Anyone have experiance with handheld GPS?

I would like to have something that I can go out and mark points, then plot them on a map. I will need to plot several dozen points in uneven terrain for a later presenation. I don't need something that accurate for official survey work, but something which is accurate enough for me to re-track my steps is necesary.

I've been considering the Garmin eTrex Vista since it's light, compact, and mudproof. It also has other features which are nice to have. Are there any other models I should consider whithin a buget of $500?

Thanks in advance!


Scott

I got the Legend. Didn't see the need for the electronic altimeter and temp, IIRC. It has an altimeter that it calculates and I have a thermometer on my keys for the temperature if I need it.

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Another vote for the eTrex Legend here. One can be had from Amazon for ~$132 with free shipping. The 8 MB memory is adequate for my needs (I'm not loading maps onto it), and I don't really have need for the altimeter and compass. The only accessory I purchased was the carry case for an additional $10.

A good person to get an opinion from is Botnst. He has a lot of experience with these units. I think he may have even been a land surveyor, or something to that affect, for the government.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

I would recommend the Magellan Meridian, either gold or platinum models. The basic difference in the two is that the platinum includes a 3-axis electronic compass... the gold model only reports inferred compass direction with movement of about 2mph, otherwise it is non-functional. Can be bought for around 200$ american.

I have a Garmin GPSMAP 76, I use it on my boat and in my car. It has built in mapping capabilities. I also interface it with my laptop while on the boat. Pretty kewl
no matter where I am on SF Bay I get a "you are here arrow" on a scrolling map on a 15 inch screen on my laptop. Now if I can just scrape together the money for new sails, autopilot, and a bottom job I'll be set

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IM (not so)UO, you can't go wrong with Garmin.

But there are lots of good manufacturers out there. My Garmin experiences have been this: They link fast under tree canopy that shut down Magellan and Trimble unless the Trimble PDOP was set so high that the error ellipsoid expanded to 30 meters x,y. The problem is in filtering spurious reflected signals from the true signals (a problem called multipath reception). See, in a forest or any other environment with lots of interference, the satellite signal from each satellite (minimum of four to fix a position on the earth's surface) can get slightly reflected and thus, confuse the receiver with multiple signals from each satellite. By setting the filtering high, you increase positional accuracy but may not receive sufficient satellite signals to get a good fix. So you lower the filter a bit and get more satellites but get a fuzzy position from multipath reflection. Its a balancing thing that impacts the error ellipsoid. I should explain that.

Every GPS will provide you with a position that is really somewhere within an error field in x,y,z (lat, lon, and altitude), a sort of egg stood on end shape. With a good single band unit receiving 12 satellites you should get about a 7-12 meter x,y and a 12-20 meter zed. It will probably report a position in centimeters, but that is precision, not accuracy. Most people don't need accuracy greater than that and so, if you pay more than $150-$200 or so you're buying bells and whistles, not more accuracy. To get decimeter accuracy you're going to spend $3-$10K. To get centimeter accuracy, double that. Now you're at 1st Order surveying capability and like, 0.001% of the planet has a need for that. I have worked on a geodetic survey problem using GPS one time and it is REALLY cool. I was awed by the process and results. Currently, the entire state of Louisiana is being constantly measured by GPS using CORS. (ww.ngs.noaa.gov/CORS/cors-data.htm). If you want to differentially correct your GPS points, find a CORS in your state. Its free.

Like with a computer that you're going to buy, go for the options you may need next year. If all you do is buy what you needed last year, you're not going to like it this year.

I would look for Firewire and/or Bluetooth, compatible map types (1:100K and 1:24K DRG's, DOQ's, DOQQ's, street maps, etc), color screen and mounting brackets that would work in a car, boat or Honda Goldwing. I doubt you'll get everything you ask for, but if you know about what you need, want, and like, you'll find somebody who sells it.

Another very cool think I have heard of are PDA's with GPS and a cell phone. I have used the GPS with the PDA running Windows CE and ESRI's moving map product. It is a near-elegant solution for people who need that stuff (field workers such as timber cruisers or ecologists).

I am sorry to say that I rarely get a chance to use the low-end and high-end products. I work in the decimeter range.

I've been thinking about GPS since last night and I wonder about using GPS for speed. I think normal GPS receivers update about every second. I'm trying to figure out what the combination of positional error ellipsoid and position update frequency might do to speed estimate.

If you're traveling say, 10 meters/sec and have a 10 meter error ellipse, does that mean in 10 seconds your speed estimate may be in error +/-10m/sec? That doesn't square with my observations when I've checked speedometer against GPS (they were pretty close). However, I think that speed on a winding and hilly road using GPS would be error-prone since the GPS would be segmenting curves into 1 sec tangents, over-estimating speed, right?

Is there an engineer in the house?

I use a Garmin 76CS the only thing, if it had Bluetooth I'd say its perfect.

I did have a Magellen Sporttrak Topo and it picked up a fix in my basement, the downfall is it couldn't survive the maids kid throwing it in the pond.

If anyone is interested Garmin gps 45 that I'm willing to part with cheap.