Dr. Octavian Andrei Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 GNSS assignment Objective: Establish a control network (control survey) Location: Otaniemi campus, Innopoli 3 park area Equipment: GNSS receivers Methodology: Relative positioning using CORS (Continuous Operating Reference Station) data Output: Geodetic and projected coordinates of the control points Deliverables: Point descriptions, baseline vectors and their precision, geodetic coordinates (EUREF-­‐
FIN), grid coordinates (ETRS-­‐TM35FIN) Deadline: TBD Assign roles for each team members (change the roles from the previous assignment): •
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assignment manager two field operators for each receiver secretary Assignment instructions Every GNSS surveying project consists of four main phases: planning, data collection (field work), data processing, and reporting. Below you can find the instructions to be followed individually during each phase of the assignment. Planning phase •
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Get an existing map or aerial photo of the Innopoli 3 park area Do a proper field reconnaissance Identify four station locations in each side of the area where there is an underground garage entrance. Pay special attention to accessibility, potential obstructions presented by trees and buildings, and interferences. In addition, assure there is clear visibility (line-­‐of-­‐sight) between the adjacent control points. The control points represent the base points for the traversing operations. Make the station descriptions and draw a visibility obstruction diagram. Produce a satellite availability plot and select the suitable observation window (good practice although this becomes less important when using multi-­‐constellations): o http://www.trimble.com/GNSSPlanningOnline o http://www.spectraprecision.com/support/gnss-­‐planning/ Develop an observation scheme o Session length: 20 min + 2 min / km (static); 10 min + 1 min / km (rapid static). o HELS, 60.212152947,25.053899180 Page 1 of 10 Dr. Octavian Andrei •
Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 o METS, 60.217470638, 24.395316020 Prepare the correct receiver settings: elevation angle (10°), observation rate (5 sec). Data collection •
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Prepare the equipment: receiver, tripod, antenna, tribrach, batteries, cables, height measuring tape, compass, and safety vests. Mark the new stations in the ground using wooden sticks or nails. Set-­‐up the equipment over the new station, align the antenna along the north direction, measure the antenna height, confirm the start of the session, collect the observations, stop the session, save the data in the memory card, measure the antenna height, move to the next point. Repeat the above procedure for the next station. Be sure that the two receivers cover the same observation window and have the same observation rate. Document properly your fieldwork with drawings, sketches, notes, photos, etc. Data processing •
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Use a dedicated processing software (e.g., Topcon Tools 8.2.3) o http://www.topconsupport.com/ Download data from the GNSS receivers to the computer. Get the CORS data (actually you will receive it from the instructor). If necessary, covert raw data to RINEX format (use manufacturer’s software) o Alternatively: http://facility.unavco.org/software/teqc/teqc.html Create a new job, choose the right configuration, import all the files, perform baseline processing, do the adjustment, compute the final coordinates. Transform the geodetic coordinates (EUREF-­‐FIN) into grid coordinates (ETRS-­‐TM35FIN) o http://coordtrans.fgi.fi/transform.jsp Reporting •
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Read the specific instructions. Include the assignment deliverables Assignment timetable Week number 38 39 40 41 Description GNSS field planning Getting used with the post-­‐processing software Data collection Data processing, coordinate transformation, reporting Page 2 of 10 Dr. Octavian Andrei Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 Week 38: GNSS field planning Objective: GNSS field planning Methodology: Group work Prerequisites: Basic skills to collect information The students should be able to carry out main preparatory activities related to the GNSS field data collection: •
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Design a network of control points Conduct proper reconnaissance Develop an observation schedule Select the appropriate GNSS instrumentation and measuring technique Identify the logistical aspects of the survey work Become familiar with various roles in group work Project planning is a critical component in obtaining successful results for high-­‐accuracy surveys. Careful planning maximizes the chances of the GNSS survey achieving the desired accuracy, within a reasonable time, and according to budget. Before commencing the planning, the following questions may be address (Please notice this is a partial list only): • What is the purpose of the survey? • What are the accuracy and reliability requirements? • What resources and budget are available? • What previous surveys have been carried out? • Are there any CORS (Continuously Operated Reference Station) GNSS reference stations nearby that could supply GNSS data or provide access to the reference frame? • Are the any special (or unusual) characteristics of the project? The following sections give you a brief description of various aspects of project planning for control surveys. Preliminary considerations •
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Obtain information on the availability of existing control stations in the GNSS project area. Plot their locations on an existing map or aerial photo of the area Select new station locations in such a way to meet the overall project objective (e.g., clear visibility in all directions for a mask angle of 15° from the horizon) Select the suitable observation window by using satellite availability plots Analyze the sky obstructions and satellite geometry diagrams Page 3 of 10 Dr. Octavian Andrei Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 Selecting the appropriate survey method Similar to traditional methods of surveying, several different methods are available with which to conduct a survey using GNSS. Each method provides a unique set of procedural requirements for field personnel. For high accuracy GNSS surveys, the static method with dual-­‐frequency receivers is the best choice. However, for small areas projects, rapid static, pseudo kinematic, kinematic, stop-­‐
