Re: deformation monitoring
- From: "Steve Bury" <steve@****nospam*****buryassociates.co.uk.remove>
- Date: Tue, 13 Sep 2005 12:30:54 +0000 (UTC)
André said: > Only use distance measurements to prisms, reflectorless is
very tricky
> especially with trimble.
Couldn't agree more with this - wouldn't be without our Trimble 5600
reflectorless instrument, great bit of kit - the reflectorless is
fantastic - but we only use it for topo & surveying building facades - can't
beat it for this - it'll get a signal off almost any surface & often get
300-400m distance out of it - but I wouldn't use the reflectorless for
precise work.
We had a contract checking someone elses setting out of some machine beds in
a factory. We often use stick-on reflective targets with out leica
reflectorless instruments - with excellent results - set up in the required
position & resect back into the co-ord system. Started this job with the
Leica, but took the 5600 to site one day - when I processed the survey back
in the office I had differences of up to 10mm in the distances to the
targets compared with data from the Leica - that was using D Bar measurement
on the Trimble. The distances measured were mostly around 15m. Couldn't get
a satisfactory answer from Trimble about why there should be such a
difference (both EDMs are of a similar precision), distances measured with
prisms compare very well.
Kind regards
Steve Bury
Bury Associates Limited
T. 01905 26222
F. 01905 22555
www.buryassociates.co.uk
"André" <andre@xxxxxxxxxxxxxxxxx> wrote in message
news:11i19pb33aicva3@xxxxxxxxxxxxxxxxxxxxx
> As to accuracy, forget distance only.
> Below are some short notes that come from experience:
>
> For best results use robotic facilities (onboard or externally controlled)
> whenever available.
> If you setup manually on tripod, etc. that is where the biggest errors
will
> be. (centering, orientation)
> If you set up on pillars with fixed mounted tribacks repeated stations
> should yield exactly the same position.
> Make sure you have clearly defined points for initial orientation or your
> field of points will float or wobble slightly.
> Good orientation points (one per station minimum) help to get the
instrument
> lined up exactly as last time, so results can be compared 1 to 1.
> Measure only with angles + distance or you will never be able to repeat or
> compare a single measurement.
> Only exception is when you measure to points relatively close together and
> over very long distances (>2km) and you don't care about movement unless
> it's in direct line with the sight.
> Monitoring is about comparing resyults from identical measurements to
track
> movement.
> Only use distance measurements to prisms, reflectorless is very tricky
> especially with trimble.
> When possible include the other stations as deformation points, this
> provides some handholds to tie the stations together.
> Make sure you have a number of very good and solid points outside the
> deformation zone, unless all stations are well outside of it.
> (Well outside means a good 100 meters or more)
> With these precautions you should be able to track the movement of points
to
> within millimeters.
> The spec's of the distancer are not so relevant. The given spec's are for
> absolute meaasurements.
> Usually a single measured distance is within these limits, but when many
> measurements are made to the same point you should see a spread that is
only
> a fraction of this. Monitoring measurements are generally relative to one
> another, so this spread is what introduces the noise in the measurements.
> Watch out for changing wheather conditions of your measurements are over
> long distances ( >200m) as meteo factors will start to influence the path
of
> the beam. During continuous monitoring over long periods I have seen a
> complete field of points to seemingly contract and expand with rising
> temperatures while going from cold winter to warm spring days.
>
> good luck
>
> "Jan" <spam@xxxxxxxx> schreef in bericht
> news:7niTe.187431$xj6.10385515@xxxxxxxxxxxxxxxxxxxxxxxx
> >
> >
> > After I did a deformation monitoring with my digital level, they ask me
to
> > do a 3D monitoring.
> >
> > I use a Trimble 1" reflectorless totalstation.
> >
> > I think I have to use 4 positions to be able to measure every point.
> >
> > Can anyone help me with some tips? Where can I go wrong, and how can I
> > avoid it?
> >
> > How accurate can I measure, the distance accuratie of the total station
is
> > 2mm + 2ppm. But with 4 places to put the totalstation (I'm sorry I
can't
> > find the English word) It's possible bigger, plusmin 4 mm?
> >
> > I would be grateful if someone could help me.
> >
> >
>
>
.
- References:
- deformation monitoring
- From: Jan
- Re: deformation monitoring
- From: André
- deformation monitoring
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