OT: Memory-Map feature

Any experienced Memory-Map users know of any clever hack or program
that will rectify the absence of one important facility that has
always frustrated me please? Namely a tool to show the cumulative
ascent & descent of a track.

Whether the track is imported from a GPS recording or drawn manually
Memory-Map can show a nice 'GPS Altitude Profile' or 'Elevation
Profile' respectively as an image. And the track properties window
shows a variety of useful text like distance, number of points, speed,
etc. But not ascent/descent ;-(

In the case of a GPS path the data could be extracted and processed in
Excel, deriving individual height differences between successive
trackpoints and accumulating them, with or without some sort of
smoothing. Maybe someone's done it? But for this case other programs
have built in tools to do it directly anyway, such as the excellent
GPS Utility.

In the case of manually drawn tracks (e.g. for planned walks, or those
for which no GPS recording is available) then Memory-Map uses its
map's underlying elevation data and no access at all seems possible to
the data used to display the Elevation Profile.


--
Terry, East Grinstead, UK

Terry Pinnell wrote:

Right click on track - Operations - Convert to Route
Right click on route - Properties

Paul
--
http://www.wilderness-wales.co.uk
http://www.wilderness-images.co.uk
http://www.uk-rec-walking.co.uk
http://www.vanishingripples.com
http://www.monochromemagic.com

Thanks Paul, I'd forgotten about Routes. (I normally work entirely
with tracks).

I've been re-reading Help but can't find answers on some basic points
I've also forgotten. For example, to get realistic ascent/descent
estimates, presumably you maximise the number of trackpoints by
changing the 'Min update distance (m):' to something very small before
doing the conversion to a route.

I already had it set to the lowish value of 15 m. For a 1 km drawn
test track up Snowdon, various values gave me the following results:

Setting Waypoints Gross Ascent (feet)
------- --------- -------------------
50 m 2 707
15 m 5 707
10 m 6 707
8 m 8 707
5 m 7 707
2 m 16 706
1 m 23 706
0 m 20 706


(The original track was sent to me with a GPS recording. The
originator used GPSU to estimate 743 feet.)

Do you have a track or route with 'good' ascent/descent data I can use
as a benchmark? That would be useful both for choosing optimum 'Min
update distance' for Mem-Map and the filter number for GPS Utility's
Smooth Altitude tool.

--
Terry, East Grinstead, UK

Terry Pinnell wrote:


Yeah, strange that they don't do it with tracks though, there's no reason
why they couldn't.


Maybe, but then again, maybe not.


Well those are virtually identical, which confirms what I suspected. The
resolution of the height grid is very low, so it looks like a more accurate
track wouldn't necessarily make much difference.


Which is much different to your above results. Assuming that reception is
good, I'd sooner trust a GPS track than a Memory Map estimation.

As a general rule, MM can give fairly accurate results for up/down walks,
where you're crossing the contours at right angles. However, when you walk
parallel to the contours you tend to get a very jagged profile (due to the
low resolution height data, which are like large square "pixels") even
though the path may be level. So following ridges (particularly on the edge
of cliffs) or rivers tends to result in far more ascent than actually
occurs. For example, there's a coast path from Mumbles where the Memory Map
track drops to sea level a few times, even though the path is high above the
cliffs.


What do you mean by "good"? Do you mean a track recorded with good satellite
reception so that it's pretty accurate? Even then it could be skewed if the
pressure was changing quickly (since I use an altimeter GPS and it's the
altimeter data that's recorded in the track - although I do use
auto-calibration so it shouldn't be much out, most of the time).

I'll have a look. It might be useful to compare an up/down type of walk with
a contour following type of walk, to compare the difference in accuracy.

I think that even a good GPS track probably over-estimates the ascent a bit.
I've often noticed that my elevation is slightly high at the start of a walk
(sometimes by as much as 10m) and lower at the end (closer to the actual
elevation), which probably indicates that it takes a while for the
auto-calibration to kick in. Also, it's usually 2 or 3 metres too high on
summits for some reason. My local hill, Kilvey Hill, which is 193m, usually
reads 196m.

If you study a GPS elevation track closely you'll see that there are often
little ups and downs, even when you were walking uphill steadily. If you
want a really accurate estimate I think it's better to calculate your own.
Use the GPS track to identify the many high and low points of your walk,
then do your own additions and subtractions to work it out. Should be more
accurate on an up/down type of walk, but not on a contour following walk
with lots of tiny undulations.

Paul
--
http://www.wilderness-wales.co.uk
http://www.wilderness-images.co.uk
http://www.uk-rec-walking.co.uk
http://www.vanishingripples.com
http://www.monochromemagic.com

Thanks Paul, very helpful.

I'm playing with various other aspects of this too. Including trying
to use Macro Express to extract elevation data from MM's elevation
profile. Once I have an apparently realistic looking profile in MM I'd
like to know the corresponding cumulative ascent/descent. I can do
that by summing the ups and downs between successive points. Of
course, if I could access the data in MM directly this wouldn't be
necessary, but I don't know where it is! My macro therefore has to use
pixel colour identification methods and scaling etc, so it's a bit
hairy. Still on the cards that I'll give up ;-)

BTW. your observations about MM elevations almost certainly explain
the bizarre results I was seeing yesterday when I tried a half mile
stretch of the M25 near Reigate!

--
Terry, East Grinstead, UK