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Deformation Scan with Ring-Laser Equipment

Version: 1.9

Date: 31/10/2023

Introduction

Welcome to the module WinCan LaserScan. This manual provides you with all information you need for the usage of this WinCan extension.

WinCan LaserScan supports the following systems for pipe deformation measurement with laser beams:

• Ring Laser: Laser rings that are created from a laser plane perpendicular to the pipe axis.

• Multi Laser: Multi-Laser-Systems beam with multiple concentric mounted lasers multiple points in regular clock hour angles on the pipe surface.

Concept

The concept of all laser-based deformation measurement systems is similar:

• The input you need is a video clip that was captured without light, only with the lasers on. For the video clip you can set a start and an end position. Currently the following video formats are supported: MPEG-2, MPEG-4, MPEG H.264 and DivX.

• Make sure a Time-Distance file is available for each video clip: the software continuously writes the MPEG time [sec] and the corresponding position [m] of the crawler during video capturing.

• The output you will get is a group of 36 radii on the pipe cross section after an interval of 10cm. These data can be drawn graphically or shown as colorized deformation grades in the WinCan ScanExplorer.

In general you can determine the 3D position of a laser dot relative to the camera as long as you know the position of the laser source and the orientation of the laser beam.

Ring-Laser System

The ring laser system creates a surface from a single laser source with a cone prism. The laser source is built into a stick which is clutched to the camera head. If the stick is parallel to the pipe axis the laser surface is perpendicular to the pipe wall and thus projects a circle line inside a pipe with a circular profile that can be seen from the camera.

You can capture the movement of this laser circle as a video clip and the module WinCan LaserScan will calculate the data. Finally a 3D profile of the pipe is generated:

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Crawler with laser stick and the camera view with the laser ring.

Multi-Laser System

The multipoint laser system consists of several laser sources that are located behind the lens and project multiple dots in a defined angle at defined clock positions onto the pipe wall surface. The LaserScan module detects these dots and interpolates a circle line through them.

Below are illustrated a multipoint laser camera head with 7 lasers and the interpolated circle line on the pipe wall surface.

Installation & Prerequisites

The module WinCan LaserScan is installed automatically together with the WinCanSETUP. Make sure the following license slot is activated:

Launching the module WinCan LaserScan

You can launch the LaserScan application in two ways:

1.) Launch WinCanVX and double-click on the grey bullet in the field

Laser in the first observation line. The LaserScan application opens and loads the existing video clip which deformation measurement is based on. The grey bullet in the field Laser is then replaced by a scan icon:

2.) Launch WinCan LaserScan directly as a Stand-Alone application via the START menu:

Ring-Laser

When working with any laser equipment never look directly into the laser beams. Despite the usage of low powered laser sources, the intensity of the laser light may still sustainably endanger your eyes.

Always follow the guidelines provided by the camera manufacturer.

Recording a Ring-Laser Video

Set the video recording format to MPEG2 or MPEG4 and drive with a constant and low speed through the pipe during recording. Especially mind the following issues:

• Additional light: The pixels in the video image that show the laser ring must be the brightest ones. So make sure you TURNED OFF any additional light besides the laser sources during the video recording.

• Text display: Overlay text must not be displayed close to the laser ring. You may move it to the edges of the vide frame and limit the text to be shown to date and distance.

• View direction along the pipe axis: Mind that you undo any camera pan and tilt rotations and that the camera is pointed to the center of the pipe straight down the pipe axis.

• Laser ring 75% of the image height: Mind that the laser ring covers about 75% of the image height when mounting the laser stick: the measurement accuracy increases with the ring laser diameter.

• Autofocus and automatic iris: Turn off autofocus and automatic iris because they do not work well without lighting. Open the iris as much as you can still see a clearly visible ring laser on a completely dark background.

• Water flow: whenever possible make sure the water flow is blocked temporarily so that the pipe bottom area can be scanned.

• Capture a sequence with calibration ruler:

Ring-Laser Calibration

The calibration of the ring laser video is the first step of the post processing in the office. The settings to be done are important for the accuracy of the measurement and consider the zoom factor and the lens distortion.

The purpose of the calibration is to relate different real diameters to pixel distances on the video image.

1.) Start the WinCan LaserScan application in WinCan, by clicking the LaserScan icon in the observation table of WinCan. Like this you open the application with the video that is attached on the same observation.

2.) Choose the video type Ring-Laser-Video.

3.) The video is loaded and paused on the first image.

4.) Position the video with the scroll bar on the bottom of the window to the position where the calibration ruler was held into the video capturing.

