Engineering Geodesy I
Exam questions of the lecture «Engineering Geodesy I» by Prof. Dr. Ingensand, D-BAUG, ETH Zürich
Exam questions of the lecture «Engineering Geodesy I» by Prof. Dr. Ingensand, D-BAUG, ETH Zürich
Kartei Details
| Karten | 59 |
|---|---|
| Sprache | English |
| Kategorie | Geographie |
| Stufe | Universität |
| Erstellt / Aktualisiert | 17.01.2012 / 30.01.2019 |
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Crack detection (due to geothermic drills in Staufen, Germany). How can you detect the crack shown in the picture?
Extensometers
How can you detect influencing parameters, like temperature?
By measuring them during data acquisition and correlate them to the measurements.
Can geodetic instruments also be used (for crack detection in a building)?
a) Tachymeter an two reflectors on SBB-bolts. b) levelling for sinking problems
What could be the reason for a trend?
* Instrument got warmer
* sinking of the tripod
Frequency measurement:
Acquisition rate of a Totalstation? Possible for this task?
5-7 Hz (leica says: 10 hz) => possible for lower frequencies.
* When the amplitude is to high for ATR without moving it’s good.
* When the tachy has to move => bad.
Frequency measurement:
Acquisition rate of a GPS? Possible for this task?
20 Hz => possible
Differences between geodetic and geotechnical instruments?
[Criteria / geodetic / geotechnical], [Accuracy/ mm (Leveling <0.5mm/km Doppelnivellement) / 2μm - mm], [Range / m - km (VLBI :-)) / μm - m], [Measuring in 2 or 3 dim. / possible with 1 sensor / usually 1 sensor for 1 dim.], [Costs/ ? (high) / ? (low)], [Absolute Measurements (Coordinates) / ✓ / ✕], [Development / for classical survey / specially for those purposes], ]Place of instrument / mostly away of the problem / directly at the problem (crackmeter, plumb)|
What is the easiest and cheapest method (to detect a crack in a wall)?
Plaster-Plate (Gips-Platte), take care that the predetermined breaking point is over the crack!
What is a strain gauge (Dehnungsmesstreifen), how does it work and how can you use it?
It’s a small device which has a long electric conductor (blue in picture) on its flexible base.
When den strain gauge is straint, the resistance of the changes.
On tension, the electric resistance increases and vice versa
Frequency measurement (Auenbrücke):
Where do you mount the sensors?
* not there where the nodes are
* to detect the maximum amplitude at the theoretical maximum
* best at the carrier: least additional swinging
What frequencies of an oscillating bridge can be expected?
in the range of 0.5 to 5 hertz???
Hopefully a civil engineer calculated these frequencies during the planing process... ask him! ;-)
Which sensors can be used to detect a bridge oscillation?
GPS
Accelerometer
Daedalus
OszilETH
Tachy
...
Boat and meter :-D
Accuracy of geotechnical sensors?
General: Microns to mm // Mikrometer or Jointmeter: 0.002mm @ 10-30cm // Wire Extensometer Distometer ISETH: 0.02mm @ 20m // Extensometer: 0.01mm @ 10m
Schlauchwaagen: ca. 0.01 mm // Optical Plumb: 1mm @ 100m // Wire Plumb : 0.05mm
How can you analyse the time series?
FT
FFT
Rainers Software (Periodogram.m)
Range of geotechnical sensors?
mm to meter
Mean value is what type of filter?
low pass filter
Can geotechnical sensors be used to measure in two directions?
Plumbs can measure in 2 directions. All other geotechnical sensors measure in 1 direction only, but can be put together to one instrument, which can measure eg. in 3 directions
How can you get ride of the noise?
Calculate mean values (take a good time interval for that ;-))
How does a Distometer work?
