[BC] GPS recommendations

[Broadcast List USER]

From: "Alan E. Gearing" <aegearing at tzsawyer.com>
>Only the professional grade GPS units (read costing multiple thousands of dollars) have sufficiently accurate internal conversion routines.

Honestly, it is not a situation of consumer grade and professional  
grade GPS receivers.

It is a matter of GPS alone or using differential signals.

There are basically two kinds of differential signals.  One is the  
transmitters situated at airports and a few harbors.

The second is a commercial unit.  The surveyor places a GPS over a  
USGS marker.  We all know where those are located.  It then has a  
signal it sends to the other GPS receiver.  The "error" signal from  
the fixed receiver is subtracted from the other receiver, automatically.

The NAD 27 vs. NAD 83 is basically a non starter.  Why does it  
matter?  It is a very simple conversion.

--chip