5.) Open the Calibration Settings dialogue by clicking on the button Calibration in the main window:

6.) The command button Set by Mouse Clicks makes diameter calibration much easier and faster via the dialogue box below: Click on the spots on the calibration ruler that are marked with green circles and ignore the spots that are marked with red crosses (smaller than 200mm or bigger than 600mm). These diameter values are automatically calculated by interpolation but can be manually adjusted later on.

7.) Confirm your settings by pushing the green OK button. The yellow calibration circles will then be displayed accordingly on the video image. A fine adjustment of the corresponding diameters can be done in the value fields of the calibration dialogue.

8.) With the checkboxes to the left of the diameter values you can activate or deactivate certain diameters. You can't deactivate the 200mm diameter which must always be visible. Make sure that only the visible diameters are activated.

9.) The yellow circles appear non-circular but oval shaped due the analogue video signal that provides rectangular instead of squared pixels. The horizontal distortion is normally determined from the video file. You can double-check its correctness using the clip sequence that shows the calibration ruler at a vertical position.

On the calibration ruler shown in the image below you can see the diameters for 200mm, 300mm, 400mm, 500mm and 600mm:

Figure 1: The calibration ruler, left about horizontal and right about vertical. In the left image you can clearly see the lens distortion because the 50mm distances get smaller the more they are located at the edge.

Manage Calibration Values

A calibration is done for a certain zoom factor of the lens and the distance to the calibration ruler (distance to the ring laser plane). If you always apply the same zoom factor and ring laser distance for a certain pipe diameter you can re-use a previously set calibration with the following commands:

Creating a Ring Laser Scan

After the calibration we can create a scan from the video. The LaserScan application will go between the start and end position stepwise through the video and extract the laser ring with image processing. From this laser ring the software calculates a cross section with all measures.

Setting the Start and End Position

As the first step we have to determine the start and end position for the scan. Befor and after no measures are calculated.

• Mind that you have a valid start and end distance in the round brackets. Without a valid distance you won't have a valid scan distance and you will not be able to start the scan. The distances are taken from the time-distance file. This text file (*.txt) is automatically created as soon as you start MPEG recording.

• Position the video with the horizontal scroll bar at the bottom of the window to the beginning of the scan area in the video. Click on Start Time.

• Position the video with the horizontal scroll to the end of the scan area in the video. Click on End Time.

By default the start time is on 0 sec. and the end time is equal to the duration of the video. If no distance can be mapped to these times  the indication (-) is written. Because of this no scan distance can be calculated either.

With a valid start and end distance you will also see a valid scan distance (8.300 m).

Launch Scan

Hitting the button Start Scan is going to scan the pipe between start and end time: the software thus calculates and saves n radii of the laser ring at regular distance steps. Activating the option Invert scan is going to scan the video clip backwards.

Time-Distance-Information

As mentioned plays the time-distance information an important role when the laser video is captured.

In the following diagram you can see the time-distance values of a video that contains the ingoing drive with continuously increasing distance values as well as the outgoing drive with continuously decreasing distance values.

From the diagram it's clear that from a certain time we always get a distinct distance value. The other way around it's not clear. For the most distances we have two times, one from the ingoing drive and one from the outgoing drive.

An image is usually are taken from the video for a given distance interval. The scan time span thus must show a continuously increasing or decreasing curve based on the distance values. You therefore can start the scan only when you have set a time span that corresponds either to the ingoing or outgoing drive. Try to drive with a constant speed through the pipe during the video capture of that part.

Figure 2: Time-distance values of a video that contains the ingoing drive to the left with continuously increasing distance values as well as the outgoing drive to the right with continuously decreasing distance values.

Scan Properties for Ring Laser Videos

Hitting the button Scan Settings opens the dialogue for the Ring-Laser Scan-Properties with the sections Scan Properties and Image Filter. If you click into a numeric field, you can easily change the value either with the mouse wheel or the value buttons to the right of the field:

• Scan step distance (cm): Step distance between two cross section measurements.

• Points on circle: No. of radius points to search on the laser ring. The points will be equally spread over 360°.

• The final detection is a search for the brightest pixels on the search rays beginning at a minimal search radius and ending at a maximal search radius.

• With the fields Ignore clock/angle 1-3 you can exclude 3 sectors from detection. This can be useful to avoid wrong detections due to water reflections, high water levels etc.

• Show processing image: show the measurement lines during the scan process

• Show negative image: invert the background color from black to white

• Write info into image: writes calculated diameters and ovality into the image.

• Draw graphics into image: draws the points detected on the laser ring into the image.