Zwischen Messbolzen wird mit dem Distometer ein Invarstahldraht kraftdefiniert gespannt und die relative Länge des Drahtes gemessen. Durch die Differenzbildung der Messungen zu zwei Zeitpunkten und mit Berücksichtigung der Kalibrierung wird die Distanzänderung zwischen den Messbolzen ermittelt.
What type of data did you get out of the bridge swinging measurements?
time series with coordinates, accelerations, …(depending on measurement tool)
How do you start with a frequencyanalyses?
Plot the raw data series (check system noise, bias, trends, time intervals)
What about the aquisition rate?
regard the nyquist-frequency!
Can movements of a bore hole also be measured with geodetic sensors?
Wire plumbs can be measured with total stations. Probably possible with the tachymeter and a reflector in the hole.
Frequency measurement (Auenbrücke):
What do you measure?
Parameters of the oscillation (mostly deviation) and time
Why did the Tacoma Bridge begin to osciallte and collapsed?
Low but constant winds put force on the wires an brought the bridge in a critical torsional swinging.
Why is it important to know the Eigenfrequencies of constructions?
* To avoid Eigenfrequencies which are close to a “userfrequency”.
* To attenuate the critical Eigenfrequencies
Instruments to measure movements in a bore hole?
Borehole Extensometer: for change of length // SOFO Dynamic: Thing with Laser distance-measurements.. // Borehole Inclination Sensor: measures the inclination of the actual part of the borehole. // Plumbs
Characteristics of oscillations?
Formula, Eigenfrequencies, Resonance, …
How does a DiNi20 work? Useful for continous measurements?
DiNi20 = Digital nivellier von Trimble, Digital Level, selbsthorizontieren, selbstablesened, selbstregistrierend, CCD und Barcode Ablesung, => anscheinend brauchbar für kontinuierliche Messung, ist wohl aber nicht sehr sinnvoll
Relation between standard deviation and tolerance?
mostly 2.5 to 3 times the standard deviation is once the tolerance
What kinds of tolerances do you know?
Production Tolerance
Assembly Tolerance
Surveying Tolerance
What type of plumps exist? Influences on the accuracy?
optical, wire, laser, inverse (bottom-up). // Accuracy is influenced by: Torsional Oscillations, Oscillations induced by spiral whirls in the shaft, Water dribs, Plumb line deviations by eccentric plumb wire, Plumb line deviations by in-homogenous gravity distribution
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Note: Das Schwimmlot bietet den Vorteil, dass die Messstrecke durch eine vertikale Bohrung ins Fundament der Sperre hinein verlängert werden kann und zwar bis in eine Tiefe, die als fest anzusehen ist, was bei den Gewichtsloten häufig nicht angenommen werden kann.
Relationship between surveying tolerance and tolerance
T_s = T*sqrt(1-(1-p)^2)
p: probability of the surveying tolerance being off.
T_s: surveying tolerance
What is being transmitted during plumbing?
relative Coordinates
How do you determin the plumb-center?
wire and inverse: compute the damped osciallations // optical: raster on the ground where you can determine the center-point
Can a plumbing been made bottom-up?
Yes, with a swimming plumb, where the bottom end of the plumb wire is fixed in a borehole and at the top end it’s fixed to a floating part.
How does a totalstation find the prisms during the first measurement?
ATR (automatic target recognition), Powersearch or measure and save the positions before.
What do you know about Indoor Positioning?
Positioning, Navigation, Tracking. Needed, because GNSS doesn’t work in buildings
Which systems do you know for indoor positioning?
Clips (LaserIgel + Kamera), Cricket Nodes, WLAN, …
Why is the national trigonometric network not used in Engineering Geodesy?
* Precision: grid: 1E-4 (1sgima); industrial requirements: 1E-5
* disortions to the Gauß-Krüger-mapping function, i.e. scaling factor varies (for D)
* point density (1 TP 4th order / km2)
* trigonometric network is hierarchic; but homogeneous network required
* location of points is driven by requirements in land surveying
