to the survey vehicle 2 and the other position finding units 35 and also monitors any vibrations, and provides and generates a vibration/attitude data signal 117.

A tachometer 40 measures the rotation of the survey vehicle wheels (or of a monitoring wheel) to measure the distance travelled along the railway 4 and generates data signal 140 relating to the distance travelled. An altimeter may also be incorporated to generate an altitude data signal 142. Other positional measurement systems 44 (for example a compass 18 P351515A etc), and indeed backup duplicate systems may also be provided to generate further positional data signals 144.

All of the data signals 116,117,140,142,144 generated by the navigational positional units 35 are sent to the computer 5 for analysis and are correlated with the laser scanner 20 generated data set relating to the radial distance RA of objects A from the vehicle 2. In the computer the suitable calculation software and processing (either online or after a survey) using the vibration and attitude data signals from the ItiU 17 compensates for vibration to improve the accuracy of the radial distance measurements from the laser scanner 20. Similarly using the other navigational positional data 116,140,142,144 the global position of the respective measurements of the radial : 15 distance RA of detected objects A is related to global S...

positions determined from the navigational and positional S...

systems 35 and data signals. The result is to build up a complete set of data defining the position of objects A and infrastructure along the railway from which a 3D model can then be generated.

The respective data signals 116,117,140,142,144 from the navigational and positional units 35 and the laser scanner 20 measurements form the data signal 102 and timing pulse 108 are correlated using a common clock 200 and time code signals. These common timing signals are, as indicated in figure 4, sent to each of the units. The timing code signals are recorded and incorporated, or otherwise related to or in, the data signals 116,117, 140,142,144 from the navigational units 35 and also with the signals 108, 102 from the laser scanner 20. In particular the timing code is most easily related to the timing pulse signal 108 sent from the laser generator 12, and or the pulse rate is controlled in relation to this timing code signal. In addition the common timing code signals are also sent to the computer 5. By using such a common timing code signal all of the respective 19 P351515A data streams 116,117,140,142,144 102/108 can be easily correlated and so then combined to provide the measured data at any one time code point, and so at any one position along the survey and so along the railway line. The use of such common timing signal and correlation of the laser distance measurement is an important further aspect of the invention.

The video images recorded by the video cameras 18 during the survey, and the video data 118 sent to the computer 5 are similarly correlated with the navigational and positional date signals 116,117,140,142,144 and laser scanner distance measurements using a common time code signal from the common clock 200.

Preferably, as described, the navigational and positional units 35 comprise a number of separate units : ** 15 16,17,40,42,44 each of which determine the position on the II..

basis of different methods. In the computer 5 the separate SI..

positional information from each of these units is cross checked and correlated to determine an aggregate positional measurement on the basis of the individual positional measurements from each of the systems. This improves the accuracy of the positional determination with any errors from one Positional unit being corrected by the measurements from the others. Overall the GPS positional information is used to monitor the system performance. However this is not always available and so in this system 10 short term losses in GPS signal are compensated by the other positional units.

In particular for example when surveying tunnels the position is determined using the other units, for example IMU 17 data signal 117 and tachometer 40 and/or altimeter 42 or ideally a combination of these units. The positional information from the IMU unit 17 alone however tends to drift over time, and accordingly suitable corrections can be made using the GPS system 16 data when available. Similarly the tachometer signals measuring the rotation of the wheels are susceptible to errors due to slippage etc. and are P351515A similarly corrected from GPS data. By combining the three (or more) different positional measuring systems 16,17,40,42,44 the advantages of the respective systems can be combined, whilst the respective disadvantages of each can be eliminated to overall produce a much more accurate and self correcting positional measurement.

Using this system 10 measurements and surveys of the position of infrastructure and objects to 1mm can be taken at survey speeds of up to 60mph which corresponds to normal line operating speeds so minimising the disruption to the operation of the rail line or road. Furthermore the accurate laser measurement information and data obtained is integrated and linked to global positional information and/or video images to provide a more comprehensive survey : ,"* 15 results. Both of these are aspects are enable by the S...

reduction in data from the laser scanner, without the loss * * S...

in data of interest prior to substantive processing.

