are you talking units of decimal INCHES? so .300" = .3 X .0833 = 0.025'
stick one tripod leg in.. hold the other two and while looking through the optical plummet, move until the Mark is roughly centered. Stick the other two legs, keeping the mark in sight. set all three legs equally. Loosen a leg at a time (if needed) to get the bubble in the center. check plummet and if needed, loosen the screw and shift the instrument to center over the mark. TIGHTEN the screw. check bubble again... run the routine and the Geodimeter should be good to go. I generally trust the digital level more than the bubble, TBH, but that's just me.
Andy, yes, that is .300" or .025'. The other one was at .100". The triangle dims were roughly 65', 71', and 115', and 114* of angle. I shot the 65' leg, set my HA at 0, then shot the 71' leg and collected that angle, then calculated the third leg length, then moved to another pin to collect the directly measured 115' leg.
Now, I probably could get closer because I realized my pole had not been calibrated for plumb. I think if I used a shorter pole, I could have done better.
I will follow the recommendation to test the EDM length against a tape measure.
sireath, post: 422865, member: 9370 wrote: I'm sorry I cant imagine what you are trying to do to level the tripod. You can try going youtube, there are many basic steps on how to set and level instruments on a tripod over a point.
Better yet. Post some videos here of exactly what YOU are doing. That might go a long way to clear up communication. Plus it would be fun to watch.
Based on some of your comments, I would seek out some training or a mentor (no offense intended). Checking and adjust all the equipment that you can.
If your rod bubble is so far out of whack that you can see it leaning in the cross hairs, you really need to get a handle on things before you worry about instrument accuracy. The bubble on the RMT is for looks only - don't use it.
Ask around here and some people will give you some neat tricks to adjust rod/tribrac bubbles as well as adjust the tribrac cross hairs . Tighten the tripod head bolts. All of your other equipment needs to be in adjustment before you can get accuracy out of a total station.
In the mean time, do some research on how to field check a total station for horizontal and vertical angle accuracy (other than the collumination routine). Take field notes. Turn turn your angles to a plumb bob string, or directly to the target..measure distance to prism.
Here's the method I use for setting up the instrument. Before you put the instrument on the tripod, set it over the point. Picture each leg as being the crossbar of a T, with the bottom of the T towards the point. Get those lined up and firmly in the ground, then eyeball level the top by sliding a leg up or down. Put the instrument on, turn the screws to get the optical plumb on the point, then adjust the legs as needed to get the bubble roughly level. You will be close enough to loosen the screw and slide it over the point, then fine tune the bubble and you're ready. Shouldn't take more than a minute. 30 seconds with some practice and level ground.
Nate The Surveyor, post: 422898, member: 291 wrote: Well, the problems you seem to be having are solvable.
"If it was built by a man, it can be fixed by a man".For starters:
Set it up, and shoot a prism, 10 feet away. NOW check that with a box tape. Get a good mechanism to MEASURE it. I'm serious. Do this.
Prisms, have offsets. Total Stations have offsets.
These offsets are CHANGEABLE. They are settings.
AFTER you confirm that EDM reads 10.000' and box tape reads 10.000' then go to step B.Step B:
Do all the above, THROUGH the data collector. DATA COLLECTORS can have offsets too. And, scale factors, for State Plane work etc.
Until you do that box tape vs edm check, this stuff will tend to obfuscate the problem.
Differing prisms have differing offsets. Do all this with ONE prism. (later, compare them)
N
I have run a quick EDM test and have a quick question. I have tested the distance to 18ft with a tape measure by setting the station up as low as I can go with the tripod. The RMT is on the ground. The offset in Z between them is approx 36". The distance returned is 17.990. Because of the angle between the gun and RMT, I am hesitant to qualify this as an accurate value and enter a prism offset. I do not have the swing bracket for the RMT to change the angle, in which that would roll the prism backwards and may in fact bring this to a value match.
If I set the station on a table, I am unable to pinpoint the vertical XY center point so I used the tripod so I could use the optical plummet.
Other posters, thank you for the recommendations! No doubt I am drinking from a fire hose a bit but enjoying the learning process. I would like to seek out of some official training but have not found much local. Mostly just OEM training by Trimble and such if you own their products, which I don't. Well, sort of....
bob james, post: 422990, member: 12050 wrote: I have run a quick EDM test and have a quick question. I have tested the distance to 18ft with a tape measure by setting the station up as low as I can go with the tripod. The RMT is on the ground. The offset in Z between them is approx 36". The distance returned is 17.990. Because of the angle between the gun and RMT, I am hesitant to qualify this as an accurate value and enter a prism offset. I do not have the swing bracket for the RMT to change the angle, in which that would roll the prism backwards and may in fact bring this to a value match.
If I set the station on a table, I am unable to pinpoint the vertical XY center point so I used the tripod so I could use the optical plummet.
There's a mark on the side of the instrument to measure from. I think you are confusing prism offset with the HT (height of target) Prism offset is the horizontal distance from the focal point of the prism to the actual center of the point the prism is over. Standard is 0 or -30mm.
Geodimeter typically used a prism offset of zero - If Geodimeter brand prisms were used.
Using anything other than Geodimeter prisms requires that the prism offset be measured/verified by the user - regardless of what is marked on the prism or product spec. sheet, you have to go through the exercise of determining what to enter as an offset.
This was provided previously when prism offsets came up earlier.....I'd set my prism offset to 0.00 when doing this check...I'd also be using 3 tripod/tribracs.
"Set two points A and B about one hundred metres apart on level ground. Set up on A and measure to B using your unknown prism.
Then set up point C on line about half way between A and B. Measure AC and CB both with the unknown prism. The difference between AB and AC+CB will be the prIsm constant."
My apology if my question was not clear. I was considering sighting errors because the RMT is sitting 3ft lower than the station center axis, but the RMT is sitting vertical. I know they make a little bracket which allows the user to angle the RMT and was not sure if the RMT sitting vertical but 3ft lower than the station would return a false distance reading?
Regarding the prism, yes, it is the factory prism and RMT for the gun and should be a zero offset. I mean, it is not a mile off, but if a few button pushes can get .125" of error out, why not. I am just not sure if you are not shooting very close to 90* VA you should not even consider the value given for setting an offset.
Bob, because of manufacturing flaws or physical limitations, the "actual" prism offset varies with each individual prism.
I have read here where some people determine this measured offset (using the method I described above) for each prism and realize a couple thousandths of additional accuracy in their least squares reports. Most boundary surveyors are happy to ignore these small discrepancies and run with a standard offset to avoid blunders.
imaudigger, post: 423006, member: 7286 wrote: Bob, because of manufacturing flaws or physical limitations, the "actual" prism offset varies with each individual prism.
At one time Geodimeter used to manufacture circular shims, I think from phosphor bronze, which could be used to shim out the prism from the housing, so that an exact zero could be set for each prism. I used them on the set of prisms we had for our calibrated 440LR back in the day.
Thank you guys but I am wondering if I am asking my question wrong.
I realize no prism would be perfect, and we are talking about 1/8" here BUT, my question is that the crosshair on the station was set to 39" to the ground, the tape measure was on the ground, and the RMT was sat on the ground in which the height from the ground was 3.625". This means the gun was shooting DOWN to the RMT.
My question is how does that angle play into the EDM returned value? How significant?
Check MENU 6.2. As I recall that enables you to enter the prism offset when using the RMT target, rather than the RPU. I would guess that it also signals the use of the RMT and alters the internal calculation such that the instrument corrects the slope distance to take into consideration that the target is vertical. (The RPU would always be pointed along the sightline using its telescope, so needed no correction).
Bummer but I do not see such a menu item in the books. I have 6.1 for just the prism constant only. I have not double verified in the gun but the book has not been wrong yet.
Bob, what year/model Geodimeter are you using?
When checking the prism offset you measure between the points to be actually measured, not some points on the ground you set over. It's really easy with a tape, you don't need to set very far apart, all you are checking is the prism offset. You don't need to think about slope, angles, ect, it's a simple measurement don't make it complicated.
It would be rare that the instrument and the prism were at the same elevation. it measures slope distance and converts to horizontal .... Unless I'm misunderstanding your comments, I think you are seriously overthinking this.
bob james, post: 423095, member: 12050 wrote: Thank you guys but I am wondering if I am asking my question wrong.
I realize no prism would be perfect, and we are talking about 1/8" here BUT, my question is that the crosshair on the station was set to 39" to the ground, the tape measure was on the ground, and the RMT was sat on the ground in which the height from the ground was 3.625". This means the gun was shooting DOWN to the RMT.
My question is how does that angle play into the EDM returned value? How significant?
I believe what I would do is to set two points and measure between them and then set a point on line between them, then setup on that point and measure both ways and see if the two distances add up to the total distance measured end to end.