Wgs84

[+MDAgent]

I did a search for WGS84 and Datum, but found nothing difinitive. Is there a geocaching standard for GPS settings?

 

This also goes to my other question about the difference between True North and Magnetic North.

 

What are the geocaching standard settings? and how much does that actually effect the accuracy?

[flir67]

alot of the geocaches are in wgs84. if not then most users post the datum(utm,nad83,etc) and then the coordinates. just change the datum in your gps and go with the new coordinates,easy as pie once u do it a few times. just make sure your on the same datum or you will end up driving for a very long time or in the wrong place.

 

good luck

 

flir67------

Edited April 21, 2005 by flir67

[+MDAgent]

I have done fine so far, leaving my eXplorist 500 on WGS84 all the time. But if there is not a geocaching standard, I wonder why there isn't.

[+EraSeek]

I did a search for WGS84 and Datum, but found nothing difinitive. Is there a geocaching standard for GPS settings?

 

This also goes to my other question about the difference between True North and Magnetic North.

 

What are the geocaching standard settings? and how much does that actually effect the accuracy?

Use WGS84 for your datum, unless otherwise specified. Use Degrees, Minutes, Decimal Minutes (such as W 122 48.366) unless there is some reason to use some other format. True and Magnetic north are different. Where I am magnetic North is 18 degrees east of True North. But which one you use in your GPS does not matter unless there is some specified reason for one or the other. True points to the North Pole, Magnetic points (like your compass) to Northern Canada.

 

When using a compass in conjunction with your GPS you want to either adjust your compass to match true, or adjust your GPS to match Magnetic so both are on the same page.

[+New England n00b]

WGS84 is the geocaching.com standard. However, some choose to use a different datum.

 

The reason for this, which is what I think you are asking for, is they usually want to present a somewhat different hunting experience. Much like there are puzzle caches, multicaches and so on - a different take on the same thing.

 

For what it is worth, if you enter a coordinate into your GPS, and switch back to WGS84, the GPS should convert the numbers so you are going to the same place.

 

Older units may not do this, and if you tell us what unit you have, some knowledgeable GPSr folks should set you right for your receiver.

[+Sputnik 57]

I'll just throw out that if you are using a USGS paper map to help you out, they generally use NAD27 instead of WGS84. If you are trying to plot your position on the map, flip your datum to NAD27. Then, to find the cache, go back to WGS84.

[+MDAgent]

I'll just throw out that if you are using a USGS paper map to help you out, they generally use NAD27 instead of WGS84. If you are trying to plot your position on the map, flip your datum to NAD27. Then, to find the cache, go back to WGS84.

The only map I've been using is the map that is pre-loaded in my eXplorist 500. But this is a good tip for me to remember in the future.

 

If I understand everything I've read: If a person marks coordinates and records them using True North, and another person navigates to those coordinates with thier GPS set on Magentic North, they will arrive at the same point.

 

But if someone says "start at X coordinates and travel 5 miles North, the person using True North and the person using Magnetic North will end up at different places.

 

Am I right?

[+Renegade Knight]

...If I understand everything I've read: If a person marks coordinates and records them using True North, and another person navigates to those coordinates with thier GPS set on Magentic North, they will arrive at the same point....

But if someone says "start at X coordinates and travel 5 miles North, the person using True North and the person using Magnetic North will end up at different places.

 

Am I right?

Yes.

 

A set of coordinates are defined by the WGS84 Standard. By default the standard uses True North. However when you tell your GPS to go to that waypoint it points at the waypoint. True vs. Magnetic doesn't matter. You also can't set a waypoint with "magnetic north" it's not built into the WGS84 standard.

 

But if you start at a known point and go 5 miles north and one uses magnetic, one uses true you end up at different locations just as you suspect.

[+planemaker]

I did a search for WGS84 and Datum, but found nothing difinitive. Is there a geocaching standard for GPS settings?

 

This also goes to my other question about the difference between True North and Magnetic North.

 

What are the geocaching standard settings? and how much does that actually effect the accuracy?

Use WGS84 for your datum, unless otherwise specified. Use Degrees, Minutes, Decimal Minutes (such as W 122 48.366) unless there is some reason to use some other format. True and Magnetic north are different. Where I am magnetic North is 18 degrees east of True North. But which one you use in your GPS does not matter unless there is some specified reason for one or the other. True points to the North Pole, Magnetic points (like your compass) to Northern Canada.

