GPS Accuracy conundrum

[+minsterley]

Sorry about this folks, but I'm confused about this!

 

My father in law (Trigger Milward) has a magellan explorist 100 GPS.

I have a Garmin Etrex Legend (which I've had for about 3 years)

 

I've been dead pleased with my Garmin and have no plans to trade it in just yet, but am confused as to why the Magellan consistently have a level of accuracy accuracy better than the Garmin. Why should there be such variation between units in exactly the same location at the same time. Suggestions welcome!

[+Renegade Knight]

For sheer overall accuracy there should be no appreciable difference between the two. On average they should read the same.

 

What the Magellan may have that the Garmin doesn't though is an averaging function built into the internal software that is used to derive the displayed location. That would have it bounce around zero less than your legend.

 

The other thing is that the Magellan is newer and should have noticibly better reception than your GPS. On the other hand, You can download all your waypoints into the Legend and not have to do it by hand.

 

When using a GPS V (Garmin) and a Sport Track Pro (Magellan) side by side neither Night Stalker and I noticed that one was more or less accurat than the other. We both took turns having one GPS be closer to the cache than the other.

[+Johnmelad]

Can you give an example of the differences?

[+Amberel]

I've been dead pleased with my Garmin and have no plans to trade it in just yet, but am confused as to why the Magellan consistently have a level of accuracy accuracy better than the Garmin. Why should there be such variation between units in exactly the same location at the same time. Suggestions welcome!

 

Have you got your Etrex set to the correct datum? This will be WGS84 for geocaching, assuming you use the published lat/long directly. If you enter the OS grid references instead of the lat/long you might have to set it to the OSGB datum.

 

Rgds, Andy

[+The Flying Boots]

I, Mrs F.B. use a Garmin gps60CSX and Mr F.B. uses a Magellan. I have never had any problems with my Garmin yet Mr F.B. because he is constantly fiddling with his settings often gets things wrong and many a time after we have hand plotted in the co-ords during a multi and set off in totally different directions only for me to end up waiting for him to come to his senses while I've found the cache.

[+minsterley]

Thanks for all your advice and tips.

This has been confusing me for a while, on our joint expeditions we noticed a difference of some 15 feet or so. (The Magellan frequently displays an GPS accuracy of 2 or 3 feet).

[+dino-irl]

If you search on this forum for accuracy you'll find some very technical and long-winded posts and threads explaining that accuracy doesn't really reflect accuracy of the signal as the GPSr can't really say how accurate it is....confused yet

 

Also there seem to be differences in the way different brands deal with poor reception areas. IIRC Magellan GPSrs tend to guesstimate where you are based on the last good lock and the direction/speed you were travelling at. Garmins tend to just say that you've disappeared

 

A better test of differences between the two units would be to compare lat/long readings at a fixed or known point such as a trig pillar or even just by marking a waypoint somewhere with good reception and seeing if there are any differences in the results

[LooneyWithGPS]

my garmin some times can be any thing upto 30ft+ ft out even on nice clear days with no clouds and then other days it is as near as dam it spot on with or with out cloud cover i think it depends on what mood its in lol

[+MartyBartfast]

Have you turned off WAAS/EGNOS on the Etrex?

[+Birders]

There's a feature called "static naviagtion" on some devices which we don't understand but have been given to understand it is why our old clockwork GPS12XL appears to be more accurate than some more recent models. We have often been out geocaching with people using "modern" gear and they gaily keep walking when our GPS says we've arrived at the cache. 9 times out of 10 we're right, but their GPS then seems to catch up and point back to us! It has happened too many times to be just a quirk. It has certainly dissuaded us from updating to a newer model until we understand all the bells and whistles on new ones.

[+dino-irl]

AFAIK "static navigation" is only with SirfIII chipsets especially Bluetooth GPSrs used in combination with PDA mapping software such as Memory Map.

 

I have a little program downloaded from MM that allows me to switch off SN though when using the GPSr in "walking" mode.

[+kewfriend]

There's a feature called "static naviagtion" on some devices which we don't understand but have been given to understand it is why our old clockwork GPS12XL appears to be more accurate than some more recent models.

These discussions are always interesting to those that are genuine anaoraks such as myself. We have three different garmins here - like the Birders I still use the GPSMap12, FewKinder has a whizzy 76csx and KewFinder has a sparkly Etrex.

 

Of these, the fastest to settle down and the most sensitive in even the most forested of conditions is of course the 76csx. It also reports the greatest accuracy often down to 2m. However when it comes to displaying the actual coordinates the GPSMap12 and the 76csx are usually identical though the GPSMap12 will 'wobble' a bit on the final digit. The GPSMap12 is the slowest to lock on but once locked on often stays glued to the sats unlike the Etrex. The Etrex might have uploadable maps etc but it is fiddly to use, and gives a worse overall performance than the GPSMap12 and - of course - the 76csx.

 

When it comes to geocaching - oddly enough I prefer to use the GPSMap12 because it is less specific about its accuracy - reporting that its confidence is usually around 7 or 8 metres unlike the 76csx and its 2m. This often gives a sensible search area. fewKinder has been known to march to where the 76csx reports a big fat ZERO metres from deviation and says: "I've arrived - its here". Well of course it often isnt - in fact it rarely is.

 

However because the 76csx has proper routing, we often use it in the car to get us from A to B, because the car SatNav does not accept coordinates - and of course it often disagrees with the car SatNav on the best route.

 

So its horses for courses:

 

The Extrex - cheap and cheerful, settles down reasonably quickly but not brilliant at holding a lock-on, fiddly but has uploadable features

 

76csx - RollsRoyce, big and chunky, floats if dropped in a river!, lots of uploadable features/maps, quick to lock-on, lovely and sensitive, colour, oddly more cumbersome to use than the GPSMap12 because of its menu strucutre, data entry method and wealth of features.

 

GPSMap12 - old fashioned brick, slow to lock-on, very accurate, easy to use, b&w reasonable size screen, hungry on batteries

[Edgemaster]

Just thought I'd ask if anyone has tried out the new H range of Garmin high-precision units?

[+Skate and Jane]

Is there any truth in the rumour that two GPSr's turned on near each other can effect the accuracy shown as compared to when they are apart?

I have seen this happen with two etrex's but wasn't sure if it was just down to random variable readouts.

[+Pharisee]

Just thought I'd ask if anyone has tried out the new H range of Garmin high-precision units?

 

Had a chance to play with the new Venture HC a few weeks ago

 

Very impressive. It does indeed have Garmin's new High Sensitivity chips not the SIRF thingies. I switched it on, indoors alongside my GPS60CSx. It acquired a 3D lock significantly quicker than the 60 although after two or three minutes the 60 was showing higher signal strengths on the acquired birds (better antenna?) and was also displaying a 'D' whereas the Venture HC wasn't. Having said that, I never checked to see if the WAAS function was actually switched on.

 

The colour display was clear and bright but smaller than the 60's. It also only had the Base Map loaded which isn't that good. This one only had, I think, about 24Mb of memory and wasn't expandable so you're not going to load a very big area of Topo map but it would probably be a big enough area for a days caching (for mere mortals like me, anyway). I believe there is a Venture HCx which has a micro SD card and may well be a better option.

 

During a days caching, it never lost lock and never appeared to be any less accurate than the 60 although we were never under really heavy tree cover.

 

I don't know how much they were retailing for but probably a chunk less than the 60CSx and it may well be a tool worth considering if you're upgrading from the bog standard Yellow and can't afford the 60.