Low cost GNSS receivers: navigation and monitoring activities

Transcription

1 PHD in Environmental and Infrastructure Engineering XXIX cycle Low cost GNSS receivers: navigation and monitoring activities Ph.D.'s activity final report Marco Negretti Supervisor: Ludovico Biagi Tutor: Giovanna Venuti

2 Low cost GNSS receivers: navigation and monitoring activities Performances assessment and improvement of Low Cost GNSS receivers Navigation: identify paths, POI correction using data from Continuously Operating Reference Stations (CORS) correction using local cartography as reference Local Monitoring (landslide monitoring): verify if it is possible do local monitoring with low cost receivers using geodetic techniques 2

3 Navigation Navigation Case study: MEP (Map for Easy Path) project Winner Polisocial Award 2014, the academic social responsibility programme launched by the Politecnico di Milano Get around the city for physically impaired people can be difficult different kinds of obstacles and dangers 3

4 Navigation MEP: aim of the projetc create a tool to map obstacles identify accessible paths data should be easily upgradeable continuously feedback to identify problems and define methods to improve mobility Three department are involved DICA, DEIB, DESIGN DICA group: manage GNSS data 4

5 Navigation The mapping activity is expected to be carried out by volunteers mappers, with mass market devices (smartphones and tablets) Improve their accuracy to warrant the identification the right side of the road if possible, otherwise only the road Example: obstacle on sidewalk it is important identify the side of the street actual coordinates collected coordinates 5

6 Navigation: correction using data from CORS Correction using data from CORS Compute individualized epoch by epoch corrections from CORS data Apply corrections to rover trajectory CORS CORS estimated coords epoch by epoch rover Rover estimated coords epoch by epoch 6

7 Navigation: correction using data from CORS Rover observes a subset of visible satellites viewed by CORS CORS rover 7

8 Navigation: correction using data from CORS Rover observes a subset of visible satellites viewed by CORS a software was developed to remove satellites not observed by rover from the CORS RINEX read from rover NMEA file the list of satellites at epoch i read from CORS RINEX file the list of satellites at epoch i compare satellites lists remove epoch by epoch from the RINEX file the data of satellites that are not viewed by the rover 8

9 Navigation: correction using data from CORS First test: static positioning Test in Milan and Como 9

10 Navigation: correction using data from CORS First test: static positioning Test in Milan and Como Data elaboration to estimate CORS positions one week for both sites RINEX files from CORS gogps ( rtklib ( Comparison between the corrections obtained using: the original CORS RINEX the modified CORS RINEX 10

11 Navigation: correction using data from CORS Example with Como Data day , north CORS, rover, rover corrected 11

12 Como u-blox [m] CORS data: point positioning day u-blox corr. [m] (modified RINEX) East -0,08 North 0,78 East -0,02 North -0,26 East -0,03 North -0,26 std 0,77 1,24 0,64 0,81 0,64 0,80 mean 0,34 0,63 0,02-0,34 0,02-0,34 std 0,84 1,39 0,64 0,81 0,63 0,80 mean 0,20 0,37 0,08-0,44 0,09-0,44 std 0,84 1,21 0,65 0,84 0,65 0,83 mean 0,19 0,68 0,13-0,48 0,14-0,47 std 0,91 1,12 0,71 0,82 0,69 0,81-0,32 0,46 0,12-0,46 0,11-0,47 0,87 1,12 0,65 0,82 0,65 0,81-0,24 1,09 0,04-0,42 0,03-0,42 std 0,91 1,20 0,68 0,88 0,67 0,86 mean 0,07 0,19 0,11-0,51 0,11-0,50 std 0,90 1,25 0,64 0,82 0,63 0,81 mean 0,41 0,47 0,09-0,27 0,09-0,26 std 0,76 1,28 0,62 0,77 0,61 mean mean std u-blox corr. [m] (original RINEX) mean 0,76 12

13 Navigation: correction using data from CORS Milan u-blox [m] u-blox corr. [m] (original RINEX) day East mean std mean std mean std mean std mean std mean std mean std North East North u-blox corr. [m] (modified RINEX) East North

14 Navigation: correction using data from CORS Milan u-blox [m] u-blox corr. [m] (original RINEX) day East North Generally East CORSNorth corrections work mean std rover mean mean std mean std mean std East Few improvements using original RINEX 1.39 std compared modified RINEX-0.68 mean std u-blox corr. [m] (modified RINEX) mean std in a1.49 good position North

15 Navigation: correction using data from CORS Second test: kinematic survey Two test paths were defined to verify different conditions of satellite visibility urban canyons areas of intermediate visibility open areas Path 1 Path 2 OpenStreetMap contributors OpenStreetMap contributors 15

