GPS query - removing spikes from tracks
Judith
(a Garmin Geko 201). At one point I could see on the GPS screen that
the track had gone a bit barmy; it looked like a spider had been
running back and forth across the screen.
I've just imported the tracks for the whole trip into MemoryMap and
can see that I have quite a few of these spikes. Most are small but
some are huge and mean I cannot rely on the GPS track as a good record
of where I went.
What is the best way to remove these tracks? MemoryMap allows you to
remove a Trackpoint and remove a Velocity Spike. By removing
Trackpoints I have managed to smooth out the track but sometimes I
have dropped a Trackpoint which ends up altering the course of the
track, eg cutting straight across a bend in my route. I'm not sure
why I would choose to drop a Velocity spike rather than a Trackpoint;
all of the spikes show a huge increase in my speed, but that is just a
simple Speed-Time-Distance effect.
Should I use another utility to edit the track before importing into
MemoryMap? Should I convert the track to a route and mess around with
it somehow?
I seem to get this problem more with my Geko than I ever did with the
original yellow Etrex. Research suggests it is due to temporary loss
of GPS signal. I could mount my GPS on my shoulder strap to improve
reception, but that still wouldn't help in woodland (but it wasn't the
forestry parts of the walk where I got the biggest spikes!) I usually
have the GPS in battery-save mode. Would normal mode help? Or WAAS?
Any tips, please?
Judith
PS TRs can be found here:
http://northernpies.blogspot.com/
http://alanrayneroutdoors.blogspot.com/
http://gemini-challenge.blogspot.com/
I really must get my own blog, one day.
Roger Chapman
> I did a 3-day backpack at the weekend and recorded the track on my GPS
> (a Garmin Geko 201). At one point I could see on the GPS screen that
> the track had gone a bit barmy; it looked like a spider had been
> running back and forth across the screen.
>
> I've just imported the tracks for the whole trip into MemoryMap and
> can see that I have quite a few of these spikes. Most are small but
> some are huge and mean I cannot rely on the GPS track as a good record
> of where I went.
>
> What is the best way to remove these tracks? MemoryMap allows you to
> remove a Trackpoint and remove a Velocity Spike. By removing
> Trackpoints I have managed to smooth out the track but sometimes I
> have dropped a Trackpoint which ends up altering the course of the
> track, eg cutting straight across a bend in my route. I'm not sure
> why I would choose to drop a Velocity spike rather than a Trackpoint;
> all of the spikes show a huge increase in my speed, but that is just a
> simple Speed-Time-Distance effect.
>
> Should I use another utility to edit the track before importing into
> MemoryMap? Should I convert the track to a route and mess around with
> it somehow?
I haven't had much of that sort of problem in the recent past (which may
be connected to my lack of activity these days) but in days of old when
I used OziExplorer frequently I used that program to modify tracks. IIRC
with Ozi you can drag trackpoints around as well as just deleting them.
> I seem to get this problem more with my Geko than I ever did with the
> original yellow Etrex. Research suggests it is due to temporary loss
> of GPS signal. I could mount my GPS on my shoulder strap to improve
> reception, but that still wouldn't help in woodland (but it wasn't the
> forestry parts of the walk where I got the biggest spikes!) I usually
> have the GPS in battery-save mode. Would normal mode help? Or WAAS?
Battery-save mode will undoubtedly make the problem worse.
snip
--
Roger Chapman
Nearest Marilyn still to be visited - Walton Hill.
101 miles as the crow flies,
considerably more as the walker drives.
Jhimmy
(not notepad) and delete the offending out. Example...
<trkpt lat="54.87413" lon="-1.99985">
<ele>282.3</ele>
<time>2011-04-17T11:42:08Z</time>
</trkpt>
Yes, yes, I know it's crude, but who cares?
Jhimmy
Judith
wrote:
>I just look at the time of the spike and then open the gpx file with Wordpad
>(not notepad) and delete the offending out. Example...
>
Ah, that looks like exactly what I am looking for.