It will be appreciated that whilst in the above systems a laser scanner 20 is used other similar scanning systems could alternatively be used. For example a radar or ultrasonic type scanner could be used. A laser scanner 20 is however the preferred systems due to its accuracy and speed.

Various other detailed modifications of the above described systems 10 and method, as will be appreciated by those skilled in the art can also be made without departing from the underlying invention.

Claims

21 P351515A

1. A surveying system for surveying and measuring the position of objects along a surveyed route, the system being mounted upon a survey vehicle adapted to travel along a survey route, the system comprising:- a scanner which emits repeated incident energy pulses and detects corresponding returned energy pulses reflected from an object at a distance from the scanner, and transmits data signals relating to the emitted and detected reflected returned pulses; a data analyser which analyses the data signals received from the scanner and compares data signals of the detected returned energy beam pulses against data signals of * , 15 the incident energy pulses to determine distance of the object from the scanner and generate data relating to the distance of detected objects from the scanner; a navigational position finding unit which determines and generates positional information which is sent to the data analyser; and a clock which provides a common clock signal to the scanner, the navigational position finding unit, and the data analyser; wherein the data analyser correlates the determined data relating to the distance of detected objects from the scanner with the positional information from the navigational position finding units using the common clock signal from the clock.

2. A surveying system as claimed in claim 1 in which the navigational position finding unit comprises one or more of a Global Positioning System, an Inertial Measurement Unit, a tachometer, and an altimeter.

3. A surveying system as claimed in claim 2 in which the 22 P351515A navigational position finding unit comprises at least two of a Global Positioning System, an Inertial Measurement Unit, a tachometer, and an altimeter; and in which the data analyser compares and correlates the positional signals from the least two of a Global Positioning System, an Inertial Measurement Unit, a tachometer, and an altimeter to determine an aggregate corrected positional information.

4. A surveying system as claimed in any preceding claim further comprising at least one video camera which generates a video image data which is sent to the data analyser and correlated with the data relating to the distance of detected objects from the scanner.

* * 15 5. A surveying system for surveying and measuring the :::::: position of objects along a surveyed route, the system being mounted upon a survey vehicle adapted to travel along a survey route, the system comprising:- a scanner which emits repeated incident energy pulses and detects corresponding returned energy pulses reflected from an object at a distance from the scanner, and transmits data signals relating to the emitted and detected reflected returned pulses; a data analyser which analyses the data signals received from the scanner and compares data signals of the detected returned energy beam pulses against data signals of the incident energy pulses to determine distance of the object from the scanner and generate data relating to the distance of detected objects from the scanner; at least one video camera which generates a video image data which is sent to the data analyser; and a clock which provides a common clock signal to the scanner, the at least one video camera, and the data analyser; wherein the data analyser correlates the determined 23 P351515A data relating to the distance of detected objects from the scanner with the image data from the at least one video camera using the common clock signal from the clock.

6. A surveying system as claimed in any preceding claim in which the scanner comprises a laser scanner which emits a repetitive series of laser light pulses.

7. A surveying system as claimed in any preceding claim in which the scanner emits a series of radially directed energy pulses which are rotated around a 3600 arc to define a rotating scanning beam.

8. A surveying system as claimed in claim 7 in which the ::::. 15 rotating scanning beam rotates at between 60,000 to 100,000 rpm. 8I*. * S * 5I

9. A surveying system as claimed in any preceding claim in which the scanner emits repeated energy pulses at a nominal frequency of 1 MHz.

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10. A surveying system as claimed in any preceding claim in which the survey route comprises a railway line.

