Legend : help required calculating total height gain.

burtonian

I have a Legend HCx and would like know how best to calculate total height gained from the daily track log. Transferring the track to MemoryMap I can convert to a route and see the gps elevation profile, but can't summarise the height gain. Transferring to MapSource gives the raw data but again no summary height gain. Is there a way of calculating this easily on either the pc or the unit, or is the only answer to manually insert the data into a spreadsheet?

Thanks for any help offered.

Prodnose · Occasional Visitor Joined: Dec 28, 2005 Posts: 42

Hi,
One problem seems to be one of deciding how the software interprets the data collected. I have been mulling over a walk I did this week in the Welsh borders. Importing the track log into Anquet Maps gave a height ascended of 2100 ft which seemed about right. Importing the same data into GPSU - www.gpsu.co.uk - gave 3600 ft!. I scanned the height data looking for obvious errors, e.g. rogue readings adding a height gain of 100's of feet but found none.
Your question has prompted me to have a bash at interpreting the height data myself.
If you want to load the data into Excel, an easy way is to first import the it into GPSU, save it as text file and then import into Excel using a space as the delimiter.
Harry

burtonian · Posted: Fri Mar 21, 2008 10:03 am Post subject:

Thanks Harry. I've just tried the GPSU demo which unfortunately limits the number of trackpoints I can import, but looks quite a neat utility. I've also tried GPSTrackmaker, which is a much bigger application and seems like taking a sledehammer to crack a nut, but I did manage to transfer the entire tracklog to Excel and produce some summary altitude information. Unfortunately, even though I know I've done the maths correctly, I don't believe the answer, it seems to overestimate in the same way you implied GPSU does!

Having locked into MemoryMap I'm not keen to start using Anquet as well. Unless someone can suggest ways of using MM I guess I'll have to register the GPSU software and do what I can with that.

Tony

Prodnose · Occasional Visitor Joined: Dec 28, 2005 Posts: 42

Hi,
Yes, I can understand that you don't want to invest in another lot of mapping software. I suppose that you have carefully serch to see if there is some obscurely named MM tool that gives the information?
I find GPSU useful and the site owner,one Alan Murphy, will answer questions.
I know that different software will sometimes give significantly different distances travelled. I suspect that this is because more "intelligent" software can reject GPS errors which, for example, may cause a deviation of a km and back in successive readings. I have some evidence to support this. There has been some discussion on this subject in this forum.
I did look at the data of my walk. But scrolling through endless columns of figures rapidly dumbs my brain. I have some ability in VB so I will search for errors and calculate my total height. I particularly want to see if my figures are close to those given by GPSU.
Harry

Prodnose · Occasional Visitor Joined: Dec 28, 2005 Posts: 42

Hi,
Just remembered, Anquet does not get height ascended by taking the GPS heights. It does it from it's own contours. The height and distance travelled is only obtained when a track is plotted and highlighted. It doesn't matter whether the path is obtained from a GPS or simply plotted by hand. Whether the stuff about intelligent analysis is a figment or my imagination or exists remains to be seen!
Do have a look to see if something similay exists with MM
Harry

Prodnose · Occasional Visitor Joined: Dec 28, 2005 Posts: 42

Hi,
Additional comments.
Taking the height data and increasing the ascent every time a reading was higher than the previous one, I got a total of 3600 ft - the same as GPSU. There were no unusually sudden increases. I set my GPS in a fixed position for 4 hours and found that I had ascended several hundred feet! Just the electronic wanderings of the GPS.
The moral is: if you want fairly accurate ascent info use mapping software that uses the it's contour data and not that of the GPS!

burtonian · Posted: Sat Mar 22, 2008 10:59 am Post subject:

Thanks for that info Harry. Yes I agree that the gps total ascent summary adds in all the vagaries of gps accuracy, but I'd have thought that the effect wasn't that great once the unit had settled after the first few minutes. Just as importantly, gps could be short if you'd gone in and out of a dip between recordings or, alternatively, map software could overstate if you went over a deep chasm and the map didn't know there was a bridge!?

In theory I can get the summary from MM, but so far I've only seen it if I generate a route on screen from scratch. If I import the track log it brings in the height data but doesn't summarise it. If I convert the track to a route then the height data doesn't get incorporated. I'll investigate further - I wonder if using OS grid coordinates rather than lat/long might cause the conversion problem?

Prodnose · Occasional Visitor Joined: Dec 28, 2005 Posts: 42

Although I first thought that some of my height errors were due to a few rogue readings (and I'm sure that they sometimes are) I now accept that it was just the GPS drifting. Some early reading do tend to hop about a bit and I usually delete the first minute or so. However the GPS will continue to drift. Heights are less accurate than horizontal ones. Just turn on your GPS and leave it in a good location for a few hours and see how you have "travelled".
You are right about chasms: OS mapping will not take into account bridges but assume that you went down and up again. A GPS with an aneroid barometer should help. I used to have one but lost it and replaced it with a more basic model. It certainly seemed to damp down the wandering height. Of course, if they ever get EGNOS going that will help too. I don't think that NGR/Lat Long is involved.
You have obviously have a good look at MM. Worth a posting on the MM part of the forum?
Harry

burtonian · Posted: Sat Mar 22, 2008 6:10 pm Post subject:

Yes there are times when I wish I'd spent the extra on a Vista, but I didn't want the added complication of calibrating altitude with barometric pressure, I've had enough of that with a wristwatch altimeter! I remember once, riding my bike along a perfectly flat road towards a thunderstorm, the temperature suddenly dropped a few degrees and I apparently climbed a big hill as the pressure fell.

I think you're right, posting on the MM forum is now the way to go. Thanks for your comments.

Tony

philpugh · Posted: Tue Mar 25, 2008 11:14 am Post subject:

burtonian · Posted: Tue Mar 25, 2008 3:26 pm Post subject:

Phil, as I responded on the thread I subsequently started on the Memory Map forum, I think you've highlighted the fact that MM elevation data is not available on the 1:250k GB map, only on the 1:50k and 1:25k area series. So although I can get an altitude profile, I can only get total ascent and descent if the tracklog is covered by the more detailed maps.

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