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Elevation Data

 
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afcbrichard
Occasional Visitor


Joined: Apr 27, 2008
Posts: 13

PostPosted: Fri Mar 16, 2012 7:11 pm    Post subject: Elevation Data Reply with quote

I have just bought a Satmap and have just transferred a route from Memory Map to the Active 10. The Max Altitude Data shown in the Profile on the Route Map Screen indicates 206ft, however the profile on Memory map indicates 162 ft. When i pass over the highest altitude WP on the Satmap Planning Scrren it correlates with Memory Map. Can anyone help I dont want to lose confidence before I have even used the thing! Thank You.
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LostMike
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Joined: Jan 17, 2008
Posts: 369
Location: Monmouthshire

PostPosted: Fri Mar 16, 2012 9:40 pm    Post subject: Reply with quote

Presumably both memory map and Satmap are working on map based data (as you have not yet used GPS). Therefore I suggest you look at your route, find the highest point and see what the map says. I and I suspect others would be interested in what you find.

I would add that height issues on GPS units are a bit fraught. For various reasons the heights from GPS are a bit suspect (though I normally use them) and the height from maps is both a little crude and assumes that you have got the location exactly right (do not walk along cliff edges!). A difference of 40/50 ft does not seem to much to me. Does the height profile look reasonable?
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LostMike
Satmap A10. Platform 21
Software version 1.5.9193
Satsync 1.525
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afcbrichard
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Joined: Apr 27, 2008
Posts: 13

PostPosted: Fri Mar 16, 2012 11:31 pm    Post subject: Reply with quote

Thanks for your response...I looked at altitude on my satmap in Planner of a cliff that I knew to be 200ft...on Memory Map it showed it being 215 ft and on my Satmap it showed 45 ft. I was wondering if the fact it appears that the Satmap takes the altitude data from the Basemap is the issue. The other point I was making is that I am confused at why the Profile data on the Satmap differs from the WP data on the Planning Screen.

Can you tell me how long the rechargeable Lithium Battery lasts on average, the advice ot taking a set of batteries is not good as you would have to take out the Lithium, replace the battery caddy before you could use spare batteries and even replacing with another rechargeable would be fiddly due to the connector being so small.

..and also the unit has frozen twice on me in 2 days....getting a bit frustrated!!

Lastly!!!! I cant seem to download a POI from Google Earth with the photo it just appears as the text....any ideas?

Sorry about all the questions but I need to ease my growing frustrations and I havent used it yet!!

Thanks
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LostMike
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Joined: Jan 17, 2008
Posts: 369
Location: Monmouthshire

PostPosted: Sat Mar 17, 2012 10:11 am    Post subject: Reply with quote

Hello again afcbrichard.

On the height issue. I am fairly sure that Satmap (and others) work on average altitude for grid squares. So if you are in a square then that is your altitude even if the map contours show it should be higher or lower. It a bit like pixels on your screen, you are given the average figure for this square. What I cannot remember at the moment is how small the Satmap squares are. Maybe others can. As I think I indicated before this has never been a problem for me but you may use it in a different way.

As for the lithium battery - I have not got one and have not used one. I use rechargeable AAs and carry a set of spares. The rechargeable AAs last for as long as I need and can easily cover a 15 mile hike. I have not heard of anyone having a lithium pack last less than a day but you might do better to wait for users of lithiums to comment. The switching of battery pack for AAs is a definite issue!

I am surprised to hear that your device has frozen. I have not heard of that happening in a long time. Have you used Satsync to check that you have the latest software? If this persists I would recommend that you ring Satmap who are invariably very helpful.

I am going to leave it to others far more used to dealing with complex POIs to comment on the issue of images. I have done it and if no one comes back I will try and give guidance but as I normally do not bother with this I think it better to try and leave you in the hands of those more experienced.

Good luck.
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LostMike
Satmap A10. Platform 21
Software version 1.5.9193
Satsync 1.525
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afcbrichard
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Joined: Apr 27, 2008
Posts: 13

PostPosted: Sat Mar 17, 2012 1:15 pm    Post subject: Reply with quote

Thank You Mike. I am going to Noth Cnwll at Easter, I will let you know how I get on. Thanks again.
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AllyCat
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Joined: Feb 23, 2005
Posts: 376
Location: Catford, London, UK

PostPosted: Mon Mar 19, 2012 10:50 am    Post subject: Reply with quote

LostMike wrote:
On the height issue. I am fairly sure that Satmap (and others) work on average altitude for grid squares. So if you are in a square then that is your altitude ....
Hi,

IMHO that's not strictly correct. Memory Map (which uses OS GB elevation data) has separate elevation files (.QED) for each map and I'm fairly sure that these files contain "spot heights" on a 50 metre grid. But the heights at intermediate locations are interpolated by taking data from surrounding points (maybe simple averaging, but I believe a more sophisticated mathematical algorithm). This is obvious from the "3D view" (on the PC software) where the terrain is "rounded" (not like a staircase of square blocks), although it can still look "wrong" at some mountain peaks, cliff edges, roads through cuttings, and rivers flowing uphill, etc..

More commonly, elevation data is in the form of spot heights on the Latitude/Longitude grid, typically spaced by say 10 seconds of arc, which represents different distances in X and Y directions (except at the equator) and generally amounts to a spacing of a few hundred metres.

I believe the Satmap has elevation data stored in its internal memory (not memory card) with a grid of no better than 10 arc-seconds, but I suspect that they also would use an averaging/rounding algorithm for intermediate points.

Cheers, Alan.
_________________
Garmin GPS72H/76/60/45, Etrex H, Mapsource v6.5.
Acer N50,HP114,Loox N560,Dell x50,CF/SD cards to 4/32GB.
RoyalTek,Holux236,Navman B10 & Copilot(Globalsat) BT GPS,TomTom5/6.
Memory Map (v5.4.2 & v5.1.3 OS & Euro), GPS gate,OSGPSconverter.
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Rogerfrit
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Joined: Dec 17, 2003
Posts: 141
Location: North Devon - England

PostPosted: Tue Mar 20, 2012 5:43 pm    Post subject: Reply with quote

Looking at the latest update to Satsync I saw this-

Changes in version 1.501
•Switched to a more reliable provider of height data (optional)

Not really sure what this means, but I guess means better height information?
But - why in Satsync and not on the SatMap itself?
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AllyCat
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Joined: Feb 23, 2005
Posts: 376
Location: Catford, London, UK

PostPosted: Tue Mar 20, 2012 6:25 pm    Post subject: Reply with quote

Hi,

Probably because it's a lot easier to change data in the Satsync files than "burned" into the Satmap's ROM.

The OSGB's elevation data should be very accurate, but I don't think it's "free" and obviously only applies to the UK. The general "free" source of elevation data is NASA's SRTM (spaceShuttle Radar Topography Mission, if I recall correctly) which I think is on a 10 arc-seconds grid, but with higher resolutions for certain areas.

Cheers, Alan.
_________________
Garmin GPS72H/76/60/45, Etrex H, Mapsource v6.5.
Acer N50,HP114,Loox N560,Dell x50,CF/SD cards to 4/32GB.
RoyalTek,Holux236,Navman B10 & Copilot(Globalsat) BT GPS,TomTom5/6.
Memory Map (v5.4.2 & v5.1.3 OS & Euro), GPS gate,OSGPSconverter.
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