gps/memory map question

Look at the track on MM and see if there are any "spikes". If you get
poor reception, the GPS will lose it's position and record false
movements. I think MM has a velocity spike remover?

druidh

"druidh" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Look at the track on MM and see if there are any "spikes". If you get
poor reception, the GPS will lose it's position and record false
movements. I think MM has a velocity spike remover?

druidh

druidh - there were spikes, but are you sayng the gps itself is intelligent
enough to filter them out in calculating the distance ?

M

the gps itself is intelligent

Quoted message said:

enough to filter them out in calculating the distance ?

the opposite i would have thought
i notice these spikes a lot and came to the same conclusion the gps was
adding these as extra distance

"arthur dent" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

"druidh" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Look at the track on MM and see if there are any "spikes". If you get
poor reception, the GPS will lose it's position and record false
movements. I think MM has a velocity spike remover?

druidh

druidh - there were spikes, but are you sayng the gps itself is
intelligent enough to filter them out in calculating the distance ?

M

rob said:

"arthur dent" <[email hidden]> wrote

Quoted message said:

Quoted message said:

"druidh" <[email hidden]> wrote

Quoted message said:

Quoted message said:

Quoted message said:

Look at the track on MM and see if there are any "spikes". If you get
poor reception, the GPS will lose it's position and record false
movements. I think MM has a velocity spike remover?

Quoted message said:

Quoted message said:

druidh - there were spikes, but are you sayng the gps itself is
intelligent enough to filter them out in calculating the distance ?

Quoted message said:

the opposite i would have thought
i notice these spikes a lot and came to the same conclusion the gps was
adding these as extra distance

The track length obtained from adding together all the distances
between the track points (which is what the computer software does)
and the track length derived by the GPS using some unfathomable
algorithm are not the same length. Of the two it is the former that is
most likely to correlate with the distance you actually walked.

My normal policy is to remove obviously spurious points or move them
closer to where they should have been and that gives me a good track
for saving.
--
Phil Cook looking north over the park to the "Westminster Gasworks"

arthur dent said:

went up Blencathra on sunday - Geko 201 recorded the distance as 5.6
miles, which seems about right. Saved the track, loaded it into
MemoryMap 2004 when i got home and it says track length 7.9 miles.

What gives ?

The GPS odometer and the track are two different things. The distance shown
by the GPS is not a measurement of the track. If you switch track recording
off the GPS will still measure the distance that you travel.

The odometer accumulates distance differently to the way that a track
measures it. For example, below a certain minimum speed (which is 1.6kph or
1mph on my Garmins) the GPS speed drops to zero, so if you are moving more
slowly than this, the distance will not increase. I believe this feature
was implented back in the days of SA when the random error caused the GPS to
"move about" even though you were standing still, so those small movements
were ignored.

With the track though, the computer measures the distance between all of the
points on the track, so no matter how slowly you were moving, the computer
will measure the distance. This is one reason why tracks tend to report a
longer distance.

Another reason is if the GPS loses the signal temporarily. The odometer
will stop measuring the distance, but the computer will still measure the
distance between the track points where you lost and regained the signal
(provided there's no break in the track, it will start a new track section
if you lose the signal for too long).

There's also the spikes issue that druidh mentioned. The track records
momentary position errors which appear in the track and increase the
distance. If these are very brief then the odometer may ignore them, but
I'm not sure about that.

Quoted message said:

druidh - there were spikes, but are you sayng the gps itself is
intelligent
enough to filter them out in calculating the distance ?

The GPS doesn't calculate the distance from the track, it merely increments
it as you move.

As Phil said, the distance on the GPS is probably more accurate, *provided*
you didn't spend much time moving really slowly, and provided you kept a
good signal lock. Otherwise you'd get a more accurate distance from the
track on the computer, *after* you remove any spikes and obvious errors from
the track.

Paul

arthur dent <[email hidden]> wrote

Quoted message said:

Hi

went up Blencathra on sunday - Geko 201 recorded the distance as 5.6 miles,
which seems about right. Saved the track, loaded it into MemoryMap 2004 when
i got home and it says track length 7.9 miles.

What gives ?

Did you have your towel? Have you asked Ford Prefect? ;-)

I would look at the track in Tracklogs or Anquet (dunno about Memorymap)
and see if their are any wild 'excursions'. If I find any such I move
or delete those extreme points and get a more sensible distance.
--
Gordon Harris

Paul Saunders said:

arthur dent wrote:

Quoted message said:

Quoted message said:

went up Blencathra on sunday - Geko 201 recorded the distance as 5.6
miles, which seems about right. Saved the track, loaded it into
MemoryMap 2004 when i got home and it says track length 7.9 miles.

What gives ?

Quoted message said:

The GPS odometer and the track are two different things. The distance shown
by the GPS is not a measurement of the track. If you switch track recording
off the GPS will still measure the distance that you travel.

Quoted message said:

The odometer accumulates distance differently to the way that a track
measures it. For example, below a certain minimum speed (which is 1.6kph or
1mph on my Garmins) the GPS speed drops to zero, so if you are moving more
slowly than this, the distance will not increase.

On my Summit the minimum speed below which it thinks I'm stationary
seems to be about 0.5mph. It's pretty difficult to keep moving at a
steady 0.5mph without introducing higher speed spikes, so I wouldn't
be surprised if the threshold was a bit lower than that. The Summit
has a few features specifically optimised for walkers, so I wouldn't
be surprised if it has a lower minimum movement threshold than others.

--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]