Google Earth or GPS?

[+Pieman]

I know that if you click on "Show position in Google Earth" for a TB the position shown is a way off the real position (for a reason unknown to me), but if you input coordinates by hand into Google Earth the position seems very good. I was wondering if it is more accurate than averaging a GPS over several readings- particularly in cities where buildings can make getting a good signal tough. This is of interest to me as I have a city centre multi and Google Earth is showing some of the stages quite a bit out. Would I be better redoing the coordinates based on Google Earth?

[+jerryo]

<snip>Would I be better redoing the coordinates based on Google Earth?

Absolutely not! You cant beat being on site to take your measurements where your errors due to signal bounce inter alia, will be the same as everyone else's. I've always found caches hidden using the "not really being there" method have coords a mile out: well hundreds of feet sometimes.

[+purple_pineapple]

<snip>Would I be better redoing the coordinates based on Google Earth?

Absolutely not! You cant beat being on site to take your measurements where your errors due to signal bounce inter alia, will be the same as everyone else's. I've always found caches hidden using the "not really being there" method have coords a mile out: well hundreds of feet sometimes.

 

I'll come down on the other side of the fence and say that we have fine tuned many of our coords using google earth, and have had nothing but praise for the accuracy of our coords, apart from one when we forgot to do this!

[+keehotee]

It's a moot point because when you place a cache and publish it on GC you agree that "You as the owner of the cache must visit the site and obtain the coordinates with a GPS" - and of course you'd have to expect finders to have a live version of Google Earth with them when they find it!!!

[+Pieman]

Deleted double post

Edited January 11, 2008 by Pieman

[+Pieman]

It's a moot point because when you place a cache and publish it on GC you agree that "You as the owner of the cache must visit the site and obtain the coordinates with a GPS" - and of course you'd have to expect finders to have a live version of Google Earth with them when they find it!!!

But if the coordinates are actually more accurate by using Google Earth then cachers using a GPS will be more likely to find the right spot if I use the Google Earth coordinates. And no need to bring a computer with Google Earth to the cache site, I think!

Edited January 11, 2008 by Pieman

[+jerryo]

It's a moot point because when you place a cache and publish it on GC you agree that "You as the owner of the cache must visit the site and obtain the coordinates with a GPS" - and of course you'd have to expect finders to have a live version of Google Earth with them when they find it!!!

But if the coordinates are actually more accurate by using Google Earth then cachers using a GPS will be more likely to find the right spot if I use the Google Earth coordinates. And no need to bring a computer with Google Earth to the cache site, I think!

The point is that you should make sure yourself that a GPSr will get you there, rather than assuming it will. I remember a cache near me with coords calculated - supposedly accurately - using Streetmap that was out by nearly 200 feet.

Edited January 12, 2008 by jerryo

[+Moote]

Oh here is a Moote point, I set all my caches on clear nights, and check their position with a sextant. You can't beat that for accuracy

 

But in all fairness, it is a good idea to check your coords on a map or Google Earth can alert you when you have a really bad set. But to use mapped ones alone is not a good idea, as maps / Google Earth are on small scale, so errors there are magnified if the waypoint is moved moved a little.

 

Now, my first mutterings, come on Pieman surely you could set a Puzzle cache using a sextant!

[+keehotee]

But if the coordinates are actually more accurate by using Google Earth then cachers using a GPS will be more likely to find the right spot if I use the Google Earth coordinates. And no need to bring a computer with Google Earth to the cache site, I think!

 

???? If your GPS puts it at point A, but using Google Earth you actually work out it's at point B, how will that make it easier for other people trying to find it with their GPS???? You're trying to get people to your cache, NOT mapping the globe to within an inch.

Using GE co-ordinates would only pay off if you had a perfect view of the sky with no chance of reflected signal - in which case there'd also be no problem with using your GPS....

Edited January 12, 2008 by keehotee

[+scottpa100]

I've corrected co-ords using Memory Map in the past, as a multi I have, I needed people to start at the beginning of a footpath that is located in a steep sided broad-leaf wooded valley. Never conducive to getting accurate co-ords. For people without Memory Map, I'd suggest using Firefox, downloading greasemonkey, and then OS map amender thing for cache pages. As this also lets you have WGS84 readings for 1:25,000 maps as per my post over here on this linky.

[+molfrew-mosstoad]

Why not put the GE coords into your gps and see how close it takes you to the cache site yourself, then you will see how accurate or how far out they compare?

[+Simply B]

The latest release of GSAK (7.2) has Google Maps integrated into it, so you could use that for a quick sanity check. I can now see at a glance where your multi will be taking me!

