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First test of Montana accuracy

Boyd 1965 Points
Hiking around yesterday, I stumbled across this


So I recorded a waypoint using averaging. After about a minute the unit claimed "100% confidence" (kind of a cocky way to put it :wink: ). Back at home I found the monument on NOAA's website

DATABASE = NGSIDB , PROGRAM = datasheet95, VERSION = 7.87.4
1 National Geodetic Survey, Retrieval Date = AUGUST 19, 2011
JU2888 ***********************************************************************
JU2888 PID - JU2888
JU2888 ___________________________________________________________________
JU2888* NAD 83(1996)- 39 23 05.48667(N) 074 43 55.09277(W) ADJUSTED
JU2888* NAVD 88 - 1. (meters) 3. (feet) SCALED

So I imported the waypoint into Globalmapper and entered the real position, generating some range rings. The green dot is the actual position and the red dot is the waypoint I created on the Montana. Not too shabby. :D



  • Boyd,
    Have any idea of the accuracy under heavy cloud cover or tree cover?

  • Boyd 1965 Points
    I never thought that cloud cover was an issue with GPS, is it? But no, I have not done any scientific testing. I do have quite a number of tracklogs though, and they look pretty good from a subjective point of view.

    But I should say that I'm not somebody who obsesses over accuracy. I don't do geocaching, so as long as the track shows me on a trail and I can find my way back to my car, I'm happy. I have hiked maybe 25-30 miles now (often under heavy tree cover) with the Montana and driven several thousand miles. I just love this unit - the screen, user interface and advanced functions are fantastic. I have even grown fond of the large size.

    I don't think it's necessarily the GPS for everyone though. I did some other, more thorough testing of my Oregon vs my 60csx recently - will start another thread about that soon. But the results seemed to show the 60csx as a clear winner when recording waypoints that were averaged over a long period of time. On the 60csx, 16 out of 22 averaged waypoints fell within a circle with a radius of 1 meter. On the Oregon, only 8 out of 22 were grouped in a 1 meter circle. Will be interesting to see how the Montana fares in this same test (when I have the time :wink: ).
  • sviking 141 Points
    I never thought that cloud cover was an issue with GPS, is it?
    Yes, it definitely can be an issue at times. Water droplets, vapor, etc ALL attenuate electromagnetic (i.e. radio) signals. That's why submarines use SONAR instead of anything electromagnetic when they're submerged. Yes, that's an extreme example of "solid" water, but any moisture affects radio waves to some extent, especially at the very low power levels of the GPS system. Saw it all the time as a former Navy helicopter pilot when deployed. Lots of crappy overcast weather at sea and it was quite common for the GPSNAV system to report less than State 5 (highest confidence/accuracy) and it often took much longer to initially acquire.
  • zee 97 Points
    Thanks for the test results, Boyd.
    The first testing for accuracy that I have seen anywhere. I've been wondering....
    Does it hang, freeze, or show any signs of sticky problem that I had with a 62s last year? I set the tracking to one second and move very slow, showing zero speed, and it slept through my movement, never keeping up.
    I wonder if one can override the short averaging period, as I like to average overnight, with the time set to x min or sec, using the roof antenna. Couldn't on the 62s.

    The User Grid on the 62s was really messed up. When I put in the numbers for the SW corner of this property, it just showed blank lines. Found out that Garmin still had the Lat tied to the Equator. Now I wonder about the Montana's User Grid.
  • Boyd 1965 Points
    They have added a new map setup option called "speed", and I assumed this was done to address your complaint about the static pointer on the Oregon (seems like a common complaint from geocachers also).

    The options are just normal and fast. When you set it to fast, the pointer gets much more "twitchy" and in track up mode it responds very quickly to all your movements. I generally like this, although it can result in some disorientation at times when you're moving slowly and the map spins. I can't say for sure exactly what the map speed option does, but that's my subjective opinion based on the "feel" of the Montana vs Oregon. It feels more like the 60csx I think, where I always found track up very hard to use because of the spinning map.

    Sorry, User Grid is something I have never used.
  • Boyd 1965 Points
    Thanks for the links Tim - that was pretty much what I thought. Maybe water on the helicopter's GPS antenna was more of an issue than the water in the atmosphere?

    Either way, those two articles suggest the "heavy cloud cover" that Jim asked about wouldn't be an issue with any GPSr.
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