Track Jumping Around When Not Moving

Forum for questions and problems regarding PathAway GPS 4 SE for Palm OS

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Track Jumping Around When Not Moving

Postby voyageurs60 » Tue Nov 06, 2007 4:50 am

I am using PA V4.00.74 with a Palm T2 and a GlobalSat BT-308

There are no maps loaded - just using the track feature at this time
for GeoCaching.

Playing around I have been following a track in my car or walking (choosing the appropriate track type) and in both situations the track
jumps around when I am standing still. I am aware that the GPS
precision changes with time. I want to make sure that the BT-308
is appropiate for use with PA for GeoCaching and to make sure
a setting is not incorrect. Not sure what the setting would be - If
I can use this setup for GeoCaching I will purchase the full registered

I am attempting to upload a track which will show the "jumping" when still
Hope this is the correct file.

Track 07-11-05 14-42.pdb
At end of track "jumping around" of track while not moving
(26.88 KiB) Downloaded 139 times

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Joined: Mon Feb 13, 2006 9:00 pm
Location: UK

Postby Antony » Sun Nov 25, 2007 6:19 am

Hi there - I get the same problem on my TX, and used to get it the same on my T2 with PW 3 and 4. My GPS is a ""Clip-On - about 3 years old now - and it has two different sensitivity levels, and I get the same problem with both settings, but it's fine when moving. I always reckoned it was to do with things trying to figure out what was happening when there was no movement to give it a clue, so I just got used to it. Would be interested to know if it is "normal" though.

olivier old
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Joined: Mon Nov 26, 2007 1:48 am
Location: Paris

Postby olivier old » Mon Nov 26, 2007 1:56 am

I use Pathaway4 with a T5 and a Kerrio blutooth/Nema GPS. When I stand up my location changes. When I register the current point I find myself 15 meter away. When I use the same GPS and the same T5 with another navigation solution (ex Viamichelin or Tomtom) I dont have any trouble.

Who has the solution and/or the why of this.

Ken in Regina
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Joined: Mon Mar 06, 2006 3:49 am
Location: N50 29 11 W104 38 37

Postby Ken in Regina » Tue Nov 27, 2007 4:00 am

If you are really interested in understanding more about how this works you need to get something that will show you the instantaneous readings that your GPS receiver is giving to the program.

I can't give you a technical description but I've seen it and it seems to be absolutely normal. Let me share a recent experience. About two weeks ago I purchased the version of MS Streets & Trips that comes with a SIRFIII receiver that's rated as pretty darned good. I don't care about Streets & Trips, I just wanted a good USB GPS receiver that I could connect to my laptop to use with Garmin's nroute program.

To get it working I needed some sort of utility to convert the NEMA data stream from the GPS to the proprietary Garmin data stream that nroute wants to see. (I chose GPSGate to do this and it works slick.)

I had some troubles at first getting things to work so I got another utility that monitors the GPS input and displays it in a variety of ways. It gives you a bar chart showing the reported signal strengths of each of the satellites the GPS is seeing. It gives you the raw NEMA data stream from the GPS. And it gives a plot of the instantaneous readings from the GPS.

I was sitting in my easy chair with the GPS receiver on a SPAM table close to the picture window with 8 satellites in view, all with pretty good signal strength. I was quite astonished at the plot that was being laid out. My house was apparently wandering all over the lot, and occasionally even into the neighbours yards!

Once I had things working properly I left nroute up with the trip meter active and watched a TV show. After an hour or so my house had clocked a distance of .26 statute miles and at one point had apparently achieved a maximum speed of over 4 miles per hour in its journey around the yard.

I have since tried this occasionally with the GPS connected to my desktop PC in my basement office with six to eight satellites in view and I have seen my house accomplish sprints of nearly 7 miles per hour. :shock:

VisualGPS is the program I used on the PC to monitor and plot the raw data from the GPS device. It has some very interesting ways to display what it's receiving from the GPS if you are interested. I think there may be some versions available for handheld devices also.

That probably doesn't help much in understanding why it happens but it appears to be quite normal. I see the same thing on my Garmin iQue 3600 (Palm OS w/ internal GPS) when I'm parked. I can tell it's happening because the arrow icon that represents my position will randomly change the direction I'm headed and it only does that if it sees "movement" from the GPS signals.

If anyone cares, I can fire the iQue up side by side with the laptop device with the tripmeters running on both and see if they both report similar distances and speed for my house. ... Anybody think their house can go faster than mine?? :P


Ken in Regina
Posts: 20
Joined: Mon Mar 06, 2006 3:49 am
Location: N50 29 11 W104 38 37

Postby Ken in Regina » Tue Nov 27, 2007 4:23 am

Okay, I did a little poking around and here's a good section on GPS on Wikipedia to read if you want to know the way the locations are calculated and the sources of error. Here's a summary:

Sources of User Equivalent Range Errors (UERE)

Source ......................... Effect

Ionospheric effects...... ± 5 meter
Ephemeris errors...... ± 2.5 meter
Satellite clock errors ....± 2 meter
Multipath distortion ...... ± 1 meter
Tropospheric effects ..± 0.5 meter
Numerical errors ..........± 1 meter

Pardon the formatting. It's a bear to do a table in forum software that doesn't do tabs, has proportional fonts and insists on compressing multiple spaces down to one. :?

Note that these effects come into play on each and every reading. Some, like atmospheric effects, change only slowly so they can be considered relatively constant over short periods. Others, like multipath distortion in near range, can change rapidly and continuously.

Anyway, check out the Wikipedia entry. If you don't want to read it all, use the table of contents to jump to the sections on calculating positions and accuracy and error sources.



olivier old
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Joined: Mon Nov 26, 2007 1:48 am
Location: Paris

Postby olivier old » Wed Nov 28, 2007 2:22 am

Hi Ken thanks

Your house is the fastest, no question about it !
GPS errors are real as in any physical measurement.

Based on the wikipedia figure this means your house could move 12+12=24 meters each sample. (Please train it up to this point).

My Garmin GPS, my TomTom software running on my palm with the same GPS I use with PA4 give a standby position when I keep still. This means there is some kind of well known algorithm to reduce the fluctuations due to errors. PA4 has to include this algoritm.

Best regards


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Joined: Thu Dec 13, 2007 4:23 am

Postby ZehHa » Thu Jan 24, 2008 10:58 pm


Probably the car's navagation programs just suppress any movements with a lower speed than that of a typical car in motion. But any filter or smoothing algorithm will reduce the accuracy. If you want to have a universal moving map program that also fits the needs of hikers or hill climbers, any reduction of accuracy will also reduce the usefullness.

If you want to suppress lower speed movements when logging tracks, you can adjust your intended level of sensibility by selecting "Preferences"->"Tracking"->"minimal speed". This is already available in Pathaway.


Kind regards


olivier old
Posts: 8
Joined: Mon Nov 26, 2007 1:48 am
Location: Paris

Postby olivier old » Sun Feb 03, 2008 11:43 pm

Thank you for your answer.

The point is, with the current PW4 solution the standsteal position swings in a circle with at least a 20 meters diameter. Hence I don't feel a minimal speed can filter this.
I use GPS solutions based on Palm or Garmin for driving and sailling, it is the first time I see such a swing. It must be an explaination and a solution.

BR, Olivier

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