Garmin Tracks vs. Routes, eTrex
nae...@my-deja.com
couple of questions:
eTrex allows 1 "route" and 10 "tracks". What is the difference between
these two?
The eTrex can store up to 2000 tracklog points. Can anyone guestimate
how many tracklog points make up a mile? In this case, the terrain I'm
riding is anything but straight lines -- there are lots of switchbacks
and turns in the trail.
I would like the ability to store a couple of different trails at a
time. Even though I may only be riding 15 or 20 miles, there are at
least 60 miles of trails that I would like to have access to in the
unit at one time.
I have noticed that the eTrex has almost twice as many tracklog points
at the 12XL. Maybe an experienced 12XL user could relay their
experience with that unit in similar conditions.
--Nate Estep
Sent via Deja.com http://www.deja.com/
Before you buy.
Peter Rathmann
> eTrex allows 1 "route" and 10 "tracks". What is the difference between
> these two?
A route is a series of waypoints that will guide you to your destination.
Typically, the waypoints are all the intersections where you need to make a
turn. The GPS will then give you bearing and distance information to the
next waypoint in the route and automatically switch to the following
waypoint when you reach the current one.
A track is the set of 'breadcrumbs' recorded by the GPS as you move along.
In the Etrex, there is both the 'active track' which is recording your
current movements (this one is up to 2000 points), and up to 10 stored
tracks, which are compressed versions of previous tracks that you stored in
the unit.
> The eTrex can store up to 2000 tracklog points. Can anyone guestimate
> how many tracklog points make up a mile? In this case, the terrain I'm
> riding is anything but straight lines -- there are lots of switchbacks
> and turns in the trail.
The number of trackpoints will depend on how straight your path is - the
unit looks at your previous path and puts in a new trackpoint when your
position departs from that predicted by a straight line extrapolation by a
preset amount.
My experience with a GPS 12 is that 1000 points are sufficient for about 40
miles of paved bike trails and somewhat less on typical mountain bike
trails.
> I would like the ability to store a couple of different trails at a
> time. Even though I may only be riding 15 or 20 miles, there are at
> least 60 miles of trails that I would like to have access to in the
> unit at one time.
That should be very easy. 60 miles may or may not fit in the 2000 point
active track, but you can also use the stored tracks. Ride 20 miles or so
and then save the active track in one of your stored track locations. This
will reduce the number of trackpoints (I think only 250 are kept per stored
track) by reducing the accuracy a little, but I find it to still be more
than adequate. That would give you 200 miles of trails in the 10 stored
tracks.
Chris Moellering
The track can be used to make a virtual map on a non-map equipped GPS. For
example, on my GPS12 I can upload a saved track from my PC to have on-screen
as a fairly detailed route map. It can be used in conjunction with waypoints
for a route.
I use GPS Utility which allows you to import all of this off of MapsOnUs.com
routes, which is WAY COOL. I did this on vacation to florida, never even had
to look at a paper map all the way there and back.
With GPS Utility you can also scan maps (or import them) and set up your own
routes and tracks off the map. Nice for off-road type stuff.
--
Grace & peace,
Chris Moellering
jp
are discarted :-)
"Peter Rathmann" <prat...@home.com> wrote in message
news:39201D7C...@home.com...
Peter Rathmann
jp wrote:
> When saving an active track accuracy isn't reduced, just the time labels
> are discarted :-)
My description was based on experience with the eMap which only stores 250
points per stored track. Since the active track has over 2000 points, some
compression and loss of accuracy occurs whenever a reasonably full active track
is stored. I thought the Etrex was similar, but have no experience with it.
Kevin Altis
understand how this works from the example of storing several different trails
on the device at once.
I would be very interested to hear more about missing features in the eTrex
compared to say a 12XL or 12Map. I'm considering getting an eTrex as well as
the TeleType software
http://teletype.com/gps/index.html
for use with my PocketPC. The PocketPC would typically only get used when I'm
in the car or if I stopped to "get my bearings." On a trail or walking around a
city I would mostly be using the GPS by itself.
It seems like it would be nice to have a basic map background available, but
that won't help me on trails or will it; for example, does the Garmin Topo maps
cover national park trails, local trails, creeks? At this point the world data
doesn't appear to be too detailed, but I would be interested in a detailed map
of London, Paris, Amsterdam... I guess what I'm asking is what additional
benefits I would get from having a 12Map or 12XL over an eTrek?
Thanks,
ka
Peter Rathmann
> So, can you "load" an old track to become your current route? I don't quite
> understand how this works from the example of storing several different trails
> on the device at once.
You can use various share/freeware programs to store your previous tracks on your
PC and then upload them back into the GPS as desired. One application of this is
as a primitive map - the tracks may consist of all hiking trails in your area and
therefore loading the tracks will show you the network of trails on the map page
and you can see where you are relative to junction points, etc. Of course it
doesn't have many of the features of a real map, like the ability to add and delete
detail when changing scales, or names and other labels to identify roads and
trails.
> I would be very interested to hear more about missing features in the eTrex
> compared to say a 12XL or 12Map.
I don't have an eTrex or 12Map, so I can't address this very well (I have a plain
12 and an eMap). Hope someone else can chime in on this.
> It seems like it would be nice to have a basic map background available, but
> that won't help me on trails or will it; for example, does the Garmin Topo maps
> cover national park trails, local trails, creeks?
Creeks are shown on both R&R and Topo, and Topo does have quite a few trails
included. I'd suggest checking out some areas with which you're familiar at the
Cartography section of Garmin's site (www.garmin.com) where you can zoom in on any
region of their US mapping products (and Worldmap too) and see how much detail is
included.
Dale DePriest
number of points stored is reduced just like it is only other units when
creating a route. In addition the knowledge of broken tracks is lost
and the time stamps are lost. This reduces the memory requirement
considerably This is why they call it "compressed". There isn't any
actually compression algorithm being used since it displays just as fast
as always (no decompression involved).
Dale
Peter Rathmann wrote:
>
> jp wrote:
>
> > When saving an active track accuracy isn't reduced, just the time labels
> > are discarted :-)
>
> My description was based on experience with the eMap which only stores 250
> points per stored track. Since the active track has over 2000 points, some
> compression and loss of accuracy occurs whenever a reasonably full active track
> is stored. I thought the Etrex was similar, but have no experience with it.
>
> >
> >
> > "Peter Rathmann" <prat...@home.com> wrote in message
> > news:39201D7C...@home.com...
--
For GPS data see: Joe -- http://joe.mehaffey.com
Peter -- http://www.vancouver-webpages.com/peter/
Karen -- http://www.gpsy.com/gpsinfo/
Dale -- http://users.cwnet.com/dalede
Peter Rathmann
> The etrex is similar. Accuracy of stored points is not reduced but the
> number of points stored is reduced just like it is only other units when
> creating a route. In addition the knowledge of broken tracks is lost
> and the time stamps are lost. This reduces the memory requirement
> considerably This is why they call it "compressed". There isn't any
> actually compression algorithm being used since it displays just as fast
> as always (no decompression involved).
The accuracy of the track is clearly reduced when fewer points are used to represent
it. The coarser turns are preserved, but some of the fine detail disappears as a
result of reducing the number of points from 2000 to 250.
There certainly is some algorithm used to reduce the number of points. This could be
as simple as only keeping every 8th point, but Garmin appears to do a bit more
sophisticated compression algorithm than that, but it is still lossy compression and
therefore accuracy is lost in the process.
There are many examples of compression algorithms that do not require
decompression. For example, a video image can be compressed by taking an average
intensity value across a rectangular set of pixels and then using a larger pixel
dimension on playback. Not an optimal technique, but still a simple example of
compression and one that requires no calculation upon playback.
Dale DePriest
loss of accuracy at all.
Dale
--
nae...@my-deja.com
Kevin Altis <al...@semi-retired.com> wrote:
> So, can you "load" an old track to become your current route? I don't
quite
> understand how this works from the example of storing several
different trails
> on the device at once.
I'm still trying to figure this one out -- If, for instance, the active
track I am following splits, and the trail I choose to follow is one of
the stored tracks, will the eTrex automatically make this the active
track?
Will the eTrex display all 10 tracks at the same time, to give me a
good idea of what trail intersections or forks are comming up ahead?
> I would be very interested to hear more about missing features in the
eTrex
> compared to say a 12XL or 12Map.
From what I can discern on the Garmin site, it seems that the eTrex
lacks the capability to store multiple routes. The 12XL allows for 20
routes each with 30 waypoints, whereas the eTrex provides 50 waypoints
over one route. There are other features like no external antenna
adapter, no Loran format, and a limited voltage range.
Additions, though, seem plentiful -- higher resolution greyscale
display (as opposed to the 12XL B&W), 2000 and 3000 tracklog plots (vs.
1024 on the 12XL), and the compact size. It would seem to me that the
additional tracklog points are a huge benefit to trail and backcountry
users.
> It seems like it would be nice to have a basic map background
available, but
> that won't help me on trails or will it; for example, does the Garmin
Topo maps
> cover national park trails, local trails, creeks?
I'm using TOPO! (www.topo.com), and the park trails it includes (from
USGS maps) are limited and inaccurate. Of far more value are the user
uploaded "TOPO! Trails", which give accurate tracks for many local
parks. The list of available trails increases regularly, and can be
uploaded to almost any GPS receiver.
>At this point the world data
> doesn't appear to be too detailed, but I would be interested in a
detailed map
> of London, Paris, Amsterdam... I guess what I'm asking is what
additional
> benefits I would get from having a 12Map or 12XL over an eTrek?
