Nice presentation on GPS, Geotagging and its Future


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Nice presentation on GPS, Geotagging and its Future

  1. 1. locate, communicate, accelerate Now, Now where was I? Dr Chris Marshall chris.marshall@u November 2010 IET Buckinghamshire region
  2. 2. Where we will go… g • Your many photos • GPS • Assisted GPS • C t Capture and P d Process l t t h l later technology • and what we can do with it • Useful information out of location
  3. 3. Imaging and the Web
  4. 4. Large photo collections lead to challenges ? Where is the photo I want? Where was this photo taken? Slide 4 © u-blox AG How do I get more from my photos? How can I share the story?
  5. 5. Need to add extra data to photos Time Location Subject London Eye Slide 5 © u-blox AG
  6. 6. Applications/Websites ready for geotagged images iPhoto 09 PicasaWeb Flickr Slide 6 © u-blox AG
  7. 7. locate, communicate, accelerate The Global Positioning System
  8. 8. The GPS satellites • US government work started 1973 • First satellite launched 1989 • 24-31 satellites, in 12 hour orbits • Altitude of ~20,200km, speed ~3.9km/s • 6 orbital planes, at 55° inclination Overnight trace of satellite orbits (2004)
  9. 9. To find your position using GPS • Just measure the distance to the satellites • And solve. In 2 dimensions… Ra2 = (X-Xa)2 + (Y-Ya)2 Rb2 = (X-Xb)2 + (Y-Yb)2 Ra A B Rb
  10. 10. To measure the distance from a satellite… • Measure the time taken for a signal to travel from the satellite to the receiver lf h lli h i • 3ns 1m • Distance = time × c
  11. 11. To measure the time accurately • Each GPS satellite transmits a Direct Sequence Spread Spectrum (DSSS) signal • Centre frequency 1.575GHz • Each satellite uses a unique pseudo-random pattern, called a “spreading code” • S th receiver k So the i knows which signal is from which satellite (CDMA) hi h i li f hi h t llit • The spreading code takes exactly 1ms to send and it is sent every ms • 1 023Mb/s 1.023Mb/s • Symbolically (the code is actually 1023 bits long): sent 0ms 1ms 2ms time 3ms 4ms
  12. 12. Measuring Propagation Time • The signal has a delay when it arrives at the receiver sent τ received time
  13. 13. Measuring Propagation Time • The signal has a delay when it arrives at the receiver sent τ received sent time
  14. 14. Measuring Propagation Time • So the receiver scans all time offsets for the signal… sent received replica time
  15. 15. Measuring Propagation Time • So the receiver scans all time offsets for the signal… sent received replica time
  16. 16. Measuring Propagation Time sent received replica time
  17. 17. Measuring Propagation Time sent received replica time
  18. 18. Measuring Propagation Time sent received replica time
  19. 19. Measuring Propagation Time sent received replica time
  20. 20. Measuring Propagation Time sent received replica time
  21. 21. Measuring Propagation Time sent received replica time
  22. 22. Measuring Propagation Time sent received replica time
  23. 23. Measuring Propagation Time sent received replica time
  24. 24. Measuring Propagation Time • To find the time where they match (“correlate”) sent received τ replica time
  25. 25. In 3 D space • Need to measure 3 di d distances • And solve with 3 equations Ra2 = (X-Xa)2 + (Y-Ya)2 + (Z-Za)2 Rb2 = (X-Xb)2 + (Y-Yb)2 + (Z-Zb)2 Rc2 = (X-Xc)2 + (Y Yc)2 + (Z Zc)2 (X Xc) (Y-Yc) (Z-Zc)
  26. 26. But, we also need to know satellite time… • Distance = speed × elapsed time • Satellites have atomic clocks, monitored from the ground, but hand held receivers only have quartz oscillators • An offset δt is caused by the discrepancy between our clock and “GPS time” p • In our 2D example: (Ra + c×δt)2 = (X Xa)2 + (Y-Ya)2 + (Z-Za)2 (X-Xa) (Y Ya) (Z Za) (Rb + c×δt)2 = (X-Xb)2 + (Y-Yb)2 + (Z-Zb)2 c.δt Ra A B Rb c.δt
  27. 27. So GPS receivers use 4 satellite signals • In 3 D space we have 4 unknowns X, Y, Z, and δt • 4 measurements, from 4 satellites, and 4 equations… (Ra + c×δt)2 = (X Xa)2 + (Y Ya)2 + (Z Za)2 (X-Xa) (Y-Ya) (Z-Za) (Rb + c×δt)2 = (X-Xb)2 + (Y-Yb)2 + (Z-Zb)2 (Rc + c×δt)2 = (X-Xc)2 + (Y-Yc)2 + (Z-Zc)2 (Rd + c×δt)2 = (X-Xd)2 + (Y-Yd)2 + (Z-Zd)2
  28. 28. The location of the satellites • Each satellite tells you where it is in space • Each transmits detailed information about its current orbit “Ephemeris” information. • The basic satellite signal is modulated with a 50 bits/s data message • The message lasts 18s, and i repeated every 30 d is t d 30s • From the ephemeris you can calculate the position of the satellite for the next 2-4hours • So now you can calculate where you are. • This is why a GPS receiver normally needs 30s to start the “Time To First Fix”.
