The native format for points in the GPS receiver is WGS 84, a Latitude/Longitude format. Since this is not compatible with X,Y,Z of CAD programs, they are converted to one of many Cartesian (X,Y,Z) formats available around the world. In the "Grids and Units" tab of Preferences you specify the Output Datum and Units for the converted points.

 

There are several Units available to choose from: 

• INT_FOOT - an International Foot, which is defined as 0.3048 Meters
• US_FOOT - used primarily with American projections, especially the State Plane Coordinate System. The US_FOOT is defined as 0.304800609601 Meters or (1200/3937 ) x Meters
• METERS - The native format of the GPS. It is also the standard measurement for UTM grids
• IRISH_FOOT - used with surveys in Ireland. Defined as .3048007491 Meters

 

It's IMPORTANT to understand that these four UNITS are used to convert the GRID COORDINATES shown when the program receives the points from the GPS unit. The numbers affected by these units are those in the "As CAD Points" column of the grid.

 

There is another Units drop-down box shown with the "Direction Distance" grid of the main program window. These units affect only the measurements in the Direction Distance grid. More on this can be found here.

 

The output grid should be selected by clicking on the desired "node". When available, comments regarding each datum appear in the "Comments" box. The Datums have been organized into "American Projections", "European Projections", "Pacific Projections", and "Universal Projections". These are our designations for simplicity, and carry no other special significance. A complete list of the supported datums is listed here. However here are some simple guidelines:

 

• UTM_NAD_27, UTM_NAD_83 - these are Universal Transverse Mercator projections based on either the North American Datum 27 or 83. Use these when you know you're trying to match up a specific projection.
• SPCS_27, SPCS_83 - These are the U.S. State Plane Coordinate System, based on either NAD 27 or NAD 83 datums. Note that you must know which State Zone the points on the GPS are in, and select that zone (since the state zones are so irregular, it is virtually impossible to derive them from the Point's Lat/Long). If you don't know the zone, find out before using the program. Note that ALL THE POINTS MUST BE WITHIN THE SAME ZONE! because the coordinate system of each zone is repeated.
• Universal Projection\UTM_NORTH - this is a simple WGS 84 datum for use in the Northern Hemisphere. If you don't have any other special requirements, and the points are in the Northern Hemisphere, try using this. If you're in the Southern hemisphere, choose UTM_SOUTH.