My Magellan Sportrak Not Accurate?

[+SnowLeopard]

Lately, my Magellan SporTrak doesn't seem as accurate as it once (maybe) was.

 

Two people visited my cache and said the coords were off by about 10-15 feet, but I didn't think anything of it since I had just double-checked and other people didn't seem to have a problem. However, more people visited last night, and they said the cache was actually 10 feet North-West of the coordinates I gave. Huh.

 

This morning, I went to double-check the coordinates of a cache I am about to place, and as I was driving, my GPS map said I was about 10-15 feet North-West of the road I was traveling on.

 

I know there may be errors matching a map exactly to the coordinates, but I have no way to check if it's the map, the gps, or me that's wrong.

Does anyone know what the heck is going on?!?

 

 

My expected display:

arrow: my position

line: the road I was traveling on

 

^

|

 

My actual display:

arrow: my position

line: the road I was traveling on

 

^ |

[+Stunod]

The maps are not very good and it is not uncommon to look like you're driving parallel to the road.

 

The complaints of the cache being 10-15' off are not worth getting worried about. That is well within the expected error.

 

If you still feel you need to confirn that your GPS is working, try plotting a waypoint on the mapmaker at LostOudoors.com. Choose a location that will show up clearly on a map (such as a corner of a parking lot or at intersecting sidewalks in an open area), take a waypoint there and plot it on an aerial photo.

[+SnowLeopard]

Thanks! I just wanted to make sure that I was correct since I'll be placing a cache that will be quite "tricky". Muhahhahahhahaha!

(Sorry, ignore the maniac behind the curtain.)

[+texastracker]

I've had similar issues with my unit. I simply erased the memory and set the unit back up! So if you see a problem with points not matching you might give that a try.

[+embra]

10-15 feet off is right on the money in a consumer handheld.

 

If you're interested in verifying accuracy, look for a benchmark that has adjusted (not scaled) horizontal coordinates. Those marks are measured with professional grade units accurate to within centimeters. Let your ST do some averaging over the BM; it should be pretty durn close.

[blocko1000]

Another thing to think about is did you recently send your unit in for repair? I sent my sportrak in for repair of the cracks in the casing. When it came back it was not accurate. Something was wrong. It wouldnt lock into 3d mode and kept switching back and forth from 2d to 3d.

[+Team Thompson]

One other thing - when driving you should really have the WAAS turned off. WAAS is really for walking - it takes readings from many satellites to really pinpoint your position. If you leave this on while driving your car is moving faster than the WAAS can keep up, so you will constantly be off a bit on the map.

[+BugznElm'r]

Is there a hill or valley wall nearby? If so it could be because of a certain type of GPS error (multipath error) that everyone is getting a consistent error. The signal from the sats being reflected before being picked up by the GPSr.

However, for 10 - 15 feet, I wouldn't worry about it! That's about as accurate as things get!

[+embra]

One other thing - when driving you should really have the WAAS turned off. WAAS is really for walking - it takes readings from many satellites to really pinpoint your position. If you leave this on while driving your car is moving faster than the WAAS can keep up, so you will constantly be off a bit on the map.

??? I'm not so sure about the speed/WAAS relationship...I thought that WAAS was developed for the benefit of airline pilots, who--when they're working--are moving at faster than walking or driving speeds. Of course, a plane will have a primo view of available satellites.

[+SnowLeopard]

At my cache location there is a slight hill and some tree cover, so I'm not surprised of the error. But on the street it was a clear shot.

[+BugznElm'r]

Speed has no effect on the accuracy of a WAAS enabled GPSr but line of sight is. The real problem with using WAAS for car and walking is that the view to the WAAS sat can be lost easily and it is errors from this constant losing the signal and regaining it that causes the problems.

WAAS or no WAAS, 10 - 15 feet error is still good accuracy!

[Kerry.]

However, more people visited last night, and they said the cache was actually 10 feet North-West of the coordinates I gave. Huh.

 

I'd being say Huh too, like what is it will some who think they can actually determine 10 feet in any direction with any confidence/integrity anyway, tell em they are kidding themeselves.

 

Cheers, Kerry.

[Magellin]

Night time will produce the most accurate reception for a GPSR.

If you placed the cache in the heat of day and then someone looks for it at night they would be on the numbers that you post only they are at the #'s at a more accurate time due to better reception/lack of atmosphiric errors

[Kerry.]

Again night time doesn't necessarily mean better accuracy.

 

Cheers, Kerry.

[+JohnnyVegas]

One other thing - when driving you should really have the WAAS turned off. WAAS is really for walking - it takes readings from many satellites to really pinpoint your position. If you leave this on while driving your car is moving faster than the WAAS can keep up, so you will constantly be off a bit on the map.

I always have waas turned on driving or otherwise, for me it is not effected by driving.

[+JohnnyVegas]

10 t0 15 feet is about the best you are going to get.