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Pocket GPS World :: View topic - SatMap Mis-reporting Height?
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SatMap Mis-reporting Height?

 
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Fraserp
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Joined: Jun 15, 2004
Posts: 297
Location: Manchester, UK

PostPosted: Wed Mar 19, 2008 7:41 am    Post subject: SatMap Mis-reporting Height? Reply with quote

Has anyone notice how the heights sometime dont report accurately as you scroll across a map?
Its not 100's of metres out but regularly 10's of meters. See NY3310 2959 - NY3248 2960 Its a gentle even slope, I've been on it.
The profile reports correctly but if you move the cursor along the route, the heights do not. Try it.
The same route in both MM and on a Garmin with Topo report accurately. The same issue occurs all over the lakes map.
It all about confidence in a new device, both for using it correctly but also in what it reports.
Is it me that's missing someting?
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mikealder
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Joined: Jan 14, 2005
Posts: 19638
Location: Blackpool , Lancs

PostPosted: Wed Mar 19, 2008 7:51 am    Post subject: Reply with quote

Have a detailed read through page 9 of the full manual, which details how the mapping height data is used/ stored on the device. The manual can be found Here - Mike
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Fraserp
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Location: Manchester, UK

PostPosted: Wed Mar 19, 2008 9:37 pm    Post subject: Reply with quote

So....... from what I can see in the 'manual' it confirms that SatMap doesnt report 'accurate' heights at the cursor location. Just some form of weighted average. Sad

Whereas the other applications such as Memory Map and Garmin Topo do!
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mikealder
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PostPosted: Wed Mar 19, 2008 9:53 pm    Post subject: Reply with quote

Your interpretation of the manual is about the same as the conclusion I came to when I read it, that said, the problems will only occur when in very steep or very variable terrain - Mike
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Fraserp
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Joined: Jun 15, 2004
Posts: 297
Location: Manchester, UK

PostPosted: Wed Mar 19, 2008 11:55 pm    Post subject: Reply with quote

mikealder wrote:
Your interpretation of the manual is about the same as the conclusion I came to when I read it, that said, the problems will only occur when in very steep or very variable terrain - Mike

What? like the lake district, or snowdonia? Shocked opps.....
It appears to affect most areas in the eastern fells. In fact the only places I dont see the issue is on totally flat areas.
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robs1972
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Joined: Mar 19, 2007
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Location: Plymouth

PostPosted: Thu Mar 20, 2008 12:01 am    Post subject: Reply with quote

Slightly different to the 'spot height every 5 metres' that was said to me a year ago from Satmap.....oh well!!
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philpugh
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Joined: Dec 28, 2005
Posts: 2003
Location: Antrobus, Cheshire

PostPosted: Thu Mar 20, 2008 10:33 am    Post subject: Reply with quote

Looks like they chose to have less data with the maps. At 200 feet per sample it's not a lot different from the publicly available DEMs from NASA (the SRTM radar modelling data) which is about every 90 metres. However on a plain slope you would expect the s/w to be able to calculate a reasonably accurate estimate of the height.
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djhpk
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Joined: Jan 14, 2008
Posts: 28
Location: High Peak

PostPosted: Thu Mar 20, 2008 7:51 pm    Post subject: SatMap Mis-reporting Height? Reply with quote

As I pointed out in my post of January 25:-

Quote:
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.


The above, of course is based on software version 1.03. Perhaps someone who has 1.15 can let us know whether this behaves differently.

That is, with 1.03, the altitude appears to be constant over 200m square tiles.

Is 1.15 the same? Is the reference to a "gridded height data set with 200 feet between grid lines" on page 9 of the full manual a misprint for "200m between grid lines"?
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