[Therion] equate to non-existant station does not raise error

[Olly Betts]

On Sun, Dec 01, 2013 at 07:52:32AM +1300, Bruce wrote:
> My inference from warnings I get on other occasions is that Survex reports
> fixed stations that are not connected to any survey leg.  I have many of
> these in other files - gps locations of surface features for example.

Yes, Survex will warn about a fixed point which isn't connected to
anything, unless you specify the fix to be a 'reference', e.g.:

*fix big_doline reference 10485 83132 1600

> I imagine the 'equate' part of the processing is different, and in any case
> neither Survex nor Therion are reporting the anomaly when Therion is run.

Survex treats an equate much like any other survey leg for these
purposes, so if you try to equate two points which aren't otherwise
referred to, you'll get an error, e.g.:

The following survey stations are not attached to a fixed point:
a.4

> This is different, and I believe it should be reported by Therion as either
> a warning or perhaps preferably should stop execution.  When equates are
> defined, I would have expected that it would be required that all equated
> stations have been defined elsewhere, and if they are not, it should be an
> exception that should raise and exception or at least a warning.

If at least one of the stations in a *equate command is used elsewhere,
it's OK to "create" stations with a *equate.  This provides a way to
create a nice alias for a station, e.g.:

*equate 4 tip_of_cairn_at_junction

Making this an error would break existing datasets, and adding a warning
would be unhelpful, unless we also provided a good way to suppress it.

But in your original example, you're linking to a non-existent station
in a different survey (if I follow the therion syntax correctly), and
the equivalent situation gets a warning from Survex:

badequate.svx:1: warning: Station "kb.kb51_29" referred to just once, with an explicit prefix - typo?

I think we made this a warning rather than an error because it makes
processing subsections of a large survey (e.g. a single cave) easier.

Cheers,
    Olly