Yet another Question for the GPS Gurus - moved from Q&A

[skiguy]

Yet another Question for the GPS Gurus

Still working with the ins and outs of using a GPS. I have noticed several times while using my GPS I get "STRAY" tracks recorded to the log. By Stray they always show up as a distinct straight line that I have not actually hiked. These lines usually go off at a distinct angle to where I have actually hiked. They seem to occur when I stop for a period of time like Lunch at the top of a peak. I have also seen them recorded at the beginning of a hike when I put my GPS out to warm up on the hood of my car while I put my boots on. They are easily ignored; but is my GPS malfuntioning or is this normal. I have included an image of a hike up Snow I did a few weeks ago. You can see the "Stray Line" leading off of the Summit. This was when I stopped for lunch on the summit for about twenty minutes. I left my GPS on the whole time even when I was stopped. Any explanations?

 

[DougPaul]

First, the GPS connects the trackpoints together with straight lines. Thus anything which causes the GPS to produce a bad trackpoint will create these straight lines off to "nowhere".

Causes of bad fixes:
* When a GPS is started up (or reacquiring a fix), the first fix or two may be way off.
* When you stop, what do you do with the GPS? Do you make sure that it stays in a good location with a good skyview and the proper orientation? If not, it can get a bad fix or lose the fix entirely and have to reacquire the satellites.
* Noise, weak signals, multipath, etc ...
* Bad satellite constellation, satellite malfunction
* "Other"...

Normal errors in the GPS system can cause the GPS to produce variations in the fix. The track will tend to look like a local scribble. (Try it--leave the GPS stationary in a good spot for an hour or more and then look at the track. 24 hours would be best, because the satellites repeat their locations above a fixed observer every 23hrs 56min.)

Some software has modes which connect separate track segments with straight lines (eg NG TOPO!). So, if you turn the GPS off at the end of a hike, drive home, and turn the GPS back on, the software may draw a straight line between the trailhead and your home.

Doug

 

[skiguy]

First, the GPS connects the trackpoints together with straight lines. Thus anything which causes the GPS to produce a bad trackpoint will create these straight lines off to "nowhere".

Causes of bad fixes:
* When a GPS is started up (or reacquiring a fix), the first fix or two may be way off.
* When you stop, what do you do with the GPS? Do you make sure that it stays in a good location with a good skyview and the proper orientation? If not, it can get a bad fix or lose the fix entirely and have to reacquire the satellites.
Doug

Thanks Doug..I thought that this might be what was going on; but needed feedback from a confirmed GPS Guru. I have noticed that keeping good skyview and orientation at rest stops has prevented my above problem from occuring.What is the best orientation for a GPS. Being strapped to your shoulder(Vertical with screen faceout from user)or being held in your hand (horizontal with screen facing up to user). I know from your bake off that an external attenna is best; but if you are not using one how should it be placed for optimal performance?

 

[DougPaul]

What is the best orientation for a GPS. Being strapped to your shoulder(Vertical with screen faceout from user)or being held in your hand (horizontal with screen facing up to user).

Depends on the model of the GPS.

The Garmin eTrex series (new and old) uses a patch antenna mounted under the Garmin symbol above the display. A patch antenna works best if its flat face is aimed straight up and thus the flat face of the Garmin symbol aimed upward works best for these GPSes. (The same orientation as when you just plop it down on a table.)

I usually carry my GPS in a small pouch on my pack shoulder strap at the front of my shoulder and carry my eTrex Vista with the antenna outward. This is a mostly vertical orientation--not optimum, but usually adequate. I can push the pouch up to the top of my shoulder, but it is hard to reach and not very comfortable. I have also carried my Vista clipped (the soft case has a nice clip) to the strap at the back of a baseball cap. Still mostly vertical, but it works pretty well up (and back) there.

BTW, most external antennas are patch antennas, so flat side up is best. (The obvious orientation if you use the magnet to stick them to the top of a car.)

The Garmin 60, 76, and Rino series have quad helix antennas with their axes parallel to the long dimension of the GPS (particularly obvious in the 60 and Rino series). A quad helix works best with its axis pointed straight up, so hold these GPSes vertical. (Works nicely in my small pouch attached to my pack strap, but not very well on the table... Would work nicely on the back of my baseball hat, but my soft case doesn't have the nice clip. )

And since flesh absorbs the GPS signals (try closing your hand over the antenna and watch the signals disappear), you want to keep the antennas as clear of your body as possible.

Doug

 

[skiguy]

Depends on the model of the GPS.

