GPS errors

Roger said:

My gps (Vista C) is telling porkies again, or at least the barometric
altimeter part is. If the gps is to believed I have managed 6883 feet
of ascent today. This of course is rubbish. I have yet to work out
what the real figure is but probably half would be about right.

The cause was the gusting wind which at times was strong enough to
almost have me over. An occupational hazard in the hills but I could
do without the gps suffering even more than me. Is there any way the
barometric altimeter can be turned off temporarily or will I have to
buy another that does not have that function just to use in windy
conditions?

You could look at the GPS height rather than the barometric ?

Also, worth checking if the GPS was loosing track during the day, and thus
getting GPS height errors, which were pushing the barometer (if in automatic
calibration mode) out of line.
My new one (Vista Cx) went wonky on a trip about two weeks ago, reporting
the first summit at 300ft above reality due to it being systematically wrong
on the GPS height data.
Turning off the auto-calibration made the barometric height behave.
Turning the GPS off then on again brought whole machine back to sanity and
correct behaviour.

Finally, they do sometimes go terminally faulty. Mine decided that I was at
30,000+ feet on various records, after calibration back to 120ft it would
shoot off up to 10,000+ feet. So, I contacted Garmin who replaced it free
of charge with a Vista Cx.

btw, couple of tips which you may have found, but I have started to use a
lot recently:
Change which screens are displayed, and in which order (its in the setup
menu). Result is that I now use different combinations for hill, cycle or
car. I turn off the menu screen (get to that with double press of the
lower left button).
Use the Trip Computer screen as one of those on the hill, set it to "Big
Numbers" and set two of the three display fields to show height and location
(OS grid). Thus, in Trip Computer mode you have in BIG TEXT the data to
transfer to a paper map. I tend to use the final field for distance to
destination.

- Nigel

--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

The message <[email hidden]>
from "Nigel Cliffe" <[email hidden]> contains these words:

Quoted message said:

Quoted message said:

My gps (Vista C) is telling porkies again, or at least the barometric
altimeter part is. If the gps is to believed I have managed 6883 feet
of ascent today. This of course is rubbish. I have yet to work out
what the real figure is but probably half would be about right.

The cause was the gusting wind which at times was strong enough to
almost have me over. An occupational hazard in the hills but I could
do without the gps suffering even more than me. Is there any way the
barometric altimeter can be turned off temporarily or will I have to
buy another that does not have that function just to use in windy
conditions?

Quoted message said:

You could look at the GPS height rather than the barometric ?

It is the height climbed that is excessive. I haven't ever caught it out
on height displayed although that is something I don't check very often
these days. Ironic really as the original reason for opting for a
barometric altimeter was accurate height output.

Quoted message said:

Also, worth checking if the GPS was loosing track during the day, and thus
getting GPS height errors, which were pushing the barometer (if in
automatic
calibration mode) out of line.

Well I did 2 little walks yesterday with the track (and gps) switched
off in between. Recorded as track one and track 2 so I assume it wasn't
losing lock. And while walk #1 went up and down through a dense forest
#2 merely skirted a forest for a few hundred yards.

Quoted message said:

My new one (Vista Cx) went wonky on a trip about two weeks ago, reporting
the first summit at 300ft above reality due to it being systematically
wrong
on the GPS height data.
Turning off the auto-calibration made the barometric height behave.
Turning the GPS off then on again brought whole machine back to sanity and
correct behaviour.

Ouch.

Quoted message said:

Finally, they do sometimes go terminally faulty. Mine decided that I
was at
30,000+ feet on various records, after calibration back to 120ft it would
shoot off up to 10,000+ feet. So, I contacted Garmin who replaced it free
of charge with a Vista Cx.

Garmin are usually good on that score but I have found their tech help
useless recently in respect to the nuvi 310 I have for in-car
navigation.

Quoted message said:

btw, couple of tips which you may have found, but I have started to use a
lot recently:
Change which screens are displayed, and in which order (its in the setup
menu). Result is that I now use different combinations for hill, cycle or
car. I turn off the menu screen (get to that with double press of the
lower left button).
Use the Trip Computer screen as one of those on the hill, set it to "Big
Numbers" and set two of the three display fields to show height and
location
(OS grid). Thus, in Trip Computer mode you have in BIG TEXT the data to
transfer to a paper map. I tend to use the final field for distance to
destination.

I am far too idle (or inept) to alter the defaults. :-)

--
Roger Chapman
Nearest Marilyn still to be visited - Great Orme.
89 miles as the crow flies,
considerably more as the walker drives.

