Now that intern season is over figured it's be a good morning to run some checks on the equipment. Arrived at the traditional company baseline, established well before my time, to find most of the point destroyed by recent construction. So in the planning stages of establishing a new one this week.
Presently thinking a right triangle, 400' long leg with a midpoint and the short leg at 300', making the hypot of 500' with los between all 4 points. Perhaps those seem a bit short to some, but figuring in our area 90% of our b.s., f.s. fall within those distances.
Appreciate any thoughts on building a better mouse trap.
I would look at the configuration of NGS Baselines. Every one I have visited is a nominal straight line with monuments at specific intervals.
thebionicman, post: 443638, member: 8136 wrote: I would look at the configuration of NGS Baselines.
There is a bit of magic in their choice of distances, such that measuring all of them gives a thorough check on an EDM.
If you are going to self check your total station why only check the EDM? I would say 50+/-feet by 500+/-feet and an angle is a better check than just 500' and 1000' on a straight line.
Paul in PA
Definitely pepper at least one line in 50 ft sta for 300 ft for calibrating chains.
I think a braced quadrilateral. Observe all angles for a very tight adjustment.
Paul in PA, post: 443663, member: 236 wrote: If you are going to self check your total station why only check the EDM? I would say 50+/-feet by 500+/-feet and an angle is a better check than just 500' and 1000' on a straight line.
The normal instrument collimation checks should deal with any small angle variations : if they are beyond the instruments normal built in adjustments then it needs a trip into service. Drift on the EDM needs some sort of baseline (but that in itself needs a calibration by an instrument of known accuracy, otherwise you just set all your gear to be wrong. AND you need to set and leave a tripod and tribrach on each point during the calibration.
To deal with scale as well as prism/instrument corrections a decent length is needed, to cover a range. Our baseline is set in metric and gives combinations of distances at 1-10 metre. Marks at 0, 5, 123, 231, 358, 477.5, 594, with a back station at 900m. Measure to all points from the first two stations. After reading the results are graphed out and the scale and prism constants deduced.
For just prism/instrument constant all you need is three points in a line. Distances don't need to be known but around 25-50 metres overall is fine.
(AC + e) = (AB+e)+(BC+e) hence AC-AB-BC = e
If you decide to use a braced quadrilateral for the angles then, again, all points must have tripods and tribrachs left untouched during the observations. Make sure all sightlines are well clear of the ground and side objects to minimise any refraction (it can happen horizontally as well as vertically - looking down a line of vehicles is asking for trouble).
Fredh, post: 443633, member: 12570 wrote: Now that intern season is over figured it's be a good morning to run some checks on the equipment. Arrived at the traditional company baseline, established well before my time, to find most of the point destroyed by recent construction. So in the planning stages of establishing a new one this week.
Presently thinking a right triangle, 400' long leg with a midpoint and the short leg at 300', making the hypot of 500' with los between all 4 points. Perhaps those seem a bit short to some, but figuring in our area 90% of our b.s., f.s. fall within those distances.
Appreciate any thoughts on building a better mouse trap.
Fredh, you haven't really explained what you are checking for. Explain to us what you intend to check for, and perhaps how you think the configuration of your mouse trap will achieve the desired outcome with the analysis you intend to perform.
Every office should at least one good, easy to use, 300-500 baseline.
Back in the day ...
We would take all of our EDMs (pre mono optic total sta) to the NGS calibrated baseline. Then, we installed reflectors, permanently, around our office at various distance, including a 15,000 ft installation, and established our own baseline array. 2-3 times a year, on a slow day, or given a new purchase, we kept a log book to see if any of has drifted. Mostly we had AGA 120, 220, an Elta, even a Range Master.
The NGS calibrated baseline program was so under used that it's no longer a program. It was interesting to see 100-500 ft discs at an airport with periodic remeasurements every couple of years, with NGS certified 1:100,000 accuracy. It was very reassuring to make a genuine check against NGS baselines. But after 5-6 years, the reflectors started to disappear. And, gps was so good, well ....
The good old days.
