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Old 06-21-05, 06:17 PM   #1
erhan
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Anybody using a GPS?

Just wondering what models you have, and which softwares you use.

A brief review would be really nice.

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Old 06-21-05, 06:27 PM   #2
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Use the search button, this has been asked about 5 times this month.
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Old 06-21-05, 06:42 PM   #3
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hmm... may be you can help me find "the 5" in this month.
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Old 06-21-05, 07:25 PM   #4
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I use GPS almost every day...I have a Trimble R8 rover bluetoothed through my cell phone into a Virtual Reference Station server that simultaneously processes five baselines and provides real-time subcentimeter positioning.

Kinda pricey at 30K, and certainly overkill for recreational use, but hey, you asked.

Has your research inclined you to any particular receivers?
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Old 06-21-05, 07:40 PM   #5
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I used an Etrex Legend on my bike for a while before I sold it. I wouldn't recommend it because it had trouble picking up a signal whenever there were trees overhead.
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Old 06-22-05, 04:30 AM   #6
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We use an older Magellan we got cheap on ebay. Pretty handy as our bush tracks don't appear on any maps. When I don't bring it, I usually get lost.
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Old 06-22-05, 03:08 PM   #7
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I use a Magellan SporTrak Pro with its TOPO mapping program, primarily for sea kayaking and hiking interests, but do have the bike mount, just don't care to crash it and usually know where I am.
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Old 06-22-05, 07:26 PM   #8
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Magellan 315-Shows altitude changes, and other stuff.
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Old 06-23-05, 07:51 AM   #9
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I use the Etrex legend and it's awesome. Tree cover hasn't hurt it's reception - I get signal inside my house with the blinds closed. It gives all one can ask for and then some for a bike computer. I run mine on the right side so my thumb can adjust the screen (direction, trip data, map, ect..), If you get one you can find the mount from amazon for around $14. Pad that with an item that is free after rebate and you wont have shipping charges:

Here you go:

Mount:
http://www.amazon.com/exec/obidos/tg...goods&v=glance

Free items after rebate:
http://www.fatwallet.com/forums/mess...hreadid=457161
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Old 06-23-05, 08:17 AM   #10
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Quote:
Originally Posted by crashnburn
Tree cover hasn't hurt it's reception - I get signal inside my house with the blinds closed.
Sorry, but I have to call BS on this one...the nature of the system requires an uninterrupted line of sight between the receiver/antenna and at least four satellites to establish a position.
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Old 06-23-05, 09:05 AM   #11
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Quote:
Originally Posted by gastro
Sorry, but I have to call BS on this one...the nature of the system requires an uninterrupted line of sight between the receiver/antenna and at least four satellites to establish a position.

Nope, he's right. Tree cover can cause some scatter of the signal, but sight-lines are not required in the band used by GPS.

The only thing that truly blocks all GPS signals on my unit is metal-roofed buildings. I can get a reasonably accurate positional fix in houses, even with another floor above me sometimes, provided there is no large expanses of metal or other electronic devices causing interference. It takes a longer time to lock, and there is more wander in the position, but it works eventually.

I keep my GPS buried in my backpack when I ride with the tracklog on, and it rarely misses. Try it, seriously. Although the newer generation units generally seem to work a little better (not sure why) in getting signals in sub-optimal locations.

Last edited by ghettocruiser; 06-23-05 at 09:05 AM. Reason: spelling
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Old 06-23-05, 09:25 AM   #12
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Quote:
Originally Posted by gastro
Sorry, but I have to call BS on this one...the nature of the system requires an uninterrupted line of sight between the receiver/antenna and at least four satellites to establish a position.
No BS with my GPS. I was surprised too, it picks up nicely. I was concerned that this would be a problem. My good reception may be a mult-regional thing and some may not get as good. Go to a sports store and demo a unit that you want

Cheap etrex Legend- about $110 with a little legwork
1. Go to ebay and buy a $30 off $150 coupon for staples

2. Buy from staples and use coupn - aprox $140
http://www.staples.com/Catalog/Brows...e=1&Sku=500921

3. After 20 min (let order get into system) intiate a live chat with a CSR and copy and paste this link to do a price adjustment
http://www.amazon.com/exec/obidos/tg...tronics&n=1000

4. Buy mount, ride and enjoy
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Old 06-23-05, 10:33 AM   #13
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Believe what you want to...just because your receiver tells you a position doesn't mean it's correct.