Image Filter

These properties are important for the correct detection of the laser ring in the image. The video image will be processed as follows:

• The value for Contrast is increased (value > 1) or decreases (value < 1) the contrast. Standard value is 1.0 (= no contrast change).

• The value for Brightness increases or decreases the luminosity of the image. Standard value is 0 (= no brightness change).

The color image will be converted to a grayscale image with gray values between 0 (black) and 255 (white). There are now two types of thresholds to choose from:

• Red Threshold: use red color components as threshold values. This option only makes sense, if the laser ring is clearly red and the pipe walls are not red (e.g. black or grey PVC pipes with white chalk spots that reflect brighter than the red laser ring).

• Gray Threshold: use brightness for the grayscale conversion (e.g. red PVC pipes)

• Automatic by %: Keep a given percentage of the brightest pixels (e.g. 3.5%) in grey whereas the rest (e.g. 96.5%) will be converted to black. This option is activated per default.

Image Cropping

With the fields in the group Image Cropping you can exclude areas on the borders of the image.

Laser ring detection with over-blended calibration rings. To the left in original color display and to the right as negative display that suits better for printing.

In the processing image you can see the search rays that detect the laser circle.

Output of LaserScan data

After the scan of the ring laser video has finished the time-distance file provides all values of the calculated radii in the header part:

The WinCan LaserScan module is going to use these data to visualize the pipe deformation with the ScanExplorer and to draw the deformation graphics on three separate report pages.

The scan data are copied into a separate folder that gets the same name as the video file.

Pipe deformation in the ScanExplorer

Compared to a normal pipe scan that shows the inner surface of the pipe, a deformation scan shows the radius that are stored as grayscale values. The smallest radius in the pipe gets black (grayscale value 0) and biggest radius gets white (grayscale value 255). For better visualizing the differences between the radii a color map is used. This color mapping can be modified in the Color Map Settings dialogue (Menu View > Show Color Map Settings):

The panel above shows the color map settings dialogue of the WinCan ScanExplorer with an ovality range between -15% and +15%.

You can move the color triangles with the left mouse button. Right-click on the color triangles to change its color or right-click between two triangles to create a new color triangle. Right-click on an existing color triangle and keep the CTRL key pressed to delete it.

The illustration above shows the result of a ring laser scan in the WinCan ScanExplorer. At each cross section measurement a front view image is stored.

In addition the current diameter and the ovality in % is shown in the status bar of all panels.

Ovality Report

Hitting the printer icon or selecting the command File > Print Ovality Report in the LaserScan application allows you to print the deformation report.

The first report page shows the ovality graph over the entire inspection length. For each section where the ovality exceeds the allowed limit a front view image is shown.

You can choose between showing only the max. peek or showing all peaks of each section. The ovality in % is calculated as follows according to the ASTM F1216-09 standard:

Ovality = (InnerDiamMAX - InnerDiamAV) / InnerDiamAV * 100 [%]

Where the average of the inner pipe diameter is calculated as:

InnerDiamAV = (InnerDiamMAX + InnerDiamMIN)/2 [mm]

The ovality limit in percent as well as the information in the report header are written by WinCan at the start up into the INI-file of the LaserScan application.

The 90%-Fraktil value corresponds to the ovality value at the position of an ascending value list where you stop after reaching 90% of the values.

Median Diameter Report

The second report page provides the radius scan as shown in the ScanExplorer. You can also modify the color map that is used for the radii.

Below the SideScan view the median diameter graph over the entire inspection length is displayed: the median value is always taken from the middle of a given list of available values that has been sorted previously in ascending or descending order:

Median diameter:
95, 98, 100, 102, 150 -> 100

Average diameter:
95, 98, 100, 102, 200 -> 119

Unlike the average value the median value reduces the effect of large peek values on a measurement result.

The lower and upper allowed limit of the diameter is written into the INI-file by WinCan.

Capacity Report

The third report page also provides the radius scan as shown in the ScanExplorer.

Below the SideScan view the capacity graph over the entire inspection length is displayed. The capacity is defined as the cross-section area of the pipe: the graph continuously draws the capacity in % of the expected capacity:

The lower and upper allowed limit of the capacity is passed by WinCan in the INI-file.

3D-View

Hitting the 3D icon or selecting the menu command File > Open 3D-Window in the LaserScan application opens a panel that illustrates the measured data as a 3D pipe:

The 3D panel provides you the following options:

• Rotate the view keeping the central mouse button/mouse wheel pressed.

