[Therion] standard deviation and survey grade

[Martin Budaj]

> What about 'position'?  I don't think the BCRA grades have much to say about
> these.  (I'm sure we can make something sensible up)

First proposal could be:

GRADE; POSITION / HEIGHT error (95% confidence); comment

0             -- position unknown
1  1000 m     -- rough estimate / memory
2  100 m      -- GPS in bad conditions (canyons, foliage, SA), small-scale map
3  15 / 45 m  -- GPS, large-scale map
4  5 / 15 m   -- GPS longer observation, distinct features on a large-scale map
5  1 / 3 m    -- GIS GPS
6  15 cm      -- geodetic GPS, theodolite/total station, technical nivelation
7  5 cm       -- geodetic GPS, precise theodolite/total station,
precise nivelation

Martin