How GPS works
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Old 06-23-05, 10:57 AM   #14
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Quote:
Originally Posted by gastro
Believe what you want to...just because your receiver tells you a position doesn't mean it's correct.
These are not survey-grade instruments. But no one needs sub-meter accuracy for mountain biking, do they? The only real objective is to follow a route or determine a speed. If the thing is giving me the position for a known object (either from a previous waypoint or a geo-referenced map) and I am standing next to said object, I think that is correct enough for most user's purposes.

In the last three years there have only been three or four times that my GPS actually claimed that I was somewhere I wasn't (i.e. showing my location on a built-in map) and the errors were corrected after a second or two. Otherwise, the thing tends to be as good as any of the maps I have.
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Old 06-23-05, 11:58 AM   #15
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Quote:
Originally Posted by ghettocruiser
But no one needs sub-meter accuracy for mountain biking, do they?
Of course not. Recreational grade receivers are just fine for most uses. I use an Etrex for recon work.

I was refuting the statements that GPS works indoors, not trying to determine the user's positional accuracy requirements. I presume no one's actually checked whether this indoor "solution" is anywhere near where it should be...if it is, I stand corrected (and puzzled).
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Old 06-23-05, 01:07 PM   #16
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I actually made a few extra-detailed maps for the etrex vista using the software found here www.geopainting.com. The program accepts import in arcview format, and I was able to add building footprints, among other things to the built-in GPS maps.

When I get a signal inside a wood-framed building (like my house) the GPS plots me somewhere in the footprint of the building in question.

Generally, with the signal bounce off the walls and ceiling, there is not enough accuracy to pick up motion or position WITHIN a building, but the position given will fall somewhere within the building's footprint on the map. Really.
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Old 06-23-05, 01:21 PM   #17
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GPS built into my cellphone. There's different software packages available depending on what you need. Mapquest has an application available good for driving and mapping directions. Trimble has one available tailored to trail use. It's pretty wild looking at the features. Looks like you can lable way points, set virtual breadcrumbs to find your way back plus more. Even a built in compass. I have no idea how it compares to a regular gps as far as features however considering the size of my cell phone it sure would be the smallest I think and make phone calls, play games and more. Check it out: http://nextelstore.cellmania.com/web...84484&IID=4540

However, the land here is pretty darn flat and one would have to work real hard here to get lost so i don't use it, although in an emergancy 911 could poll my cell phone to get my location.
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Old 06-23-05, 01:35 PM   #18
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For ghettocruiser:

A single (autonomous) GPS receiver in an optimal environment (no multipath or obstructions) receiving no differential corrections has an accuracy of +/- 10 meters 95 % of the time. How it is getting better than that inside your house is a mystery to me.

Is your receiver WAAS enabled? Does your house have south facing windows?
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Old 06-23-05, 02:06 PM   #19
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Yep, the vista is WAAS, and Toronto is only about 50km from the WAAS corrections ground station in Youngstown, NY (across the lake). The waas satellite signal is a little weaker it seems, since that satellite is in a much higher geosynch'ed orbit than the others, but generally it is strong enough to be picked up indoors too without benefit of a direct sightline.

WAAS, however, was primarily designed to correct error introduced from the upper atmosphere (ionosphere), which, as I understand it, is the biggest source of variability once they disabled SA (selective availability).

Errors that would come from being indoors or under tree cover are much more local problems obviously .

Without a doubt windows offering skyview improve the speed and accuracy of a GPS position lock, but are not required, as the strongest signals tend to come from sats. near the zenith, i.e. directly through the roof.

Bear in mind that the accuracy statistics are generalized across the continent; results will vary locally. Also, if 95% of the time there is 10 m accuracy, then 90% of the time there will be even better accuracy and so on.

