Utm Lat/lon Question

[planewood]

I understand one can enter either type of coordinate into a GPS. But when entering lat/lon is it necessary to also set the datum to WGS84? Also, isn't NAD83 just an old name for WGS84?

 

I guess that since all my work with be in UTM zone 15R and using WGS84/NAD83 that I should just set those in and forget it??

[GeoidPS]

In principle, the three-dimensional coordinates of a single physical point should therefore be the same in both the WGS84 and NAD83; in practice, small differences are sometimes found. (The discussion is technical so go here):

 

http://www.mentorsoftwareinc.com/resource/Nad83.htm

 

If your working with US maps, I think it would more likely then not using the UTM projection from the NAD83 system. However, from the article, it's nothing to worry about if using one or the other:

 

"If such a set of three-dimensional Cartesian coordinates is converted to latitude and longitude using the two coordinate systems, there would be no difference in the longitudes, and the latitude difference would be

 

~ f sin 2Ø/sin1"

 

which reaches a maximum value of 0.000003 second of arc (or 0.0001 meter) at a latitude of 45 degrees. It is assumed that most users will ignore this very small difference."