All right guys
I was told that there is no such thing as a stupid question so here goes!
I use a Trimble S7 3 second Total Station with the large Leica round prisms for control. I usually do 3 rounds of angles on each set up with autolock on.
I've noticed recently (maybe its just starting happening or I just started noticing it) that sometimes the delta angles are large. Please see below - stn98 was a short backsight (no choice I'm afraid) of 15 ft and stn4 was a long foresight of about 150ft. So the delta horizontal angles on the short back sight station were nothing and the delta horizontal angles to the long foresight are large. I've noticed that sometimes the delta HAs to a long backsight are small and the delta HAs to a short foresight are large. It seems to happen?ÿ when one of the stations is a short distance away.
Is this normal or do I need to consider re-calibration. When both stations are a long distance away everything seems fine.
Cheers, Andrew
Tan 25" * 15 = .00182
If possible, could you set a point "past" the 15 ft. for line only?
IE sight 100 ft past the 15 ft planned traverse point and set a point on line. Now, break setup and move ahead the 15 feet. Backsight the point you set on line and turn back to the point you moved from. You might get a better closure.
Well yeah, this is exactly why short backsights are bad.?ÿ The prism is the size of a basketball from 15 feet away so if it locks out by the edge and then you foresight 150 feet away you're going to get an ugly delta.?ÿ I don't see anything unusual about what you're experiencing.
Ah, the dreaded 15 foot shot made with autolock?ÿ to?ÿ a prism.?ÿ I'd suggest thinking outside the box and change your procedure.?ÿ Can you literally sight the tack (or whatever)?ÿ on the short leg??ÿ If so, manually point the crosshair to the middle of the tack when turning your angles.?ÿ If not (assuming you're not solo) sight a plumb bob string held by your crewperson, as low as possible.?ÿ It'll tighten things up but as noted above,?ÿ such a short leg is bad ju-ju when seeking a tight closure.
Great approach. I did something like this only more extreme one time.
My brother wondered what he was seeing on the horizon several miles away through a gap in the trees. I set up two points only 30+ feet apart, limited by some trees partway between us and the object, and couldn't get anything reliable for an answer.
So I put one of my points on line with a distant object and repeated the measurement. I came out with an answer of about 8 miles and we looked on Google Earth to find his mystery object at about 10 miles. Not great accuracy, but with that limited baseline I was satisfied.
Cheers guys - I get great control accuracy figures even when there are short legs - because I do 3 rounds of left and right as the errors cancel out.
I was curious as to the reason why the deltas are crap when I short leg is involved. The crap deltas can be on a long foresight when there was a short backsight. ?ÿ
If you see this error amplifying on short legs, I would speculate that the epicenter of your scope is "slightly" high or low of the vertical axial node. Imagine a telescope hanging from a rope. Now twist the rope so the scope is on top of the rope. You'll notice a difference in vertical angle (more at shorter sight legs).
The probability that the correct bearing and distance between two points that are 15?ñ feet away from each other is obtained when locating them both with a TS from a distance of 1000ft away is very impractical because there is too much room for error.
