Active 10 Altitude reading

mikealder · Posted: Tue Jan 08, 2008 8:36 pm Post subject:

Most normal disposable batteries output 1,5V the NIMH output 1,2V the Lithium cells when new can be outputting around 1,8V each that is 5,4V applied to the device which is considerably higher than normal batteries, it is the over voltage that is causing the issue rather than the output being too low.
I still maintain the Lithium cells are by far the cheapest battery in terms of hours of use from a single set, I have experianced screen flicker but it soon goes away on my unit.
The LiPo cell looks interesting but with the cost of high power rechargable NIMH cells and a charger this might be the way to go, a couple of spare sets of cells in a box designed to carry them when setting out for a couple of days walking - Mike

LostMike · Posted: Fri Jan 18, 2008 5:44 pm Post subject: Altitude Discrepancy

Though this thread seems to have moved on I don't think anyone has yet come up with why there should be a 40m height discrepancy.

In the hope that it helps I quote from the Ordnance Survey web site.

Quote:
Q27. Why does my handheld GPS display a height of 40m when I know I'm at sea level?

A. The model of the Earth's surface used by many handheld GPS receivers is often a mean fit for the entire world. Because of this the model may not fit Great Britain very well resulting in a height discrepancy. Height is always the least reliable element in a GPS position fix especially for a navigated position.
Unquote.

robs1972 · Posted: Fri Jan 18, 2008 7:38 pm Post subject:

I don't think that does help as your problem seems to be a difference in the OS elevation data rather than GPS derived height.

Does the very near area around this odd spot have any major difference too?
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LostMike · Posted: Fri Jan 18, 2008 7:49 pm Post subject: Altitude discrepancy

But the difference is between what the device says and what the OS map shows which is exactly what the OS quote refers to. Doesn't it?

robs1972 · Posted: Fri Jan 18, 2008 7:59 pm Post subject: Re: Altitude discrepancy

LostMike · Posted: Fri Jan 25, 2008 11:15 am Post subject: Altitude

If it does take data from the OS mapping then its doing it in an odd was as I have just been looking at my map in "planning" mode (I had no Sat lock) and the height reported stayed constant over a substantial distance (maybe 1/2 mile) despite the cursor crossing several contour lines.

Odd me thinks!
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LostMike
Satmap A10. Platform 21
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kidstypike · Posted: Fri Jan 25, 2008 11:33 am Post subject:

The height information that a GPS displays, comes from the satellites that you are locked onto, NOT from the map data. You need to be locked onto at least three satellites to receive height data. The height that you can see displayed when you are not locked onto ANY satellites, is probably the height retained from the last known location.

kidstypike

robs1972 · Posted: Fri Jan 25, 2008 6:58 pm Post subject:

kidstypike · Posted: Fri Jan 25, 2008 7:14 pm Post subject:

robs1972

Do you still get a height reading if you remove the map card?

kidstypike[/quote]

robs1972 · Posted: Fri Jan 25, 2008 7:23 pm Post subject:

Yes....it has elevation data in the base map and the height still changes as you move around in GPS or Planning mode on the base map.....scrolling is a hell of a lot quicker too!!
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I like mapping, I like mapping, I like mapping and I like to map!

kidstypike · Posted: Fri Jan 25, 2008 7:46 pm Post subject:

djhpk · Posted: Fri Jan 25, 2008 8:32 pm Post subject: Active 10 Altitude Reading

As has been already noted, the basic road map which comes with all Active 10s is accompanied by "something" that enables it to give altitude readings even though the contour information is not present. Presumably, therefore, hidden in the system is some sort of altitude database. Most likely, this comes from a Digital Terrain Model (DTM).

If one looks at a trip profile as recorded in the trip log, one can see that it consists of a number of steps, rather than a continous variation of height. This suggests to me that the Active 10's DTM consists of "tiles" with the altitude constant in each tile.

Careful study of the altitude display and grid reference when scrolling around shows that the altitude indicated only changes when the last two digits of either Easting or Northing pass an even number of 10s (or 00). For example, only when either Easting or Northing goes from xx39 to xx41 (or any other reference where the 3rd digit is even) will the altitude reading change. Thus, the DTM tiles appear to be 200m square.

All the above is apparent in planning mode and was verified this afternoon while on a local walk in the area of SK 03 80.

Also, I checked that this seems to apply in planning mode, at least, in the vicinity of the summit of Snowdon where I was disappointed to see the altitude given as 1.02km!! Changing to mile/feet units this altitude was given to 4 figures in feet, pity the metric version did not keep to metres rather than km.

Obviously, the indicated altitudes could be made more precise by using a smaller tile size for the DTM and Ordnance Survey appear to have a DTM with 5m tiles but this would need vastly more storage space than the one with 200m tiles.

kidstypike · Posted: Fri Jan 25, 2008 8:48 pm Post subject:

robs1972 · Posted: Fri Jan 25, 2008 9:36 pm Post subject:

kidstypike · Posted: Fri Jan 25, 2008 9:52 pm Post subject:

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