Bulzeye

Hey everybody, I've seen some posts recently with new guys asking about GPS's usefulness and accuracy. I thought I should pass along a little tidbit the I heard from some folks "in the know".

Although I find a GPS to be very useful for a variety of applications, you will not find them to be as accurate now as they have been in the past. The U.S. government is, and has been since shortly after 9/11/01, intentionally introducing significant errors into the GPS readings for security reasons. Both horizontal and Vertical aspects of your position can be affected.

I have personally seen this while using my GPS. While hiking to a given landmark, I'll find that when my GPS tells me that I'm right on top of the point, I'll still be something like 75 or 80 feet off horizontally.(My unit would normally be no more than 15 feet off.)

And it changes from time to time. One time I'll be to the N/W of my landmark, and then later I'll be straight East of it, even if I never moved. Now, 80 feet of error may not sound like a big deal, but it might make a difference when going into dense woods where you haven't been in a while. It recently took me about 10 extra minutes to locate my tree because of an innaccurate GPS reading,the fact that the landscape looked different with new-fallen snow, and because I apporached my stand from a new direction due to the wind. With an accurate reading I could have avoided making all the extra noise and leaving all that extra scent while searching for my destination.

Also, the variation in Elevation I witnessed recently was quite dramatic. While sitting still in my stand playing with my GPS (it was a slow day) I saw my elevation reading change over 150 feet during the space of a half hour. Although elevation variations will not get you lost in the woods, they may be a source of confusion when trying to pinpoint your location on a topo map.

Sorry for the long-winded commentary.
I just wanted to let everybody know what to expect out there so they can plan around a little less reliability than they are used to.

Anybody else noticed this?


Keep 'em all in the Bull.

Deleted User

[Deleted by Admins]

nate68123

Under Pres. Clinton, the "scrambling" code (called "selective availability" by GPS users) was discontinued. Receivers with WAAS were released which were/are accurate to 15 ft. with appropriate differential beacons in place. I haven't read anywhere about selective availability being turned back on, but it would make sense with the current national situation. I have an old Magellan hand-held receiver and I certainly noticed a difference about a week after it was discontinued a couple years ago, but I haven't noticed a decrease in accuracy since...

Nate

Bulzeye

Yeah, I knew it wasn't new, but I've definitely noticed a difference since I first started using them. I've been in the same general area, with good coverage from several satelites, and I've waited to create a landmark until my GPS has avereageed my position for a few minutes.

Hey, maybe the deer are jamming my signal. I DID see a big buck carrying a technical manual last week, but I didn't think anything about it at the time since Illinois deer are known to be pretty smart.
<img src=icon_smile_big.gif border=0 align=middle>

Keep 'em all in the Bull.

T_in_PA2

SA has not been turned back on. http://www.igeb.gov/sa.shtml
http://joe.mehaffey.com/saoff.htm

It will probably never be turned on again.

WAAS is still in an experimental phase and probably will be for the next couple of years. http://www.gpsinformation.net/waasgps.htm

jpm8920

I find that my GPS unit works great until i'm about 100-150 feet from where I want to be. Then I start getting false readings.

timbercruiser

I was talking with a surveyor a couple of months ago and he claimed his GPS system was acurate within 3 milimeters. Probably a very expensive system though.