11. A surveying system as claimed in any one of claims 1 to 9 in which the survey route comprises a road.

12. A surveying system for surveying and measuring the position of objects along a surveyed route, the system being mounted upon a survey vehicle adapted to travel along a survey route, the system comprising:- a scanner which emits repeated incident energy pulses and detects corresponding returned energy pulses reflected from an object at a distance from the scanner, and transmits data signals relating to the emitted and detected 24 P351515A reflected returned pulses; a data analyser which analyses the data signals received from the scanner and compares data signals of the detected returned energy beam pulses against data signals of the incident energy pulses to determine distance of the object from the scanner and generate data relating to the distance of detected objects from the scanner; and a navigational position finding unit which determines and generates positional information which is sent to the data analyser; wherein the navigational position finding unit comprises at least two of a Global Positioning System, an Inertial Measurement Unit, a tachometer, and an altimeter; and the data analyser is adapted to compare and correlate the positional signals from the least two of a Global Positioning System, an Inertial Measurement Unit, a I...

tachometer, and an altimeter to determine an aggregate corrected positional information.

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13. A surveying system as claimed in any preceding claim :. * further comprising a data gate operatively disposed between the scanner and data analyser, the data gate adapted to enable registration in the data analyser of the data signals from the scanner relating to reflected pulses from objects within a predetermined distance range, such that only data signals relating to reflected pulses from objects within a predetermined distance range of interest are registered in, and analysed by the data analyser.

14. A surveying system for surveying and measuring the position of objects along a surveyed route, the system being mounted upon a survey vehicle adapted to travel along a survey route, the system comprising:- a scanner which emits repeated incident energy pulses and detects corresponding returned energy pulses P351515A reflected from an object at a distance from the scanner, and transmits data signals relating to the emitted and detected reflected returned pulses; and a data analyser which analyses the data signals received from the scanner and compares data signals of the detected returned energy beam pulses against data signals of the incident energy pulses to determine distance of the object from the scanner and generate data relating to the distance of detected objects from the scanner; wherein the system further comprises a data gate operatively disposed between the scanner and data analyser, the data gate adapted to enable registration in the data analyser of the data signals from the scanner relating to reflected pulses from objects within a predetermined * *, 15 distance range, such that only data signals relating to reflected pulses from objects within a predetermined distance range of interest are registered in, and analysed by the data analyser. I'... * I

15. A surveying system as claimed in claim 13 or 14 in which at the same time as the scanner emits a incident energy pulse, a synchronisation signal is sent to the data gate, the synchronisation pulse controlling the operation of the data gate to selectively enable the registration in the data analyser of the data signals from the scanner.

16. A surveying system as claimed in claim 15 in which the data gate is adapted to selectively allow registration of data signals which are received by the data gate a predetermined minimum time (tmtri) after the synchronisation pulse.

17. A surveying system as claimed in claim 15 or 16 in which the data gate is adapted to disable registration of the data signals which are received by the data gate a 26 P351515p, predetermined maximum time (tmin) after the synchronisation pulse.

18. A surveying system as claimed in any one of claims 15 to 17 further comprising a timing unit associated with the data gate which is triggered by the synchronisation pulse to after a predetermined time period selectively control the operation of the data gate.

19. A surveying system as claimed in any one of claims 15 to 18 further comprising a delay cable through which the synchronisatjo pulse is transmitted from the scanner to the data gate, the delay cable having an extended length such that transmission of the synchronisation pulse along the : * 15 length of the delay cable to the data gate is delayed by a S...

period corresponding to the period for a data signal relating to a reflected light pulse from an object at the limit of the predetermined distance range to be received at * . . .. S * the data gate.

20. A surveying system as claimed in any one of claims 13 to 19 in which the predetermined distance range comprises 1 to 5m.

21. A method of surveying and measuring the position of objects along a surveyed route, in which a scanner emits repeated incident energy pulses and detects corresponding returned energy pulses reflected from an object at a distance from the scanner, and transmits daLa signals relating to the emitted and reflected pulses; and a data analyser analyses the data signals received from the scanner and compares details of the detected returned energy beam pulses against details of the incident energy pulses to determine distance of the object from the 27 2351515A scanner and generates data relating to the distance of detected objects from the scanner; wherein the method comprises selectively registering in the data analyser only the data signals from the scanner relating to reflected pulses from objects within a predetermined distance range, such that only data signals relating to reflected pulses from objects within a predetermined distance range or interest are registered in, and analysed by the data analyser. * ** * . * S.. S... * S S... * * S 5 * * S * I *

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