and-­‐go, or RTK even using single frequency receivers may be sufficient. All these methods allow relative positioning with respect of a known located station. On the other, due to the technological advances in algorithm design, one can use precise point positioning (PPP) using code and phase data from a dual frequency receiver in combination with precise orbits and precise satellite clocks. The figure below illustrates various GNSS positioning methods used in the surveying, mapping, and geodetic community. GNSS posigoning Surveying Point Carrier phase (PPP) Navigagon Relagve Post-­‐
processed Stagc Rapid stagc Pseudokinemagc Real-­‐gme Kinemagc Stop & Go Differengal Point Pseudorange (DGNSS) Pseudorange (SPP) Carrier phase (RTK, Network RTK: FKP, VRS, MAC) Figure 1 – Schematic representation of various GNSS positioning methods The selection of the appropriate survey method is dependent on (not only): •
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Desired level of accuracy in the final coordinates Intended use of the survey Type of the equipment available for the survey Size of the survey Overhead viewing conditions for the survey and other local conditions Available software for reducing the data Field reconnaissance Once the existing nearby control points and new stations have been located on paper, a reconnaissance trip to the field should be undertaken to check the selected observation sites for: Page 4 of 10 Dr. Octavian Andrei •
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Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 Overhead obstructions that rise above 10-­‐15° from the horizon Reflecting surfaces that can cause multipath (i.e., signal arrives from multiple directions) Nearby electrical installations that can interfere with the satellite signal Other potential problems If the reconnaissance reveals that any preliminarily selected point locations are unsatisfactory, adjustments in their positions should be made. Once the final sites have been selected for the new stations, permanent marks1 (spikes, stakes, wooden pegs, concrete nails, screws, drill holes, etc.) should be set, and positions of these stations documented with ties to the nearby objects, photos, rubbings, and any other useful information to allow the field operator to reach the station later. At this time, point description cards and accurate station visibility diagrams should be prepared. Developing an observation scheme The existing nearby control points that will be used in the survey and the new GNSS stations comprise what is termed the ‘network’. Depending on the nature of the project and extend of the survey, the network can vary from only few stations to very large and complicated configurations. Figure 2 illustrates a small network consisting of two existing points and four new stations. New GNSS station
Figure 2 – Example of GNSS network GNSS After the network has been established, an observation scheme is developed for performing the fieldwork. The scheme consists of a planned sequence of observing sessions that accomplishes the objectives of the survey in the most efficient manner. As a minimum, it must ensure that every station in the network is connected to at least one other station by an independent baseline. However, the plan should also include some redundant observations (i.e., baseline observations between control stations, multiple occupations of stations, and repeat observations of certain baselines) to be used for checking purposes and for improving the precision and reliability of the 1
http://www.surveyingequipment.com/cat4/marking/ http://docs.jhs-­‐suositukset.fi/jhs-­‐suositukset/JHS184/JHS184.html 3
http://docs.lib.noaa.gov/noaa_documents/NOS/NGS/Geom_Geod_Accu_Standards.pdf Page 5 of 10 4
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Monuments used to mark stations in the ground have metal caps that give the name of the point and other information about the 2
station. This information is stamped into the cap. An imprint of the cap is obtained by laying a piece of paper directly over the cap, and Dr. Octavian Andrei Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 work. The principal factor governing the number and type of redundant observations is the desired accuracy. Many survey authorities at the national level have developed specifications a set of standard and specifications for GNSS positioning that specify the number and types of redundant observations necessary for different accuracy classes (e.g., E1, … E62) or orders (e.g., AA, A, B, C3). Please notice that different countries may not only have a different classification system for accuracy, but also have different recommended practices for each class of GNSS survey. Availability of Reference stations A number of public and commercial GNSS data sources are available specifically for GNSS surveying usage, primarily on the Internet. These data are available in the form of a base station and precise ephemeris. Many national mapping agencies and commercial organizations are developing active and passive reference stations and networks. A network of Continuously Operating Reference Stations (CORS) provides GNSS data consisting of carrier phase and code range measurements in support of three dimensional positioning, meteorology, space weather, and geophysical applications throughout a predefined area. •
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Global: International GNSS Service (IGS) o http://www.igs.org Regional: EUREF Permanent Network (EPN) with about 274 stations4 o http://www.epncb.oma.be National: Leica SmartNet systems, Trimble Trimnet o http://www.smartnet-­‐eu.com/ o https://tpsstore.trimble.com The CORS data files are easily downloaded using a dedicated web-­‐based utility. This utility provides user with an interactive form which requests the starting date, time, duration of the survey, site selection, and the collection interval among other things. A server interprets the request and the appropriate data is sent via the Internet, to the user within minutes. Keep in mind that various factors may affect the data collection at a particular CORS site for short time periods. Thus, it is important to check the availability of the reference station just before the beginning of a survey to ensure it is functioning properly, and the necessary data will be available following the survey. In this case, you will use two CORS stations: HELS and METS. Use for example Google Earth to have an idea how far they are from the surveying area. HELS, 60.212152947,25.053899180 METS, 60.217470638, 24.395316020 2
