Tree cover comparrison

[Guest arffer]

Maybe this is old news to many of you, but I just found it by accident and thought some might find it usefull. It is the results of a scientific comparrison of many GPSR units under tree cover done by the U.S. Forestry Department:

 

http://www.fs.fed.us/database/gps/mtdc/gps2000/gps_comparison.htm

[Guest gstrong1]

Thanks arffer. III Plus seems to have hung in there pretty well with some of the big boys if I'm at all understanding their results.Especially when you consider the III Plus can be had for $279.00 & the other units,except for the Mag.,are in a price range way in excess of 10 times that.I wish we could find some test results that include some of the units that have been discussed on these forums.Some folks seem to think I'm goofy when I post that under heavy tree cover,my III Plus outperforms my MAP76 & that deep in the woods,my eTrex Vista doesn't even belong in the same category.I really like all 3 units & all I attempt to do is pass on my experiences with each unit under different conditions to be of some assistance to fellow cachers looking to purchase the right unit for their needs. .--Gimpy--

 

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Gary "Gimpy" Strong

Rochester,NY

 

[This message has been edited by gstrong1 (edited 01 August 2001).]

[Guest gstrong1]

Thanks arffer. III Plus seems to have hung in there pretty well with some of the big boys if I'm at all understanding their results.Especially when you consider the III Plus can be had for $279.00 & the other units,except for the Mag.,are in a price range way in excess of 10 times that.I wish we could find some test results that include some of the units that have been discussed on these forums.Some folks seem to think I'm goofy when I post that under heavy tree cover,my III Plus outperforms my MAP76 & that deep in the woods,my eTrex Vista doesn't even belong in the same category.I really like all 3 units & all I attempt to do is pass on my experiences with each unit under different conditions to be of some assistance to fellow cachers looking to purchase the right unit for their needs. .--Gimpy--

 

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Gary "Gimpy" Strong

Rochester,NY

 

[This message has been edited by gstrong1 (edited 01 August 2001).]

[Guest Bob Bowter]

I also have a Vista and a III+. Last weekend I took both into the Adirondack Woods (N44 10.962 W74 11.080).

 

Our group hiked up several heavily wooded peaks. Under dense arboreal cover, the III+ clearly performed better than the Vista, but the Vista was the GPSR that was in my hand most of the time. The reason being that I was more interested in my elevation than horizontal position. The GPS derived elevation displayed on the III+ wandered about considerably. The Vista's barometric altimeter was stable and had the peaks tagged within 12 feet.

 

For the duration of our journey, the III+ rode in an upper side pocket of my pack and recorded a solid track log. Unfortunately the default resolution set into the unit at the factory resulted in too few points being saved. My fault for not checking this before heading into the woods.

 

Above 3000 feet or so, the Vista had no problem staying locked. The tree cover was moderate and we were not in gullies. At lower elevations is where the III+ had the advantage. When satellite geometry was such that there were an insufficient number of birds in good position well above the horizon, the Vista lost lock. This condition would persist for about 15 minutes until the satellite geometry improved. Each time the Vista had trouble, there were three or four satellites overhead that were all along a single line; poor geometry. The III+ was able to receive additional birds closer to the horizon and continued to show my position.

 

I have said in previous posts, the Vista's performance in the woods is adequate for hiking. It has never been out of service very long. I just keep walking, knowing that the satellite geometry will improve and there will probably be a clearing ahead. The Vista's size and features make it the unit I want to use most of the time, but when reception conditions are poor the III+ rules.

 

If I had to give up one of my GPSR's, I'm not sure if it would be the Vista or the III+. Fortunately I have two hands and plenty of pockets in my pack.

[Guest Geoffrey]

I have the Vista and the 3plus, and find that they are great. I wish that that motion sensor technology could be put into a consumer GPS, so that it knows better how your moving about.

 

Take a Garmin Etrex Vista, and put in a motion sensor in it, then you would have a good GPS. Set the GPS on a flat surface for 5 or 10 minutes. The motion sensor would tell the GPS that it is absolutly still. When the GPS knows that it is still, it would give a good position fix after a few minutes, including a better elevation readout.

GPS with Motion sensor Technology:

http://www.axiomnav.com/BuildingBlocks2.asp

 

In reality:

For now you can get USGS topographical maps at some Outdoor recreation stores, and use that with your GPS. If your elevation is way off on your GPS, then you can adjust your elevation on the GPS to match your Topographical map. If your Elevation is way off, would not the Latitude and Longitude be way off too??

 

Topo Maps http://navigator2.maptech.com/homepage/index.cfm

 

 

[This message has been edited by Geoffrey (edited 03 August 2001).]

[Guest Kerry]

Arrfer, interesting article. Little surprised with the results of the PLGR especially the dual freq capability as it should have done much better regarding iono corrections?

 

Also the note about non post processing of the Garmin. Most of the Garmin 12 family and Etrex's can output carrier phase measurements and there is both shareware and buyware software that uses this undocumented Garmin capability. Garmin neither confirm or deny this capability.

 

Cheers, Kerry.

[Guest brokenwing]

There is a similar Forestry Service report available here: http://www.fs.fed.us/database/gps/mtdc/gps2000/Nav_3-2001.htm What I find interesting about this report is that it shows real data confirming my observations that averaging for even 60 seconds makes a marked improvement in accuracy when in tree cover. I, and many others that use averaging in the post SA world have seen this quite clearly, yet some have posted that averaging does nothing. This data certainly seems to suggest otherwise...

 

brokenwing

[Guest Kerry]

Brokenwing, here's some other real data on averaging which I'll also put in the FAQ section just as general interest.

 

http://www.cqnet.com.au/~user/aitken/gps/gps_avg.htm

 

Cheers, Kerry.

 

[This message has been edited by Kerry (edited 02 August 2001).]

[Guest Geoffrey]

You can do position averaging on most GPS receivers now.

 

Heres how:

Have the tracklog cleared and turned off, then go to the site that you want to save as a waypoint. If you can set the track recording interval to Distance, Time, Resolution, or Automatic, then set it to Time interval(in the Tracklog setup menu). Have it setup to record a tracklog point every second or so. After 5 minutes or so, your GPS page that shows the tracklogs plotted(Map page on some units), will show a ball of tracklog points. Pick a spot in the middle of that mess of tracklog points on the screen to use as your "averaged waypoint" and mark it as a new waypoint or landmark.

 

This is one instance that a motion sensor in the GPS will greatly help with accuracy.

 

[This message has been edited by Geoffrey (edited 03 August 2001).]

[Guest arffer]

Geoffrey,

 

I follow you all the way to the last step of picking a waypoint in the middle of the "ball". Can I assume that you first have to download the track to some software that will display the "track" and allow you to pick one in the middle to display the co-ords? Or does your GPSR allow you to zoom in on a track and display the co-ords of waypoints it recorded directly? If so, what GPSR do you have?

 

Thanks!

[Guest Geoffrey]

Garmin 3plus and Etrex Vista.

 

Zoom in on your position as far as you can on the Map page or plot screen of the GPS, and you should see the tracklog. If you had the GPS set to record a Breadcrumb or tracklog point every second, you would see a bunch of points in the center of the GPS screen. You should be able to move the cursor to the center of the ball of tracklog points to see the Latitude and Longitude that you want. I have done this before, and it works.

 

You would need a GPS with a map page, and be able to pan the map, while seeing the Latitude and Longitude, and write that on a piece of paper(if you have to).