Hi guys
Was on a construction site yesterday doing a survey of a steel frame building. I was set up internally and had to survey the large upright steel columns, arranged in a grid pattern. The columns were about 600mm x 200mm in section.
I shot them reflector less. When I processed the data I noticed that two of observation were way out. One was 300mm to the left of where it should have been and 500mm too far. The other was 200mm to left again but 1000mm too short. The plotted observations are not even in the place where the columns were!
I have check all the dodgy obs on my data collector. The were shot using angles and distance, i.e no angular or distance offsets.
Anyone got a clue what may have gone wrong. Inside the building the contractor had arranged festoon lighting hanging off the walls near the columns I shot - the bulbs were LEDs (like a large version xmas tree lighting). Could this be the problem?
Cheers, Andrew
Reflectorless is always a bit of a gamble.
I dont think the fancy lights will be the issue
Reflectorless is always a bit of a gamble. The total station will fix on the strongest return signal - anything in the beam is fair game. Usually it will grab the nearest return, but a strong one in the background may also be got.
Make sure there is nothing else in the viewfinder and don't rely on a single shot - get three and make sure they line up, before accepting the data
Just my $0.02
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I have found that when in reflectorless mode that unexpected locations are frequent and not always obvious for their occurance.
When monitoring construction or locating existing structures it is always important to introduce redundancy into toe collection process by observing from more than one viewpoint.
Some instruments are better than others with reflectorless. I??ve used a trimble (i think s5) that would often return a distance to a wall behind the object it was focussed on. Might be your issue?ÿ
Reflectorless is always a bit of a gamble.
I dont think the fancy lights will be the issue
Reflectorless is always a bit of a gamble. The total station will fix on the strongest return signal - anything in the beam is fair game. Usually it will grab the nearest return, but a strong one in the background may also be got.
Make sure there is nothing else in the viewfinder and don't rely on a single shot - get three and make sure they line up, before accepting the data
Just my $0.02
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Jim - when you write get three and make sure they're line do you mean get three on a face. How do you check they're in line in the field before proceeding??ÿ I actually shot the corners, using a note pad to stop the beam spilling off external corners. Its difficult to shoot 3 in a row on a two of the sides of a steel column as they are an I shape.
I guess I could shoot the columns at a couple of different heights and compare the results.
I'm fairly new to surveying and had no idea that reflector less was a gamble. I have noticed in the past when red dotting the outline of buildings that some shots look out of place by 4 inches of so but yesterdays results really were poor.
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I guess I could shoot the columns at a couple of different heights and compare the results.
That's exactly what you need to do.
Once you have three points you can calculate a line between any two, project the third to that line and see how far of it stands.
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Or use stick on reflector targets - we use these from JustRetros.com.au - cheap and effective
Some instruments are better than others with reflectorless. I??ve used a trimble (i think s5) that would often return a distance to a wall behind the object it was focussed on. Might be your issue?ÿ
I believe some Nikon units also check the distance at which the gun is focused for deciding distance.
The Trimble S6 and S8 units I use seem to have a very wide beam. Anything in the viewfinder is fair game...
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mine is a Trimble S7
You could also measure from the map view and use some linework to detect blunders. set your zoom factor to 1 m.
However I would prefer the 0-offset mini prism for columns (if they're accessible of course)
Chr.
Not sure what brand of TS you use but with my older Topcon the relectorless beam gets wider as it travels away from the ts. Also the higher the angle of incidence to the measured object the lower the accuracy. It is impossible to shoot corners directly with it, I generally have to use a line and corner routine.
I personally wouldn't use reflectorless to locate these columns. Get out a mini prism.
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Or use stick on reflector targets - we use these from JustRetros.com.au - cheap and effective
Used that technique just last week in a fuel tank farm. At 80m, couldn't get a ping off a 10m dia steel tank that had been painted black. So, just told the chainman to go around the tank holding a retro target against the tank but perpendicular to the instrument, that way you aim at the tank at the target edge to get the correct angle, and the retro does its bit for the distance.
After that exercise, part two was to take said retro and stick it on to the middle of the tank (as per what the instrument could see) as a permanent backsight. However the excitement of part one must have got to the chainman as he was blank when he got back to the middle of the tank, so rather than try and shout 8om (radios not allowed in the farm) or get dangerously close to him, I spent the next two minutes miming the words "wipe", "peel" and "stick it".
BTW I'm sure I read somewhere (I think it was on a retro tape manufacturer's website) that white is the best retro, yellow not so good.?ÿ
I think the older Nikon one (eg NPL-332) worked on a different technology (time-of flight?) that would only get a reading from a focused object.
Leica has the narrowest beam as far as I can tell.?ÿ
I have had problems with reflections off dust before. Don;t suppose this could be the problem?
Many years ago I had problems with my Trimble, due to it's design, which may be similar in other units.
Trimble uses the exact same beam strength for prism and prismless shots. The difference is that for a prism shot an internal motor drives a filter down?ÿto lessen the signal strength.?ÿMy motor was going bad and the filter was not getting into proper position messing up the signal and distances were way off, some way long. Battery strength and temperature can affect the motor performance, but it will probably get worse. I had to return it for factory not dealer?ÿrepair.
I am not certain but think my errors were multiples of the correct distances.
Paul in PA
I spent the next two minutes miming the words "wipe", "peel" and "stick it".
Reminds me of a great old joke.?ÿ It is a visual joke.?ÿ The punch line goes, "I left (t)it in the box."
I spent the next two minutes miming the words "wipe", "peel" and "stick it".
Reminds me of a great old joke.?ÿ It is a visual joke.?ÿ The punch line goes, "I left (t)it in the box."
I need a hammer. :p