[Therion] sd for a vertical pole

[Tarquin Wilton-Jones]

> I guess this could just as easily be a Survex question as a Therion
> question.

Actually, it's not. In Survex terminology, it would be done like this:

*sd length 0.001 metres
*sd plumb 0.125 degrees
gps surveystart 2.000 - DOWN

That is how you are supposed to do a vertical leg with variable
clinometer accuracy and length accuracy, but no compass reading (this is
taken from Survex's "How do I?" article, when talking about a radio
location fix).

In Therion, this generates an error "invalid quantity -- plumb".

sd length 0.001 metres
sd plumb 0.125 degrees
gps surveystart 2.000 - DOWN

So how do you do the equivalent in Therion without being allowed to use
"sd plumb"? Is this a bug in Therion? Does it use clino instead? Can it
pass this to the underlying Survex correctly?

Cheers,

Tarquin

> I have GPS readings taken on a pole, with the position being given for
> the top of the pole. Subsequent Disto readings are taken from the bottom
> of the pole. The pole is brought to vertical using a spirit level. I
> have checked the accuracy of the spirit as being 0.125°.
> 
> I have the (measured) standard deviations of the GPS positions, so I can
> specify the standard deviations for the location fix. What I need to
> work out is how to specify the standard deviation for the pole. It's not
> a plumb measurement, because it is not purely gravitational. So although
> I could use "DOWN" that is not actually accurate, since it is really a
> nearly-vertical measurement depending on the accuracy of the spirit
> level. It's really a length and clinometer reading.
> 
> #length of the pole accuracy measurements
> sd length 0.001 metres
> #accuracy of the spirit level
> sd clino 0.125 degrees
> 
> But when working with a supposedly vertical position, even the slightest
> error in the clinometer angle of the pole could cause the compass
> bearing to flip to any angle at all. But this seems extreme:
> sd compass 360 degrees
> 
> So what would be the right way to specify it?
> 
> Cheers,
> 
> Tarquin
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