<Snip>
>
>
>Yes, yes, I know it's crude, but who cares?
That's ideal, thanks.
Judith
Ted Ferenc
You could try gpsbabel from http://www.gpsbabel.org/ this does just about
anything you could possibly want to do to gps files, it is very
comprehensive and a real pain to figure out.
I think you want the 'Remove Points Within Distance (position)' filter
http://www.gpsbabel.org/htmldoc-1.3.6/filter_position.html
It is a freeware console application.
--
Ted Ferenc. (http://walks.ndrw.co.uk http://ndrw.co.uk)
Mike Clark
Judith <no.spam.for....@aol.com> wrote:
[snip]
>
> What is the best way to remove these tracks?
I use GPS Utility for editing my GPS tracks
It allows you to view the entire set of track points as a table and you
can then manipulate individual points in whatever way you wish e.g.
deleting them or replacing them with an interpolated point.
> MemoryMap allows you to remove a Trackpoint and remove a Velocity
> Spike. By removing Trackpoints I have managed to smooth out the track
> but sometimes I have dropped a Trackpoint which ends up altering the
> course of the track, eg cutting straight across a bend in my route.
> I'm not sure why I would choose to drop a Velocity spike rather than a
> Trackpoint; all of the spikes show a huge increase in my speed, but
> that is just a simple Speed-Time-Distance effect.
>
> Should I use another utility to edit the track before importing into
> MemoryMap? Should I convert the track to a route and mess around with
> it somehow?
>
> I seem to get this problem more with my Geko than I ever did with the
> original yellow Etrex. Research suggests it is due to temporary loss
> of GPS signal.
The Geko can show this problem if it is held incorrectly and the aerial
is shielded. For best reception it should be held horizontally and your
hands should not cover the faceplate. Worse reception can be if it is
placed vertically and in a pocket held against the body.
> I could mount my GPS on my shoulder strap to improve reception, but
> that still wouldn't help in woodland (but it wasn't the forestry parts
> of the walk where I got the biggest spikes!) I usually have the GPS
> in battery-save mode. Would normal mode help? Or WAAS?
WAAS is probably not of much use in the UK at the moment. Battery save
mode will certainly make things worse.
>
> Any tips, please?
>
> Judith
> PS TRs can be found here:
> http://northernpies.blogspot.com/
> http://alanrayneroutdoors.blogspot.com/
> http://gemini-challenge.blogspot.com/
>
> I really must get my own blog, one day.
Mike
--
o/ \\ // |\ ,_ o Mike Clark
<\__,\\ // __o | \ / /\, "A mountain climbing, cycling, skiing,
"> || _`\<,_ |__\ \> | caving, antibody engineer and
` || (_)/ (_) | \corn computer user" http://www.antibody.me.uk/
mechanic
> I really must get my own blog, one day.
--
mechanic
Yo$$1960
> It is a freeware console application.
There's a GUI for gpsbabel at their website. A bit of a PITA to compile
(if you're a Linux user, and looking at your User-Agent string, you
appear to be) but works quite nicely.
Of course, it may not allow access to all the switches, bells and whistles
that gpsbabel has to offer, but I've not had any problems. OTOH, I'm not
a power use of the program.
--
Regards _
/ ) "The blindingly obvious is
/ _)rad never immediately apparent"
Only the wounded remain, the generals have all left the game
Generals - The Damned
Ted Ferenc
> On Wed, 20 Apr 2011 17:55:06 -0500, Ted Ferenc wrote:
>
>> It is a freeware console application.
>
> There's a GUI for gpsbabel at their website. A bit of a PITA to compile
> (if you're a Linux user, and looking at your User-Agent string, you
> appear to be) but works quite nicely.
>
> Of course, it may not allow access to all the switches, bells and
> whistles that gpsbabel has to offer, but I've not had any problems.
> OTOH, I'm not a power use of the program.
Yes, I am using Ubuntu, I use gpsbabel to upload my track as a gpx file
from my GPS via a script. On my web site I wrote my own code to remove
the spikes, turning off battery save on the GPS did remove most of them.
