WO2007029038A1

WO2007029038A1 - Laser imaging apparatus and method

Info

Publication number: WO2007029038A1
Application number: PCT/GB2006/050277
Authority: WO
Inventors: Ala Al-Obaidi
Original assignee: Sld Limited
Priority date: 2005-09-05
Filing date: 2006-09-05
Publication date: 2007-03-15
Also published as: EP1922523A1; GB0517992D0

Abstract

The invention relates to laser imaging apparatus which obtains a three- dimensional image of the external surface of a structure. The apparatus has a laser device which projects a laser beam upon a portion of the structure such that a portion of the beam corresponding to the portion of the structure is reflected therefrom. An image capture device then detects that reflected portion. A laser imaging pig, which obtains a three-dimensional image representative of the inner surface of a structure being scanned, and a method of obtaining a three-dimensional representation of a structure is also provided.

Description

"Laser Imaging Apparatus and Method"

The present invention relates to a laser imaging apparatus and method, particularly but not exclusively, a laser imaging apparatus and method used in a subsea environment in order to create a three dimensional representation of a subsea structure such as a pipeline.

In the offshore exploration and production industry it is often necessary to inspect subsea structures for any damage such us overstressing, corrosion etc. This can be difficult since the structure often lies in a hostile environment which is poorly lit. This limits the value of conducting a manual visual inspection using a camera and diver. Laser based imaging systems exist; however, these are often too slow and inaccurate and/or not suited to subsea use.

According to a first aspect of the present invention there is provided laser imaging apparatus for obtaining a three-dimensional image external surface of a structure being scanned, the apparatus comprising:- a laser device adapted to project a laser beam upon a portion of the structure such that a portion of the beam corresponding to the portion of the structure is reflected therefrom; and an image capture device capable of detecting the reflected portion.

Optionally, the laser emitting device is adapted to impart a plane of laser light on the external surface of the structure being scanned. Preferably, non-Gaussian generating optics are provided in order to emit the laser light as the plane of light.

Optionally, the laser emitting device comprises a linear laser emitting unit which emits a laser beam in a linear manner. Alternatively, the laser emitting device comprises a rotational laser emitting unit which emits a laser beam in a reciprocating motion.

Preferably, means are provided for mounting the laser emitting device and image capture device at an angle relative to one another.

Preferably, the image capture device comprises a camera, preferably having a CCD array configured to detect the required image.

Typically, the laser emitting device is adapted to emit a blue laser beam or alternatively a green laser beam.

According to a second aspect of the present invention there is provided a laser imaging pig for obtaining a three-dimensional image which is representative of the inner surface of a structure being scanned, the pig comprising:- a body member; a laser emitting device capable of projecting a laser beam upon a portion of the structure inner surface such that a portion of the beam corresponding to the portion of the structure is reflected therefrom; and an image capture device capable of detecting the reflected portion.

Optionally, the laser emitting device is adapted to project a cone of laser light on the internal surface of the structure being scanned. Alternatively, the laser emitting device is adapted to project at least a plane of laser light on the internal surface of the structure being scanned. More preferably, the laser emitting device is adapted to project at least two planes of laser light on the internal surface of the structure being scanned, the at least two planes being angled relative to one another. More preferably, the at least two planes of light are derived from a single laser beam which is split by a partial mirror prior to being emitted by non-Gaussian generating optics. Alternatively a pair of laser emitting devices are provided in order to emit the at least two planes of light.

Preferably, the image capture device comprises a camera, preferably having a CCD array configured to detect the required image. Typically , the camera is provided at a central position between the at least two planes of laser light.

According to a third aspect of the present invention there is provided a method of obtaining a three-dimensional representation of a structure, the method comprising:- projecting a series of laser beams on locations of a structure spaced apart by a lateral distance using a laser emitting device; detecting the images reflected from each location of the structure using an image capture device in order to arrive at a two dimensional representation of those locations of the structure; and collating the two-dimensional representations in order to arrive at a three- dimensional representation of the structure.

Preferably, the step of detecting the series of laser beams further comprises detecting each portion of the beam reflected using a CCD array such that the CCD array produces an output representative of the image reflection.