 

When using a compass in conjunction with your GPS you want to either adjust your compass to match true, or adjust your GPS to match Magnetic so both are on the same page.

True North to Magenetic North depends on where you are on the planet.

 

The magnetic meridians do not coincide with the true meridians because the north magnetic pole does not coincide with the true (geographic) pole. Avver avereaged over a thousand years the position of the magnetic pole will roughly conincide with the true (geographic) pole, however they can (and are now) be very far apart. In 1999 the north Magentic pole was 1,200km (750 miles) south of the Magnetic Pole.

 

Variation depends on where you are on the planet. They draw Isogonic lines on maps to join areas that have the same variation.

 

To Convert True and Magnetic Headings (In the northern hemesphere only!):

 

Magnetic to True

Westerly Variation Subtract

Easterly Variation Add

 

True to Magnetic

Easterly Variation Subtract

Westerly Varation Add

 

An easy way to remember this is: Variation West, Magnetic Best, Variation East, Magnetic Least.

 

For example:

To convert a magnetic bearing of 80 deg to a true bearing when the varation is 10 deg West:

 

80-13 Deg W=True Bearing of 6 deg

 

In Oshawa the varation is 11 degrees west.

 

I hope this helps!

[dsandbro]

A shareware program for calculating the magnetic declination for any point on Earth for any date.

 

http://www.interpex.com/geomagix/magfield.htm

 

Declination does change over time. A rough rule of thumb is 1/2 degree over ten years, but it varies across the country. If your source is twenty years old (many topo maps have not been updated in that long or longer) then the published declination can be in error significantly.

 

Aeronautical sectional maps are updated every six months with current declination. If you know a pilot, ask to see his charts.

[+Runfrog]

I do believe that all Caches are WGS 84. It has repleced WGS 83 adn I'm not sure there is a big difference. Seems that I have found them both ways. But, I'll have to check, I can display both at the same time.

[dsandbro]

I do believe that all Caches are WGS 84. It has repleced WGS 83 adn I'm not sure there is a big difference. Seems that I have found them both ways. But, I'll have to check, I can display both at the same time.

NAD83 and WGS84 are so close together the difference is way out in decimal-place land of a meter. For all practical intents and purposes you can use them interchangeably.

[+Sputnik 57]

NAD83 and WGS84 are so close together the difference is way out in decimal-place land of a meter. For all practical intents and purposes you can use them interchangeably.

NAD27, on the other hand, can be 100 meters off of WGS84. If you have your GPSr set to NAD27 for whatever reason when you enter the coordinates, you'll likely have a very hard time finding the cache.

[+MDAgent]

Variation depends on where you are on the planet.  They draw Isogonic lines on maps to join areas that have the same variation. 

 

To Convert True and Magnetic Headings (In the northern hemesphere only!):

 

Magnetic to True

Westerly Variation Subtract

Easterly Variation Add

 

True to Magnetic

Easterly Variation Subtract

Westerly Varation Add

 

An easy way to remember this is:  Variation West, Magnetic Best, Variation East, Magnetic Least.

 

For example:

To convert a magnetic bearing of 80 deg to a true bearing when the varation is 10 deg West:

 

80-13 Deg W=True Bearing of 6 deg

 

In Oshawa the varation is 11 degrees west.

 

I hope this helps!

Ok, well all that math is confusing - which is kinda why I ask the question in the first place. It's much easier if I can just use WGS84 and True North and not worry about it.

Edited April 21, 2005 by MDAgent

[+Thot]

Ok, well all that math is confusing - which is kinda why I ask the question in the first place. It's much easier if I can just use WGS84 and True North and not worry about it.

I use WGS84 and Magnetic North and don’t worry about it unless I get instructions in the cache description to do something different.

 

Occasionally you may want to use a compass with the bearing your GPSr gives. Since a compass uses Magnetic North you want your GPSr to give you bearing in Magnetic North.

[+MDAgent]

Occasionally you may want to use a compass with the bearing your GPSr gives. Since a compass uses Magnetic North you want your GPSr to give you bearing in Magnetic North.

That's a good tip. Using Magnetic North, I can always double-check it with a compass.