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  1. #1
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    Reputation: amaurosis fugax's Avatar
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    My new Edge 305 - brilliant toy

    My Edge, ordered through GeoMan, arrived within 72 hours. It had to travel 7,200 miles to me in New Zealand. Charged it up, downloaded latest firm-ware, attached to stem and off.

    Four rides so far totalling 32 miles (including Makara), lots of data to pour over. I have started with SportTracks and it seems ideal. Being able to export to Google-Earth is fanatstic. I can see myself wanting to go out over the coming winter months just so my weekly mileage doesn't drop too low. So it will be a good motivator.

    Only gripe is with Google-earth, and the fact that my route is offset by about 2 metres. I have read other threads about this and it would appear there is no fix. Is it something that varies from country to country?

  2. #2
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    If there's a regular offset like that, it usually means that there is a discrepancy between the map datum your gps is using (and saving the data in) and the map datum your display software is using. If you tell the software the wrong datum (or, you don't tell it which datum and the software assumes incorrectly), then you will end up with an offset. This could also be a problem if you're using a map datum based on a region COMPLETELY different from the one where you are. For example, I usually use WGS 84 because it's a worldwide datum. However, if I was using NAD 27 and I traveled to Europe, there would be some display issues and I'd have to change the datum on the gps to either a europe-specific datum, or one that has a worldwide extent.

    In this case, it's unlikely that the problem lies with Google Earth. I imagine the problem is arising somewhere else. What map datum is your GPS set to? Also, does any of the software you use ask which datum you're using?

  3. #3
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    NH,
    thanks for your reply.
    I use SportTracks software. They don't ask what 'datum' I'm using.
    The Garmin 305 doesn't ask what 'datum' I am using either.

    Oddly, when I use the street-map in SportTracks it plots it exactly, but when I bring up the satellite image (or export to Google-Earth) it shows the off-set.

  4. #4
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    The GPS won't specifically ask you. It probably has a datum preset, and if you bought one marked for sale in the US that was then shipped to you, it's probable that it's set for a US datum. I would look in the manual about choosing the datum.

    In Sporttracks, does it give you a street map/aerial image (sat images are usually radar based, basic photos are done with airplane flyovers with a camera mounted to the plane) combination option? I'd be curious to see how the vector streets line up with the streets as shown in the aerial imagery.

  5. #5
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    NH,
    The 305 manual makes no mention of being able to choose the datum. I shall have a look on their web-site.

    In SportTrack, you can choose to show either: street map, satellite, aerial(US) ot topo(US). Here in New Zealand I can only choose the first two, but not simultaenously. The street map is perfectly aligned while the satellite is mis-aligned same as google-earth.

    Have a look at the image half way down this thread and I get a similar offset (but only 2-3 metres) Edge 305 first ride......

    If a US-sourced unit is preset for the US, I hope I can reset it for NZ.

  6. #6
    Just a punk in the street
    Reputation: Last Child's Avatar
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    My Edge 305 uses the NAD 27 datum. I also use SportTrack and Maptech Terrain Navigator. If I set Maptech to NAD 27 the tracks/routes come in right where they are supposed to. Most GPS units will let you select the datum. I have yet to find that function on my Edge 305.

    This is my last ride logged. This route falls right on top of the trails/roads found on the USGS Quad map.
    Attached Images Attached Images

  7. #7
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    I love my garmin 205, HOWEVER, it can not get the elevations right... it always overcalculates by about 30%, a real bummer. I do the mb gravity edit and smoothing and it still over calculates. Anyone found a way around this problem? Anyone have this problem with the 305?
    Ride to Live... Live to Ride

  8. #8
    Double-metric mtb man
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    I`m having great fun with my 305. The Garmin Training Centre map is a little off, but I find the Google Earth outputs are spot on.

    Btw, I agree that Geoman rocks
    As if four times wasn't enough-> Psycho Mike's 2013 Ride to Conquer Cancer Page

    Moran? Let your opinion be free -> F88me

  9. #9
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    Quote Originally Posted by Last Child
    My Edge 305 uses the NAD 27 datum. I also use SportTrack and Maptech Terrain Navigator. If I set Maptech to NAD 27 the tracks/routes come in right where they are supposed to. Most GPS units will let you select the datum. I have yet to find that function on my Edge 305.

    This is my last ride logged. This route falls right on top of the trails/roads found on the USGS Quad map.
    Ding ding! This is going to the the source of your offset problem. NAD27 is set for north america only. In NZ, you'll have some offset if the base data is using something else. Likely the difference you see is due to the fact that in sporttracks, the road data and aerial data must be using different datums, as well.

    Sounds like a little bit of sloppy engineering to me. ANY software used with a GPS should be able to at least make adjustments for the datum the GPS is using...and why a GPS comes preset with an arcane datum with no apparent option to change it is beyond me.

  10. #10
    Just a punk in the street
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    With the last ride I posted above I was able to process 3 different elevation profiles. Garmin software, SportTracks, and Maptech. All 3 gave results within 50 feet of each other. Which was consistent with what the 305 reported itself. I was quite happy with those results.

    While skiing this year I found that the reported elevations at the top and bottom of the lifts varied throughout the day by up wards of 50 feet also.

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