16 Navigation: correction using data from CORS Test with geodetic receiver, tablet/smartphone and u-blox Path 1 Leica GX 1230 Samsung Galaxy Tab2 Path 2 Leica GX 1230 Samsung S5 u-blox EVK-7P evaluation kit 16

17 Navigation: correction using data from CORS Geodetic receiver reference to evaluate tablet survey data processed with double different method Path 1 a good accuracy will be reached only if it is obtained a fixed phase solution N of points fixed/total 1886/2144 fixed solutions 88% 36% / % 33% / % N of points fixed/total 1805/4038 fixed solutions 45% / /3547 Path 2 17

18 Navigation: correction using data from CORS Statistical errors before and after the correction with CORS data along the Path 1 Day tablet collected [m] East corrected mod RINEX North East North mean std std mean std mean 18

19 Navigation: correction using data from CORS Statistical errors before and after the correction with CORS data along the Path 2 Day smartphone collected [m] mean std mean std mean std East North u-blox corrected mod RINEX East North collected East North corrected mod RINEX East North

20 Navigation: correction using data from CORS The accuracy after the CORS correction does not improve Local disturbances particular properties of the area local effects are prevalent reference points corrected points collected points 20

21 Navigation: correction using local cartography as reference Correction using local cartography as reference Reference map: OpenStreetMap (OSM) Database: PostgreSQL/PostGIS points detected with mass market devices paths and buildings from the OSM maps in the neighborhood of the points detected script to implement the data correction procedures 21

22 Navigation: correction using local cartography - on segments Correction on segments Chose the segment OpenStreetMap contributors distance from the point collected to the candidate segment the bearing from the previous to the current point the bearing of the candidate segment the distance from the current corrected point to the previous corrected point Drawback: could corrects too much 22

23 Navigation: correction using local cartography - out of buildings Correction out of the buildings to avoid overlap between points collected and buildings For each point query to check if it is inside a building in case, the point is projected outside 23

24 Navigation: correction using local cartography - out of buildings Example of correction effective 24

25 Navigation: correction using local cartography - out of buildings Example of correction ineffective 25

26 Navigation: correction using local cartography - on buffers Correction on buffers 1.Searching and selection of a potential path choice of a set of segments candidates to be part of the potential path 1,4 m 0,5 m 0,0 m every collected point assigns a score to the closest n segments 0,7 1,0 1,0 total score: 2,7 26

27 Navigation: correction using local cartography - on buffers 1. Searching and selection of a potential path identification of the potential path: segments selected every collected point selects, between the n nearest segments candidates, the one with the highest score 27

28 Navigation: correction using local cartography - on buffers 2. Building of the buffer around of the selected potential path 28

29 Navigation: correction using local cartography - on buffers 3. Correction of position of points that are outside the buffer 29

30 Navigation: correction using local cartography - on buffers Buffer size fixed: 7 m urban two-lane road with the sidewalks 30

31 Navigation: correction using local cartography - on buffers Buffer size variable dseg= distance between segment and the nearest building buffer size: 2 < dseg < 7 [m] 31

32 Navigation: correction using local cartography - on buffers In case of very bad quality of signal a wrong segment can receive an high score and be selected as segment path 32

33 Navigation: correction using local cartography - on buffers Reclassification: reduces the score for handling segments one vertex not shared with others candidate segments suspected to be erroneously selected (A) cover the holes: adds the segments not selected both the vertexes shared with others candidate segments suspected to be erroneously discarded (B) segments selected segments not selected 33

34 Navigation: correction using local cartography - on buffers 34

35 Navigation: correction using local cartography - results Comparing results Around to the true path two tolerance areas were defined: 2.5 m and 5 m it was checking how many points were inside Total points: 5879 Proximity areas 5m 2.5 m collected out of the data buildings on buffers constant variable correction on variable segment with reclass. points inside % points inside % Day

36 Navigation: correction using local cartography - results Great difference due to the reference used to do the correction "on segments" method => moves all points on the segment "on buffers" methods => define an area where the points are not corrected 36

37 Navigation: correction using local cartography - results Tolerance area of 5 m all corrected points are inside tolerance area true path OSM segments buffer around segments 37

38 Navigation: correction using local cartography - results Tolerance area of 2.5 m points corrected with "on segment" method are outside: the method corrects too much tolerance area true path OSM segments buffer around segments 38

39 Navigation: correction using local cartography - results This is clearly a particular case In general the choice of correction method is not easy The final results are very dependent on the site characteristic and from the cartography used as reference an incomplete or wrong reference datum can lead to consider a point position wrong when the problem can be the map itself it is important to have cartography updated and easily upgradeable, like OSM, that permits to add a new path as it becomes available 39