  29. 29. Summary of GPS Fundamentals • GPS works by measuring the time it takes signals from satellites to reach a receiver • Spread spectrum signals received all at the same time • separated • measured d • The satellites describe their orbits with a slow additional modulation of the signal which takes ~30s to receive • GPS receivers requires measurements from 4 satellites to calculate their position in 3D space and GPS time
  30. 30. Assisted GPS
  31. 31. GPS Signals are very weak Earth radius 6,378 km • 45W transmitter , y • 20,180 km away • 10 million times weaker than WiFi signals Slide 31 © u-blox AG
  32. 32. It can be difficult to download the data from the satellites • You need a reasonable signal (-142dBm) for f reasonable time ( bl i (>18s) ) • to demodulate the data message • to get ephemeris orbit information • to calculate the satellites’ location • This limits practical performance • Starting in urban canyons • Using indoors Slide 32 © u-blox AG
  33. 33. Assisted GPS • Ephemeris information gathered from all satellites, worldwide. f ll lli ld id • Satellite orbit information provided on request to user over communication channel • Current ephemeris data: 1-3KB valid f 2 4 h lid for 2-4 hours Receiver Receiver Internet Satellite it Orbi ase Databa cellular Merge Internet
  34. 34. Benefits of Assisted GPS • Faster response • No need to wait 30s to download ephemeris information from the GPS satellites • Better coverage and availability • Do not need to be able to see satellites at -142dBm • Sensitivity can be -147dBm … -155dBm • The device can use more satellites and get better accuracy • As a result of communicating with the satellite monitoring infrastructure at some time
  35. 35. Software GPS and Capture and Process technology
  36. 36. Software GPS Research • Started in 2000 at Philips Research, Redhill • Consumer devices should be aware of their location • Just as they are aware of the time • C Consumer devices will i d i ill increasingly contain processors and memory i l t i d • Able to share resources with other functions • Continuing improvements from Moore s law Moore’s • The most expensive part of GPS is the baseband processing chip y g position-aware, can we implement baseband p • To make everything p processing in software? • Standard software (C), processor platform, and memory • A ti it acquired b u-blox i 2009 Activity i d by bl in
  37. 37. The GPS processing task • GPS is lots of “correlations” • To seek and find (acquire) each weak satellite signal in the noise • To measure the timing of each signal • To demodulate data • Plus high accuracy calculations • For position calculation p 6% 3% 91% Acquisition Measure easu e Fix
  38. 38. Conventional, hardware signal processor • Baseband signal processing i.c., containing banks of correlators • Real time signal processing • Signal processed, then discarded • R l time output of “pseudo-ranges” Real ti t t f“ d ” • Fix calculated live from the current pseudo-range values
  39. 39. Capture and Process later concept • Separates the two steps, Capture the GPS signal and then Process it later • Capture is instant and takes little energy
  40. 40. Capture and Process later concept • Separates the two steps, Capture the GPS signal and then Process it later • Capture is instant and takes little energy • Processing is done later by software running on a PC
  41. 41. Application and advantages of C&P using software GPS • Device capture instant – perfect for Cameras • Device capture very low energy – perfect for logging • Processing • Flexibility • Access to PC processor and memory resources • Access to internet and assistance services • Provides the satellite location information
  42. 42. Assisted GPS C&P system • Uses internet connection to the PC • Database of historical satellite orbit information built (since Nov 2007) • Worldwide orbit information provided on request for the time when the GPS signal captured
  43. 43. Assisted GPS use for Capture and Process GPS • No need to recover the information from the GPS signals themselves • Can use weak satellite signals (<27dB C/N) • Can use short signal samples (e.g. 200ms) • Satellite information conveniently provided over internet • when the processing is carried out and the location desired • not at the time of signal capture. g p • Accurate and correct information for the time of the capture
