Geology and Surveying
70380
(Part B - Surveying)
Distance Measurement
Objectives• Select suitable distance measuring
equipment for a particular task.
• Take Chaining measurements.
• Reduce and correct field chaining measurements.
• Understand fundamental principles of EDM.
General
• Direct– “Chaining”– EDM
• Indirect– Triangulation– Optical distance measurements
• Approximate– Pacing– Measuring wheel– Optical range finders
Chaining Equipment• Plumb Bob
• Spring Balance
• Thermometer
• Steel Band / Tape / Chain
• Clinometer (or theodolite)
Standardisation of Survey Tapes
• To provide legal traceability of measurements to a known standard.
• Accounts for– Expansion and contraction with change in temperature
– Elasticity of steel tape with variations in length and tension applied.
• Hence subsidiary standard tapes note a standard temperature and tension at which indicated distance is true.
Field Procedures - Chaining
• Fully supported– Level– Slope
• In Catenary– Level– Slope
• In all cases ensure the tape follows a straight line
Measuring Between Stations
• Hold even metre mark on one peg.
• Pull required tension while plumbing over marks.
• Read leader.
• Record readings.
• Add distances:– 2 m division 58
Leader 1.987
Total Distance 59.987
Setting out a Station
• Hold desired even metre mark.• Calculate required leader reading.• Pull required tension while plumbing.• Place peg under leader at required reading.• Add distances:
– Set out 85.692
Even metre 84
Leader 1.692
Fully Supported M’mt
• Should only be done when surface is even and free of obstacles.
• Ensure tape is aligned with terminal points.
• Measure slope if necessary.
• Avoids necessity for making a sag correction.
Measurement in Catenary
• Should only be done when necessary.
• Ensure full catenary where possible.
• Ensure tape is aligned with terminal points.
• Measure and record tension applied.
• Measure slope if necessary.
• Must use at least one plumb bob.
Step Chaining
• Avoids the need to make repeated slope corrections
Level Chain
Level Chain
Plumb bob line
Surface
Measuring Long Distances
• Ensure a straight line is maintained.
• Use accurate temporary intermediate marks.
• Keep a running record (chainage) in field notes.
Care of the Steel Band
• Do not pull the chain tight if there are any “kinks” in it - IT WILL BREAK!
• Do not form any “loops” when unrolling of rolling up.
• Do not “double back” - keep band straight.
• Do not allow vehicles to drive over the band.
• Apply light oil when necessary.
Reductions and Corrections to be Applied
• Temperature Correction
• Tension Correction
• Sag Correction
• Slope Correction
Temperature Correction
Temperature Correction - Example
Tension Correction
Tension Correction - Example
Sag Correction
Sag Correction - Example
Slope Correction
A B’
B
l
d’
Combining Corrections - Example
Combining Corrections - Example
Corrections when Setting Out
Setting Out - Example Answer
Electromagnetic Distance Measuring Equipment (EDME)• In common use from around 1960s.
• Work on:– Light waves– Microwaves– Pulse laser (no reflector required)
• Common accuracy today 3mm ± 3ppm– Equates to 6mm over 1 Km
• Must be corrected for atmospheric and many other effects including standardisation
EDM Signal
EDM Return Signal
EDM Prism
Total Stations
Measure H and V distances
Measure Distances
Use COGO functions
Use other in-built functions
Summary• Understanding of accuracy means you are
able to select suitable distance measuring equipment for a particular task at hand.
• We investigated different Chaining measurements and saw how to carry out reduction and correction of field chaining measurements.
• We looked at the fundamental principles of EDM.
Self Study
• Read Module 18
• Do self assessment Questions
• Access edm.exe
Questions?