Re: [Therion] Cartesian STD for individual legs
*Hi Marcelo,* Hi Tarquin, thanks for your kind answer.
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.* I believe that a typical speleological topographer thing: being a little bit ingenious and a lot insane... *Pretty sure a Total Station can cope with this magnetic rock situation.Perhaps someone else on this list can offer advice...* For sure, but total stations are expensive, cumbersome and time consuming. Our idea is to provide a cheap fast way to deal with magnetic anomalous caves..
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.* Thanks for the suggestion, I will try it for sure. Nevertheless I will prefer to use cartesian data and dX, dY and dZ notations. It is because transversal and longitudinal expected errors are very different in trilateration methodology and I have been able to estimate it in cartesian coordinates. I am a little worried if it will also work in "leap-frogging" legs, but I will check it, for sure. *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.* I will try this option too. Right now, that calculations have been done in an Excell spreadsheet,it is verbose, for sure. But the idea is to include in our TOPGRU software package (https://see.ufop.br/topgru) in the future. So, after coding, it will only lead to larger lines centerline blocks, that can be copied directly into Therion. TOPGRU right now is only in portuguese and have a more educational characteristics, but one of our 2021 goals is to release an english version and maybe moving it to GNU compliant. *Hope this helps.* It helped a lot, Tarquin. Many thanks. Marcelo Taylor Cel: +55 21 9 9344 5196 marcelo.taylor@gmail.com
I believe that a typical speleological topographer thing: being a little bit ingenious and a lot insane...
Well indeed. It reminded me of the original UK OS triangulation pillars, but they used angles instead of lengths. Most of us cannot even dream of getting the accuracy they did.
Nevertheless I will prefer to use cartesian data and dX, dY and dZ notations. It is because transversal and longitudinal expected errors are very different in trilateration methodology and I have been able to estimate it in cartesian coordinates.
No problem. If you are using position fixing, you can of course use the inline standard deviation statement. fix 1@surfacelegs 12345.123 23456.234 102.304 0.17 0.24 0.29 And if you are doing it for individual station position: https://survex.com/docs/manual/datafile.htm#AEN1286 sd dx 0.123 metres (Therion uses Survex processing for the statement, so you can see the finer details of its meaning within the Survex manual.)
I am a little worried if it will also work in "leap-frogging" legs, but I will check it, for sure.
There are actually options relating to that. Such as: data normal from to backlength ... etc. now you can set the "sd backlength" differently from the "length". But I think that since "sd dx" relates to the station position, it might only refer to the station you are "leaving" or both stations at once (since it is perhaps better described as "how well you held the tape measure onto the station itself, or whether you allowed the station position to move because it wasn't a fixed object"). Perhaps Wookey can say which stations it really relates to when leap-frogging, or whether it just adds to the overall "this leg has a large error margin" for use when deciding where to distribute errors, rather than being a specific error in each dimension. The latter is certainly a possibility. When I tested, I found that I had to supply sd for more than just the single thing that I was trying to affect. When I tried to specify sd for just compass, it ignored me. When I specified it for length, compass, clino, it worked correctly. Experiment, and see if you need to add sd for the other dimensions.
participants (2)
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Marcelo Taylor -
Tarquin Wilton-Jones