Terrestrial Laser Scanning assignment

Transcription

1 Terrestrial Laser Scanning assignment Objective: Underground 3D survey using terrestrial laser scanning Location: Otaniemi campus, Innopoli 3 Business Area Equipment: Faro Focus 3D Methodology: Multiple scans using the TLS control network established during previous assignment Output: 3D object modelling Deliverables: Survey report including scanning plan, equipment, parameters, targets, georeferencing report with target registration analysis, screenshots of the produced model Deadline: TBD Assign roles for each team members (change the roles from the previous assignment): assignment manager field operators for each scanning station secretary General instructions As with previous assignments, the TLS assignment consists of four phases: planning, fieldwork data collection, data processing, and reporting. Below you can find the general instructions to be followed during each phase of the assignment. More instructions that are specific will be provided during each phase. Planning phase Do a proper field reconnaissance of the project area. Draw a sketch of the underground tunnel. Identify the location of control points (metal washers) on the concrete pillars. Develop an observation scheme o Include observation times for assignment time management. Verify and prepare the instruments. Data collection Assignment leader takes care of the equipment and manages the fieldwork. Prepare the instrumentation: laser scanner, tripod, reference targets, batteries, safety vests, etc. Set- up the reference targets on pre- mounted washers so that the geometry is optimal in reference to the scanning location. o Minimum of 3 targets visible in different directions. o Max distance between scanner and target dependent on scanning resolution and target size, in this exercise ~20 m. o Handle the spherical targets with care, avoid touching the sphere surface. Page 1 of 9

2 Set- up the scanner on pre- planned location, level the instrument, set/check the scanner parameters o Project name, scan name, scanning resolution, operator. o Use Inclinometer, Use Compass and Use Altimeter: all on. Start scan, during the scan make sure that scanner field of view is clear o No persons in the line of sight!!! o Note: laser is measuring on both faces! o Take extra care that no- one is looking at the laser beam within the eye- safety distance! Keep a field log (drawing) of used scanning and target locations utilizing the sketch of the tunnel. Move targets and scanner to the next scanning location after the scanning has ended and scanner shows that the scan was successful. Data processing Use a dedicated processing software (we use FARO SCENE) o Software is available on the 4 th floor of Gentti (room 4.115). With FARO SCENE software, you process point clouds with following steps: o Import the data collected in the field (scans, pictures and control points) o Filtering the point clouds for reducing noise and other unnecessary and false points from the data o Automatic recognition of the sphere targets in each scan o Georeferencing o Registration of the scans using sphere targets o Assign colour to points. During laser scanning there is camera integrated to the system. With this, we can define a colour value for each point in the point cloud. 3D- object measuring and modelling o Take some measurements from the point cloud (e.g., the diameter of the concrete pillars) o Create some 3D- models of walls, pillars or other objects Reporting Read the specific instructions. Include the assignment deliverables Screenshots of the different processing steps Assignment timetable Week number Description 42 Field planning: network design 47 Data collection: field scanning 48 Data processing: registration & georeferencing 49 Data processing: 3D modelling + reporting Page 2 of 9

3 Week 42: TLS Assignment Specific instructions for field planning Objective: TLS field work planning Methodology: Pairs/group (recommended) Prerequisites: TBD The students should be able to carry out main preparatory activities related to the field data collection: Conduct proper field reconnaissance Identify the potential location of the scanning stations Develop an observation plan Select the appropriate instrumentation and measuring technique Identify the logistical aspects of the terrestrial laser scanning work Become familiar with various roles in group work Read the general instructions first! Additional reading Schofield 1, section 14.9, Uren, section 10.8, handouts Electronic copies of the reading material are provided in Moodle. 1 Surveying- 6th- Edition Page 3 of 9

4 TLS Assignment Specific instructions for data collection Objective: To take scans in multiple locations along the tunnel Methodology: Pairs/group (recommended) Prerequisites: Reference network from the TS & DL assignments The students should be able to carry out laser scanning measurements using the control network established in the previous phase. Read the general instructions first! Additional reading Schofield 2, section 14.9, Uren, section 10.8, handouts Electronic copies of the reading material are provided in MyCourses. Keep in mind! Take useful field notes and photos even though much of the work is done automatically. 2 Surveying- 6th- Edition Page 4 of 9

5 Week 47: TLS Assignment Specific instructions for data processing and reporting Objective: To become familiar with the TLS data processing workflow Methodology: Pairs/group (recommended) Prerequisites: Complete previous phases of the assignment The below instructions are prepared courtesy to Dr. Matti Vaaja ( , matti.t.vaaja(at)aalto.fi) In this exercise you process scans with following steps: Filtering the point clouds Registration of the scans using sphere targets Assign colour to points 3D- object measuring and modelling In the case of difficulties, take contact with TBC We use dedicated processing software (we use FARO SCENE) for the TLS data processing: Software is available on the 4th floor of D- talo, room (right side) in computers Nstar and Lasertyöasema. Similar to other courses, please book a time for the computer in Optima ( GMA- atk- luokka - folder). Login with user: Laser and password: kurssi1 The scanning folders locates in \\work\courses\t\maa\6\3261\students\tlsdata\faro_scans (Copy this address and put it to windows search) TBC Open FARO SCENE software and create new scan project for your group. Select a location \\work\courses\t\maa\6\3261\students\... TBC Drag and drop your scan folders to the Workspace under Structure view Start the Quick- view of a single scan via the command View > Quick View in the context menu of the scan. Next you can open the 3D- View of your scan View > 3D- View. Page 5 of 9

6 Filtering the point clouds As you probably have noticed, data contains among others a lot of noise. For reducing noise and other unnecessary and false points from the data, different filtering methods are used. In the 3D- View you can filter your data with Stray, Distance Based, Dark Scan Points or Smooth tool. More information about the filtering you can have by opening Help > Contents. Registering Scans (from Contents:) Scan points are recorded and saved in a coordinate system which is relative to the scanner. The point of origin for this scan coordinate system is the position where the laser meets the mirror. The coordinates of this point are x = 0, y = 0, z = 0. If you have two or more scans taken at different locations in a room, right after scanning they will only know their own scan coordinate systems. But of course in reality the origins of these scan coordinate systems have been at different positions in the room, and therefore it is necessary to determine the spatial relationship between them. This is called registering the scan, and the step from the scan coordinate system into the overall coordinate system is called transformation. The basic principle behind scan registration is very simple: so called reference objects are identified for which not only the scan based coordinates can be determined, but for which also their coordinates in a more general overall coordinate system are known. If there are at least 3 reference objects in a scan, it is mathematically sufficient to calculate the transformation, i.e. the exact position and orientation of the scan. Then not only the selected reference objects, but all scan points get their coordinates in the overall coordinate system. In SCENE various types of reference objects can be used for the registration. Common references are natural references, such as planes, slabs, pipes, corner points, or rectangles, and manually placed Page 6 of 9

7 references, such as spheres or paper references (circular flat or checkerboard references). In addition, the inclinometer can be used as a reference. In this exercise, we use sphere targets for the registration and we add GPS information to spheres. SCENE use latitude / longitude or UTM coordinates. Our control points use ETRS- TM35FIN coordinates, which have UTM - projection. Hence, we have to add the UTM zone 35 N. Example 35 N To begin with registration, we have to identify each sphere targets in Quick- or Planar- View We fit the spheres with preset radius. You can predefine one or more sphere radiuses under Tools > Options > Matching > Match Sphere Settings. The radius of our spheres was m. Find the spheres for each scan Operations > Find Object > Spheres. If the automatic recognition doesn t work, you can fit spheres manually selecting Sphere Selector tool on the toolbar Note! If the sphere locates further than 20 m from scan station then the software may not recognize it. Next, we add GPS position for every sphere targets by selecting the object in Quick- View or 3D- View or in the context menu of the sphere and opening Properties. You can enable the use of GPS information for registration in the Place Scans Settings under Tools > Options > Matching Add GPS position for every sphere targets (or at least for 3 sphere targets in a scan) by selecting the object in Quick- View or 3D- View or in the context menu of the sphere and opening Properties In the sphere object window, add GPS position, height and accuracy. Page 7 of 9