Preferably, the output of the CCD array is further processed in a processor which is able to calculate the position in free space of the reflected image. Optionally, the series of laser beams are produced using a linear scanner. More preferably, the further processing method using the linear scanner involves calculating the three-dimensional Z-coordinate using a lateral two-dimensional column position (U), vertical two-dimensional row position (V) resultant on the CCD array and a three dimensional X co-ordinate obtained from the linear distance moved by the apparatus in gaining the series of strips. More preferably, the three-dimensional Z co-ordinate is calculated using the following equation:-

Z = CIxU² + C2xU + C3

where C1 , C2 and C3 are co-efficients of this second order equation.

More preferably, the three-dimensional Y co-ordinate is calculated by calibrating the system with a calibration target having a known area S. More preferably, the Y co-ordinate is calculated using the following equation:-

(SxV)

Y =

(CIxU² + C2xV + C3)

where S is the actual size of the calibration target and C1 , C2 and C3 are co-efficients of this equation.

Alternatively, the series of laser beams are produced using a rotational scanner whereby the beam is oscillated back and forth over the structure. More preferably, the step of further processing using the rotational scanner involves calculating the vector λC at which the image capture device views each image reflected by the surface of the structure 116 by relating this to a distance vector D, defined by the vector between the image capture device and the laser emitting device, and a laser incidence vector L using the following equation:-

λC = D + L

where λ is an unknown.

Preferably, the step of further processing using the rotational scanner further involves calculating the laser incidence vector L using the following equation:-

L = ηl_1 + μl_2

Where L1 and l_2 are the direction vectors in the laser plane and η and μ are unknown.

More preferably, the step of further processing using the rotational scanner further involves rotating the laser around the Z-axis of the apparatus and calculating the laser direction vectors L1 and L2 according to the following equations:-

L1 = (0,0,1 )

L2 = (-cos(Φ), sin(Φ), 0)

where Φ is the angle of rotation of the laser emitting device at a particular point in time relative to the image capture device.

More preferably, the step of further processing using the rotational scanner further involves calculating the three-dimensional co-ordinates λ, η and μ of the points pointed at by the laser emitting device using the following matrix:-

Optionally, the method of emitting the laser beams involves emitting a plane or cone of laser light. Alternatively, a plurality of planes and / or cones are emitted.

Preferably, the method further comprises only scanning an area in which the structure is expected to reside. Preferably, the area scanned is a toroidal shape. Optionally, the limitation of the scanned area is further provided for by only activating a corresponding portion of the CCD array.

Embodiments of the present invention will now be described, with reference to the following drawings, in which:-

Fig. 1 is a perspective view of a first embodiment of the apparatus according to the present invention; Fig. 1 A is a schematic representation of a sample image detected by the apparatus of Fig. 1 ;

Fig. 2 is a perspective view of the apparatus of Fig 1 mounted on a clamp arm;

Fig. 3 is a series of schematic representations taken from varying angles of the apparatus of Fig. 1 mounted on a clamp arrangement;

Fig. 4 is a graphical representation of a sample image received by a CCD array of the apparatus; Figs. 5A, 5B and 5C are output diagrams detailing the convolution process for each line in the laser strip respectively showing row signal, filtered signal and first derivation signal against light intensity;

Fig. 6 is schematic representation showing how the z co-ordinate of received image may be determined using a calibration target;

Fig. 7 is a further schematic representation of the process shown in Fig. 6;

Fig. 8 is a schematic representation showing how the lateral and vertical positions of the image received are determined;

Fig. 9A shows a photograph of a sample tubular section and the 3-D image obtained thereof using the apparatus of the present invention;

Fig. 9B shows a photograph of a sample tubular section having a cut therein and the 3-D image obtained thereof using the apparatus of the present invention;

Fig. 9C shows a photograph of a bent sample tubular section and the 3-D image obtained using the apparatus of the present invention;

Fig. 10 is a schematic diagram of apparatus according to the present invention where an alternative rotational scanner rotational scanner is provided;

Fig. 11 is a schematic representation illustrating the principle used by the rotational scanner of Fig. 10 in determining the co-ordinates of the image viewed;

Fig. 12 is an illustration of the method of calculating the laser vector of the rotational scanner;

Fig. 13 is a further schematic representation illustrating the principle used by the rotational scanner of Fig. 10 in determining the co-ordinates of the image viewed;

Fig. 14 is a schematic representation showing how the lateral and vertical positions of the image received using the rotational scanner are determined; Fig. 15 is a transverse partial cross sectional view of laser imaging apparatus according to a second embodiment of the present invention where the apparatus is provided on a pig within a well bore;

Fig. 16 is a schematic diagram showing a more detailed view of the components of the apparatus of Fig. 15;

Fig. 17 is a schematic diagram showing a preferred laser arrangement of the apparatus of Fig. 15;

Fig. 18 is a perspective view of the optical output of the apparatus of Fig.

15; Fig. 19 is a representation of the area treated by the apparatus of Fig. 15;

Fig. 20 is a representation of the data received on a CCD array of the apparatus of Fig. 15;

Fig. 21 is a block diagram of the scanning method according to a second aspect of the present invention; Fig. 22 is a representation of the multi-tasking time-line used in the method of Fig. 21 ;

Fig. 23A shows a sample pipe along which the pig according to the second embodiment may be passed;

Fig. 23B is an image of the apparatus of Fig. 15 being passed along the sample pipe of Fig. 23A;

Fig. 23C is a schematic representation of a single image detected by the apparatus of Fig. 23B;

Fig. 23D is a schematic representation of collated images detected by the apparatus of Fig. 23B; Fig. 24 is a series of schematic representations of a modification of the present invention, where the apparatus is provided on a clamp attached to a mooring chain;

Fig. 25 is a further series of representations of the apparatus of Fig. 24; Fig. 26A, B, C and D are series of representations which show a further alternative modification of the apparatus slideably mounted on a mooring chain;

Fig. 27 is a modification of the present invention where a pair of cameras are used to detect the image of a mooring chain;

Fig. 28A is an image of a sample section of mooring chain; and

Fig. 28B is a sample of the image of Fig 28A obtained using the apparatus of Fig. 27.

Referring to Figs. 1 to 3, laser imaging apparatus 10 comprises a camera unit 12 (provided with a Charge-Coupled Device (CCD) array) and a laser imaging unit 14 mounted at an angle relative to one another. The laser unit 14 is typically a low power laser which emits plane of laser light 14A such that it impinges upon a subsea structure such as a pipe 16. As the light impinges on the pipe 16, it is reflected by the pipe surface. The reflected light is captured by the camera 12 as represented by dashed view envelope lines 12A. The two dimensional image captured by camera 12 is represented by line 18 in Fig. 1A. Clearly since the apparatus is intended to be used in a subsea environment, it may be provided in a water tight housing (not shown).

As shown in Fig. 2 the camera unit 12 and laser unit 14 may be spaced apart and mounted on a clamp arm 20. With reference to Fig. 3, the clamp arm 20 may be part of a clamp arrangement 22. The clamp arrangement 22 can be adapted to include a number of the lasers and / or cameras which are able to view the pipe 16 from a number of different angles. In this way, a large circumferential area of the apparatus may be scanned in a single step. In order to maximise the efficiency of the imaging apparatus, only the area of the camera's CCD where the strips of light are expected to be detected are analysed. This also reduces background "noise" detected.

The laser imaging method will now be described.

In use, a raw laser beam 14B (Fig. 1 ) is emitted from the laser unit 14. This passes into a converter 14C which converts the raw laser beam into a plane of laser light 14A. The plane of light 14A is directed toward the surface of a structure to be scanned such that a profile of light is formed thereon. This light is detected by the CCD array of the camera 12 which typically operates at a frequency of around 25 frames per second. The image detected by the CCD array is depicted by line L on CCD array 24 of Fig. 4. In this regard the intensity of the light arriving at the CCD array may be controlled using optical filters and / or a polarizer (not shown). In addition, in order to detect and record the two dimensional strip image, the grey level of the CCD array is set such that a black and white image representative of the strip image is detected as shown in Fig. 4. The resultant signal (represented by Fig. 5A) may be filtered in a standard fashion using a first derivation equation in order to arrive at the signal represented by Fig. 5B. The first derivation signal (represented by Fig. 5C) of the row signal can then be computed using a typical convolution equation.