Craig Wallace
> remove a Trackpoint and remove a Velocity Spike. By removing
> Trackpoints I have managed to smooth out the track but sometimes I
> have dropped a Trackpoint which ends up altering the course of the
> track, eg cutting straight across a bend in my route. I'm not sure
> why I would choose to drop a Velocity spike rather than a Trackpoint;
> all of the spikes show a huge increase in my speed, but that is just a
> simple Speed-Time-Distance effect.
>
> Should I use another utility to edit the track before importing into
> MemoryMap? Should I convert the track to a route and mess around with
> it somehow?
I usually use Garmin MapSource for this sort of track tidying. I think
its much better for this than Memory Map - MapSource shows the
individual trackpoints, so you can select them and delete them. Plus
there is an undo option (something Memory Map seems to be lacking?),
useful in case you delete too many points and mess up the track shape.
> I seem to get this problem more with my Geko than I ever did with the
> original yellow Etrex. Research suggests it is due to temporary loss
> of GPS signal. I could mount my GPS on my shoulder strap to improve
> reception, but that still wouldn't help in woodland (but it wasn't the
> forestry parts of the walk where I got the biggest spikes!) I usually
> have the GPS in battery-save mode. Would normal mode help? Or WAAS?
>
> Any tips, please?
How are you currently carrying the Geko? On the top of the shoulder
strap or on top of a rucksack would probably be the best.
I think battery save mode is best avoided. I think it works by switching
off the GPS receiver most of the time, and only switches it on every 5
seconds or so. So the GPS can struggle to get a signal, especially if
you are moving between fixes.
And the batteries in the Geko usually last long enough on normal or WAAS
mode anyway (about 12 hours on good rechargeables).
I don't think WAAS/EGNOS would help much with your problem of track
spikes, its more to do with accuracy on a smaller scale. And it does
need a mostly clear view of the horizon to the south. Though I usually
switch it on on my Garmins anyway, it might help a bit.
--
Craig Wallace
http://craig.neogeo.org.uk
http://www.neogeo.org.uk
Craig Wallace
If you're going to use a text editor, there are much better options than
Notepad or Wordpad. I'd at least use something with syntax highlighting.
I like Notepad2 for this: http://www.flos-freeware.ch/notepad2.html
It does syntax highlighting for GPX, plus loads of other useful features
and improvements over the original Windows Notepad.
Or Foxe: http://www.firstobject.com/dn_editor.htm
Its an XML editor, so can do syntax highlighting, plus show a tree view
and validate the XML etc.
Judith
<craigw84@fast_NOSPAM_mail.fm> wrote:
>I usually use Garmin MapSource for this sort of track tidying. I think
>its much better for this than Memory Map - MapSource shows the
>individual trackpoints, so you can select them and delete them. Plus
>there is an undo option (something Memory Map seems to be lacking?),
>useful in case you delete too many points and mess up the track shape.
I've now got MapSource and I am impressed. Like you say, I can see
each leg of a track segment and delete it if it is obviously out of
place. And, yes, I can undo, unlike MemoryMap.
>
>How are you currently carrying the Geko? On the top of the shoulder
>strap or on top of a rucksack would probably be the best.
Usually it's in a pouch on my belt, which means it is lying
horizontally but may be shielded by my body, eg when climbing stiles
or even just walking over rough ground.
>
>I think battery save mode is best avoided. I think it works by switching
>off the GPS receiver most of the time, and only switches it on every 5
>seconds or so. So the GPS can struggle to get a signal, especially if
>you are moving between fixes.
In MapSource I can see that my Active Log is actually made up of
dozens of little sections, each one a few seconds or minutes after the
next. Next time I go out, I will not use Battery Save and see what
difference that makes.
Judith
Ted Ferenc
> If you're going to use a text editor, there are much better options than
> Notepad or Wordpad. I'd at least use something with syntax highlighting.