8 When you have added GPS positions for spheres, you can execute the registration. To do this, select the command Operations > Registration > Place Scans in the context menu of the scan or the scan folder. After registration finished, the scan manager dialog will open and show the registration results. The registration can be done in different ways. More information about the registration you can have by opening Help > Contents and chapter 5. If all means fail and a scan cannot be automatically registered in a good way, you may also place the scan manually. Assign colour to points The scanner- based pictures are stored within the scan and can be seen in the structure view. Select the command Operations > Color/Pictures > Apply Pictures in the context menu of the scan. This will first load the scan and all its pictures. Then it will remove any distortions from the pictures. Finally, it will add the colour information to the scan points. If you get an out of memory error during applying the pictures, you should check the colorize all scan points option under Tools > Options > Scan Data. If it is switched off, switch it on and try again. 3D- object measuring and modelling To start a measurement between two or more scan points, click on the button in the toolbar. Point- to- point measurements are available in the planar view, the quick view and the 3D view. To select measure points, select valid scan points in the respective view with the left mouse button. To select the last measure point and finalize the measurement, double- click with the mouse. To cancel the current measurement, click the right mouse button or press the Esc key. To leave the measurement process, click the right mouse button or press the Esc key again. Take some measurements, example from pillars or pipes. Give an approximation of the height of the car, which can drive in the garage. SCENE supports the creation and fitting of a variety of simple geometric objects, like points, planes, spheres, pipes or lines. You can use manually selection or automatic object recognition: Manually from a selection of scan points: To do this, select an area of scan points in the quick view or in the planar view of a scan and instruct SCENE to fit the geometric object by selecting the appropriate command in the context menu of the selection under Create Objects. With the automatic object recognition: You may also let SCENE automatically search for certain objects in a scan point selection or in a complete scan. For this, use the appropriate command in the context menu under Find Objects. Objects found by the automatic search are saved to the AutoFeatures folder in the structure view. When you have created some planes, try to analyze the surface. More information by opening Help > Contents and Surface Analysis. Reporting When preparing the report, please follow the following structure. Each section is compulsory and gives you hints what it should contain. The report should illustrate the learning objectives acquired by the participants. It is worth maximum 100 points. Page 8 of 9

9 1. Introduction (10 points) Give a short description of the project including location (area), purpose, date of the survey, equipment used, followed or intended specifications, etc. 2. Reconnaissance (10 points) Describe the outcomes of the reconnaissance trip in the field including identification of any existing points, final sites selection for the new stations 3. Monumentation (10 points) Explain how the stations were marked in the field (if any) including station description, photos, close- up view, horizon view, and general overview site map. 4. Observation scheme (10 points) Develop an observation scheme for performing the fieldwork including the time management for each scanning station. 5. Field data collection (20 points) Describe briefly the terrestrial laser scanning measuring technique and the reference datum chosen. Include photos and digital copies of the scan files. 6. Office data processing (20 points) Explain briefly how the data processing is carried out including software used and screenshots of different processing steps in order to illustrate what have you learned about it. 7. Learning experiences (20 points) Describe the learning experiences (as a group) you had during the assignment. How did you organize as a group? How was the communication between the group members? What did go well? Why? Did you encounter any problems? Why? Did you solve them? How? How was the management of the assignment? Were the team members committed? Did you divide the work? What was the contribution of each team member? How many hours did you spend for this assignment? Where there any skills you have gained? etc. These are some example questions, but you may write about any other experience that you find it relevant/irrelevant for your learning. Constructive criticism in the spirit of good will is encouraged! In the end of the section, please include a table with Member Name, Role, Tasks executed during the assignment, Number of hours spent for the assignment. Date: Teacher in charge: Dr. Octavian Andrei Page 9 of 9