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Active 10 Altitude reading
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Brian
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Location: Lancashire, England, Great Britain

PostPosted: Fri Jan 25, 2008 10:20 pm    Post subject: Reply with quote

You could establish whether the elevation data is derived from satellites or solely from map data by getting a fix top and bottom of a high building, ie: block of flats etc !
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robs1972
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PostPosted: Fri Jan 25, 2008 10:50 pm    Post subject: Reply with quote

Nooooooo a suspension bridge is far more dramatic!!
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djhpk
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PostPosted: Sat Jan 26, 2008 7:14 pm    Post subject: Active 10 Altitude Reading Reply with quote

Further to my previous post, perhaps I should have mentioned that I took my Active 10 to Switzerland where I did a number of walks at altitudes between 1200 & 1600 metres over the Xmas period.

At all times the Active 10 altitude reading stubbornly remained at zero!

This, together with the evidence given in my previous post, leads me to conclude that the Active 10 altitude reading is not based on gps data, but relies totally on an onboard DTM.

Perhaps this will change in a future software update, at least for parts of the world for which the Active 10 in use does not have any map based altitude data.
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LostMike
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PostPosted: Wed Jan 30, 2008 6:41 pm    Post subject: Reply with quote

Did robs1972 fall off the bridge into the Tamar or are you still trying to work out what height Satmap thought it was? Wink
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robs1972
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PostPosted: Wed Jan 30, 2008 6:56 pm    Post subject: Reply with quote

Hello.....sadly....or maybe happily...my two rides over the weekend didn't go anywhere near the Tamar but based on it's reaction to cycling acoss the Meldon Viaduct...plus a couple of viaducts on the Plym Valley Trail I have come to the decision that I was right in the first place!! Cool Laughing
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Brian
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PostPosted: Thu Jan 31, 2008 4:38 pm    Post subject: Reply with quote

robs1972 wrote:
Hello.....sadly....or maybe happily...my two rides over the weekend didn't go anywhere near the Tamar but based on it's reaction to cycling acoss the Meldon Viaduct...plus a couple of viaducts on the Plym Valley Trail I have come to the decision that I was right in the first place!! Cool Laughing


So is it getting the data from the maps or satellites? it wasn't exactly clear to me reading through the posts .. I think satellites is prefereable!
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robs1972
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PostPosted: Thu Jan 31, 2008 8:02 pm    Post subject: Reply with quote

As far as I was told by Satmap in the months leading up to it's release and the behaviour I have seen, the elevation displayed is derived from the map data just like the elevation figure at the cursor in software like Memory Map...but with the GPS controlling the position of that cursor rather than your mouse.

At the time the Satmap guy was talking about the spot height data held by Ordnance Survey was every 5 metres in a grid....but I'm guessing that whilst that's true it doesn't mean the Satmap uses a 5 metre grid...judging by the frequency of change whilst riding I expect it's more like a 50 metre grid.
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LostMike
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PostPosted: Sat Feb 02, 2008 3:10 pm    Post subject: Altitude Reply with quote

I must admit that I did not think robs1972 had understood correctly as it does not make sense to me, to have a sensitive GPS device calculating the height from the map data rather than the satellite. However I must apologise for doubting you as I have just carried out my own test at my home and cannot but conclude that it is using the somewhat crude map data even when it has GPS lock.

Reading from a detailed paper OS map the height of my house is about 591 ft. The height shown in planning mode with a 1:50,000 map is 652 ft at the east of the house and 551 at the west. When I get a GPS lock it shows 652 ft at the eastern end of my terrace and 551 ft at the West. Walking up the hill makes no difference if I stay within what appears to be the 652 ft square.

I do hope Satmap change this on future software releases. Fine to take the height from the map in planning mode but please lets make use of the GPS signal when we have it!

Do others agree or do you prefer the Satmap solution?
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mikealder
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PostPosted: Sat Feb 02, 2008 3:27 pm    Post subject: Reply with quote

My preference would be to use the height from the Map data, GPS altitude is generally poor in terms of resolution and accuracy, it is also based upon a false level, the GPS altitude is not referenced to sea level whereas the OS data is - Mike
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Brian
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PostPosted: Sat Feb 02, 2008 9:24 pm    Post subject: Reply with quote

I initially would have thought altitude derived from satellites would be better particularly if it was taking data from a lot of satellites (not just 3 or 4), but Mike has a well put argument, I would expect OS mapping contour data is fairly accurate but I would have at least thought the device would default to satellite data if there was a lack of mapping height information (I'm thinking of djhpk using his SatMap in Switzerland ), surely it wouldn't be difficult for SatMap to implement this into the firmware.
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LostMike
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PostPosted: Sun Feb 03, 2008 9:08 am    Post subject: Altitude readings Reply with quote

The map derived data is always available, as a touch of a button takes you back to planning mode. But we have already noted that the map height data is fairly crude (see comments above) and why effectively throw away data that is available from the device. Particularly as given the price of the maps and their limited coverage (UK only) you may one day want to use the device in an area without map coverage. Not to mention going over suspension bridges!

So I would still like Satmap to give us access to the satellite derived height data when it is available.
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