Questionable Oregon 650t GPS Accuracy

[+crites]

I've been geocaching with my Oregon 650t lately and have been disappointed with the apparent accuracy.

 

I would think if I turned on GPS + GLONASS and WAAS/EGM options that it shouldn't get any better than that. I know it could be that my Oregon 650t is dead nuts and the published coordinates aren't that great but it still doesn't seem I'm that close when my GPS says "I'm there!"

 

Is there anything else I can do to improve geocaching accuracy?

[+kunarion]

Is there anything else I can do to improve geocaching accuracy?

Place the GPSr in one spot and let it think. Or find a clearing, and guesstimate GZ based on displayed distance and bearing ("in line with that tree, 150 feet is 50 paces").

 

A whole bunch of waypoints at one spot, averaged, at various times of day, on various seasons, can produce pretty decent coords, but you probably don't have that much time to find one cache. Plus you'd have to reposition the GPSr, since by definition, it's not at GZ.

 

WAAS sends some correction info. You could try it without that. See if it makes a difference.

 

I've read that the addition of GLONASS doesn't increase the accuracy, it just speeds up the lock on satellites, the ability of the GPSr to show coordinates quickly. The accuracy is what it is, due to refraction, reflection, interference, all kinds of things. Sometimes my Oregon is almost dead on, sometimes kind of off. Once it was 180 feet off for several minutes. Weird.

Edited August 26, 2014 by kunarion

[+andyakashrek]

Try using it with gps set to normal only. No waas or glonass. There is a discussion on here, do you use waas, egnos, in which I found my 550t to be poor compared to a vista hcx but it has improved significantly since switching to basic gps only. I am in UK though, try it you have nothing to lose.

[+The_Incredibles_]

I think what you mainly need is more experience finding caches. Most devices will get you within 10 meters, then it's up to you to search and develop your geosenses. Just like riding a bicycle, finding caches will get easier with practise.

[+nosynellies]

I just logged a DNF where my Oregon suddenly decided to only have 20' accuracy. 20' accuracy plus the standard 15' allowance plus the 15' allowance for the CO's unit. I don't want to wander that much looking for a micro in bull-thistles!

[+CanadianRockies]

I just logged a DNF where my Oregon suddenly decided to only have 20' accuracy. 20' accuracy plus the standard 15' allowance plus the 15' allowance for the CO's unit.

I'm not sure what the "standard 15' allowance" is in this sentence. Around here, our search area is a combination of my unit's inaccuracy and the hider's unit's inaccuracy. Are you suggesting hiders in your region also typically throw in up to 15' of random inaccuracy (i.e. "soft coordinates")?

[+kunarion]

I think what you mainly need is more experience finding caches. Most devices will get you within 10 meters, then it's up to you to search and develop your geosenses. Just like riding a bicycle, finding caches will get easier with practise.

+1

 

I don't usually try to get it to show "Zero Feet". I still do the bee dance under heavy canopy in a forest, but after a few minutes, I've somehow decided where "GZ" is, by mentally locking to the spot where the GPSr points most.

 

I agree with andyakashrek, to try shutting off the fancy calculations (WAAS, GLONASS) that some hiders don't even use.

Edited August 26, 2014 by kunarion

[+The_Incredibles_]

I just logged a DNF where my Oregon suddenly decided to only have 20' accuracy. 20' accuracy plus the standard 15' allowance plus the 15' allowance for the CO's unit. I don't want to wander that much looking for a micro in bull-thistles!

 

Maybe you'd be better off with a smartphone?

[+Panther&Pine]

I have the same model you do, while it might be more accurate than my previous ones it doesn't do anything about the accuracy of the device that was used by the cache owner.

I expect to search at least 15 feet around where the gps says I thinks GZ should be and up to 30 feet.

[+narcissa]

I just logged a DNF where my Oregon suddenly decided to only have 20' accuracy. 20' accuracy plus the standard 15' allowance plus the 15' allowance for the CO's unit. I don't want to wander that much looking for a micro in bull-thistles!

 

I think you're spending too much time looking at your GPS and not enough time looking for the cache. Once I'm within 15 metres, I'm looking for likely hiding spots.

[+mrreet]

I don't want to wander that much looking for a micro in bull-thistles!

 

[+nosynellies]

I just logged a DNF where my Oregon suddenly decided to only have 20' accuracy. 20' accuracy plus the standard 15' allowance plus the 15' allowance for the CO's unit.

