What GPS unit?????

[ShaneFl'06]

Okay I want a new GPS.I have a $200 limit.BPS and Cabelas both have several GPS's from $145 to $200.The ones I am looking at are the Garmins 12,2 Plus,the Magellan 315 and 320.I don't need all the map stuff included if the unit will allow me to load my own.I want the unit to be able to interface with my computer.The unit would used for mainly hunting and fishing in all sorts of weather.

 

[BuzzH]

I've used several brands both on the job and for private use. The one I like best is the garmin. They are fairly easy to operate and you can load up to about 500 points with them. Saved waypoints can be downloaded onto a computer, but remember the accuracy is not going to be that great. Although much better now that the selective variability (scrambling by military) has been turned off. Accuracy of +/- 30 meters is common.

They are a great unit for the money and will work for marking waypoints and navigation purposes. You can save waypoints(500 of them) in either UTM or lat long, whichever you prefer. I personally use UTM, one grid will fit anywhere (absolute coordinate system). Lat Longs change as you move from the equator (grid narrows as you move from the equator to account for the curve of the earth). No big deal, just so long as you know that.

For the utmost in accuracy, a unit such as a trimble is the only way to go. These units allow you to collect a file of points and then allow for differential correction. These units get you into the GNATS ASS range (+/- 1 meter), but they are spendy. Plus they are not necessary for basic orienteering or navigation needs.

Hope this helps if you have any other questions let me know, I will try to answer them.

 

[ShaneFl'06]

BuzzH
A garmin rep emailed with a few suggestions.There are two new units that will be in Febuary.the Etrex Camo and the Etrex Venture,both under $170 and will do everything the GPSll Plus will but they do not have the datamaps built in(which I don't need)The Veture come with PC cable for $169.

I know nothing realy about them.A buddy I hunted with this year had one and it came in handy twice.

 

[BuzzH]

I wouldnt hesitate to buy either of the 2 you mentioned. Good luck and let me know how you like whichever you choose to buy. I have a garmin 2 plus, its a good unit.

I really think the garmin is the most user friendly of the ones I've used.

 

[cameras eye]

I recently responded to a question posted by VPHUNTER about the same topic. If you go to his post, you'll see my entire response. Below is a response specific to your question.

.....Now for some suggestions on equipment needed. First, if you plan on using a computer, then the U.S.G.S. has topo maps on cd that you can use with your computer as a data cd. Fugawi is the name of a computer software that I use along with the U.S.G.S. data cds. As for the brand of GPS, I can only tell you that I've had two GARMIN GPS Units and both are fantastic. I've never had any trouble with them. They are very durable. They both work very well with my computer and GPS software. The older unit, Gramin's gps12, is over fifteen years old. It has been on several trips to the wilderness of Utah and is now my GPS used with Microsoft Streets and Trips in my car. The newer model is the Rhino. It has performed perfectly since I removed it from its box when new. I hope this helps a little. Hopefully, others will help with their experiences and ideas.

 

[krshunter]

Shane,

Like Buzz said you could be happy with either unit but I too prefer the Garmin. As a total package they are the leader in this particular industry. The Garmin units are a bit more user friendly and the new Magellan units are difficult to use especially with gloves or larger fingers. I am a Professional Land Surveyor and have a background in Geodesy so myself and my crews have used almost everything out there for the last 20 years. We have very strong opinions about equipment like this because we use it so frequently. Handheld units are very useful for a number of applications since "Selective Availability" has been turned off. Many units will talk about +/- 1 meter accuracy but you'll find that to be more like 3 meters repeatably which is typically adequate for the intended uses. You may occassionally come within 1 meter of a previous waypoint or a known point but not most of the time.