• Pan the view /mouse wheel and the CTRL key pressed

• Zoom the view keeping the central mouse button and the SHIFT key pressed or just rotate the mouse wheel.

• Change the color map by clicking on the coloured toolbar button.

• Hide/Unhide the surface grid and the shadow below the pipe.

• Export the 3D data into a DXF or DWG file (compatible with AutoCad).

2.4.5.1      Scan Data in Excel

Hitting the button Excel Export or selecting the menu command File > Open Scan Data in Excel you can open the scan data in Excel. During the scan procedure a CSV file (Comma Separated Values) is written with the same name as the video file but with the extension *.CSV. This file type can be opened in Microsoft Excel or OpenOffice Calc.

If you modify the data or the format you should save the file as an xls or xlsx-file.

Figure 3: Scan data in Excel with the corresponding ovality chart.

Accuracy of the Measurement

The accuracy of the diameter measurement depends on the following parameters:

• video image resolution

• calibration of the video

• inner pipe diameter

• laser ring size on the video image

The accuracy describes how much the calculated diameter changes in mm when the laser circle diameter on the video image changes on one pixel.

Under the condition that the calibration was done correctly and that the center of the laser line can be detected properly the accuracy can be calculated as follows:

Accuracy = Inner Pipe Diameter [mm] / Pipe Diameter on Image [pixels]

Based on a sample image of a 300mm pipe taken from an MPEG1 video clip (resolution: 320 x 288) the accuracy is calculated as follows:

Accuracy = 300 mm / 222 pixels = 1.35135 mm / pixel

The error tolerance for diameters of 300mm thus can be calculated:

Error tolerance = (1.35135 / 300 *100) = 0.45%

Figure 4: The zoom angle produces a laser ring diameter of 222 pixels which corresponds to 77% of the image height.

The larger the laser ring appears in the video image the better is the accuracy. The laser ring should always cover about 75% of the video image.

If you capture the same pipe with an MPEG2 video format (resolution: 720 x 576 (PAL)) the accuracy will be doubled:

Accuracy = 300 mm / 444 pixels = 0.6757 mm / pixel

The error tolerance for diameters of 300mm thus can be calculated:

Error tolerance = (0.6757 / 300) *100 = 0.23%

Multi-Laser

For the detection of the circle line multiple laser dots are searched. In the example below 7 laser sources are mounted in 45° angle steps around the view axis (at 12,1.5, 3, 4.5, 7.5, 9 and 10.5, o'clock).

The laser dots are only searched within a narrow range around the 45° axis (green lines). In addition a certain angle (cyan dashed lines) around 6 o'clock is also ignored to avoid wrongly calculated dots due to reflections.

Creating a Multi-Laser Video

Follow the guidelines from the camera manufacturer. Here are some general tips:

• Caution Laser: Do NOT to look into the laser beams. Even if only low power lasers are used, the strong radiation of the laser light are still dangerous for your eyes.

• At the beginning of the video turn on light for a moment: At the beginning or end of the video you must turn on the light for a short moment, so that the full view circle is visible and that the position can of it can be controlled.

• NO additional light during laser scan: In general must the pixels of the laser dots be the brightest in the video image. Therefore it is absolutely necessary to TURN OFF any additional lights beside the lasers during the laser video recording.

• NO data overlay: Because the laser dots should be the brightest dots in the image there should be no overlay information turned on in or near the laser dot ring. In the corners of the video frame are overlays allowed.

• View direction along the pipe axis: Pay attention that you undo any camera pan and tilt rotations and that the camera looks in the center of the pipe straight down the pipe axis.

• Large video format: Choose a large video format such as MPEG-2. The larger the image, the higher the measurement precision will be. See chapter Fehler! Verweisquelle konnte nicht gefunden werden..

• Constant speed: Drive as constant as possible in the section where you capture the laser dots.

Creating a Multi-Laser Scan

Launch the WinCan LaserScan module hitting the grey bullet in the first observation line of the LaserScan column in the observation grid. Next choose the MultiLaser Video as video type.

1. The video will be loaded and the first image is shown.

2. Position the video with the scroll bar on the bottom of the window to the start of the scan and click on the button [Start Time]. With the button [Reset Times] you can set the video start time to 0.

3. Position the video to the end of the 360° rotation and click on the button [End Time]. With the button [Reset Times] you can set back the video end time to the video duration time.

4. With the button [Play Video] you can play back the video in normal speed between the start and the end time.

5. With the button [Start Scan] you can scan between the start and end time. At regular steps 7 radii on the laser ring are detected and measured. Between the 7 dots n interpolated radii are calculated. With the option “Reverse Scan” the video will be scan backwards. You cannot start a scan if the distance between start and end time are not continuous. If the video contains the forward and the backwards drive you can only scan the forward or the backward part but not both at the same time.

