HI Daniel, We had a similar problem on a mine called Speedwell in the UK. Our problem, we found out, was that we had very few points in a straight line of passage leading to a middle entrance of the system. The model we were using had quite long lengths for this part of the survey, so when therion was trying to distribute errors across the whole survey, the least accurate part of the survey it decided was this straight bit of passage. so there was some big distortions. I would ask whether you have entrances or other radio location points on both sides of the siphon. If the radiolocation for one of the sides of the siphon is not accurate then including both radiolocation points could introduce distortion. I would consider not using the radiolocation point on the "entrance" side of the siphon. or if the distance between the entrance and the entrance side of the siphon is small in comparison to the cave, then keeping the radiolocation here and removing the radiolocation on the far side of the siphon. Say your model is: Entrance Grid ref (accurate) ~some normal cave survey (really accurate) *. radiolocation of entrance side of siphon (possibility for error?)* ~siphon survey (really accurate) radiolocation of far end of siphon (possibility for error?) ~some more dry cave survey (really accurate) second entrance (accurate) or distant third radiolocation point. (possibility for error?) I am only suggesting removing one of the radiolocation points because your siphon survey sounds like it's fairly accurate, and as tarquin says not likely to be causing the error. I would think the accuracy of the radiolocation could be the weak link, but i'm no expert with radiolocation. Alastair. On Thu, 25 Aug 2022 at 07:51, Daniel Chailloux <danielchailloux@orange.fr> wrote:
Hi,
We are facing a problem with Therion and fixed points obtained by radiolocation.
This is the survey of a very long siphon taken with the SeaCraft ENC3 tool.
There are many many stations saved automatically with the device.
We fixed two points determined by radiolocation, one at the beginning of the siphon and another at the end.
When after Therion compilatione, the survey is completely distorted.
Doesn't the problem come from too many shots and Therion not being able to compensate for the very small shots?
Have you encountered this problem before?
Thanks for your help,
--
Daniel Chailloux.
_____________
*Daniel Chailloux*
17, avenue Gabrielle d’Estrées
91830 Le Coudray-Montceaux - France
Mobile : +33 6 8290 7375
Email : danielchailloux@orange.fr
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