40 local monitoring Local Monitoring Research to assess precision and accuracy of low-cost GNSS receivers in monitoring displacements with low latency Controlled movements imposed to a low cost rover, estimated displacements compared with the imposed ones accuracy of low cost GNSS receivers how reliable are the results obtained or rather, how many false or missed alarms are expected per unit of time 40

41 local monitoring Two different analysis have been performed Significance analysis based on Fisher test this procedure allows a separation of the results into two groups: coordinates significantly changed with consecutive sessions and coordinates unchanged compared to the actual values Congruence analysis the aim of the congruence analysis is to verify whether the estimated coordinates differences are congruent with the imposed displacements 41

42 local monitoring: test 1 Test 1: points of survey Reference station Valleggio 1: COMO CORS (EUREF network) receiver: Topcon Odyssey RS antenna: TPSCR3 GGD Rover: ublox NEO 7P (evaluation kit) about 100 m from the reference station 42

43 local monitoring: test 1 m Points of survey m 43

44 local monitoring: test 1 Points of survey 44

45 local monitoring: test 1 Simulation slide test started on GPS Day two days of static acquisition to compute the reference start position the antenna was shifted horizontally 5 mm for each session three session per day, three hour per session total displacement of 10 cm was aimed but, due to an instrumental problem, the test stopped at 5.5 cm Data processed with LGO and rtklib 45

46 local monitoring: test 1 Data processed with LGO and rtklib LGO rtklib Estimated displacement Imposed displacement 46

47 local monitoring: test 1 Congruence analysis: number of couples class 0 class 1-2 class 3-5 LGO 43.9 % 48.8 % 6.4 % rtklib 46.5 % 49.0 % 4.5 % 47

48 local monitoring: test 2 Test 2: points of survey: Reference station Valleggio 1: Reference station Valleggio 2: COMO CORS (EUREF network) receiver: Topcon Odyssey RS antenna: TPSCR3 GGD receiver: ublox NEO 7P (evaluation kit) antenna Tallysman TW31525* about 10 m from the reference station Rover: receiver: ublox NEO 7P (evaluation kit) about 130 m from the reference station * Many thanks to Geomatics Research & Development (GReD) 48

49 local monitoring: test 2 Points of survey 49

50 local monitoring: test 2 Points of survey reference station Valleggio 2 reference station Valleggio 1 50

51 local monitoring: test 2 Points of survey N 45 Rover is installed on a device* (slide) that allows to apply controlled displacements E * Many thanks to the colleagues of the Politecnico di Torino - DIATI 51

52 local monitoring: test 2 Initial position of the receiver was determined by a 24 hour session with a geodetic receiver and estimated respect COMO CORS From day to The rover antenna was moved, alternately in horizontal and down in vertical every 2 hours 5 mm in horizontal (0 10 cm) 5 mm in vertical (0 10 cm) The data were processed with LGO software two times: once using Valleggio 1 as reference station, the other one using Valleggio 2 52

53 local monitoring: test 2 Horizontal displacement estimated imposed 53

54 local monitoring: test 2 Vertical displacements estimated imposed 54

55 local monitoring: test 2 Statistical errors [cm] mean std E N vert. horiz Reference station: Valleggio 1 [cm] mean std E N vert. horiz Reference station: Valleggio 2 55

56 local monitoring: test 2 Significance analysis 78 % 85 % 80 % Movements between couples % 14 % 28 % 2 29 % 17 % 3 63 % 4 5 Movements between couples 0 2D UP 3D 2D UP 3D 88 % 84 % 92 % 1 14 % 14 % 14 % 46 % 2 23 % 18 % 21 % 28 % 68 % 3 31 % 27 % 31 % 88 % 31 % 90 % 4 64 % 33 % 61 % 99 % 38 % 100 % 5 84 % 36 % 88 % Reference station: Valleggio 1 Reference station: Valleggio 2 56

57 local monitoring: test 2 Congruence analysis East North Vertical Horizontal class 0 16 % 14 % 2% 18 % class % 52 % 9% 58 % class % 31 % 12 % 23 % 1% 3% 77 % 1% over Reference station: Valleggio 1 East North Vertical Horizzontal class 0 17 % 14 % 2% 19 % class % 46 % 8% 58 % class % 35 % 12 % 22 % 4% 5% 78 % 1% over Reference station: Valleggio 2 57

58 local monitoring Generally the estimated displacements follow the trend of the imposed displacement Low cost receiver can be used, under specific constraints, in monitoring activities vertical component is not well recognized main displacement in the monitored area should be in the horizontal component It is possible to use a low-cost receiver also as a reference station enhanced antenna 58

59 Future work Future work Monitoring test with better antennas, but always low cost Navigation trajectory estimation using neural networks 59

60 Reference MEP - PostgreSQL - PostGIS - gogps - RTKLIB - Cartography OpenStreetMap - Orthophoto AGEA 2012 from WMS service of Regione Lombardia: