Fun and games with the Garmin European Basemap and MapQuest

[Lee&Jackie]

After setting our first cache (Under Lock and Quay) we reported the details on GC.com. Then checked the MapQuest and it was showing it in the wrong place. RATS! GPS playing up we thought. Back to the cache location and tried a few more times, checked that we were using the right datuum etc.

 

It was only then that I zoomed the map on the Garmin Etrex right in and noticed that the railway line was in the wrong place on the basemap! Then the penny dropped ... not only was the railway line in the wrong place but part of the River Trent was missing.

 

Anybody else noticed anything like this!

 

Lee&Jackie

 

We're not lost .... just temporarily misplaced

[dodgydaved]

Yup,

 

The Garmin Roads and recreation software shows one of my caches as being North of the very busy and Electric Waterloo/Reading line when in fact it is South of the line!!!!!!

 

I just made a big WARNING on the cache page!

 

dodgydaved

 

I'm NOT lost, I know exactly where I am, I'm here!

[Moss Trooper]

You gotta remember that maps aint accurate.. even OS maps. Maps are a representation.. and can be as much as 100 mtrs out..

 

Moss the Boss... Sorta

[+The Merman]

I remember my Emap showing that Walking on Water was situated in the middle of the Hamble and I had to toss a coin to decide which bank it was actually on!

 

I woke this morning and my boat was not rocking...for one horrid moment I thought I lived in a house!

[MCL]

I recently stayed down in Torquay in an hotel which is right on the sea front. My room had a sea view out of the window, with the sea being about 50m from the hotel.

 

Imagine my surprise when I looked on my laptop at Mapsource (the Garmin software) and discovered there was meant to be a railway line between me and the sea!

 

In fact, the railway was on the other side of the main road, away from the sea, so the order things went in was: sea>hotel>road>railway as oposed to Garmin's idea of sea>railway>hotel>road.

 

Being more interseted in railways than I am in the sea, I would have preferred the Garmin version of reality, but had to make do with the God version. Oh well, you can't have everything.

 

No trees were harmed during the production of this posting, but a large number of electrons were terribly inconvenienced....

[+Richard & Beth]

If you are talking about the default basemap that comes with the eTrex, it is dire. I have had a similar experience in Micheldever, where the place I used to work came up on the wrong side of the railway line.

 

The problem is that all the Garmin maps are vector based, the basemap being with less resolution, so many features are represented by a long straight line. In my experience the Garmin Roads and Rec maps are considerably better as the vector data is of higher resolution. For any navigation with GPS maps they are well worth the money when compared to the basemap. Having said that there are still errors, for example although my office was in the right place on Roads and Rec, Micheldever Station isn't...

 

Richard

[+Longitude]

Owning a Garmin receiver has allowed me to walk on water. On a couple of walking holidays on the Southwest Coast path the tracklog has shown that at times I have wandered well off course out to sea without getting my feet wet. Remarkable.

[+Lizzzzeeeee]

quote:

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Originally posted by The Merman:

I remember my Emap showing that Walking on Water was situated in the middle of the Hamble and I had to toss a coin to decide which bank it was actually on!

---

 

Exactly the same thing happened to us in the same place with our eMap, and we really managed to walk on water to get to Solent Way!!! It was only the basemap though, now I've loaded Mapsource maps it's pretty good. I've never had a problem with the actual coordinates it gave me though, just the map - you can always check accuracy pretty well by going to a trig point.

 

Lizzzzzzzzzzzzzzeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

 

Why is it that when you're out for a walk carrying a map everyone asks if you're lost?

[+Lassitude]

Yep I also have had errors so large when viewing mapsource maps that they cannot be put down to GPSr inaccuracies. Quite often I use the map on my eMap to (try to) navigate to caches it indicates are on one side of a river or railway line only to find they are on the other side.