  44. 44. Key benefits of Capture & Process • Instant capture of location data: No waiting No change in user experience g p • Very l low power consumption: Battery lif of months, not hours i life f h h Virtually no impact on battery life. • Lowest cost Only require a GPS radio, antenna and software Slide 44 © u-blox AG
  45. 45. Doing things with Capture and Process GPS
  46. 46. Adding to a camera • Just add antenna and front end radio • Captured GPS signal data stored with photo Prototyping C17-C1 board Slide 46 © u-blox AG • Processed later when picture uploaded to PC
  47. 47. Making a camera accessory • Held and triggered by the camera h shoe h hot h • JOBO PhotoGPS • No waiting when taking a photo • No on-off switch • No manual clock alignment needed (to synchronise the accessory and camera) Slide 47 © u-blox AG
  48. 48. Jobo photoGPS • Accessory device • Captures 200ms GPS signal • Stores up to 4000 geotags y • 120mAhour internal battery recharged by USB, lasts up to 4 weeks • PC p ocess g so t a e C processing software • matches captures with photos • GPS position accuracy 10m • finds Reverse geocode • places result in photo EXIF • Distributor MINOX (GB) Ltd, Luton. Slide 48 © u-blox AG
  49. 49. Making a long term location logger with C&P GPS • Energy used only for receiving and storing a GPS Capture - no processing • Energy <50mJ/Capture • Battery life of up to 3 months on just a 130mAhr battery 100000 • Memory for storing Captures • Capture size typically 128KB • 8Gb memory g gives >8000 Captures p • Capacity for a 1 month sampling every 5 minutes Captures per day s 10000 1000 Battery empty Memory f ll M full 100 10 1 0 10 20 30 40 50 60 Days usage 70 80 90 100
  50. 50. Taking the students to university • Crossing Europe • 5 days • Captures every 2.5min Slide 50 2010 Copyright © 2007: u-blox AG, 5 December
  51. 51. Taking the students to university • Driving around Belgium and the Netherlands d h h l d Slide 51 2010 Copyright © 2007: u-blox AG, 5 December
  52. 52. Taking the students to university • Boarding the ferry at Rotterdam d Slide 52 2010 Copyright © 2007: u-blox AG, 5 December
  53. 53. We’re all going on a summer holiday… • For 2 weeks • Sailing around Fynn, Denmark • Samples every 3min Slide 53 © u-blox AG
  54. 54. locate, communicate, accelerate 51º14.51’N, 000º12.29’W What next? h
  55. 55. Maps used to be expensive • Nokia acquired Navteq, for $8.1bn navigation now free on their phones i i f h i h • except that you have to pay for the data traffic for the maps p • TomTom acquired TeleAtlas for $4.3bn • f use with their navigation devices for ih h i i i d i • Google provides maps for free • except that you look at their advertising Ordanance Survey National Library of Scotland Slide 55 © u-blox AG
  56. 56. Open Street Map • A map for all, by all • Hosted at UCL • Supported worldwide • Lots of content • 321 114 contributing users 321,114 • Governments and organisations also making their data available • 2 054 774 073 GPS points 2,054,774,073 i • 829,249,405 nodes 69,300,449 ways • Highlights at Slide 56 © u-blox AG
  57. 57. Mapping of photos, good for routes and trips pp g p g p
  58. 58. Describe the location by “Reverse Geocoding” • Converts lat-long lat long coordinates into: • Road • Nearest town • Region • Country • Also add nearby Points Of Interest Slide 58 © u-blox AG
  59. 59. Location labelling service • Labelling with address, or points of interest • Database of worldwide geographic information • Generated using OSM data • “R “Reverse G Geocoding” service di ” i • Using the internet connection
  60. 60. Finally, label the image • Geotag in standard EXIF f format • Read by most photo applications • (XMP sidecar for RAW images) • Latitude and Longitude • Address label & tags
  61. 61. The end of our journey
  62. 62. So, Where was I? • GPS is fantastic! • Assistance from a service is a Good Thing • it improves performance • and allows t t ll diff d ll totally different thi t things • You can Capture the signal, and Process it later • instant convenient operation instant, • very long battery life • Then you can do all sorts of things with the location • Identify, remember, label, find, sort, share, discover… and plot on a map! • It’s not “GPS” = “navigation” • E Everything can be aware of where it is (or was) – even photographs… thi b f h i ( ) h t h
  63. 63. Thank you! locate, communicate, accelerate
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