This illustration shows a WinCan LaserScan based on a video clip recorded with a MultiLaser-System: The top left image shows the laser dots on the current image of the video. The black & white image at the bottom left shows the image after processing. (radius scanning) The large image to the right shows the laser dots on the video image together with the positions of the calculated radii (small red dots on the circle line).

Time-Distance-Settings

The MultiLaser video clip also uses a time-distance.

Scan Settings for Multi-Laser-Scans

First we will do the settings that have to be done in principal only once. Open there for the Scan Settings dialogue with the option Expert checked:

The fields that can only be modified in the expert mode have a green background. These are mainly the configurations for the lens and lasers. Simply place the cursor into the desired field and change its value with the mouse wheel or hit the corresponding value buttons.

• The first 4 parameters concern the position and size of the View Circle. Switch on the light and place the yellow circle precisely around the view circle so that it fits tightly. Check the position of the yellow circle regularly. The view circle of the fish eye lens is slightly oval due to the distortion of the frame grabber conversion. The precise fit of the yellow circle measures this distortion.

• The next parameters correspond to the Laser and Lens Settings:

For the systems known at the time of writing these parameters can be taken out of the following table:

Variable MultiLaser settings

The following settings can vary from scan to scan.

• Scan step distance (cm): Step distance between two cross section measurements.

• No. of radii per 360°: No. of radii over 360° that are interpolated in between the 7 detected radii from the laser dots.

• Axis tolerance (+/-°): Angle containing the range of detectable laser dots.

• Camera Rotation (°): The camera head of most systems can be manually rotated and therefore have a slight rotation so that the laser dots also appear slightly rotated. The average rotation angle is shown in the last parameter on the image. For a good laser point detection this angle should be as small as possible.

• Find Minimum: Find automatically the correction angle so that laser rotation gets minimal.

• Min. Radius (%): Minimal allowed search radius in percent.

• Max. Radius (%): Maximal allowed search radius in percent.

• Ignore Angle at 6h: Size of the angle around 6 o'clock in witch no laser dots should be searched. It could make sense to change this value from scan to scan if you want to avoid the search of laser dots in that area because of water reflections.

• Recenter camera: If the camera is not exactly in the center of the pipe the radii are recalculated as if the camera would be in the center. The offset from the pipe axis is stored and used by the ScanExplorer.

• Write info into image: Option for writing information into the image.

• Draw graphics into image: Option for drawing the graphics into the image.

The Image Filter properties are important for the correct detection of the laser dots in the image. The video image will be processed as follows:

• The color image will be converted to a grayscale image with gray values between 0 (black) and 255 (white).

• The Contrast is increased by a factor of normally 1,5 to 2,0.

• The Brightness is reduced by a value of normally 0 to -50.

• If lots of single white pixels remain in the image the Median filter can be used to remove those pixels. A value of greater than 1 will increase the denoising filter. A value of 1 (standard) will not do any change.

• At the end the grayscale image will be converted to a black & white image by setting all pixels with a value smaller than a B/W-Threshold to black and all other to white. After this final step only the laser dots should remain in the image. The B/W-threshold is normally on a value of 240 - 250.

• With the Gamma value you can change the brightness of the big preview image. It has no influence on the laser detection.

Result of a Multi-Laser Scan

The result of a Multi-Laser scan is identical with the ones from a ring laser scan

Accuracy of the Measurement

The precision of the diameter measurement depends on the video image resolution, the inner diameter of the pipe and the projection angle of the laser beams:

Single laser geometry with a laser angle of 35° (a) and a laser offset distance (c) of 120mm. The radius r can be calculated because we know the laser angle (a) and the view angle (b) of the laser dot out of the image. You can see that the view angle (b) becomes smaller the bigger the pipe gets. The same is the case for the angle (γ) between the laser and the view direction to the laser dot.

The accuracy in % shows how much the radius changes when the laser dot moves in- or outwards one pixel. The accuracy is not constant and decreases with the pipe diameter. The graphic below shows the accuracy in % in relation to the view angle (b) (IPEK DS3 system). The accuracy decreases to infinity when the view angle (b) will be equal to the laser angle (in this case 35°):

This graphic illustrates the accuracy in % in relation to the pipe radius in mm:

With an image height of 576 pixels (PAL, MPEG-2) and a perfect orientation of the camera head to the pipe axis, the accuracy in % for different pipe diameters looks as follows: