quick gps question

[EBES]

Last time I used my eagle explorer gps [older model], I was doin the harrison/chehalis traverse in reverse and wanted to find my way through. I took the proper turn-off at the Mamquam fsr with the club but my gps showed the trail off to the right of our position. It stayed absolutely parellel to us the next few k's. We ended up missin the turnoff and turned back to play at Hale.

My question is this. Is my gps hooped or is this just user error? It was really odd as it has never done this before and I know there was no trail parallel to us all that way. Any ideas would be appreciated.

[canadazuuk]

I'll have to look at a map and see what you are refering to, BUT, are you sure the datum on the GPS was set to match what you were expecting? The difference between two common datums is 150 metres approx...

[lars]

Originally posted by canadazuuk
I'll have to look at a map and see what you are refering to, BUT, are you sure the datum on the GPS was set to match what you were expecting? The difference between two common datums is 150 metres approx...
I'd suspect a datum error or even a map error. The older topo maps aren't necessarily going to be as accurate as your GPS.

Even the urban maps that I upload to my Garmin are sometimes off by a little bit. That's why street nav. software has a "snap-to" function which fudges your position a little bit so it shows you on a street where, without it, it may show you driving THROUGH buildings.


...lars

[EBES]

I can't upload maps to mine. I was just following a track with waypoints that I had set earlier in the year. It should have been bang on.

"Holy GPS Batman, I'm lost !!!!"

[canadazuuk]

Hmm, that is odd. So you drove the SAME road, but all the points were off?

Did this cause you to lose a place you were expecting to find again?

Can't say I know what the problem is, but when did you record the first tracks?

[Jason Funk]

I use my GPS all the time, following a track that I have recorded previously. Sometimes it will follow the track exactly other times it will follow parallel to but slightly off of the recorded track. As far as I can tell it might just be the accuracy of the GPS system. The accuracy can very from day-to-day depending on the strength of the satellite signals.

Jason

[EBES]

That makes sense. Didn't know it could do that.

Thx.
Kev.

[canadazuuk]

but it should not be radically off, maybe 15 metres, that is all you should expect...

[EBES]

Originally posted by canadazuuk
but it should not be radically off, maybe 15 metres, that is all you should expect...

I'm gonna try layin a new track from port moody to burnaby along the barnet and then back track it another day. I may figure it out then.

thx for the advice.
Kev.

[Jarett]

could it be that your GPS is too old and does not use that newer WAAS(or whatever it is called) -that system that they can turn on or off to limit the accuracy of the GPS units.

[lars]

Originally posted by Jarett
could it be that your GPS is too old and does not use that newer WAAS(or whatever it is called) -that system that they can turn on or off to limit the accuracy of the GPS units.

You're thinking of Selective Availability (SA) which affects ALL civilian GPS units. That has been turned off for quite a few years, now (in fact, I don't even think the US turned it back on during the Iraq war).

WAAS is an additional correction signal that is generated from ground-based reference stations. AFAIK, these stations only exist in the USA so I don't know how useful the WAAS signal would be in Canada, particularly when you get farther from the Canada/USA border.

From the Garmin website:
"You've heard the term WAAS, seen it on packaging and ads for Garmin® products, and maybe even know it stands for Wide Area Augmentation System. Okay, so what the heck is it? Basically, it's a system of satellites and ground stations that provide GPS signal corrections, giving you even better position accuracy. How much better? Try an average of up to five times better. A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS."


...lars

[DMMcG]

WAAS appears to be functional in and about the lower mainland. My unit claims accuracy down to 17 feet with the WAAS activated.

[EBES]

Originally posted by Jarett
could it be that your GPS is too old and does not use that newer WAAS(or whatever it is called) -that system that they can turn on or off to limit the accuracy of the GPS units.

Could it be that my gps was being used by my navigator and he didn't know what he was doing? LOL.

[Jarett]

Originally posted by EBES
Could it be that my gps was being used by my navigator and he didn't know what he was doing? LOL.

A distinct possibility....LOL:D

[Bronco Boy]

Originally posted by EBES
Last time I used my eagle explorer gps [older model], I was doin the harrison/chehalis traverse in reverse and wanted to find my way through. I took the proper turn-off at the Mamquam fsr with the club but my gps showed the trail off to the right of our position. It stayed absolutely parellel to us the next few k's. We ended up missin the turnoff and turned back to play at Hale.



Easy, the Mamquam doesn't connect to the Harrison/Chehalis traverse. Your GPS must have heard you and your voice threw it off. :laugh

[EBES]

Originally posted by Bronco Boy



Easy, the Mamquam doesn't connect to the Harrison/Chehalis traverse. Your GPS must have heard you and your voice threw it off. :laugh

Hey Jarett, did we not end up coming out on the mamquam? I'm pretty sure we did cause we started the reverse trip at the waypoint I plotted for that turnoff.

[Bronco Boy]

Originally posted by EBES


Hey Jarett, did we not end up coming out on the mamquam? I'm pretty sure we did cause we started the reverse trip at the waypoint I plotted for that turnoff.


The Mamquam is in Squamish. I figured you were talking about Mystery Creek or Norrish Creek.

[Jarett]

I realy don't remember the road we came out on. All I know is all the maps I have ever seen say that it is not supposed to connect through, and several people have said that as well. I know the roads in there are kinda a maze so perhaps we just got lucky

[EBES]

Originally posted by Bronco Boy



The Mamquam is in Squamish. I figured you were talking about Mystery Creek or Norrish Creek.

I remember now, it was Walian Creek fsr we came out on.

My bad.