>
> Thanks,
>
> ka
>
> Peter Rathmann wrote:
>
Peter Rathmann
> Save your tracklogs before the 250 limit is exceeded. Then you get no
> loss of accuracy at all.
I'd first like to note that I never complained about the loss of accuracy - I merely
pointed out that saving the tracks does lead to compression and associated loss of track
accuracy. Second, saving before reaching 250 does not guarantee that there will be no
compression. I'm not familiar with the details of Garmin's algorithm, but it does not find
the 250 points that best define the track. Sometimes far less than 250 points are used.
For example, I just saved a track with 430 points and it was stored with 170 points. I
have previously stored tracks with less than 250 points and there was still a significant
reduction in the number of points when they were stored.
Dale DePriest
stores timepoints and will store a point based on significant (undefined
word) changes in speed as well a direction (defined to be 89 ft sideways
from projection of present track). The saved log always removes the
speed change log data wich does not decrease accuracy for a saved log.
I do agree that the reduction algorithm might remove other points. Did
you see any?
Dale
--
Peter Rathmann
> Ah, yes there is something we didn't discuss earlier. The full tracklog
> stores timepoints and will store a point based on significant (undefined
> word) changes in speed as well a direction (defined to be 89 ft sideways
> from projection of present track). The saved log always removes the
> speed change log data wich does not decrease accuracy for a saved log.
The accuracy would not be decreased only if those speed-change data points fall exactly on the
previous track course. But if my actual course has a slight wander of say 60' back and forth
from the projected track course and has significant speed variations, then the extra log points
recorded due to the speed variation will also add to the accuracy of the recorded track and that
accuracy would be lost when the points are removed.
> I do agree that the reduction algorithm might remove other points. Did
> you see any?
I no longer have any of the original tracks with less than 250 points, but comparison of the 430
point track that was saved with 170 points shows a number of places where additional points would
improve the accuracy of the saved track.
Peter Rathmann
> In article <39221146...@semi-retired.com>,
> Kevin Altis <al...@semi-retired.com> wrote:
> > So, can you "load" an old track to become your current route? I don't
> quite
> > understand how this works from the example of storing several
> different trails
> > on the device at once.
>
> I'm still trying to figure this one out -- If, for instance, the active
> track I am following splits, and the trail I choose to follow is one of
> the stored tracks, will the eTrex automatically make this the active
> track?
The active track is the set of breadcrumbs the eTrex is currently recording
of your path. Therefore, it can't 'split', and the eTrex can't make
anything else the active track. Unlike a route, where the eTrex will keep
track of where you are relative to the next point and switch over when that
point is reached, a track is just a line that shows where you've been - all
the eTrex will do with it is to display it on the map page. The 'Trakback'
feature does let you choose a track and convert it into a route, complete
with named waypoints at each turn.
> Will the eTrex display all 10 tracks at the same time, to give me a
> good idea of what trail intersections or forks are comming up ahead?
Yes, for each stored track you can specify whether or not you want it to
appear on the map.
>
>
> > I would be very interested to hear more about missing features in the
> eTrex
> > compared to say a 12XL or 12Map.
>
> From what I can discern on the Garmin site, it seems that the eTrex
> lacks the capability to store multiple routes. The 12XL allows for 20
> routes each with 30 waypoints, whereas the eTrex provides 50 waypoints
> over one route.
That's currently true, but note that the eMap had the same one route
limitation until the last software upgrade when this was changed to 50
routes of 50 waypoints. I don't know Garmin's plans, but maybe they'll
enhance the eTrex as well.
Mike Teague
>From what I can discern on the Garmin site, it seems that the eTrex
>lacks the capability to store multiple routes. The 12XL allows for 20
>routes each with 30 waypoints, whereas the eTrex provides 50 waypoints
>over one route.
According to the manual (downloadable from Garmin's site), even though it
only has 1 route, you can use your saved tracklogs to generate a route with
the tracback feature, essentially giving you as many "routes" as the track
memory will hold..
So, you go from A to B... save the track.. you then go from B to C. save
that track. If you need a route from B to A, or A to B again, or C to A, you
can re-load a track and generate a tracback route and use that for
navigation (one at a time).. If that doesnt work for ya (i.e. you are
planning a route for somewhere you've never been), you can always write down
the routes on a piece of paper and take em with.. enter em in when ya need
em..
My Etrex should be arriving in a day or two, I think it should work
nicely -- I like the size! I currently have a GPS III, and it has 20 routes
of 30 wpts.. I must say I've never used more than 1, (you of course can only
actually USE 1 at a time:) so this "limitation" of the Etrex didn't bother
me...
Mike Teague - http://www.triax.com/yngwie
GPS Stash Hunt Homepage - http://www.triax.com/yngwie/gps.html