Reply To: Need help with GIS data conversion to NAD83

[Steven Callaghan]

How many points are you converting?  100, 200, 5000????  The etrex collects data in Latitude-Longitude, WGS84 only…the data can then be converted from the coordinate system to any other coordinate system on the fly in the etrex…btw this is the abbreviated explanation.   However, the etrex is not very robust when converting coordinates… NADCON is the standard software used by the US government for converting coordinates from Lat-Long to NAD83…However you need 2 more pieces of information…the AutoCAD drawing is probably in a NAD83 State Plane Zone Projection.  It is also in a “unit.”  This unit is feet, meters, etc.  You do not mention the State Plane Zone in your post, you only mention NAD83.  Find out what the drawing units are in the AutoCAD drawing.  Pure NAD83 uses GRS 80 Lat-Long, essentially a spheroid…difference between GRS80 and WGS84 is insignificant for what you are doing…NAD83 projected coordinates, aka State Plane Zones, convert Lat Long to x,y, or northing, easting using lots of mathematics.  NADCON converts your lat longs to the appropriate State Plane Zone in the units you choose, feet or meters.  ESRI ArcGIS uses this in the background.  However there are more rigorous and accurate ways of handling the conversion other than using NADCON…NADCON needs to be configured for the appropriate coordinate system and format, degrees, minutes, seconds, or decimal degrees for the input of the lats and longs, and then the output coordinate system needs to match your AutoCAD drawing, and an example would be NAD83, Alaska State Plane Zone 4, US Survey feet.  NADCON has the option to batch process a text file or individually convert a single point,  if it is less than 100 points, might as just individually convert each one.