Some Very Newbee Questions

[+Black Hat Guy]

I have never been able to figure out the diference between WGS84, UMT and Lattatude/Longitutd. Is there a way to convert these? Which is used these days on the USGS topo maps?

 

Thnaks.

[+hoovman]

Check the glossary here for the "datum" and "WGS84" entries.

 

Most GPSr's are set to use WGS84 by default, as are caches on the site.

 

[+Black Hat Guy]

Thanks Hoover, but I would still like to figure out how to convert WGS84 datum into Lat and Long so I can cache using orientering skills too.

[+DustyJacket]

quote:

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Originally posted by looneyman:

Thanks Hoover, but I would still like to figure out how to convert WGS84 datum into Lat and Long so I can cache using orientering skills too.

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You are confused WGS84 is a datum. Geocaching.com and GPS units use Lat/long, but with the newer datum.

 

My area topo maps use NAD83 which is extremely close to WGS84. Others may use NAD27.

 

You can convert coordinates here:

http://jeeep.com/details/coord/

 

DustyJacket

...If life was fair, a banana split would cure cancer.

[+brad.32]

Longitude and latitude coordinates are used for a geographic coordinate system, which are locations on a 3D spherical surface, not a projection. The spheroid is based on a datum. The spheroid defines the shape and size of the surface and the datum defines the position of the spheroid relative to the center of the earth. The datum is a frame of reference (the origin and orientation).

 

Early datums were local and not based on the center of the earth, but a particular area on the earth. NAD27 is/was designed to fit North America, particularly Kansas. NAD27 is based on the Clarke 1866 spheroid, which was based on the best surveying measurements and calculations of the day. NAD83 is based on the GRS1980 spheroid, which is an earth-centered spheroid derived from ground and satellite data. The GRS1980 and WGS1984 spheroids are almost identical, so the WGS1984 and NAD1983 datums (both earth-centered) are very similar.

 

A projection uses coordinates on a flat, 2D surface. These projected coordinates are calculated from a transformation of the 3D surface into the flat surface. The spheroid and datum define the shape if the 3D surface. The projection defines the transformation. The flat surface is usually a cylinder (Mercator and UTM) or a cone (Albers Equal Area), but sometimes a plane.

 

[This message was edited by brad.32 on March 17, 2003 at 02:37 PM.]