I'm not sure what the "standard 15' allowance" is in this sentence. Around here, our search area is a combination of my unit's inaccuracy and the hider's unit's inaccuracy. Are you suggesting hiders in your region also typically throw in up to 15' of random inaccuracy (i.e. "soft coordinates")?

Sorry, the 15' I was referring to was the inaccuracies of both the CO's as well as another 15' for my unit.

 

I don't want to wander that much looking for a micro in bull-thistles!

You, sir hit the nail on the head!!! In reality I only made a feeble attempt at walking a large circle and got back in the car.

 

Narcissa, all I can say is within 15 meters in bull thistles and you'd begin searching? You my friend are a stud! I don't care if you are male or female (can I use those terms, I don't remember? ). You rock!

 

Now it's time for me to put on my dunce cap. I'm starting to feel like I don't understand how the units work. Sorry crites, I'm hijacking this thread, but maybe others will find this useful as well. My understanding is that the CO's unit can be off 15'. Then my unit can be off an additional 15' if it zeroed out which doesn't happen. That possibly puts me at roughly 30' from GZ depending on circumstances. Then with my unit having 20' accuracy, it leaves me at 50' from GZ (I know that it is as unlikely to be maximally inaccurate as it would be to be dead on). Now with this reference, I don't know if I'm off to the East, or West (for sake of argument). Than means that I have to search a 100' circle to cover "GZ". Mostly not a problem for me til I see the thorns . But is this not how the accuracy works? For what it's worth, it was a crystal clear sky with not trees anywhere near.

Edited August 29, 2014 by nosynellies

[+The A-Team]

Now it's time for me to put on my dunce cap. I'm starting to feel like I don't understand how the units work. Sorry mrreet, I'm hijacking this thread, but maybe others will find this useful as well. My understanding is that the CO's unit can be off 15'. Then my unit can be off an additional 15' if it zeroed out which doesn't happen. That possibly puts me at roughly 30' from GZ depending on circumstances. Then with my unit having 20' accuracy, it leaves me at 50' from GZ (I know that it is as unlikely to be maximally inaccurate as it would be to be dead on). Now with this reference, I don't know if I'm off to the East, or West (for sake of argument). Than means that I have to search a 100' circle to cover "GZ". Mostly not a problem for me til I see the thorns . But is this not how the accuracy works? For what it's worth, it was a crystal clear sky with not trees anywhere near.

I think you're putting too much stock in accuracy figures. First of all, I recommend you ignore the "accuracy" field on your GPSr. All that is is a representation of the statistical probability of your GPSr being correct, not a hard distance that your GPSr is off by. I would only start considering this value if it exceeds something like 30+ feet (ie. when there are significant obstructions, like tall cliffs or buildings), in which case you'll want to use things like the hint, description, and searching a much wider area. It's good as a guide, but never confuse that value with being an accurate distance to the cache. After all, even if it says it only has 100' accuracy, the cache could still be right under your feet.

 

(Side note: If you really do want to use the "accuracy" figure on your GPSr for something, what you need to do is double it. It will then mean that there's a 95% chance that the coordinates you're trying to locate are within that doubled-distance from where you are now. This still doesn't really help you find a geocache, though, because it assumes the CO's GPSr was perfect when they hid the cache. Since their GPSr is likely inaccurate to some degree, finding the posted coordinates generally won't necessarily find the cache, so not much is gained.)

 

Second, your math is a bit off. The first 15' is a rough average we can use to represent the inaccuracy of the CO's GPSr. The second 15' is the equivalent representation of your GPSr's inaccuracy. Your addition of another 20' is duplicating the previous distance, so that isn't necessary. Therefore, you come out with a search area of 30' from where your GPSr says the cache is. This is the distance usually recommended to new cachers as the distance at which you stop watching the distance count down on the GPSr and start looking around with your eyes. Due to the inaccuracies in both the CO's and your GPSrs, it isn't all that common to actually find the cache exactly where your GPSr says it should be. Blindly staring at your GPSr will therefore usually not bring you to the cache, so you need to actually look around the area for possible hiding spots or items that match the hint, description, cache name, D/T ratings, container size, etc.

[+nosynellies]

Nice. Thanks for the info. I really did have that figure off. FWIW I will probably still use that as an excuse when I see to many pokeys!