The Garmin eTrex series (new and old) uses a patch antenna mounted under the Garmin symbol above the display. A patch antenna works best if its flat face is aimed straight up and thus the flat face of the Garmin symbol aimed upward works best for these GPSes. (The same orientation as when you just plop it down on a table.)

I usually carry my GPS in a small pouch on my pack shoulder strap at the front of my shoulder and carry my eTrex Vista with the antenna outward. This is a mostly vertical orientation--not optimum, but usually adequate. I can push the pouch up to the top of my shoulder, but it is hard to reach and not very comfortable. I have also carried my Vista clipped (the soft case has a nice clip) to the strap at the back of a baseball cap. Still mostly vertical, but it works pretty well up (and back) there.

BTW, most external antennas are patch antennas, so flat side up is best. (The obvious orientation if you use the magnet to stick them to the top of a car.)

The Garmin 60, 76, and Rino series have quad helix antennas with their axes parallel to the long dimension of the GPS (particularly obvious in the 60 and Rino series). A quad helix works best with its axis pointed straight up, so hold these GPSes vertical. (Works nicely in my small pouch attached to my pack strap, but not very well on the table... Would work nicely on the back of my baseball hat, but my soft case doesn't have the nice clip. )

And since flesh absorbs the GPS signals (try closing your hand over the antenna and watch the signals disappear), you want to keep the antennas as clear of your body as possible.

Doug

Your the MAN Doug! Thanks for filling me in. When's the next Bake Off?
I could be the guy to carry all the electronics...I'm good at being the "Gopher"...that is go for that and go for this and go find that while you(Doug) tweak this and estrapulate and interpolate that and...............

 

[Raymond]

What if you don’t use a backpack, just a fanny pack, as is my situation? Should I not even bother looking into acquiring a GPS receiver anymore?

 

[DougPaul]

What if you don’t use a backpack, just a fanny pack, as is my situation? Should I not even bother looking into acquiring a GPS receiver anymore?

The lower the GPS is on your body, the greater the signal blocking.

I haven't tried it myself, but I have read a report by someone who likes to carry his GPS on his belt that he liked the Garmin 60CSx because it worked much better on his belt than the other GPSes that he had tried. (In the bake-off tests, the 60CSx on a pack shoulder strap appeared to work as well as a 60CS with a head-mounted external antenna.)

BTW, I wouldn't carry a GPS on my belt--too prone to being damaged or knocked off by vegetation. A fanny pack should be ok from a mechanical standpoint.

BTW2, On the bake-off, Mohamed carried his GPS in front in a small waist pack, an antenna on his hat, and ran the cable down close to his body (or perhaps under clothing (better, IMO)). He seemed happy with the arrangement. (Perhaps he will chime in...) Once you have the antenna mounted in a good spot, the GPS can be anywhere within the reach of the cable.

Where you carry the GPS (or an external antenna) is only an issue if you are recording a track while you hike. If you are only using it for spot checks, you can leave it in your pack when you are not using it. And when making spot checks, it is easier to acquire the satellites if you are stationary.

Doug

 

[ken]

What if you don’t use a backpack, just a fanny pack, as is my situation? Should I not even bother looking into acquiring a GPS receiver anymore?

my fanny pack came with a shoulder strap to carry it as a shoulder bag if you chose - i took an extra buckle, found a spot on the front and sewed it so the strap would come from the back, across my shoulder and to the front and i put a pouch up on that strap (the strap was also useful getting the fanny pack on when carrying 4-5 quarts of water since it was hard to buckle the belt with all that weight pulling down) - i have since gotten dual straps for my fanny pack (like backpack straps) the dual straps are for mountainsmith fanny packs, but can be made to fit any (i have also carried my gps in my fanny pack facing up and also in my bicycle wedge (behind the seat) and it works well...

as to the GPS filling in blanks with srtraight lines - i own the $100 dollar yellow etrex and was very happy with the way the tracks got broken up and didn't fill in the blanks - then i bought the map60 and it was filling in the blanks - i then bought the vista and compared them side by side - the map60 lost the track more often (and filled in the blanks with a straight line) - the vista lost the track less often and didn't fill in the blanks - - i did a figure "8" for about 1 mile - the vista showed the 8 while the map60 showed an oval - i returned the map60 and kept the vista...

 

[Rob S]

I have also seen them recorded at the beginning of a hike when I put my GPS out to warm up on the hood of my car while I put my boots on.

