Mag dec from date. was Re: Survex 1.1.1 test version uploaded

[Michael Lake]

Wookey wrote:
> No-one is arguing that the ability to specify explicit
> calibrations/declinations should be removed or overruled - we're looking at
> ways to more conveniently specify that data (i.e. in one place, not hundreds
> of time in loads of files), and/or to use models to pick better defaults,
> when no calibs are provided.

I follow that. One would just need to make clear if a global setting 
overrides or not a local one - I presume a local one ( *calibrate 
declination -12.0 ) would take precedence. The reason is that a global 
setting probably comes from 'interpolated data' whereas a local 
calibration may have come from a field measurement on that date.

Perhaps a text file that sets specific dates with known declinations for 
the global data e.g.:

; Declinations from Aust Govt data for Yaggangobilly Caves
2004.10.01 
-11.0 

1997.06.06 
-11.2
1985.01.01 
-11.8 
	
1980.01.01 
-12.0

It would use whatever format was in use for the date and declination by 
default and could be loaded via a command line option.

cavern --with-global-declinations=my_decs.txt

Mike