1st time failure--disparity between GPS and Google?

[gandrin]

We just tried our first trip ever, at parks very close to our own house in Greater Philadelphia. The GPS coordinates for all three items (3 different cachers) were wrong on my Magellan Roadmate 2000, but perfect on Google Maps. This is not subtle--our GPS put us about half a mile away from the park each time. It was impossible to search with the GPS.

 

So, is this a problem with my GPS or with google maps? My GPS has been extremely reliable and I've used it a ton for driving, so if its coordinates are wrong they are self-corrected within the device. So does that mean Google maps are wrong, and people are posting with them? I am confused.

 

Bad problem to have for a first timer... Luckily we knew the parks and did it without the GPS, but the experience was poor (couldn't get close to one well-hidden cache and had to give up.

[Motorcycle_Mama]

Are you sure you used the correct coordinate format?

[gandrin]

Are you sure you used the correct coordinate format?

 

I was just simply opening up the GPS screen that displays current position. The coordinates are of the same format as the posting (i.e. N 39° 59.090 W 075° 17.145), although there were only 2 digits after the decimal point (N 39° 59.09 W 075° 17.15)

 

Ooohhhh, wait a minute....

 

I'm an idiot. My GPS is in seconds, not decimal minutes. And I just found the conversion thingy. Any way to make the main page list the coords in MM SS instead of MM.MMM?

[+Cardinal Red]

Are you sure you used the correct coordinate format?

 

It seems they're GC nubies. They probably don't even know what a format is.

 

You should be using HDDD MM.mmm format.

 

NOT the HDDD.ddddd format or the HDDD MM SS.s format.

 

Are you using the WGS84 Datum?

 

You should check out the SEPAG (SouthEastern Pennsylvania Geocachers) Forums for more local help.

[jholly]

 

Ooohhhh, wait a minute....

 

I'm an idiot. My GPS is in seconds, not decimal minutes. And I just found the conversion thingy. Any way to make the main page list the coords in MM SS instead of MM.MMM?

 

Perhaps you asked the wrong question. Maybe the correct question is how to change the display format on your GPS to match the GC.com page.

 

Jim

[+clevek]

Once you get the display format set to the listed coordinates you are seeking you'll hopefully get closer to finding a hidden cache. I have found that my Garmin NUVI used in the car does not work too well for geocaching. The newer hand held GPSr's today work much better for this sport. You should be able to pick up a nice entry level high sensitivity model for less than $139.00, take care and keep on caching!

TKAKOC

[4wheelin_fool]

Are you sure you used the correct coordinate format?

 

I was just simply opening up the GPS screen that displays current position. The coordinates are of the same format as the posting (i.e. N 39° 59.090 W 075° 17.145), although there were only 2 digits after the decimal point (N 39° 59.09 W 075° 17.15)

 

Ooohhhh, wait a minute....

 

I'm an idiot. My GPS is in seconds, not decimal minutes. And I just found the conversion thingy. Any way to make the main page list the coords in MM SS instead of MM.MMM?

There should be a conversion link next to the coords. It probably would be easier to change your GPS to accept the DD. MM.MMM format rather than the other way around.

[+HaLiJuSaPa]

Once you get the display format set to the listed coordinates you are seeking you'll hopefully get closer to finding a hidden cache. I have found that my Garmin NUVI used in the car does not work too well for geocaching. The newer hand held GPSr's today work much better for this sport. You should be able to pick up a nice entry level high sensitivity model for less than $139.00, take care and keep on caching!

TKAKOC

 

That is also true of the Magellan Roadmate mentioned by the OP and most "car" GPSr's. They are designed to work well on the road, but not in the woods. I totally concur with this. Good luck!

[+Annie & PB]

First - change you GPS so that it is using the WGS84 Datum and change you GPS so that it displays the co-ordiantes in the same format as the Geocaching.com website. We use a Garmin GPS so I can not tell you how to do that with a Magellan. But I am sure that someone will be along soon who knows!

 

Then is it is possible - turn the 'road lock' type function OFF. This is a function that will cause you GPS to continue routing on a road, if one is nearby, even though the co-ordiantes you seek are NOT on the road. It will just keep you to the closest bit of road. As your GPS is primarily designed for on-road use, you may, in fact, not even be able to change this setting.

 

After that -- buy a Garmin hand held - because by now you are addicted anyway!!!!!

[+paleolith]

People have mentioned format, datum, road lock, and quality of unit.

 

Quality of unit might be an issue down the line, once you get within 50' of the cache, but would not cause the problems you are seeing.

 

I haven't used a unit with road lock, but I think that might affect it. You should definitely have road lock turned off for geocaching.

 

Datum (NAD27 vs WGS84) can cause discrepancies up to, IIRC, 200m. This is much less than you are reporting, so that's not the cause of your problem. But you should be set to WGS84 for geocaching. NAD83 is equivalent for geocaching purposes (less than 1m discrepancy). Many printed USGS topo maps use NAD27, and this is probably the only time you need it. (Cartographers and other serious users prefer UTM, which among other things has the advantage that one unit on the scale is one meter on the ground. Despite this clear advantage, you'll hardly ever see geocachers using UTM.)

 

The obvious problem, as you already figured out, is the format -- minutes and seconds vs decimal minutes. AFAIK, all GPS receivers use the format setting on input. For display, they are capable of converting the stored data to any setting. If your unit can be set to decimal minutes, that's the best way to go, since geocachers almost always user decimal minutes.

 

Edward