GPS breadcrumb trails

[BogMonster]

I have just got to the bottom of a GPS track problem I have been noticing for some time. When I save a track to use at a later date I quite often find the saved track doesn't take me exactly where expected - always within a few hundred metres but often some way off which can be a pain if there is a particular place to get through ditches, stone runs or whatever, which is hard to see. The GPS is a basic yellow eTrex.

The reason for this seems to be that the "active track log" (what the eTrex is recording as you drive, and what you get as the active log when you download it to the PC) has many many more waypoints than the saved logs. I just looked at one I recorded the other day and it has over 800 points and is very detailed (even without a basemap I can visualise some of the route just by looking at the log on screen on the PC). However when you save it, it seems to sample the waypoints at a rate of only about 10% and a saved track from a previous visit to the same place only has 90 points and is quite noticeably different - it joins these up with straight lines and quite often misses out a lot of the finer detail on a zig-zag track.

Do all GPS's do this or can one get a more sophisticated one for in-vehicle use which actually saves the full detail? It isn't something I remember seeing before - I suppose they do it to save memory in the GPS - but I want one that gives the full detail if possible. I've also found the available space within the eTrex is becoming a limitation so something with removable storage would be good. Don't want to spend mega bucks and most basemaps are a waste of time in this part of the world so a mapping GPS is a bit pointless - just interested to hear what other people's experiences are and/or whether anybody else has noticed this "feature" in their GPS? Maybe it is just because the eTrex is a budget GPS but I'd like to know whether better ones get away from this problem and if so, how much you need to spend to do what I want. Hopefully not too much!

Thanks

[TomG]

Depends on the GPS / software is used.

Some Handheld GPS's (older ones) have a limited amount of memory for the track log so it's a tradeoff between track frequency / resolution and total record time / distance.

On my eTrex Venture, from the Main Menu, go into Tracks

In the tracks screen with move the cursor to the Options button (it's at the top right, just to the left of the X) and select it

Choose 'Setup Track Log'

then 'Interval'.

Options are:

Most Often, More Often, Normal, Less Often and Least Often.

Be aware that Most Often will use up the storage much quicker so you'll run out of trackpoint memory sooner.

Also, Record Method switches between distance based (e.g. X points per kilometer) or time based (X points per minute) or 'Auto' decides which is best.

Wrap when Full will overwrite the oldest points with new ones - use with caution if you're relying on this to get back to base

With a laptop recording the route which has buckets of storage (unlike the GPS itsself) hooked upto Memory Map using NMEA you can record upto about 1 point per second which gives loads of detail (too much probably)

HTH

[jwriyadh]

Bogmonster, we used breadcrumb trails for a similar purpose in Saudi. The topography was a waste of time, so breadcrumbs indicate the path we drove to avoid impossible obstacles and when saved would indicate a drivable route on future visits. I have just checked an old file and relived a trip to the Empty Quarter passing through "Streakies Arrow Head Souk" on the 15 February. What year I haven't worked out yet, messed up the filing system somewhere.

The saved trail was/is quite accurate, one in particular just southwest of Riyadh taking a track round a cliff-face, this I actually drove at night with headlights out, just keeping the cursor on the breadcrumb trail. It was good enough to get me home in one piece.

The GPS was Garmin 162 which came with a simple "World Map", just major roads and details, the software was MapSource.This was run on a laptop wedged on the passenger seat. I acquired a large number of waypoints and breadcrumb trails over the years.

This setup was very useful in later years when work prevented me from leaving on trips with the rest of the group, I would agree an area or campsite then set off later after work. It was quite amusing to turn up at the campsite in the dark. Got me a few rollockings from various "desert gurus" as well.

jw

[streaky]

Another way to make your own tracks is to save waypoints as you drive and then join them up to make a track. This is called a 'Route'.

This doesn't consume so much of your storage for easy sections...so long as you remember to punch in the relevant waypoints for areas that require carefull navigation..ie. left here, right, straight on at farm etc. It's daft to save track data for straight lines, motorways etc.

My unit is a 182c which can save a whole load of track data...enough for four days of driving with bread crumb data intervals of around 30 seconds or so (great for five day long rally raids).

The higher up the chain of GPS models...the better the track data saving capability.

John...send me that file will you mate? I lost a lot of my Saudi data in the great PC crash of 2002.

Cheers.

S.

[Brian]

I have just got to the bottom of a GPS track problem I have been noticing for some time. When I save a track to use at a later date I quite often find the saved track doesn't take me exactly where expected - always within a few hundred metres but often some way off which can be a pain if there is a particular place to get through ditches, stone runs or whatever, which is hard to see. The GPS is a basic yellow eTrex.

The reason for this seems to be that the "active track log" (what the eTrex is recording as you drive, and what you get as the active log when you download it to the PC) has many many more waypoints than the saved logs. I just looked at one I recorded the other day and it has over 800 points and is very detailed (even without a basemap I can visualise some of the route just by looking at the log on screen on the PC). However when you save it, it seems to sample the waypoints at a rate of only about 10% and a saved track from a previous visit to the same place only has 90 points and is quite noticeably different - it joins these up with straight lines and quite often misses out a lot of the finer detail on a zig-zag track.

Do all GPS's do this or can one get a more sophisticated one for in-vehicle use which actually saves the full detail? It isn't something I remember seeing before - I suppose they do it to save memory in the GPS - but I want one that gives the full detail if possible. I've also found the available space within the eTrex is becoming a limitation so something with removable storage would be good. Don't want to spend mega bucks and most basemaps are a waste of time in this part of the world so a mapping GPS is a bit pointless - just interested to hear what other people's experiences are and/or whether anybody else has noticed this "feature" in their GPS? Maybe it is just because the eTrex is a budget GPS but I'd like to know whether better ones get away from this problem and if so, how much you need to spend to do what I want. Hopefully not too much!

Thanks

Have a look at this thread on a South African forum, about a data logger. This is quite cheap and will log a lot more detail than a commercial GPS. The T4A map contributors use them for fine detail of remote tracks. The logged routes can then be put back down to your etrex with mapsource.

Hope it helps. You may find other sources of data loggers, of course, the link is just for the idea.

[TomG]

For best accuracy, worth switching on WAAS

Also, there's a community mapping project here: http://www.openstreetmap.org/

[BogMonster]

My eTrex doesn't have that setup facility AFAIK. I don't think I could be bothered with recording lots of waypoints, and the track facility "sort of works" as it is - just sometimes it can pay to read it with a pinch of salt handy! I'll look at a more sophisticated GPS at some stage I think.