Dropped my 320, now I don't trust it...

[Guest alexm]

but otherwise appears to be unscathed.

 

Now for the stupid question: Is there anything inside the unit that could get "jolted" to make my unit start acting a bit weird?

 

Since that time, I tend to get "strange" reactions when caching or returning to known "good" points. For 5 minutes the cache will definitely be "75 feet West", then all of a sudden, "300 feet South" for 10 minutes, usually pointing back in the same general 3 or 4 areas.

 

I first thought signal strength, satellite geometry, etc... But then again, as far as I really know, this thing runs on magic.

 

I had the opportunity at LAGG1 today to calibrate my 320 versus ClayJar's 330 and Meridian gold. My 320 was within 5 one-thousands of a minute with the both of 'em (standing still at two different times).

Strangely enough, while looking for caches at the get-together today, my unit did the same thing it did the last 3 times I've had it out. It started out pointing me to the right place, then after a few minutes.... 300 feet WAY OFF. It doesn't appear to be the slingshot effect as I re-powered the unit at least twice during the "errant" phase(s).

 

Any ideas? At least 2 other GPS's in the area stayed on track while mine went out to lunc0h (an e-trex vista? and a magellan blazer 12?).

 

Thanks!

[Guest alexm]

After I posted that and got to thinking about it... The only other thing(s) I changed are:

 

1. Started using a neoprene "sleeve" for the unit. It does the same with or without the sleeve as that was my first guess.

 

2. Started using Energizer nimh rechargeables (1200 mAh).

 

???

[Guest Rootbeer]

quote:

---

Originally posted by alexm:

Is there anything inside the unit that could get "jolted" to make my unit start acting a bit weird?

---

 

Yup. For example, the connection between the antenna and the rest of the electronics may have become loose, so you may lose contact with some satellites when you shouldn't. Or maybe there is a loose data connection somewhere, and so bad data gets passed around inside the unit. These aren't too likely, but they could happen.

 

It's probably worth sending it in for a repair checkup since you're seeing it act flaky. (But a perfectly fine GPSr will seem flaky some of the time...) Get an estimate first, though; you may be better off buying a new one and selling this one as-is to someone who is less worried by a flaky GPSr.

[Guest Rootbeer]

quote:

---

Originally posted by alexm:

Is there anything inside the unit that could get "jolted" to make my unit start acting a bit weird?

---

 

Yup. For example, the connection between the antenna and the rest of the electronics may have become loose, so you may lose contact with some satellites when you shouldn't. Or maybe there is a loose data connection somewhere, and so bad data gets passed around inside the unit. These aren't too likely, but they could happen.

 

It's probably worth sending it in for a repair checkup since you're seeing it act flaky. (But a perfectly fine GPSr will seem flaky some of the time...) Get an estimate first, though; you may be better off buying a new one and selling this one as-is to someone who is less worried by a flaky GPSr.

[Guest alexm]

I think I figured out what *I* unknowingly did to it.

 

I ran several backyard "mark the birdbath", "mark the driveway" and navigate to them from several different distances. The GPS was off the mark, in general from 70-100 feet. I swapped the batteries for alkalines, same problems. Initialized the unit, same problems.

 

After realizing that "yes, it's doing it now", I re-loaded the firmware, re-marked some points and it was amazingly more accurate.

 

So while I'm sitting there re-customizing the unit to 'my taste', shutting off the road nav screen, etc... I hit the 2D/3D screen. I think about it for a moment and decide to run some more tests. Basically, in 2D mode, the unit is MUCH less precise than in 3D mode. I had switched to 2D mode at some point thinking that 2D might 'be good' in some way, either by doing less calculations or requiring less satellites to maintain a 'lock' under treecover.

 

Now that I look back on it, without some guess as to what my elevation MIGHT be at any given point in time, the unit is probably going to use my entered elevation '0' in coordinate calculations, thus throwing the coords off a bit.

 

I guess 300 feet away may REALLY mean 300 feet DOWN

 

Even standing at known waypoint (the birdbath, in this case), switching between 3D and 2D varies the "distance" from about 3-7 feet to 20-40 feet.

 

I guess I've learned my lesson. Hope my stupidity can help someone else in the future.

[Guest alexm]

I think I figured out what *I* unknowingly did to it.

 

I ran several backyard "mark the birdbath", "mark the driveway" and navigate to them from several different distances. The GPS was off the mark, in general from 70-100 feet. I swapped the batteries for alkalines, same problems. Initialized the unit, same problems.

 

After realizing that "yes, it's doing it now", I re-loaded the firmware, re-marked some points and it was amazingly more accurate.

 

So while I'm sitting there re-customizing the unit to 'my taste', shutting off the road nav screen, etc... I hit the 2D/3D screen. I think about it for a moment and decide to run some more tests. Basically, in 2D mode, the unit is MUCH less precise than in 3D mode. I had switched to 2D mode at some point thinking that 2D might 'be good' in some way, either by doing less calculations or requiring less satellites to maintain a 'lock' under treecover.

 

Now that I look back on it, without some guess as to what my elevation MIGHT be at any given point in time, the unit is probably going to use my entered elevation '0' in coordinate calculations, thus throwing the coords off a bit.