>
> I like Notepad2 for this: http://www.flos-freeware.ch/notepad2.html It
> does syntax highlighting for GPX, plus loads of other useful features
> and improvements over the original Windows Notepad. Or Foxe:
> http://www.firstobject.com/dn_editor.htm Its an XML editor, so can do
> syntax highlighting, plus show a tree view and validate the XML etc.
As an aside my favourite free ware editor is pspad http://pspad.com has
syntax highlighting and just about anything else you can think of.
Gordon H
<no.spam.for....@aol.com> writes
>
> By removing
>Trackpoints I have managed to smooth out the track but sometimes I
>have dropped a Trackpoint which ends up altering the course of the
>track, eg cutting straight across a bend in my route.
I never delete a track from GPS nor PC until I am satisfied with the
corrected track. (Not much help, I suppose).
If you can't access the original, ie - download it again, I would add
extra trackpoints to represent the curve as accurately as possible.
Who's to dispute the result, apart from yourself?
I use Tracklogs, BTW, it seems much simpler to correct tracks than all
the other suggested solutions!
I never used battery save mode on my older GPSRs, and the Satmap I've
had for 12 months never seems to lose lock even in wooded areas,
probably why it's outrageously expensive, bearing in mind map card
purchases... ;-)
--
Gordon H
Remove "invalid" to reply
Yo$$1960
> Yes, I am using Ubuntu, I use gpsbabel to upload my track as a gpx file
Thought so; Using Pan is (almost) a dead giveaway. :-)
> from my GPS via a script. On my web site I wrote my own code to remove the
> spikes, turning off battery save on the GPS did remove most of them.
That prompted me to visit your site, not to nick code or anything, but
just to have a look. I was thinking this might be a good way of using the
web space available to me. Anything I could come up with would look
really, really awful compared with your site.
In short, a very well laid out site.
--
Regards _
/ ) "The blindingly obvious is
/ _)rad never immediately apparent"
We're going to hell anyway, let's travel first class
Saturday Night - Kaiser Chiefs
Ted Ferenc
> On Thu, 21 Apr 2011 14:06:28 -0500, Ted Ferenc wrote:
>
>> Yes, I am using Ubuntu, I use gpsbabel to upload my track as a gpx file
>
> Thought so; Using Pan is (almost) a dead giveaway. :-)
>
>> from my GPS via a script. On my web site I wrote my own code to remove
>> the spikes, turning off battery save on the GPS did remove most of
>> them.
>
> That prompted me to visit your site, not to nick code or anything, but
> just to have a look. I was thinking this might be a good way of using
> the web space available to me. Anything I could come up with would look
> really, really awful compared with your site.
>
> In short, a very well laid out site.
Thanks for the kind comments, a cheque in the post would be preferable!
If you look at the info menu link it will tell you how the site was
created with hopefully enough info for you to create your own site..
Yo$$1960
> Thanks for the kind comments, a cheque in the post would be preferable!
:-)
YW and will a virtual beer token suffice?
> If you look at the info menu link it will tell you how the site was
> created with hopefully enough info for you to create your own site..
Will do, thanks.
--
Regards _
/ ) "The blindingly obvious is
/ _)rad never immediately apparent"
I hope I live to relive the days gone by
Old Before I Die - Robbie Williams
Michael Chare
Buy and iBlue 747 as sold on ebay for about £25.
This has a much better GPS receiver than the Geko 201 and comes with
Windows software that lets you display your track against a Google Maps
Satelite background. It has a Lithium battery which will last all day.
It does not have a display but will supply WGS84 data by bluetooth to a
mobile phone/laptop etc.
The software lets you edit your track.
I managed to accidently record the track of an Easyjet aircraft when I
left the unit switched on in my jacket pocket. The jacket was in an
overhead locker.
--
Michael Chare
Judith
wrote:
>> I really must get my own blog, one day.
>
>http://wordpress.com/
Oh, go on, then.
My last two TRs are here: http://aroundthehills.wordpress.com
Judith