Roger <[email hidden]> writes

Quoted message said:

My gps (Vista C) is telling porkies again, or at least the barometric
altimeter part is. If the gps is to believed I have managed 6883 feet of
ascent today. This of course is rubbish. I have yet to work out what the
real figure is but probably half would be about right.

The cause was the gusting wind which at times was strong enough to
almost have me over. An occupational hazard in the hills but I could do
without the gps suffering even more than me. Is there any way the
barometric altimeter can be turned off temporarily or will I have to buy
another that does not have that function just to use in windy
conditions?

Was that taken from the plotted track in a mapping program, or from the
GPS screen? I don't trust the latter.
--
Gordon H
(Remove invalid to email)

The message <[email hidden]>
from Gordon H <[email hidden]> contains these words:

Quoted message said:

Quoted message said:

The cause was the gusting wind which at times was strong enough to
almost have me over. An occupational hazard in the hills but I could do
without the gps suffering even more than me. Is there any way the
barometric altimeter can be turned off temporarily or will I have to buy
another that does not have that function just to use in windy
conditions?

Was that taken from the plotted track in a mapping program, or from the
GPS screen? I don't trust the latter.

The gps screen.

Generally I find the figure agrees fairly closely with what I get from
Fugawi 1:5000 but in windy conditions the 2 diverge. Per Fugawi my 2
little walks added up to approximately 3200 feet of ascent, a little
less than half actually recorded.

--
Roger Chapman
Nearest Marilyn still to be visited - Great Orme.
89 miles as the crow flies,
considerably more as the walker drives.

The message <[email hidden]>
from Roger <[email hidden]> contains these words:

Quoted message said:

Quoted message said:

Was that taken from the plotted track in a mapping program, or from the
GPS screen? I don't trust the latter.

Quoted message said:

The gps screen.

Quoted message said:

Generally I find the figure agrees fairly closely with what I get from
Fugawi 1:5000 but in windy conditions the 2 diverge. Per Fugawi my 2
little walks added up to approximately 3200 feet of ascent, a little
less than half actually recorded.

Afterthought.

I looked at part of the track uploaded to Fugawi. The multiplication is
there as well so the gusting must be creating false height variations as
I originally surmised.

--
Roger Chapman
Nearest Marilyn still to be visited - Great Orme.
89 miles as the crow flies,
considerably more as the walker drives.

Roger said:

The message <[email hidden]>
from "Nigel Cliffe" <[email hidden]> contains these words:

Quoted message said:

Quoted message said:

My gps (Vista C) is telling porkies again, or at least the
barometric altimeter part is. If the gps is to believed I have
managed 6883 feet of ascent today. This of course is rubbish. I
have yet to work out what the real figure is but probably half
would be about right.

The cause was the gusting wind which at times was strong enough to
almost have me over. An occupational hazard in the hills but I could
do without the gps suffering even more than me. Is there any way the
barometric altimeter can be turned off temporarily or will I have to
buy another that does not have that function just to use in windy
conditions?

Quoted message said:

You could look at the GPS height rather than the barometric ?

It is the height climbed that is excessive. I haven't ever caught it
out on height displayed although that is something I don't check very
often these days. Ironic really as the original reason for opting for
a barometric altimeter was accurate height output.

I've found that height climbed on walks which just meander up and down a few
feet can be very large. I have a stand alone barometric altimeter (Suunto),
and that would report about 10 or 20 percent more than my map calculations
depending on the setting. The Garmin is similar. On some routes it would be
50% extra. Never seen 100% extra.

I have the height on the display in one of the boxes on the screens almost
all the time when walking. Reason I have the Vista was the altimeter which
keeps working if the satellite lock disappears.

Quoted message said:

Quoted message said:

btw, couple of tips which you may have found, but I have started to
use a lot recently:
Change which screens are displayed, and in which order (its in the
setup menu). Result is that I now use different combinations for
hill, cycle or car. I turn off the menu screen (get to that with
double press of the lower left button).
Use the Trip Computer screen as one of those on the hill, set it to
"Big Numbers" and set two of the three display fields to show height
and location
(OS grid). Thus, in Trip Computer mode you have in BIG TEXT the
data to transfer to a paper map. I tend to use the final field for
distance to destination.

I am far too idle (or inept) to alter the defaults. :-)

Really is worth playing with to get the most useful screens and the most
useful data visible, makes a big difference !

- Nigel

--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

The message <[email hidden]>
from "Nigel Cliffe" <[email hidden]> contains these words:

snip

Quoted message said:

I've found that height climbed on walks which just meander up and down
a few
feet can be very large. I have a stand alone barometric altimeter
(Suunto),
and that would report about 10 or 20 percent more than my map calculations
depending on the setting. The Garmin is similar. On some routes it
would be
50% extra. Never seen 100% extra.

