Mini-Grid Data File Format
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3 columns of data:

Col 1: Latitude

Col 2: Negative West Longitude

Col 3: Elevation in meters. (z is positive upwards) 

Water depths are negative values.  The vertical datum is a unique 
"CBASS Datum" created by Tom Lippmann while hanging in gravity 
boots from his office doorway to sense the location of the geoid.  
CBASS=0 is 11cm above MSL.   Add 11cm to z values in column 3
to get elevations relative to MSL.