It a wonder we can find it at all

[Guest RXQ]

adings were exactly as those listed on Geocache.

 

[This message has been edited by RXQ (edited 04-02-2001).]

 

[This message has been edited by RXQ (edited 04-02-2001).]

[Guest Markwell]

This reply also falls under a different topic covered under the topic at http://forums.Groundspeak.com/ubb/Forum1/HTML/000091.html but I thought it could be answered here...

 

When I go to the MapBlast website and key in an address, the system gives me the coordinates in decimal format (35.123456, -85.123456). I understand that positive latitude is N and negative longitude is W.

 

How do I convert those decimals to data used in WGS-84 (e.g. N 41° 48.985 W 088° 08.691)? Is the decimal version UTM?

 

HELP! I'm confused!

[Guest bacpac]

quote:

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Originally posted by RXQ:

It a wonder we can find it at all

 

Who is right when it comes to coordinate translations.

 

I recently came back from a cache and from my notes, found the following discrepancies in the coordinate translators provided by the this web site and my Garmin GPS12.

 

Notice the differences when it come to UTM (NAD27)

 

 

Geocache N 42° 50.556 W 071° 39.368 (WGS-84)

 

GPS12 N 42° 50' 33.4" W 071° 39'22.1" (WGS-84)

 

...

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In the first two sets of coordinates you have posted in two different formats.

 

Set your Garmin12 to Hddd mm.mmm format. This is the format used by GeoCaching.

 

The format you posted on your GPS12 coordinates was hddd mm ss.s.

 

These are similar, but not the same. I suspect the other variations were a result of this problem too.

[Guest bacpac]

Markwell,

 

Your GPS should display in several different formats. The confusion is how each format is converting minutes to the decimal equivalent.

 

35.123456 = 35 degrees and (.123456 X 60) 7.40736 minutes

 

or

 

35.123456 = 35 degrees and 7 minutes and (.40736 X 60) 24.4416 seconds.

 

Let the GPS do all the calculating for you. Just be very careful to match format and datums when checking against different maps and geographic sources.

 

Make sure Apples = Apples and not Apples = Pineapples.

[Guest bob_renner]

First the coordinate system and the datum are two different things. You need both to specify a location.

 

Two of the major coordinate systems are degrees and Universal Transvers Mercator (UTM). The degree system is probably better known to more people. It consists of dividing the earth up into 360 degrees of longitude (180E and 180W), and 180 degrees of latitude (90N and 90S). There's only 90N/S since any further would overlap the other side of the globe.

 

Each degree can be subdivided into smaller parts in several ways. Decimal degrees just uses tenths, hundredths, thousandths, etc.

Other ways are minutes (60 per degree) and minutes/seconds (60 min/deg and 60 sec/min).

 

To convert decimal degrees to deg/min, take the decimal portion and multiply by 60.

 

35.123456 deg = 35 deg (.123456 x 60) min

= 35 deg 7.40736 sec.

= 35 deg 7 min (.40736 x 60) sec

= 35 deg 7 min 24.4416 sec

 

UTM is very different. It takes a N/S strip of the globe and calls it a zone. Each zone is about 6 degrees wide (I may be wrong on the width). The position within the zone is measured in meters east of the center of the zone (eastings) with the center having an easting of 50,000. West of this would have a smaller number.

 

The N/S location is also measured in meters with the equator having a similar offset. The grid is therefore always square rather than converging the farther north you go from the equator like degrees. However, the grids tilt from true north the farther away you get from the center of the zone, and they bend at the junction of two zones.

 

The datum (e.g. WGS84, NAD27) is used to define the placement of these grids on the earth. Think of them as defining the origin of the coordinate system (center of the earth), where the zero degree or first UTM zone is located, and the shape of the earth - it's not a sphere.

 

The GPS will convert from one to the other for both coordinate and datum. Just make sure everything matches when you are entering the values from the cache page.

 

Hope this helps rather than confuses.

 

Bob

 

[This message has been edited by bob_renner (edited 04-02-2001).]

[Guest RXQ]

Bacpac,

 

What I did was entered the Geocache coordinates into my GPS12 and changed formats and noticed that the coordinates where different form those offered by the links from this web page. I posted different formats to show that Jeep.com and Topozone.com show different results when the Geocache coordinates are translated into different formats. That these results are different then those of my GPS12.

 

So whose translator is correct when changing formats?

 

Has anybody else notice a difference between your GPS coordinate translator and the ones on Jeep.com and Topozone.com?

 

I also noticed, that people are having trouble finding cache when they translate the coordinates to UTM(NAD27).

 

Pineapples are not apples, because they don't grow on trees.

 

 

[This message has been edited by RXQ (edited 04-03-2001).]