I have had more than 100% twice and on both occasions the wind was
strong and gusty. The earlier instance led me to doubt the accuracy of
the accumulated ascent and these days I mostly do an independent check
either beforehand as part of the planning process to make sure I don't
bite off more than I could chew or afterwards just to be sure.

Quoted message said:

I have the height on the display in one of the boxes on the screens almost
all the time when walking. Reason I have the Vista was the altimeter which
keeps working if the satellite lock disappears.

I try and avoid situations where I lose lock. :-) Doesn't happen very
often and even outbreaks of spiders web are infrequent. However I still
remember the first time I used the Vista C (Expedition #? to Sykeside)
where my results were totally bonkers while the massed ranks of the
other GPSs in the party performed perfectly.

Quoted message said:

Quoted message said:

Quoted message said:

btw, couple of tips which you may have found, but I have started to
use a lot recently:
Change which screens are displayed, and in which order (its in the
setup menu). Result is that I now use different combinations for
hill, cycle or car. I turn off the menu screen (get to that with
double press of the lower left button).
Use the Trip Computer screen as one of those on the hill, set it to
"Big Numbers" and set two of the three display fields to show height
and location
(OS grid). Thus, in Trip Computer mode you have in BIG TEXT the
data to transfer to a paper map. I tend to use the final field for
distance to destination.

I am far too idle (or inept) to alter the defaults. :-)

Quoted message said:

Really is worth playing with to get the most useful screens and the most
useful data visible, makes a big difference !

Too much choice. Once started I can see myself spending days ringing the
changes. :-)

--
Roger Chapman
Nearest Marilyn still to be visited - Great Orme.
89 miles as the crow flies,
considerably more as the walker drives.

Roger <[email hidden]> writes

Quoted message said:

The message <[email hidden]>
from Gordon H <[email hidden]> contains these words:

Quoted message said:

Quoted message said:

The cause was the gusting wind which at times was strong enough to
almost have me over. An occupational hazard in the hills but I could do
without the gps suffering even more than me. Is there any way the
barometric altimeter can be turned off temporarily or will I have to buy
another that does not have that function just to use in windy
conditions?

Was that taken from the plotted track in a mapping program, or from the
GPS screen? I don't trust the latter.

The gps screen.

Generally I find the figure agrees fairly closely with what I get from
Fugawi 1:5000 but in windy conditions the 2 diverge. Per Fugawi my 2
little walks added up to approximately 3200 feet of ascent, a little
less than half actually recorded.

I wish I could still manage 3200ft. 8-(
--
Gordon H
(Remove invalid to email)

In message <[email hidden]>, Gordon H
<[email hidden]> writes

Quoted message said:

Quoted message said:

Generally I find the figure agrees fairly closely with what I get from
Fugawi 1:5000 but in windy conditions the 2 diverge. Per Fugawi my 2
little walks added up to approximately 3200 feet of ascent, a little
less than half actually recorded.

I wish I could still manage 3200ft. 8-(

Same here.....on the flat that is :-x
--
Bill Grey

In message <[email hidden]>

Roger said:

The message <[email hidden]>
from Roger <[email hidden]> contains these words:

Quoted message said:

Quoted message said:

Was that taken from the plotted track in a mapping program, or
from the GPS screen? I don't trust the latter.

Quoted message said:

The gps screen.

Quoted message said:

Generally I find the figure agrees fairly closely with what I get
from Fugawi 1:5000 but in windy conditions the 2 diverge. Per Fugawi
my 2 little walks added up to approximately 3200 feet of ascent, a
little less than half actually recorded.

Afterthought.

I looked at part of the track uploaded to Fugawi. The multiplication
is there as well so the gusting must be creating false height
variations as I originally surmised.

A gusting wind is obviously going to generate barometric oscillations,
that's why it's gusting...... The air is rushing to get from a higher
pressure area to a lower pressure area. Also when air is moving and
it comes across different shaped surfaces the pressure can be higher on
one side than on the other. That's why planes take off when air moves
across the wing. If you put your barometric altimeter on the top of the
wing it would give a lower pressure to the underside of the wing.
Similar differences occur as wind moves across the surface of the land,
eg over a mountain-top or through a col.

Mike
--
o/ \\ // |\ ,_ o Mike Clark
<\__,\\ // __o | \ / /\, "A mountain climbing, cycling, skiing,
"> || _`\<,_ |__\ \> | immunology lecturer, antibody engineer and
` || (_)/ (_) | \corn computer user"