Compare a track log to a map

Discussion in 'Mapping & Navigation' started by bfgjohno, Feb 17, 2009.

  1. bfgjohno

    bfgjohno Guest

    Hi,

    I'm scratching my head and would value your help!

    I've software (Mapwel) which can create a map which I can then download to my GPS 60 to use as the base map. In my case the "map" is simply a tracklog converted into a map - so just a single wiggly line.

    What I want to do is let my buddies ride the same trail following the map which I've downloaded to their units. To introduce a bit of fun into the proceedings, I want to be able to compare their tracklogs with each other and with the "gold standard" - the map. The guy that sticks closest to the provided trail wins.

    Is there any way to do this - compare tracklog with map??

    Cheers

    John
    #1
  2. rwamf

    rwamf Follow me

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    I am sure there are many ways to do this but if you have Delorme Topo 7.0 you can down load Aerial Photos for the area you are planning your ride, You can draw the track line on the actual photo and then save it as a "gpx" file that you can import into Mapwell. then after the ride you can bring the riders saved track files and display them in different colors over the Baseline track you have, Not sure if there would be a mathematical solution to the track that would be closest but you sure can see them clearly on the map.
    below is a map from Delorme Topo 7.0 with a track I downloaded from a Countdown Ride and my actual Gps track from that ride.
    [​IMG]
    #2
  3. Countdown

    Countdown Long timer

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    That is what they do in Baja now. Every one caries a GPS they download tracks at the end and see if any one cut the course. the tracks also have time stamps so when I download friend's tracks I can see every place they stopped.
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  4. eakins

    eakins Butler Maps

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    use google earth 5. to show gpx files and compare the 2.

    you can also use google earth to create a "path" overlay on a ride you would like to do. click along and create waypoints. save this as a kml file and then use gpsbable to convert this file to gpx file that then is uploaded into your gps. same idea as with delorme topo 07 but it's all free.
    #4
  5. Countdown

    Countdown Long timer

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    Or just draw a track in Mapsource and download it to Garmin GPS.
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  6. rwamf

    rwamf Follow me

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    Only one slight problem with that Jerry, Mapsource is not always close to the real trail or road, if it is even on the map, Google shows a high res image as does Delorme so you can draw with a little more accuracy . Even your GPS track can vary quite a bit (+_ 30ft). So if you draw it on an Image you are a little closer to the actual line.
    of course that is JMO.
    #6
  7. bfgjohno

    bfgjohno Guest

    Thankyou for all the input. I am busy creating paths in Google Earth already and find it really easy. I guess what I was hoping was that there would be a mathematical way to compare the tracklogs to the map. I can convert the vector tracklog to a raster image and thought I might be able to compare raster image with raster image.

    One thing that will always screw this up is the variation between units - two folk might follow identical routes but the two GPS units record paths differing by say 10 metres.

    Another option might be to create GPS waypoints along the route and then assess whether riders are ticking those off by riding over them.

    It may just come down to squinting at the downloaded tracklogs and sucking my teeth before deciding on a winner but I'm sure there must be a more scientific way.

    Cheers

    John
    #7
  8. intothenew

    intothenew Briar Patch Navigator

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    G7toWin will out put in spread sheet format that you may could copy and let excel work some magic. It's a strong piece of software, there may be something internal to do what you want. Oh, and it's free.
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  9. rwamf

    rwamf Follow me

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    May be you could combine the Geocaching thing with this, Say you put a bunch of coffee cans out there with items that everyone has to get, make some of them a little ways off the trail and compare the tracks and items recovered. ?????? something like that???
    #9
  10. HogWild

    HogWild Scott Whitney

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    There are several problems. One is the natural error the GPSr has in recording its position. That can change from unit to unit, point to point, and minute to minute. Take 10 units mounted on your bike and ride one perfectly straight path for a mile. You'll see 10 slightly different recorded tracks even though they all were on the same bike at the same time. Another problem is the gap between points. If you let the GPS or MapSource type program reduce the track points, then you get long straight lines that don't really show exactly the path you took. And even if you have the GPSr record say every 10 seconds, each GPSr will make a point at a slightly different location because their sampling clocks are not synchronized. Your idea of looking at just a couple of wapoints may also have a problem because one GPSr might just happen to record a point exactly when the rider arrived there, and another might record a point just before and just after that intended waypoint, with a straight line between that doesn't show that the person hit the waypoint dead on. A good programmer could take two recorded tracks and come up with some sort of integrated sum of the differences between tracks, but it would be somewhat challenging and still prone to the other errors described above.

    Since you're now into Google Earth, try this for a mind twister. Save your Google Earth track (in .kml format), including a few hand entered key waypoints (placemarks) along the way. Make your filename something like "MyFunTrack.kml". Now rename that file to "MyFunTrack.xls". That's an Excel spreadsheet format. Now open that file using Excel and look at what's in there!
    #10
  11. mcnut

    mcnut Long timer

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    As suggested in the prier post, the time of day is also a problem. The constellation of satellites used for GPS navigation is always changing, not in geosynchronous orbit. Because the satellite location is ever changing so is the geometry. As the geometry changes so does the location accuracy change. The reason they have done this is so the bad reception/geometry locations are ever changing, they don't remain bad forever. Of coarse this also means the good spots also move around as well. Have a bad fix with lots of error, try the same location 4 hours later, the error should have changed for better or worse because the satellites have.

    This one of the reasons that the more technical GPS units (GPS V, 60, etc) offer the user the option to average a waypoint or fix location over time using many fixes as opposed to the usual single point fix marking a location.

    So for your concept to work with high (say +-30ft or 60ft min) accuracy all riders/GPSs would have to be in the same general location at the same time, a rider on the exact same path 2 hours later would get different error and therefor generate a different track.

    Bruce

    P.S. As a side note, remember the consumer is still using a dumbed down GPS, the military and some commercial users have access to much better technology. Years ago GPS receivers were set up at either end and in the middle of an aging concrete dam above LA. With the best equipment and local differential correction they were able to measure the deflection of the dam over time, as the water level changed or the temperature changed.
    #11