Dear all, I am a brazilian cave topographer and I am developing a methodology of planimetric trilateration for magnetic influenced caves (Brazil has thousands of caves in iron formation rocks). These surveys only use tape and clinometer, surveying triangles, starting from two coordinates known stations. I have been able to calculate coordinates for all the stations and predict specific cartesian standard deviations for each leg, and prepared both normal and cartesian output that can be read by Therion (I suppose that by Survex too, although I am not a Survex user). Is there a way to specify specific standard deviations for each leg in Therion? I understood that the SD command is only for surveys, isn´t it? Because of trilateration a complex triangle network is created in this kind of survey and it will be very useful to close them in a least Squares algorithm, such as Therion´s. I am sorry if this is a too basic question, but I got stuck in this. Regards, Marcelo Taylor Cel: +55 21 9 9344 5196 marcelo.taylor@gmail.com
Hi Marcelo,
These surveys only use tape and clinometer, surveying triangles, starting from two coordinates known stations.
That's ... both cool and insane at the same time. Pretty sure a Total Station can cope with this magnetic rock situation. Perhaps someone else on this list can offer advice...
Is there a way to specify specific standard deviations for each leg in Therion?
As far as I know, SD affects all legs specified after it, until another sd command changes it. Similar to the "calibrate" command or "units" command. sd compass 0.3 degrees 1 2 12.5 315 17 sd compass 0.5 degrees 2 3 7.2 220 33 It is a Survex command (most things inside a Therion centreline block are a direct copy of their Survex equivalents, and can be passed through to Survex for processing; group/endgroup is an exception, which is begin/end in Survex syntax). I tested it with a loop where every leg is set to sd 0.1, but one single leg set to 200. Therion gave that single leg most of the error. If that doesn't work for you, you can use: group sd compass 0.3 degrees 1 2 12.5 315 17 endgroup group sd compass 0.5 degrees 2 3 7.2 220 33 endgroup It's quite verbose, but that is explicitly stated as being possible in the Therion book. Hope this helps. Tarquin
participants (2)
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Marcelo Taylor -
Tarquin Wilton-Jones