Let me also provide you some background about coordinates. You'll be best served if you utilize geodetic coordinates which we commonly call Lat/Lon. The basis of all Cartesian cooridnates is Lat/Lon. UTM, state plane, etc. are all Cartesian coordinates calculated on flat planes at some elevation below the surface of the earth. Northings and eastings are calculated on flat planes and a flat surface can only approximate a curved surface such as the earth for short distances. That being said there are 60 UTM zones and probably hundreds of State Plane zones in the US if you were to count them all. There are 4 in Wyoming, 3 in Montana, 3 or 4 in Idaho, etc. Wyoming exists in two UTM zones and so does Montana and Idaho. Therefore you have to know where you're at and what zone to have your unit set in. The further you get outside of the zone the more exponentially the coordinate error increases.

The best way I can explain planar coordinate error potential is by visualizing an orange peel. A small portion of that peel can approximate a flat surface. If you were to take a plane and cut through the orange peel the peel would intersect the plan on opposite sides. Those intersecting points are the limits of your UTM or SP zone. If you try to work outside of them your error increases drastically. If you were to try to flatten that orange peel it would start to stretch and rip apart more and more as you leave the intersection points. That is distortion or error potential which is why there are so many different zones. The UTM zones are so large however (6°) that they have an error potential of 1' in 2500' within the zone. Not enough to worry about for handheld units but unacceptable by land surveying standards. We utilize units that cost in excess of $60,000and are capable of measurement errors of 1:2,000,000 or so. To get accuracies like this you have to set up over known points and have more than one unit running so that you can differentially correct or post process.

State plane coordinates are on a calculated on a plane at approximately sea level and UTM coordinates are on a plane that is approximately 5500 feet below mean sea level therefore they are also the least accurate cooridnate system available to us. Handheld units do not contain the complex software routines necessary to differentially correct positions, or project to your elevation so the further you get toward the mass center of the earth from where you are at, the less representative a distance is between two points. A wedge is the best example. The tip is the center of the earth. A planar surface is somewhere in the middle of the wedge and you are at the exterior end of the wedge. The distance between the two endpoints of the wedge is longer there than measured in the middle of the wedge where the cartesian points are being calculated. That is why even though UTM is a popular system it is the least accurate available to us.

Sorry to go so far outside of the question about recommended units. As a land surveyor I try to educate people every chance I get so that they understand what we do and can hopefully better use their equipment. Geodesy is the foundation of GPS and coordinate systems and most people and even a good number of surveyors don't understand this foundation before utilizing their equipment. If you have any questions or would like to understand a little more I can recommend a couple of very good online tutorials that explain Selective Availability, Trilateration, Ellipsoids and just how everything works in general.

 

[Oak]

Good info there. I'm guessing Shane found a GPS he liked sometime in the last 9 years.

 

[krshunter]

Good info there. I'm guessing Shane found a GPS he liked sometime in the last 9 years.

Easy there. It only took 5 years to write that..... Easy for me to ramble on about geodesy and GPS as I have been using it and teaching it for almost 20 years now. Being charged with protecting the public I always feel like I need to help educate the general public for free whenever I can whether they are ordering a survey of their land which is valued at $5k and acre or just using a unit recreationally. Some find it interesting and some just don't care. I feel good about sharing when I can though.

 

[Oak]

Well I know who to ask if I have a cartography question. I meant it when I said good info. I learned something about my beloved UTM system....

 

[fowladdict]

Well I know who to ask if I have a cartography question. I meant it when I said good info. I learned something about my beloved UTM system....

Dang, I'm a Licensed Land Surveyor here in Idaho and I even learned something! Very nice KRS, however when I go into that much detail on things people tend to just stare right through me or look at me like "I have lobsters coming out of my ears"...Yup I just watched A Christmas story!

 

[krshunter]

Dang, I'm a Licensed Land Surveyor here in Idaho and I even learned something! Very nice KRS, however when I go into that much detail on things people tend to just stare right through me or look at me like "I have lobsters coming out of my ears"...Yup I just watched A Christmas story!

fowladdict,

You're exactly right. I love it though when I get that look at a survey seminar. It's so easy to tell which guys are think GPS makes physical measurements on the ground and which guys have some geodesy background. All of my field staff have been through a college level geodesy course before using GPS.

Did you say a Christmas Story? You'll have a hard time holding my attention if that is on...... What were we talking about????