Xmas gift help - GPS unit

[arghman]

wally2q: I thought DGPS required the use of some kind of beacon: you place the beacon at a known point (e.g. at your car, or at a property corner), and the GPS receiver then receives signals both from the satellites and from the beacon (which also receives signals from the satellites), & for whatever mathematical reason is involved, the differential (D) measurement between beacon and GPS receiver is much more accurate than the absolute measurement of the GPS receiver relative to the satellites.

or am I missing something?

 

[wally2q]

Waas & Dgps

You're right arghman. True Differential GPS is based on supplemental fixed earth-station receivers, which then send data to mobile receivers that are coupled to the GPS unit.

The DGPS feature implemented in the Vista, uses WAAS Satellites for the same "similar" differential mode correction. The WAAS Satellites are in geostationary orbit, thus produce similar results to earth based receivers. Think of these satellites as fixed earth station's sitting on antenna towers that are located on the equator, and are 60,000 km high.

So, true DGPS can yield accuracy = to 1/2 inch. WAAS DGPS accuary yields 1 foot accuracy, although the Vista specification states that the unit will produce 3 foot accuracy 95% of the time (implying that the 1 foot accuracy will be produced with some lower level of probability).
Allowing the unit to receive the same signals (in other words, keeping the unit stationary) for several minutes, would allow the unit to collect many samples of data, which are then averaged (to some extent) to produce an accurate AND reliable fix.

I know that when I started to dig a 2 foot hole for the metal demarkation stake, the stake was right there - I guess I could have just been lucky, but nontheless - with accuracy at those levels, you can't ask for anything better in a hand held unit that size and weight.

the wall....

 

[spider solo]

Had good luck getting waypoints using some of the recommmended settings.
From the summit of the mnt (Mt Adams NH) I set it for 'Go To' the next waypoint ( I had made 5 all together) that I had established on the way up and compared it to my hand held. Conditions and visibility were excellent so I could wander off course on the snowfields and see how things worked out. All went well with both showing me where I needed to go.
However once I went beyond the waypoint it still showed it was in front of me as a matter of fact I went beyond all the waypoints and it still showed them to be in front of me.
It recognized that the summit was behind me but as I went by a waypoint I thought the direction arrow would tell me to turn around and go back to the waypoint I was looking for...but it never did even when I was back to the trail head !
So does it freeze up in cold temps ??
The batteries say they are good to -30 F
Temps were about 0 and though I kept it fairly warm I, of course, had to hold it in my hands to use it and see how it worked.
I often see them touted as being usefull in a whiteout... but I literally walked by each point without it telling me I had arrived or in fact gone beyond them.
So basically the only line I walked was between keeping my fingers warm or not as I used it.
Think the temps threw it off ??

 

[DougPaul]

> Think the temps threw it off ??

Unlikely.

Were your waypoints set accurately? (If they were transferred by lat and lon, did you set the Datum on the GPS to match the map?)

If you execute a "goto a waypoint", the GPS should point back to the waypoint if you pass it. If you are following a route (ordered list of waypoints), the GPS will recognize when you pass a routepoint and point toward the next routepoint.

How far did you go past the waypoint? Remember typical accuracy is on the order of 10m.

My Vista will point toward the waypoint if I walk by or past it. (If very close to the waypoint, it may point in any direction due to the position measurement and wapoint location errors.)

For best outdoor operation, turn off the battery-saver mode--it can cause the GPS to lose lock in the trees or other poor signal conditions. (Signal conditions are generally good at a bare summit such as Mt. Adams.) WAAS is rarely needed for outdoor navigation and consumes battery power.

The best orientation for the Vista is level (display pointed up). I carry mine on the top of my shoulder in a small pocket attached to the pack strap. Another good position is properly oriented in the top of your pack. Best position is in your hat...

For lots more info, see www.gpsinformation.net.

Doug

 

[spider solo]

Nice link ...thanks
I went about 3 miles past my waypoints. Marked my waypoints as I went along ...not from maps.
I'll be spending more time with it, perhaps it was user error but thought I was
on a roll till I walked right past them. Didn't know if I locked on a 'course'...but thought the pointer would still show my waypoint locations in relation to where I was .

.. ......after more review I think I was following a 'course direction' instead of a 'bearing pointer' which I should have been using to show me where I was in relation to where I wanted to be.......

 

[DougPaul]

> .. ......after more review I think I was following a 'course direction' instead of a 'bearing pointer' which I should have been using to show me where I was in relation to where I wanted to be.......

That would do it. I have "bearing pointer set".

The course direction indicator (CDI) display shows an arrow pointing on the heading between two waypoints with a movable center section. (The course is a straight line between two waypoints.) The center section represents the course line and the offset shows how far one is from the course. (Modeled on the aircraft instrument of the same name--part of the instrument landing system (ILS) displays--the center section represents the centerline of the runway.)