The resultant two-dimensional image data may then be stored for further processing as discussed subsequently.

Once the two-dimensional image has been obtained for one section of the structure being scanned, the apparatus can be moved along the structure by a small amount such that another strip of the structure may be scanned. In this way, a number of two-dimensional strip images are gathered, each of which is spaced apart by a small distance along the structure. These strips may subsequently be collated into a three dimensional "cloud" which represents the surface of the structure. The collating process involves using a number of equations to compute the three dimensional co-ordinates of each point in space based upon the two- dimensional co-ordinate data. With reference to Fig. 8, the strip of light impinging upon the CCD array 24 has a lateral two-dimensional column position (U) and a vertical two-dimensional row position (V). The three dimensional X co-ordinate is known since the linear distance moved by the apparatus in gaining the series of strips will be known. The three- dimensional Z co-ordinate of the strip can then be solved using the following equation:-

Z = ClxU² + C2xU + C3 - Eqn (1 )

where C1 , C2 and C3 are co-efficients of the second degree equation.

With reference to Fig. 7, the three-dimensional Y co-ordinate can be solved by calibrating the system with a calibration target having a known area S. As the target S3, S2, and S1 are moved closer to the apparatus, the apparent height on the CCD array will increase. The Y co-ordinate can therefore be calculated using the following equation:-

(SxV)

Y = K* ^ " ) (CIxU ^r τ2 ^ - Eqn (2) ² + C2xV + C3)

Where S is the actual size of the calibration target and C1 , C2 and C3 are co-efficients of the second degree equation. Examples of the three dimensional cloud obtained using this process are shown in Figs 9A, 9B and 9C.

In an alternative embodiment of the present invention a rotational scanner 30 is used whereby the beam 3OA is cast upon the structure 116 of concern. The beam 3OA is oscillated back and forth over the structure in the direction indicated by arrow D in Fig. 10. This allows a greater length of the structure to be scanned without moving the apparatus along the structure.

In this embodiment, since the angle of the laser light impinging upon the structure 116 will be different for each image gathered, a different method of calculating the three-dimensional co-ordinates of the image detected is required. With reference to Fig. 11 to 14, vector algebra is employed. From the geometrical relationship shown in Fig. 11 , the vector λC at which the camera views the image reflected by the surface of the structure 116 is related to the (fixed) distance vector D between the camera 32 and laser 30 and the laser incidence vector L by the following equation:-

λC = D + L - Eqn (3)

where λ is an unknown.

Referring to the laser plane in Fig. 12, the laser incidence vector L may be calculated using the following equation:-

L = ηl_1 + μl_2 - Eqn (4)

Where L1 and L2 are the direction vectors in the laser plane and η and μ are unknown. Since the laser 30 rotates around the Z-axis (of Fig. 11 ) the laser direction vectors L1 and l_2 are given by:-

L1 = (0,0,1 ) - Eqn (5)

L2 = (-cos(Φ), sin(Φ), 0) - Eqn (6)

where Φ is the angle of rotation of the laser 30 at a particular point in time relative to the camera 32.

Incorporating the above equations into a single equation it can be seen that the three-dimensional co-ordinates may be solved using the following equation:-

λc = d + ηl_1 + μl_2 - Eqn (7)

Eqn (7) may be expanded to the following matrix:-

Equation (8) may be solved in order to determine λ, η and μ which represent the three-dimensional co-ordinates of the points pointed at by the laser 30.

