[Therion] standard deviation and survey grade

Bruce Mutton bruce.mutton at paradise.net.nz
Sun Nov 16 09:48:01 CET 2008

Just want to check on the recommended way to manage survey accuracy within


I have a hierarchal dataset with a three cave system, set up with index and
configuration files so that I can compile any individual or combination of
the caves.  I'm about to expand the dataset to accommodate perhaps a dozen
caves, and many more minor holes / karst features.  Likewise they will need
to be compiled individually or in sets.  To date I have not included 'grade'
or 'sd' statements in my survey.th files, except for 'sd' statements where I
know the survey quality is really poor.


Recently I have put together a single top level grades.th file, and
referenced this in my top level index files only. 


I assume that the 'correct' way is to apply a grade statement(and infer
plumbs on/off) in each and every low level survey-endsurvey block.


Instead, I have cheated perhaps, by adding a grade statement (and infer
plumbs on) to AllThreeCavesSystemINDEX.th.  If I then add a grade statement
in one of the sub-surveys, am I potentially changing the grade applied by
Therion to the whole cave system?


I'm not sure, but I seem to be getting odd results, in that the corrections
applied to different parts of loops do not seem to respond to changes as I
expect.  I'm not sure of the scope implied by the last sentence in this
extract from the Therion Book.



grade <grade list> . Sets standard deviations according to the survey grade
specification (see grade command). All previously specified standard
deviations or grades are lost. If you want to change an SD, use the sd
option after this command. If multiple grades are specified, only the last
one applies.



Any suggestions on where I should be putting grade statements?


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