 

The answer is that the maps do not seem to be very accurate when it comes to things that are not roads. I wonder if they just drew lines for road and rail in the rough area when they wrote the map database thinking that people would not actually use the maps to walk along riversides.

 

Cheers

 

Chris

 

LASSITUDE- (noun) Tiredness and apathy: a state of weariness accompanied by listlessness or apathy[15th century. Via French from Latin lassitudo , from lassus 'weary'.]

[+The Hungry Caterpillars]

Moss Trooper,I use maps an awful lot and find errors every so often but I have not often found too many problems with OS maps.Does this up to 100m problem occur on OS maps?

[+Pharisee]

I recently did one of Huga's caches, the one at Denver Sluice. Once I'd collected the relevant data and plugged in the co-ordinates for the cache, I have to admit to being a bit confused as the Legend was showing me to be on the wrong side of the river (which I wasn't). I ignored it and carried on. I was amused to see me apparently walking on water as my track on the Legend gradually merged with and then crossed the river .

In general I've always found the roads on MapSource to be just about spot on but rivers and railway tracks do sometimes seem to be a bit out.

 

John

 

Age and treachery will always triumph over youth and ability.

[+Richard & Beth]

quote:

---

Originally posted by Pharisee:

but rivers and railway tracks do sometimes seem to be a bit out.

 

John

 

Age and treachery will always triumph over youth and ability.

---

 

Certainly found that today Going Wild On The Moor near Basingstoke. The Vista showed the River Loddon as a single channel, which it wasn't. Thankfully I had a Landranger OS map for the area with me, so we didn't get wet feet.

 

Richard

[Lee&Jackie]

Take the point about maps not being accurate and I've noticed this with maps in the Republic of Ireland before (roads being the wrong place etc). It just seems to me that MapSource or the database it is derived from is a bit worse than most. All of the "funnies" we've found so far seem to be railway lines in the wrong place ....

[MCL]

Yes I can confirm that, Lee&Jackie. Wronskian and myself found another glitch involving a railway line only yesterday. The one I mentioned in my last post, the one in Torquay, was again a rail line in the wrong place. The roads in Mapsource seem to be spot on.

 

No trees were harmed during the production of this posting, but a large number of electrons were terribly inconvenienced....

[Moss Trooper]

Yep.. 100m slight exaduration sorry but they are inacurate at times, all depends on the amount of information they are trying to get on the map. And after all they are a representation. The smaller the scale the more accurate they become.

 

I travel to work across the Redhugh Bridge here in Newcastle, I use ipaq/Navman GPS and Memorymap. I know I'm on the bridge but the ipaq shows I'm flying!!!!

 

Then again on other parts of my trip you can tell which side of the road I'm on.

 

Don't get me wrong, OS maps are the best in the world, and Ive used them for as long as I can remember.

 

Moss the Boss... Sorta

[+John Stead]

Try following a canal on a Mapsource map then! But I'm surprised at Moss falling off a bridge (as far as MemoryMap is concerned) as I have rarely found any significant positional errors with OS maps in spite of using them at larger scales for all my professional life. Could the misposition be the result of the bridge structure interfering with the GPS signal?

[+Team Paradise]

I've found with Memory-Map on a couple of occasions that small ponds are often out by about 50ft, but other than that it's usually very accurate.

 

Steve

 

If you can see the 'light at the end of the tunnel', it's usually a train coming !

[+Pharisee]

Ok... so we have rivers that aren't where they should be. Railway lines that may or may not be in the right place. Small ponds that are 'often out by 50ft'. Canals that give problems and people falling off bridges.

Apart from that, they're VERY ACCURATE.... great

 

John

 

Age and treachery will always triumph over youth and ability.

[Moss Trooper]

Right.. as I was falling offa me bridge on the way to work this mornin.. I was thinking.. (Two bad things at once!!)

 

I been using OS maps fer most of my life as well and found them very accurate.. but.. could you say from standing on the ground and looking at the bend in a road that it was accuratley portraid on the map.. I doubt it.. but as you are looking at map and the bend is there then everything ties up..