http://docs.jhs-­‐suositukset.fi/jhs-­‐suositukset/JHS184/JHS184.html http://docs.lib.noaa.gov/noaa_documents/NOS/NGS/Geom_Geod_Accu_Standards.pdf 4
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Page 6 of 10 Dr. Octavian Andrei Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 Week 39: Getting used with the post-­‐processing software Objective: Getting familiar with the post-­‐processing software Methodology: Pairs/group (recommended) or individual studying (if you prefer) Prerequisites: basic skills in using computers The students should become familiar with the Topcon Tools post-­‐processing software by studying in pair/group (recommended) or individually (if preferred). Topcon Tools can be used in two versions: free version (up to five points) or licensed version (no restrictions). If later, one needs to use the USB dongle (ask the course assistant). The software can be accessed from the Geodesy computers (T205-­‐POG106203 & 04) from the lab in D-­‐building (room 1.062) or student’s own computer. If the former, skip steps 1-­‐3, otherwise follow the following steps: 1. Log in the Topcon support website using the following credentials: maa.geodesia@gmail.com (userid) and kidhunx9nd (password). 2. Install the Topcon Tools v8.2.3 by downloading the *.exe installer from this link: o http://www.topconsupport.com/documents/download/33366 3. If the direct link does not work go to: o Software » Surveying Software » Topcon Tools » Topcon Tools Web Setup v8.2.3 4. Start Topcon Tools 5. Follow the instructions given in the Topcon Tools Quick Reference Guide (in Moodle). Use the RINEX files given as attachments to exemplify various steps of the instructions. o data.zip (in Moodle) o Use HELS station coordinates from the RINEX observation file to fix the point as a control point 6. A complete reference manual can be downloaded from here: o http://www.topconsupport.com/documents/download/27796 Page 7 of 10 Dr. Octavian Andrei Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 Week 40: GNSS field data collection Objective: GNSS field data collection Methodology: Pairs/group (recommended) Prerequisites: Basic skills to set-­‐up a tripod and operate GNSS receiver Read first the general instructions! The students should be able to carry out GNSS field measurements in a station session. Use your action plan defined in the planning phase to carry out GNSS field measurements. Be neat (tidy), legible, accurate, and redundant when collecting field measurements. Document properly your work. Page 8 of 10 Dr. Octavian Andrei Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 Week 41: GNSS data processing, coordinate transformation, reporting Objective: GNSS data processing, coordinate transformation, reporting Methodology: Pairs/group (recommended) Prerequisites: Complete previous phases of the assignment The students should obtain the grid coordinates for the control survey network after field data processing. These coordinates become the input for the next assignment. In addition, a GNSS assignment report should be produced (one per group) and uploaded in Moodle (by the assignment manager). Data processing Read first the general instructions! Follow the same steps as in the training session with post-­‐processing software to perform baseline processing, to execute adjustment, and to compute the final geodetic coordinates. Remember to fix the CORS station coordinates both horizontally and vertically before doing the computations. If this is not done, the network is adjusted as a free network. And we don’t want this! Coordinate transformation Transform the geodetic coordinates (EUREF-­‐FIN) into grid coordinates (ETRS-­‐TM35FIN) using FGI coordinate transformation service: •
http://coordtrans.fgi.fi/transform.jsp The input coordinates can be uploaded as a text file or from the keyboard. If first option, check the Help for more information. Below you can see the correct transformation settings: Page 9 of 10 Dr. Octavian Andrei Maa-­‐6.3261: Engineering Geodesy 5 ECTS, fall 2015 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. 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, station visibility diagrams, etc. Include an appendix if necessary. 3. Monumentation (10 points) Explain how the stations were marked in the field including station description, approximate coordinates for field identification, ties to nearby objects, rubbings5, photos, close-­‐up view, horizon view, and general overview site map. Include the point cards into an appendix. 4. Observation scheme (10 points) Develop an observation scheme for performing the fieldwork including network design, vectors (baselines) to be measured, their approximate lengths (km), minimum session lengths (min), and observation itinerary. 5. Field data collection (20 points) Describe the GNSS survey measuring technique (e.g., static relative positioning) and the reference datum chosen. Include the GNSS field log sheets and digital copies of the GNSS data files. 6. Office data processing (20 points) Explain how the data processing is carried out including software used, vector processing and their precision, network adjustment, final geodetic coordinates (EUREF-­‐FIN), as well as grid coordinates (ETRS89-­‐TM35FIN) and their orthometric heights (N2000). Include an appendix if necessary. 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 learning 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 summary table with Member Name, Role, Tasks executed during the assignment, Number of hours spent for the assignment. Use may use the Word template provided in MyCourses. 5
Monuments used to mark stations in the ground have metal caps that give the name of the point and other information about the station. This information is stamped into the cap. An imprint of the cap is obtained by laying a piece of paper directly over the cap, and rubbing across the surface with the side of the pencil lead. This helps to eliminate mistakes in station identification. Page 10 of 10