 

You could also try using the Magic site. The link below shows your cache's starting point. Use the box below the map to zoom in to 1:2500 scale, then the first tool above the map to click exactly where your point is to see its OS grid reference. You'll need to convert back to WGS84 lat & long, but this should still be accurate enough for that warm fuzzy feeling that you do care about the sanity of your fellow cachers. (Something I've often questioned while doing some of yours...)

 

http://www.magic.gov.uk/website/magic/view...ridref=SJ837983

[+Birders]

Anyone who has tried viewing caches using the GC link to Google earth would immediately bin GE. The positions change every few seconds so, IMHO, there is no accuracy at all. GPS is the only sensible method of locating/ laying caches. Just consider this - would you prefer an airline pilot to get you to destination using his electronics..... or GE on his laptop??!!

[Deceangi]

Anyone who has tried viewing caches using the GC link to Google earth would immediately bin GE. The positions change every few seconds

 

This is a piece of deliberate coding by GC, as Geocaching is a GPSr based hobby.

 

And it clearly states in the guidelines

You as the owner of the cache must visit the site and obtain the coordinates with a GPS. GPS usage is an essential element of geocaching

 

The word must means it's not open to Reviewer discretion so is mandatory.

[+Stuey]

Don't assume the google maps are correctly calibrated. I adjusted the co-ords on one of my own caches once (now archived) when I noticed that the co-ords were on the wrong side of a bridge when plotted on a 1:25000 Ordnance Survey map. First finders all mentioned that the co-ords took them to the wrong side of the bridge, so I used the co-ords from my GPS as I had done originally.

 

I was surprised that the OS was a bit out, but it's inevitable when you think about it.

[+FollowMeChaps]

Anyone who has tried viewing caches using the GC link to Google earth would immediately bin GE. The positions change every few seconds so, IMHO, there is no accuracy at all. GPS is the only sensible method of locating/ laying caches. Just consider this - would you prefer an airline pilot to get you to destination using his electronics..... or GE on his laptop??!!

 

But if you cut/paste the actual coords it doesn't jump around but is spot on! As Decanci says the icons are deliberately offset - though for the life of me I can't really understand why - they didn't used to be and as you can cut/paste anyway I don't see the point of doing so!

 

I go with both sides of this debate:

 

1) GE is a BRILLIANT tool for cachers (but only in the areas where it has high definition - for example it's currently useless in Snowdonia or the Isle of Man) and I often use it to check my coords, etc. I have even used it setting one of my caches to find a target in a dense woodland when I didn't know where it was. I also often used GE in this way to see if I can locate a cache using just GE - originally when my gps was off for repair but since for fun - or giving newbies who don't yet have a gps a chance to have a go.

 

2) Yes you MUST visit the site with a gps when setting a cache; not only is it the rules but it makes total sense as we are creating a gps game.

 

FMC

[+keehotee]

Perhaps Groundspeak could set up a new site for Googlecaching......... and stick all those bl876y armchair virtuals on it too

[+Team Sieni]

It would seem that a lot of these answers are on a matter of principle - that Geocaching co-ordinates should be obtained with GPS because them's the rules - rather than practicality.

 

That's entirely fair enough, Geocaching is a game, and has rules we should follow. As Deciangi says - the rules are not discretionary on this point.

 

That said, GE is a superb tool, and I have often noticed that if GE show a GPS reading to be away from where I thought, then the GPS reading does indeed turn out to be duff. We are all aware of the limitations of the consumer GPSrs that we use.

 

So it would seem that the best way to use GE (and other tools like GMaps, Fugawi etc) in Geocaching would be to double-check your GPS-obtained co-ordinates are where you think. If GE puts you co-ords 50m out, don't publish. Go back to the site and take another reading, or, better still, a set of readings. This is the approach I have often taken with GPS readings (not in a Geocaching context).

[+jerryo]

It would seem that a lot of these answers are on a matter of principle - that Geocaching co-ordinates should be obtained with GPS because them's the rules - rather than practicality.

I disagree. It's the best way to do it and I can't see what all the fuss is about with inaccurate coords.

 

4 ish steps for better caching:

 

1) Hide cache

2) Mark coords

3) Retire a good few metres - or out of the trees etc

3) See if you can find the cache with your own GPSr

3a) Remember this is how other people are going to do it.

4) Repeat steps 2-5 if not satisfactory.

 

I've never had any problems.

[+J10fly]

I just recently started using my iPhone to cache with. I actually have an offline database of all the local caches on it to load faster so I dont have to go online unless I really need to, but anyway, google earth is standard on the iphone and I have been using it while out there to get a general idea where the cache is but i still depend on my gps to get me to GZ.