One way to avoid stray tracks is to simply keep the track log option turned off until the moment you start to hike. Unless some GPS units don't allow this option? In my Garmin Etrex Legend, this option is found within the "Main" menu and submenu "Tracks". If you click on "Tracks" the On/Off option is directly above the memory gauge. Anyway, what I do is this: when at home uploading maps, routes, etc the track log is set to "Off". When I arrive at a trailhead, I'll turn the GPS on to allow it time to acquire satellites while I'm getting my stuff together. Once I'm ready, and the GPS is "Ready to Navigate", I'll turn the Track Log "On" and begin walking. Later, if I know I'm stopping for any length of time exceeding about 10 minutes, say lunch for example, then I may turn the track log off until I'm ready to move again. I don't always do this, and only had a stray line one time which I assumed was a bad fix due the location being very heavily treed. And I very rarely lose satellites, but when I do, about 10% of the time there is a small stray line that is obviously an error. At the end of the hike, as I enter the parking lot (or wherever I turned the track log on), I will then turn the track log option to Off and power down the GPS. The additional advantage of this practice is that when you turn the GPS on at home, you don't get a long line from the trailhead back to your home as DougPaul mentioned.

 

[DougPaul]

At the end of the hike, as I enter the parking lot (or wherever I turned the track log on), I will then turn the track log option to Off and power down the GPS. The additional advantage of this practice is that when you turn the GPS on at home, you don't get a long line from the trailhead back to your home as DougPaul mentioned.

The long line between the trailhead and your home is inserted by your downloading program and/or display program. A simple power cycling of the GPS will cause a break in the tracklog. Look at the GPX format tracklogs--they are human readable.

Doug

 

[Neil]

Straight lines.

I avoid them via the software (NG Topo!). Upon tracklog download there is a dialogue box wherein you can have Topo start a new track either every time the gps had to search the sky anew or whenever the distance bewtween trackpoints is "greater than x " distance. You can set x to whatever value you want. Takes care of the problem.


Those "rogue" trackpoints that make it look like you took a very quick detour can be deleted in GPSU. From there you can open the newly saved log in another program.

(FWIW, some tracklogs I save in GPX, TXT and TPO formats.)

 

[Rob S]

The long line between the trailhead and your home is inserted by your downloading program and/or display program. A simple power cycling of the GPS will cause a break in the tracklog. Look at the GPX format tracklogs--they are human readable.

As I mentioned, I first turn off the tracklog. Therefore, regardless of the unit being turned on or off, the tracklog starts and ends where you want it.

 

[DougPaul]

As I mentioned, I first turn off the tracklog. Therefore, regardless of the unit being turned on or off, the tracklog starts and ends where you want it.

That is one way of causing a break in the tracklog--there are others. The GPS also inserts breaks whenever it is turned off, whenever the satellite reception is turned off, or whenever it loses satellite lock for a sufficient period of time.

I personally tend to leave the tracklog recording turned on, power cycle the GPS to put additional breaks in the tracklog as needed, and use the trackpoint time stamps and Garmin Mapsource to identify the desired track segment. Then, I simply hand edit the GPX file to select the segment that I want. (It is a text XML format which is human readable and easy to edit.)

There is more than one way of doing any of the above...

Doug

 

[DougPaul]

I avoid them via the software (NG Topo!). Upon tracklog download there is a dialogue box wherein you can have Topo start a new track either every time the gps had to search the sky anew or whenever the distance bewtween trackpoints is "greater than x " distance. You can set x to whatever value you want. Takes care of the problem.

Yeah, took me a while to find it, but I also use the "start a new track every every time the gps had to search the sky anew " (ie whenever there is a break in the track) mode. If there are breaks in a track, I want to see them. Loss-of-signal breaks indicate that the GPS was having trouble tracking the satellites and the nearby track is probably less accurate. If one wants, it is trivial to remove the breaks by editing a GPX file.

Garmin Mapsource doesn't seem to want to connect the track segments so I haven't observed the problem there. Haven't tried any other mapping software, so I don't know where else this problem might occur.

(FWIW, some tracklogs I save in GPX, TXT and TPO formats.)

I have sometimes saved tracks in GPX (vendor independent), MPS (Garmin), and TPO or TPG (NG TOPO!). For the bakeoff, we saved the tracks in GPX, MPS, and TPO.

Since the bakeoff, I've been saving some tracks directly into GPX using GPSBabel on Linux. (Saves booting my laptop into XP for the sole purpose of downloading the tracks...) I can then view and edit the tracks in my preferred environment.

GPSBabel can also convert trackfiles from one format to another, but unfortunately, writing TPO (NG TOPO!) files is disabled in the current version due to some unresolved bugs. Using GPX files as masters and converting to manufacturer's proprietary formats as need is a great convenience...