The "bearing pointer" display is a simple arrow pointing toward the waypoint.

I generally put any waypoints and routes of interest in at home using Garmin Topo software (can also be done from the front panel, but the computer is faster and easier). Also have the topo map for the area loaded in. Of course, additional waypoints can be added in the field.

I suspect that you know this part already:
If you set the waypoints as you go, you will need to place the next waypoint manually and then goto it. Easily done if you have the appropriate maps loaded. (Can also be done by entering lat and lon, but it is a pain to do.)

It is frequently easier to set and follow a route.

> I'll be spending more time with it

A GPS is a complex (but amazing) little beast. I spent a week or so studying mine before I felt I understood all (most?) of its features. (And I am an electrical engineer...) Many (most?) user complaints are due to user error, ignorance, or unrealistic expectations. I also play (use when not needed) with it so if I ever do need it, I will be comfortable with it.

Doug

 

[CaptainJim]

Holdstrong... Hold On... to that GPS

I also have a E-Trex Vista. Being a boat captain I've come to rely on GPS (and Radar) for some time now. Iagree with most of the posts... this is a good unit. It'll do everything you'll need in the backcountry.
A few things though:

The "basemap" that comes with it is pretty general. I'd get the MapSource CD for the area you're backpacking. I don't think you can download the actual "map" from National Geographic Topo New England onto the GPS, just the waypoints (lat/long) so I believe you sit at home, plot your course than download the waypoints. I'm sure someone will correct me if I'm wrong. But with Garmin's own MapSource software you download the actual topo map complete with contours, trails waypoints etc, etc, etc.

I purchased the CD they call (something like) National Parks of the North East for my Mt. Washington climb. It has al the National (and some State) parks on it. Now granted Mt Washington trails are pretty well marked and travelled, since I was climbing solo and in December, I thought it might be good to bring it along just in case I got lost in a whiteout above the treeline or later bushwacking somewhere along the Presidentials.

I was pretty amazed that the trails as they were marked on the MapSource CD were right on. I mean I thought I'd be in the general area, but it was better than that. I followed an existing trail on the map while sitting at home on my computer, clicking in waypoints to mark main turns and intersections, downloaded it to the GPS (along with all the features that are already on the topo map), and to my amazement when I came to an intersection, I'd glance at the GPS and it was right on. Sometimes I'd look at it when I thought I should be at the next point by now, see that it's ahead 800 feet and up another 100, and by golly again it was right on.

The only disadvantages are:
1) small screen - with 50 year old eyes I had to keep stopping to pull out the reading glasses to see the screen... which became even more of a PITA once above treeline in the wind driven snow.
2) loss of signal under a heavy tree canopy or even heavy cloud cover - sometimes I had to wait till I got out fron under trees and in the open
3) it does slow you down a little at first - until you get used to it and learn how to best use it. I don't look at it that often any more. Once in a while to make sure I'm on track or see how far, Or if I'm unsure of where I am. Other than that, I'll check it and walk quite a way (especially if I'm on an established trail) before checking again.

Good Luck & have fun with it. It can be a useful tool, but don't spend more time looking at it than the scenery

Capt. Jim

 

[spider solo]

Captain Jim........"small screen - with 50 year old eyes..."
You certainly hit the nail on the head wiith that one . Glasses icing up ... I find myself putting them on and off a dozen times while reading the info. Of course I had the same problem reading map and compass but find the problem exacerbated now that I'm practicing with the GPS.
This time I thought ahead and brought a magnifying glass to read bearings on both the GPS and my compass so I could compare. Sure enough with temps in the -20's my glasses froze up but the magnifying glass didn't...but boy that's one quick way to feel mighty old !
Talked with a young guy on a previous hike he said contact lenses are the way to go. He was wearing them as we spoke. I'll be checking that out even if it's just for the hiking.
GPS...right now I'm getting better at it, but I'm still pretty primative with it. It's more like GPS use... by Attila the Hun.
In the spring I'm going to tackle loading some canadian Topos on it..or any topos for that matter...Do you think it has the capacity to load what I need from both countries?

 

[DougPaul]

> In the spring I'm going to tackle loading some canadian Topos on it..or any topos for that matter...Do you think it has the capacity to load what I need from both countries?

You can only load Garmin topos in Garmin GPSes. (There is a DIY project, but it is not for beginners.)

Don't know what you need... from either country.

I have the Daks, VT, NH, and northern MA stored in my Vista (Garmin US topo 100K maps). The 100K maps are not detailed enough to plan a route, but one can easily transfer one's location to a paper map by inspection.

As you may have noticed, the GPS display has a very small window viewing a very small portion of a large map. OK for determining position, poor for planning a trip of any distance.

Doug