The garmin mapping GPS units project an “uncertainty circle” (I’m sure there’s a better term than that) over the onboard map that contracts as the signal improves and the position solution improves. And I’d say about 90% of the time, to the limits of the accuracy of the maps, I appear to be at the centre of the circle.

Hand held GPS units do give garbage readings sometimes. It’s just that less than 5% of the time isn’t very often for a cyclist. If I was trying to land a plane with it, I might be more skeptical.
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Old 06-23-05, 02:30 PM   #20
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Quote:
Originally Posted by ghettocruiser
Yep, the vista is WAAS, and Toronto is only about 50km from the WAAS corrections ground station in Youngstown, NY (across the lake). The waas satellite signal is a little weaker it seems, since that satellite is in a much higher geosynch'ed orbit than the others, but generally it is strong enough to be picked up indoors too without benefit of a direct sightline.

WAAS, however, was primarily designed to correct error introduced from the upper atmosphere (ionosphere), which, as I understand it, is the biggest source of variability once they disabled SA (selective availability).
Actually, I believe the WAAS birds are in a significantly *lower* orbit (3-500 miles) than the Navstar GPS satellites (12,500 miles). WAAS are geosynchronous, Navstar are not. With WAAS enabled, autonomous receivers can attain 0-4 meter accuracy. The WAAS hang out near the equator, which is why I asked about the south facing windows.

Thanks for a good discussion.
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Old 06-23-05, 03:43 PM   #21
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I have the Magellan Meridian Gold, which has a removable SecureDigital slot for up to 128MB disks (so far). I have most of western Colorado (mountainous areas) in it via the Topo software I got off Ebay for $50.

The software is pretty good, but is definitely not as good as USGS 7.5 minute maps. Doesn't have hiking trails in, but most roads except some 4wd trails are in there. Lakes, streams, elevation profile, etc. In my mind, if it doesn't have these things, then what use is a squiggly line on a blank screen? Useless unless you are lost and are only trying to get back to point A.

I'm happy with mine. I wouldn't bother with anything less, as they are just toys.
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Old 06-24-05, 01:02 AM   #22
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Quote:
Originally Posted by gastro
For ghettocruiser:

A single (autonomous) GPS receiver in an optimal environment (no multipath or obstructions) receiving no differential corrections has an accuracy of +/- 10 meters 95 % of the time. How it is getting better than that inside your house is a mystery to me.

Is your receiver WAAS enabled? Does your house have south facing windows?
We can get repeatable results to within 1 metre for various waypoints we've set. We're in the Southern hemisphere, if that makes any difference.
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Old 06-24-05, 10:33 PM   #23
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Quote:
Originally Posted by gastro
Actually, I believe the WAAS birds are in a significantly *lower* orbit (3-500 miles) than the Navstar GPS satellites (12,500 miles).
Since I have already shown to anyone actually reading all this rambling what a complete geek I am, I might as well finish this thought. Geosynchronous orbits (actually, geostationary is the term we are after, since these orbits are supposedly circular) are actually about 35,786 km above the equator... quite a long ways up, about 1/10th of the way to the moon.

An expensive altitude to reach.

Hence unless there is a particular reason to go that high, most sats. are quite a bit lower. The lower the orbit, the more rapid the apparent sky motion. Hence the Navstar (and the old Russian Glonass) can be seen to rise and set on the little display screen the the etrex, whereas the geosynchronous sats, (which garmin units always assign an ID number in the 30's) are always in the same spot.

The further you are from the equator, the closer the WAAS sats are to the horizon and the more often they are obstructed and therefore, useless.

Trimble www.trimble.com has free software that plots the locations of the GPS (and Glonass, for the old-schooler) constellations to determine when the sats are positioned so it's possible to get a signal with a partly obstructed sky. Believe it or not this does have (dubious) applications in mountain biking, as I wanted to tracklog a trail that was at the bottom of an east-facing ravine, the sides of which were steep enough to block much of the sky. The software gave me dates and times when there would be enough GPS sats. visable in the sky overhead at the bottom of the ravine to ride through and log the trail.

Last edited by ghettocruiser; 06-24-05 at 10:34 PM. Reason: spelling
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