Backsights

[Olly Betts]

On Tue, May 14, 2002 at 08:37:08AM +0100, Graham Mullan wrote:
> | You can set the calibrations, units, and standard deviations for compass
> | and backcompass (and clino and backclino) separately:
> |
> | *calibrate compass 0.5 degrees
> | *calibrate backcompass 0.0 degrees
> |
> | Or if they're the same, you can set both at once:
> |
> | *calibrate compass backcompass 0.5 degrees
>
> This means that you must ensure that each of the two instruments is used
> exclusively  in one direction during the course of the trip. If they are
> swapped at any time (or, as in the 1974 data that I have each set
> "leapfrogged" the other) then this approach is invalid. Previously, with one
> instrument, you just needed to be aware whether a reading was forwards or
> backwards.

You can use the "direction" reading to specify which sight is forwards on each
leg (if you actually recorded the information - if you didn't, then since you
can't tell which readings are which, all you can really do is specify a higher
standard deviation on the clino and backclino).

Or at least you can use "direction" from the next release.  I was adding a test
for it last night and discovered it doesn't currently work because it doesn't
skip the F or B once it has read and dealt with it.  The fix is one line, and
will be in 1.0.9:

*data from to direction tape compass clino backcompass backclino
1 2 F 1.23 102 -01 280 +02
2 3 B 2.21 073 +10 250 -09
3 4 F 4.87 011 -07 190 +07

If you leapfrogged the compass and clino independently, you'll have to swap one
of them round by hand, or split the data into two.  But that wasn't the
situation you described as I understand it.

Cheers,
Olly