As will be understood by those skilled in the art, every element of the CCD array has a direction vector which varies according to the focal length of the camera 12; 32. As illustrated by Fig. 13, the relationship between the elements of the CCD array and the physical points on a plan surface 116 may be determined. For example, in order to configure the system, a camera having 5x4 pixels may be used to monitor an area of 50x40 cm from a distance of 100 cm. Clearly area 5 on the plan area 116 correlates to pixel 5 of the CCD array 7. In this controlled situation Y is known to be 100cm, X is 25cm since it is half the breadth of the area viewed, and Z is 20 cm since it is half the height of the area viewed. Scaling factors may therefore be obtained to be used in all conditions where Y is 100cm from the following equations:-

- Eqn (9)

2 Ph 5

- Eqn (10)

2 Pv 4

In the above equations Xp and Yp are the positions of brightest detected pixels of each row of pixels in the CCD array and these can be used to calculate the direction vectors C, D and L in conjunction with the angle of rotation of the scanner.

Referring to Fig. 15 a further embodiment of the present invention is described where apparatus 110 comprises a pig (also know as scraper) 50 for deployment in a well bore 52. The apparatus 110 has optics comprising a laser 54, camera 56 and generator 58. The laser 54 is typically capable of producing a raw laser beam 55 of green or blue light suitable for use within a subsea environment. The camera 56 is typically able to record around 25 images per second which allows it to record an image at appropriate points along the well bore 52. For example with a camera taking 25 images per second and moving along the wellbore at 0.5 metres per second, an image will be recorded approximately every 20mm along the wellbore. The generator 58 interferes with the raw laser beam 55 in order to produce an optical cone 57 or plane of laser light. The apparatus 112 also comprises collection optics (not shown), spectral laser line band-pass filter (not shown) and a processing unit 60.

The processing unit 60 may comprise a number of processing and / or storage devices capable of holding a large amount of data. In addition, the processing unit 60 may be provides with means for communicating information collected back to a surface based controlling unit (not shown) by any suitable means.

A housing 62 surrounds the components of the apparatus 110 and is designed such that it is able to resist the shocks and loads likely to be placed upon it in a down hole environment.

The apparatus 110 may produce a cone of light as shown in Figs. 15 and 16 or may produce a pair of angled non-Gaussian laser lines as shown in Fig 17 and 18. In this arrangement, the raw laser beam emitted from laser 54 is split into two beams using a 50/50 partial mirror beam splitter 64. Once split, the beams are independently directed toward first and second non-Gaussian laser line generating optics 66, 68 which reflect the laser beam as planes of light 70. The camera 56 is located at the centre of the resultant angled planes of light 70 in order to provide the correct triangulation angle required for a three dimensional image to be obtained. In an alternative embodiment, a pair of discrete lasers could be located at either side of the camera 56.

Referring to Figs. 19 and 20, the system may be arranged such that only a toroidal shape 21 is surveyed, that is, where the actual pipe walls are likely to be. This may be realised by only activating CCD pixels 21 C on the CCD array of the camera which correspond to the toroidal zone. This makes data collection faster and requires a smaller amount of storage space to store the resultant files. This is important since the apparatus is likely to be used in very long pipelines and hence collect a large amount of data.

As shown in Fig. 21 , the process carried out by the present invention may be summarised as 1) capture of the image, 2) fast data recognition due to the relatively small steroidal (doughnut) shape scanned, 3) re-arranging the data using the equations given above, 4) applying the convolution process, 5) storing the data, and 6) manipulating the data in order to arrive at the final three-dimensional output. Referring to Fig. 22, this process may be carried out in a multi-task fashion wherein the processor switches between processing tasks. In the example shown in Fig. 22, a series of images 1 to 5 are taken with short blanking time there between where no image is collected. This blanking time allows separation of the images from one another. Each image is then processed in turn in order to arrive at captured image for each viewed image.

It should be noted that the present invention may be used with a variety of suitable batteries or alternative power sources which are able to supply power to the apparatus for sustained periods of time.

The systems described provide a rapid, accurate, non-contact, laser imaging system which employs a safe visible laser light. In addition, the features of the apparatus allow a large amount of collected data to be stored which can be used in future comparisons on the condition and integrity of the structure being surveyed.

Modifications and improvements may be made to the foregoing without departing from the scope of the invention, for example:- Although the previous description discusses use of the imaging apparatus in a subsea environment it could be in any environment where remote inspection of structures is necessary.