 

Jayman

[+Moote]

It would seem that a lot of these answers are on a matter of principle - that Geocaching co-ordinates should be obtained with GPS because them's the rules - rather than practicality.

I disagree. It's the best way to do it and I can't see what all the fuss is about with inaccurate coords.

 

4 ish steps for better caching:

 

1) Hide cache

2) Mark coords

3) Retire a good few metres - or out of the trees etc

3) See if you can find the cache with your own GPSr

3a) Remember this is how other people are going to do it.

4) Repeat steps 2-5 if not satisfactory.

 

I've never had any problems.

Maybe a point 5 is a good idea

 

5] Go home and revisit a few days later, using GPS to find from scartch

[+Team Sieni]

It would seem that a lot of these answers are on a matter of principle - that Geocaching co-ordinates should be obtained with GPS because them's the rules - rather than practicality.

I disagree. It's the best way to do it and I can't see what all the fuss is about with inaccurate coords.

[...]

I've never had any problems.

 

Well, no one's saying you have to validate your GPSr co-ordinates with GE (or any other computer cartography tool) if you have a theological objection to it. Just that it might be a handy idea, that's all.

 

I've certainly done more than one cache that had to have its co-ordinates corrected - sometimes quite significantly - after initial publication. A quick double check on MM, or Fugawi, or GE or whatever may possibly have saved this. ... Or may not. Who knows?

[+Pieman]

Thanks for all the suggestions. Just to make it clear- I am not suggesting not using a GPS to set caches! I saw GE as a way of checking that my coordinates were reasonable and where a little out because of high buildlings amending them slightly. To answer Keehotee's point, where you have high buildings you get all kinds of variable effects that increase the inaccuracy of the GPS- it doesn't normally just lead you to a point 40ft away from the right location for instance, so anything that helps give the right coordinates will help someone on the ground with their GPS. They may still have a huge error, but at least it is around the right point!

 

I think my question has been answered in that GE is very accurate to judge from the responses and as such has value in amending coordinates in some circumstances.

 

To answer Moote, I'll be straight on to ebay for that sextant.

[+Team Sieni]

To answer Moote, I'll be straight on to ebay for that sextant.

There's a German company called Astromedia who do cardboard ones. Only £18! cheaper than a GPSr

http://www.green-witch.com/acatalog/Working_Model_Kits.html

Edited January 13, 2008 by Team Sieni

[+Master Mariner]

I'll be straight on to ebay for that sextant.

 

You will also need:

1. Experience in removing or minimising the errors in the sextant

2. Nautical Almanac Data

3. Sight reduction tables

4. Nories Tables (or equivalent) if you are not going to use sight reduction tables

5. A highly accurate watch chronometer

6. A mercury bath to create an artificial horizon

7. Knowledge of navigation for using a sextant.

 

I suppose that there is software available today that does away with items 2 to 4.

 

The last time I used a sextant was just as GPS was being introduced to Merchant ships and was prior to 1984. The tables, formulae, etc that I used to use were not based on WGS84 but on the assumption that the earth was a sphere. Can anyone tell me if the formulae that is used today, for celestial navigation, is for WGS84 and point me towards it?

 

Did sextant development stop with the readily available GPS system?

[+Archer4]

I'll be straight on to ebay for that sextant.

 

You will also need:

1. Experience in removing or minimising the errors in the sextant

2. Nautical Almanac Data

3. Sight reduction tables

4. Nories Tables (or equivalent) if you are not going to use sight reduction tables

5. A highly accurate watch chronometer

6. A mercury bath to create an artificial horizon

7. Knowledge of navigation for using a sextant.

 

 

That'd be easier than a lot of his previous ones

 

We were hoping to start your Manchester Invasion Multi today (it's going to take a while at toddler speed ) but didn't get out of the Lowry soon enough. I'd printed out the bumph last night and as well as the GSAK street level map I also found that there was an A-Z map demo with my copy of Memory Map which happens to exactly cover the area. The waypoints are flagged differently on each so it'll be interesting to see which, if either match up with GZ...

[+Pieman]

 

That'd be easier than a lot of his previous ones

 

We were hoping to start your Manchester Invasion Multi today (it's going to take a while at toddler speed ) but didn't get out of the Lowry soon enough. I'd printed out the bumph last night and as well as the GSAK street level map I also found that there was an A-Z map demo with my copy of Memory Map which happens to exactly cover the area. The waypoints are flagged differently on each so it'll be interesting to see which, if either match up with GZ...

That's the cache where I have noticed this. I also noticed the odd thing with Memory map that you mention. I haven't checked which turned out to be more accurate.