Wow, thanks Tarquin! And Ollie, too. I tried a few things, but the spike still exists in the .lox file. I changed the connecting shots from 3 to BU1 and BU2 from splay to duplicate. After recompiling, the spike is still there. Next I change the shot from BU1 to BU2 so that it has no LRUD data. Recompile, and the spike is still there. Hmmm.... I think I need to change most of the splay shots to duplicate, but that seems to not be the reason for this anomaly. I double-verified the LRUD data for stations BU3, BU4 and BU5. The passage makes a sharp turn at BU4, and a bad left measurement would go about the same direction as the spike. The LRUD data for those stations is all correct. One thing that strikes me is that the spike is not horizontal. It angles upward by about 20 degrees. If it were the result of bad LRUD interpretation, I would expect it to be horizontal. I included the data line in my extract. It is indeed the same line as you deduced by looking at the data. Therion does produce warnings about "forwards and backwards bearing readings do not match". There are about 20 of these in the therion.log file. I have checked every one against the original notes. It really is off. Most are under ten degrees. The worst is 17 degrees off. Most of this cave was surveyed with DistoX2 devices. The compass and inclination readings go to two decimal places (0.01 degree). I do not believe for a New York minute that the DistoX2 is really that accurate. I suspect it is no better than a Suunto. The readings in the book are rounded to the nearest tenth, and I count on Therion averaging the two shots to get a somewhat better consensus. In this cave, especially around the tour trail, compass readings are difficult because there is so much metal. Hand rails, electric lighting fixtures, rebar in the concrete, support pillars and framing for the overlook platform ... It is a magnetic mess! We did the best we could, but there is just a lot of noise in the data. Some time ago I asked about reverse tape readings. That is a fairly new feature in Therion. For this cave we did not record any reverse distance data. The distances are in Imperial measurements to the nearest 0.1 foot. The DistoX2 displays to the nearest 0.01 foot and we round that to 0.1 before writing it down. I found a photo of the area we are looking at. https://campercaver.net/MiscFiles/P1100940-Small.jpg This shows the stairs leading up to the overlook. Station 3 is just out of sight on the left of the photo. BU1 and BU2 are out of the photo at upper right. The BU side passage is reached by getting onto the rock ledge on the right, then coming toward the camera. The passage goes off to the right of this photo. There is an electric light fixture just about dead center in the photo. If you levitate about 8 feet up from that fixture and look right, that is the passage entrance. =============== Bill Gee On 8/16/23 02:18, Tarquin Wilton-Jones via Therion wrote:
Hmmm..... Maybe I am not using the splay flag correctly? Is there another flag that might be more appropriate?
flags duplicate = a leg that must not count towards the length. It can count towards the vertical range, if it is the highest or lowest point in the cave. Use this when you have had to survey twice (or more) down the same passage. Also use it if you are going from a station in a passage whose length was already included with the legs going down the passage itself, and the new legs are used to reach the start of a side passage, where the main passage is really wide (such as a station on the left wall of a 50m wide passage, and you need to get to a side passage on the right wall). This is particularly useful when you have a side passage you did not have a useful fixed station for, and the nearest fixed station is a long way down the passage, so you will need to resurvey from that fixed station, back down the passage you already surveyed, to reach the side passage. As Olly said, this is the one you want.
#survey from fixed station to AB side passage flags duplicate megacairn AB1 12.34 27.5 1.5 AB1 AB2 8.97 42.93 -21.5 #AB2 is start of side passage flags not duplicate
flags splay = a shot from a station towards a wall, ceiling, floor or other solid object, such as a stalagmite. Therion uses these to build the walls in the .lox file. Normally, you use anonymous splays like this ("-" instead of a station name): AB1 - 1.234 12.5 -17.5 However, sometimes *rarely* you might want to name a splay, such as a splay that hits something important like a named formation. Imagine you have a stalagmite called "Medusa", you might do this to tell Therion "I know this looks like a station, but it's a named splay":
flags splay AB1 medusa 1.234 12.5 -17.5 flags not splay
flags surface = a leg or splay that is on the surface, not in the cave. This will not be used for length, depth, or wall generation. It basically tells Therion to ignore it for cave statistics, and for wall generation. This might be used for the legs that go from the cave entrance to your fixed location on the surface, or for splays that go from a surface station to a surface feature, such as a cliff face outside the cave.
station 2 "Alpha Cave" entrance flags surface fixedpoint 1 12.345 27.5 1.5 #splays around the outside of the entrance 1 - 0.555 237.50 -37.67 1 - 0.882 258.89 -16.29 1 - 0.895 296.19 -14.58 1 - 1.198 320.46 -3.11 1 2 1.266 62.55 -31.87 flags not surface
BU1 BU2 11.6 53.1 84.4 228.4 -84.9 16.8 2.2 1.1 11.6
Oh, this is interesting. I was wondering if you had used "UP" to get from BU1 to BU2. In such a case, LRUDs are quite useless, as a leg has no direction, so Therion has no information about which direction is "left" or "right", so it might have had to make things up and got it wrong. (Splays are vastly superior to LRUDs, because each one has an explicit direction, so you can point to all walls of a pitch, not just 2 of them.)
I had expected maybe it was generating walls without any idea where to point them, but that seems not to be the case, since you have an actual direction for that leg.
So it seems the most likely cause for your problem is indeed the "flags splay" where you meant "flags duplicate".
However, I would need more of the data forming that part of the cave to be sure, since when I tried to compile your snippet, it did not show the problem. Maybe it only shows up when you have both the old and new data.
I also have never seen data in this format, and am curious as to what your "data" command looks like. It looks like it should be this:
data normal from to tape compass clino backcompass backclino left right up down But Therion won't let me use that, because the compass and backcompass are not perfectly opposite. I am wondering if it gets confused when you ask it to use all the data columns (I told it to ignore the backcompass).
Equally curious about what your measurement device is, since you are getting only 10 cm accuracy (suggesting a measuring tape) and yet .1 degree precision compass and clino, which seems incredibly precise for manual tools, especially considering the forward and backward devices seem to disagree with each other by as much as 2.1 degrees (compass) and 1.1 degrees (clino). There is a huge 4.7 degree disagreement on the BU1-BU2 leg. (Because the devices are being used nearly vertically, so compass error is increased. Plumbed legs would normally be recommended when using manual devices.) Whenever I have seen high quality data from manual devices, the compass and clino have been given to 0.5 degree precision, because that is the reading limit of the devices. _______________________________________________ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion