On a training exercise recently several of my team-mates used a dumpy level to measure the height-below-ground-level of several points around a simulated gravesite. However, they failed to record the distance from the dumpy level to each measured point (I take full blame - I was the team leader, I should have been on top of things), and I’m tearing my hair out here trying to use their information to draw a sketch of the grave.
If I have the upper crosshair (UC) reading and the lower crosshair (LC) reading, can I relate that to distance? I’m imagining drawing an isosceles triangle with the short edge being the difference between the UC and LC readings, then bisecting the triangle to get 2 right triangles where the shared long edge will be the distance from the dumpy level. I’m OK with the trig for that, but I need to know the value of the angle that I’m bisecting in order to do the calculations.
Does anyone know what that angle is? Is it standard for all dumpy levels, or am I out of luck? I’ve tried a Google search for “dumpy level” +distance, but haven’t been able to find any specifics.
That site explains very well how it works (if you click through enough) but doesn’t tell me the angle made between the upper crosshair, lower crosshair, and dumpy.
Reading through the Google cache of this PDF file seems to imply that the distance away from the dumpy level can be calculated by (UC-LC)x100. [This information on page 29.]
However my eyes kind of glaze over when I read the examples, as I’m not good at figuring out what’s going on. Is this being presented as a general fact, or is it unique to the example?
Can anyone confirm this information?
I’d try to sense-check the resulting distances, but I cannot - cannot! - think in metres.
Surveyor here… (oh wow, something I can answer in GQ!)
Anyome needing info on this should Google Stadia Tacheometry or Theodolite Tacheometry.
To answer your specific query… it depends on the level probably, although all levels I have ever used (and this is dredging up from memory) have the angle set so that the distance is 100 times the dh read on the staff… err, I think. If you have the level handy, it’s easy to check of course.
Sadly, I don’t; our supervising archaeologist owns the equipment, not my facility, so I can’t pop in and check. (And silly me, I didn’t get his contact details. I am not fit for Team Leader positions!)
However - I Googled it and someone on the SDMB independently verified it, so as long as I’m not taking this to court, I’m happy to accept that!
Thanks a billion (US or UK, take your pick), Kymodoce! If I’m ever up UK-ward, or you’re ever in Canberra, I owe you a custom cheesecake.
A level is a tool that measures elevation (the difference in height between 2 points)
Basically, it is a telescope with a carpenter’s level-bubble mounted on it.
A dumpy level is an old-fashioned, outdated version.In 1940’s (I think), it was a new improved version of the standard level then used by surveyors,.It had a shorter telescope (i.e. “dumpy”, which apparently was slang for short)
A transit is a tool for measuring angles. Basically, it is a telescope mounted on a circle marked into 360 degrees(and smaller units) .No longer in use–because it has been replaced by :
A theodolite–a more precise version of the transit. Instead of a metal circle with the 360 degrees inscribed by mechanical means, it uses a glass circle, with the 360 degree marks cut into the glass with much more accuracy.But this tool is not in use much today, because it has been replaced by:
A Total Station Instrument.Basically, an electronic theodolite, and measures distances as well as angles.And is computerized.