BTW, GPSBabel also runs on MS and Macs. It can upload and download info from/to the GPS and perform file format conversions. See http://www.gpsbabel.org/

Doug

 

[Rob S]

There is more than one way of doing any of the above...

OK, I see what you mean, and wholeheartedly agree ........ BUT ........ isn't it still much easier to simply toggle the tracklog on and off as necessary? I don't mean to be argumentative, and I am still learning myself, but my way seems so easy and works so well that I cannot imagine a reason for doing it any other way.

Furthermore, NG Topo creates a nice solid route (if using the correct options that Neil pointed out). So even if I lose satellite reception for 10 minutes in the woods, the software would create a straight line between my last known point and the point where satellite reception was re-attained. I can live with that. By manually turning the tracklog on at the beginning of a hike and off at the end, there is no reason to edit anything later .........

A case of "Potaeto" or "Potahto", I reckon .......

 

[Rob S]

Garmin Mapsource doesn't seem to want to connect the track segments so I haven't observed the problem there. Haven't tried any other mapping software, so I don't know where else this problem might occur.

Exactly!

I can see by your last post that we want different things. I WANT all the tracklogs connected. Reason is simple as building an elevation profile to attach to my trip reports. The Garmin Mapsource doesn't connect my entire hike so therefore the elevation profile is only for a segment of the hike.

Now I see why we use our GPS differently ....... we expect a different output. Nothing wrong with that .......

 

[DougPaul]

OK, I see what you mean, and wholeheartedly agree ........ BUT ........ isn't it still much easier to simply toggle the tracklog on and off as necessary? I don't mean to be argumentative, and I am still learning myself, but my way seems so easy and works so well that I cannot imagine a reason for doing it any other way.

Personal preference. I think it is simpler to power cycle than to find my way through the menus. Doesn't matter which method you use as long as it gets the job done without messing something else up.

Furthermore, NG Topo creates a nice solid route (if using the correct options that Neil pointed out). So even if I lose satellite reception for 10 minutes in the woods, the software would create a straight line between my last known point and the point where satellite reception was re-attained. I can live with that. By manually turning the tracklog on at the beginning of a hike and off at the end, there is no reason to edit anything later .........

I found the straight lines between unrelated tracklogs distracting in too many cases. So I prefer to manually insert breaks when desired, and manually edit the track after the fact to remove breaks, insert breaks or truncate tracks to suit my needs. In some cases, I have processed the same raw track into several versions for various purposes. (See my earlier post about editing GPX tracks.) The first and/or last point (sometimes points) in a track can also be bad--hand editing makes it trivial to remove them. I am in the process of doing some careful comparisons between a 60CS and 60CSX and these capabilities have been very useful.

A case of "Potaeto" or "Potahto", I reckon .......

Ayup! Choice is good here.

Doug

 

[DougPaul]

I can see by your last post that we want different things. I WANT all the tracklogs connected. Reason is simple as building an elevation profile to attach to my trip reports. The Garmin Mapsource doesn't connect my entire hike so therefore the elevation profile is only for a segment of the hike.

In the process of analyzing the bakeoff tracks, I wrote a trivial program which takes a GPX file, removes all of the breaks, and writes a new GPX file. Gave me the capability of analyzing the same track segment sequence as multiple segments or combined into a single segment.

Now I see why we use our GPS differently ....... we expect a different output. Nothing wrong with that .......

Agreed.

I just prefer to keep the raw data as is. Then I can make multiple versions without disturbing the original. (A bit like keeping your photographic negatives back in the film days or raw image files in the digital camera age.)

Doug

 

[Neil]

I spent 2 weeks hiking in the Adirondacks this summer and recorded several different logs. When I got home I downloaded them all into one TPO file and by using the "start a new track every time the gps had to search...." feature was able to avoid getting a mish-mash of straight lines all over my map. On a single hike I think the best remedy is to remember to make sure the tracklog is empty when starting the hike and turning it off before turning off the gps. At home, you can decide how to deal with any breaks in the record according to your software and needs/wants.

BTW, I never save the log on my gps. Then, unless you delete the active log, you will download both the saved and active versions onto your computer. If you save, then delete the live tracklog on your gps you will lose your elevation data, timestamps and a lot of trackpoints. On my unit, (Garmin RINO 130)if you want to use the backtrack feature you have to save the active log first.

I wrote to Garmin about that and they shrugged their shoulders and said it was to save memory. (I get a gig - no,not a Giggy - of removable memory in my camera dirt cheap but my gps has something like 25 meg which is supposed to be a big deal).

 

[Rob S]

Doug and Neil, thanks for your very informative posts. Very useful information and I've learned a few new things. And thanks to Skiguy for starting this thread.

Rob