Elevation Data

[fausto]

I'm a new user of Satmap but an experienced walker using Sunnto and etrek and 1;25000maps to navigate by elevation where necessary (in cloud). Satmap I believe uses the base map for elevation data based on a 200ft grid. Why, when the 25000 map card has grid lines 5m apart? Also the users guide claims that this is more accurate than gps, quoting 50m inaccuracry. In all my years comparing gps height with the map and Sunnto (baromtric heigt) I've never found the gps with more than a few metres difference compared say with a spot height. It's really bugging me this 200ft business - it seems crazy.

[4ndynorfolk]

I had a conversation with Satmap about this last summer after I found that the steep ascent to Helvelyn from Thirlsmere showed as large steps on the profile. (This is only an issue if the Satmap is set to get the elevation from maps. The default setting is to get the elevation from the GPS).

I was told that the only grids available from OS were the 200m grid or a very expensive and bulky centimetre grid not intended for this type of application. I was told that they were considering moving to a NASA grid using 60m squares and that if they did that would be implemented in a future upgrade. I was a little surprised that this data was not contained on the map cards, but was assured that it is part of the firmware.

I guess non-UK manufacturers automatically go down the NASA route.

I am not aware that this has been implemented yet (though it could have been, as I for one don't know how to tell), but it may do in the future. Two constrants that spring to my mind are that they may be contractually tied to OS until a certain date, and also that there may not be sufficient space in the ROM given other firmware improvements that have been rolled out.

Many of the new features with V1.4 have come from the military version - hibernation, red screen etc., so that may be what drives this.

[Tony_P1]

I always take the elevation from the GPS. I have found it to be very close to the spot heights/contours on the maps (contrary to Satmap's statement) whereas taking elevation from the map is next to useless due to the reason mentioned above. However....the total ascent/descent recorded in the triplog is a gross overestimate of reality (even the map-based total ascent/descent is an overestimate, but not as bad). I have always assumed the problem is down to the smoothing (or lack of smoothing) algorithms used by the Active 10. I mentioned this to Satmap last year but they didn't seem to see this as a priority.

[fausto]

As I say I'm new to Satmap but my concern re elevation was sparked off very early when the height ascended seemed optimistic using the map as the base rather than gps as recommended in the guide. Apart from elevation I'm also interested in this aspect because it is used in some classes of cycling to define how hard the route is. There is some controvesy with this depending on which route planning set up is used, Bikehike, Bikely, Multimap Garmin etc. I like Bikehike because of the integration of OS mapping alongside the Google map. I have found that the Bikehike height climbed is in line with my Sunnto but I now think that Satmap may be adrift on this aspect which is a shame. I don't know on what basis Bikehike calculate the height climbed and that will be good to find out. This topic to me seems quite wideranging affecting various gps systems and measuring devices. Interesting and I've learned stuff from the posts, thank you all.

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