Referring to Figs. 24 and 25, the imaging apparatus may be mounted on a clamping chassis C. The chassis C is able to lock onto links L of a mooring chain when scanning the links of the chain. This ensures that the imaging apparatus is fixed relative to the chain (which may be moving through the seawater relatively quickly due to strong current) and therefore provides a stable scanning platform. When a different part of the mooring chain is to be scanned, the apparatus may be unlocked and moved along the chain to an appropriate location using e.g. an ROV or other transportation means. This allows any corrosion, frictional wearing and elongation of the links L to be monitored.

Referring to Fig. 26A, B, C and D, in a further modification of the apparatus of Fig. 24 and 25, the chassis of the apparatus 1C may be mounted on a guide track T clamped to the mooring chain at either end. Once positioned on the chain, the apparatus 1C may slide along the track T in order to scan the links L therealong. In this regard, the extent of movement along the track T may be monitored and used as the X coordinate in order to determine the point in space detected by the imaging apparatus. As shown in Fig 26D a housing H may also provided along the chain, to store the apparatus when not in use.

As shown in Fig. 27, a modification is shown where instead of a single camera being provided on the clamp arm a first camera C1 and second camera C2 may be angled toward the intended scanning zone (typically at an angle of 45 degrees relative to one another). A laser 54 is provided between the pair of cameras and emits a laser strip 54A. the angle of the cameras C1 and C2 allows a portion of the inner connection of the links L to be viewed. The provision of two cameras also minimises any dead areas in the gathered image. Fig. 28A shows a sample connection between links L and Fig. 28B shows an example of the three dimensional image obtained by this modification.

Claims

1. Laser imaging apparatus for obtaining a three-dimensional image of the external surface of a structure being scanned, the apparatus comprising:- a laser device adapted to project a laser beam upon a portion of the structure such that a portion of the beam corresponding to the portion of the structure is reflected therefrom; and an image capture device capable of detecting the reflected portion.

2. Laser imaging apparatus according to claim 1 , wherein the laser emitting device is adapted to impart a plane of laser light on the external surface of the structure being scanned.

3. Laser imaging apparatus according to claim 2, wherein non-Gaussian generating optics are provided in order to emit the laser light as the plane of light.

4. Laser imaging apparatus according to any preceding claim, wherein the laser emitting device comprises a linear laser emitting unit which emits a laser beam in a linear manner.

5. Laser imaging apparatus according to any of claims 1 to 4, wherein the laser emitting device comprises a rotational laser emitting unit which emits a laser beam in a reciprocating motion.

6. Laser imaging apparatus according to any preceding claim, further comprising means for mounting the laser emitting device and image capture device at an angle relative to one another.

7. Laser imaging apparatus according to any preceding claim, wherein the image capture device comprises a camera having a CCD array configured to detect the required image.

8. Laser imaging apparatus according to any preceding claim, wherein the laser emitting device is adapted to emit one of a blue laser beam or a green laser beam.

9. A laser imaging pig for obtaining a three-dimensional image which is representative of the inner surface of a structure being scanned, the pig comprising:- a body member; a laser emitting device capable of projecting a laser beam upon a portion of the structure inner surface such that a portion of the beam corresponding to the portion of the structure is reflected therefrom; and an image capture device capable of detecting the reflected portion.

10. A laser imaging pig according to claim 9, wherein the laser emitting device is adapted to project a cone of laser light on the internal surface of the structure being scanned.

11. A laser imaging pig according to claim 9, wherein the laser emitting device is adapted to project at least a plane of laser light on the internal surface of the structure being scanned.

12. A laser imaging pig according to claim 11 , wherein the laser emitting device is adapted to project at least two planes of laser light on the internal surface of the structure being scanned, the at least two planes being angled relative to one another.

13. A laser imaging pig according to claim 12, wherein the at least two planes of light are derived from a single laser beam which is split by a partial mirror prior to being emitted by non-Gaussian generating optics.

14. A laser imaging pig according to any of claims 9 to 11 , wherein a pair of laser emitting devices are provided in order to emit at least two planes of light.