 

This problem has only come about since we are now using GPS's and moving maps to go find our caches. The problem arises as to whats at fault .. the map or the GPS.. I recon the map.. remember they are only a graphical representation of what is on the ground.

 

As fer Jsteads coment.. it's one of those bridges which is 4 lanes wide and a 6ft fence to stop yer actually falling off..

 

Glad I just fall off on me iPaq.. it's a loooooooooooong way down and the Tyne aint best river fer swimming

 

Moss the Boss... Sorta

[+John Stead]

Glad you didn't get your feet wet then Moss. I'm no tech wiz but although your GPS signal clearly isn't being impeded by the steelwork of the bridge, could the signal be interfered with by reflections from the structure like we used to in the old days of TV with ghost images?

I'm hoping to be in your neck of the woods in July (Seahouses, actually) so may well cross the bridge, which road is that?

[Moss Trooper]

A 189 offa the A1 but wouldn't have thought yer would cross it as it takes yer into Newcastle City.

 

Stay on A1 fer Seahouses

 

Moss the Boss... Sorta

[+The Hungry Caterpillars]

This really interests me as I come from the old school(the non-digital era,map and compass etc,B.G.P.S.).I am more wary of the gps than the map.This is because there is always an error with the gps whatever it says on the screen.For instance my gps says error to 12 ft I have a sneaky feeling that mathematically the error is in fact possibly a lot larger.Having done quite alot of trigpointing recently even when minimal error is reported by my e-trex there can be quite a difference in the reading given by the OS and the reading given by the e-trex.I have found this to be true even for FBM,s whose position is very carefully checked. Can anybody help?

[+Richard & Beth]

I'll have a dig around and see if I can find the article, but I do remember reading that the Garmin error estimate is regarded as optimistic.

 

So if the error is reading at 10m, in the same way as the location that it is reading could be a lot closer to the correct position, there is a possibility that the position being shown is more than 10m out.

 

Richard

[+The Hungry Caterpillars]

Richard and Beth I think it is more complex than that.For instance if your gps suggests a12ft error it will also suggest that also 12ft from that position.I am sure that as I said that it is not just to do with the gps reading being optimistic or not.I have a feeling it may be a statistical problem that multiplies up the larger the reported error

[+Teasel]

quote:

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Originally posted by The Hungry Caterpillars:

For instance my gps says error to 12 ft I have a sneaky feeling that mathematically the error is in fact possibly a lot larger.

---

I suspect it actually means that there's a 50% chance of it being within 12 ft, or something similar.

quote:

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Originally posted by The Hungry Caterpillars:

I have found this to be true even for FBM,s whose position is very carefully checked

---

<pedantic git mode>Unless the FBM is part of the new passive network, then its only purpose in life will have been height measurement (levelling, not triangulation) and its exact position will never have been accurately determined (my figures are only accurate to 10m for old FBMs) </pedantic git mode>

 

Also, the conversion algorithm between WGS84 and OSGB in your GPSr will not be as accurate as the one used by the OS, so that'll add another 5m of uncertainty on top of the figure quoted by the GPSr. And if you downloaded the coordinates from T:UK or Chris and Maria's site in WGS84, that'll be another 5m (though hopefully that will tend to cancel, rather than add to the other errors).

 

A 1:25000 map, a decent compass and a knowledge of how long your paces are, is still just as accurate as a GPS in most places (though far less convenient!)

 

GeocacheUK - resources for the UK Geocaching community.

[MCL]

Well OS maps themselves are not always so accurate either...I once bought an OS motoring atlas of Britain, all spiral-bound and expensive, only to find they had forgotten to print Lake Windermere on it! The blue blob was simply not there....which was unfortunate, since when I discovered this fact, I was driving along the edge of said lake in the pitch dark!

 

No trees were harmed during the production of this posting, but a large number of electrons were terribly inconvenienced....