Backsights and default accuracy estimates

[Andy Waddington on Survey stuff]

> 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

And how does Survex deduce which of the two readings is which ? It would
seem to depend on the ordering of the legs to deduce which "direction"
the survey is going, but one of the nice things about Survex is that
you can reorder the survey legs for easier human comprehension without
affecting the output. This would destroy that. (For instance, if you
break off surveying a main line to look up an inlet, find it doesn't
go, and survey back to the main line, it is often easier for the human
reader of the data to put the legs into the opposite order, and perhaps
at a later point in the file, so the main line is all together. I often
used to do this sort of thing in old datasets).

Additionally, if both foresight reader and backsight reader are
leapfrogging, you need to have some sort of tag to identify which reading is
which. It is more important to identify which calibration applies, rather
than which sight is arbitrarily considered the "foresight" and which the
"backsight".

Andy