 

I guess 300 feet away may REALLY mean 300 feet DOWN

 

Even standing at known waypoint (the birdbath, in this case), switching between 3D and 2D varies the "distance" from about 3-7 feet to 20-40 feet.

 

I guess I've learned my lesson. Hope my stupidity can help someone else in the future.

[Guest Rootbeer]

Well, it's good that it's working now. These gadgets are made pretty tough, as if someone expected them to be dropped from time to time.

[Guest Rootbeer]

Well, it's good that it's working now. These gadgets are made pretty tough, as if someone expected them to be dropped from time to time.

[Guest ClayJar]

quote:

---

Originally posted by alexm:

I guess 300 feet away may REALLY mean 300 feet DOWN

 

Even standing at known waypoint (the birdbath, in this case), switching between 3D and 2D varies the "distance" from about 3-7 feet to 20-40 feet.

---

Actually, I believe the distance to waypoint calculation is along the ellipsoid (basically, a line along the surface of the ellipsoid between the points nearest you and the waypoint, respectively). To put it more simply, height/altitude is irrelevant to the distance calculation: you could set two waypoints, one at (N30 0.000, W91 0.000, 0ft) and the other at (N30 0.000, W91 0.000, 15,000ft), and the length of the route between them should show as 0.

 

Anyway, what was apparently happening is that in 2D mode, the unit uses the altitude you input in the calculations instead of having to solve for it. If you know your altitude, you can get more accurate results, or alternately, you can find a solution for X, Y, and time (using at least 3 satellites) instead of solving for X, Y, Z, and time (using at least 4 satellites).

 

To put in in simple English, having the correct altitude and selecting 2D will get you results with fewer satellites, but having the wrong altitude will indeed throw bad data into the calculations and give you consistently bad results (i.e., you could get the same wrong result repeatedly).

 

(Now I just have to ask myself why I didn't think of the 2D/3D thing yesterday. I may have to do some multidimensional differential equations as penance. Well, or I'll just go caching next weekend.)

 

[For those mathematicians around, I know {x,y,z,t} is not the customary coordinate system for postion on an ellipsoid plus time, but since you would already understand how multidimensional nonlinear equations are solved, you needn't care.]

 

[This message has been edited by ClayJar (edited 21 October 2001).]

[Guest ClayJar]

quote:

---

Originally posted by alexm:

I guess 300 feet away may REALLY mean 300 feet DOWN

 

Even standing at known waypoint (the birdbath, in this case), switching between 3D and 2D varies the "distance" from about 3-7 feet to 20-40 feet.

---

Actually, I believe the distance to waypoint calculation is along the ellipsoid (basically, a line along the surface of the ellipsoid between the points nearest you and the waypoint, respectively). To put it more simply, height/altitude is irrelevant to the distance calculation: you could set two waypoints, one at (N30 0.000, W91 0.000, 0ft) and the other at (N30 0.000, W91 0.000, 15,000ft), and the length of the route between them should show as 0.

 

Anyway, what was apparently happening is that in 2D mode, the unit uses the altitude you input in the calculations instead of having to solve for it. If you know your altitude, you can get more accurate results, or alternately, you can find a solution for X, Y, and time (using at least 3 satellites) instead of solving for X, Y, Z, and time (using at least 4 satellites).

 

To put in in simple English, having the correct altitude and selecting 2D will get you results with fewer satellites, but having the wrong altitude will indeed throw bad data into the calculations and give you consistently bad results (i.e., you could get the same wrong result repeatedly).

 

(Now I just have to ask myself why I didn't think of the 2D/3D thing yesterday. I may have to do some multidimensional differential equations as penance. Well, or I'll just go caching next weekend.)

 

[For those mathematicians around, I know {x,y,z,t} is not the customary coordinate system for postion on an ellipsoid plus time, but since you would already understand how multidimensional nonlinear equations are solved, you needn't care.]

 

[This message has been edited by ClayJar (edited 21 October 2001).]

[Guest navdog]

ouncing around inside your head I don't know why you bought that new Meridian. All you need to do is slap a patch antenna on top your head and you could be a human GPSR!!!

[Guest navdog]

ouncing around inside your head I don't know why you bought that new Meridian. All you need to do is slap a patch antenna on top your head and you could be a human GPSR!!!

[Guest ClayJar]

I tried something like that, but my glasses kept messing up my attempts at wrapping a quadrifilar around me.

[Guest bunkerdave]

Too Funny!

 

I understand much of what you are saying, only because the Trimble Website gives such a great tutorial on how GPSRs actually "do their thing." The whole thing about calculating position and the process of elimination the GPSR uses to do it fascinates me, particularly considering the sheer scale involved. 11,000 miles away and it zeroes me down to a couple of feet. Suddenly $300 seems CHEAP.

 

bd

[Guest ClayJar]

Wouldn't it be something like $22,000,000,300? Of course, it wasn't quite a 50-50 split.

[Guest ClayJar]

Wouldn't it be something like $22,000,000,300? Of course, it wasn't quite a 50-50 split.