15. A laser imaging pig according to any of claims 9 to 14, wherein the image capture device comprises a camera having a CCD array configured to detect the required image.

16. A laser imaging pig according to claim 15, wherein the camera is provided at a central position between at least two planes of laser light.

17. A laser imaging pig according to any of claims 9 to 16, wherein the laser emitting device is adapted to emit one of a blue laser beam or a green laser beam.

18. A method of obtaining a three-dimensional representation of a structure, the method comprising:- projecting a series of laser beams on locations of a structure spaced apart by a lateral distance using a laser emitting device; detecting the images reflected from each location of the structure using an image capture device in order to arrive at a two dimensional representation of those locations of the structure; and collating the two-dimensional representations in order to arrive at a three- dimensional representation of the structure.

19. A method of obtaining a three-dimensional representation of a structure according to claim 18, wherein the step of detecting the series of laser beams further comprises detecting each portion of the beam reflected using a CCD array such that the CCD array produces an output representative of the image reflection.

20. A method of obtaining a three-dimensional representation of a structure according to claim 19, wherein the output of the CCD array is further processed in a processor which is able to calculate the position in free space of the reflected image.

21. A method of obtaining a three-dimensional representation of a structure according to any of claims 18 to 20, wherein the series of laser beams are produced using a linear scanner and the processing method using the linear scanner involves calculating the three-dimensional Z- coordinate using a lateral two-dimensional column position (U), vertical two-dimensional row position (V) resultant on the CCD array and a three dimensional X co-ordinate obtained from the linear distance moved by the apparatus in gaining the series of strips.

22. A method of obtaining a three-dimensional representation of a structure according to claim 21 , wherein the three-dimensional Z coordinate is calculated using the following equation:-

Z = ClxU² + C2xU + C3

where C1 , C2 and C3 are co-efficients of this second order equation.

23. A method of obtaining a three-dimensional representation of a structure according to claim 21 , wherein the three-dimensional Y co- ordinate is calculated by calibrating the system with a calibration target having a known area S.

24. A method of obtaining a three-dimensional representation of a structure, wherein the Y co-ordinate is calculated using the following equation:-

(SxV)

Y =

(CIxU² + C2xV + C3)

25. A method of obtaining a three-dimensional representation of a structure according to any of claims 18 to 24, wherein the series of laser beams are produced using a rotational scanner whereby the beam is oscillated back and forth over the structure.

26. A method of obtaining a three-dimensional representation of a structure according to claim 25, wherein the step of further processing using the rotational scanner involves calculating the vector λC at which the image capture device views each image reflected by the surface of the structure 116 by relating this to a distance vector D, defined by the vector between the image capture device and the laser emitting device, and a laser incidence vector L using the following equation:-

λC = D + L

where λ is an unknown.

27. A method of obtaining a three-dimensional representation of a structure according to claim 26, wherein the step of further processing using the rotational scanner further involves calculating the laser incidence vector L using the following equation:-

L = ηl_1 + μl_2

Where L1 and L2 are the direction vectors in the laser plane and η and μ are unknown.

28. A method of obtaining a three-dimensional representation of a structure according to claim 27, wherein the step of further processing using the rotational scanner further involves rotating the laser around the Z-axis of the apparatus and calculating the laser direction vectors L1 and L2 according to the following equations:-

L1 = (0,0,1 )

L2 = (-cos(Φ), sin(Φ), 0)

29. A method of obtaining a three-dimensional representation of a structure according to claim 28, wherein the step of further processing using the rotational scanner further involves calculating the three- dimensional co-ordinates λ, η and μ of the points pointed at by the laser emitting device using the following matrix:-

30. A method of obtaining a three-dimensional representation of a structure according to claim 29, wherein the method further comprises only scanning an area in which the structure is expected to reside.

31. A method of obtaining a three-dimensional representation of a structure according to claim 30, wherein the area scanned is a toroidal shape.

32. A method of obtaining a three-dimensional representation of a structure according to either of claims 30 or 31 , wherein the limitation of the scanned area is further provided for by only activating a corresponding portion of the CCD array.