How does a surveyor measure distance?
There are several ways for a surveyor to measure distances these days. There are numerous different measurement instruments a surveyor will use depending on what they are measuring.
Years ago, when surveyors had to measure long distances, they would use a chain of a certain length. The length of a chain is an eightieth of one mile. One chain is about 20.117m long. When surveyors were using chains to measure distance, they would have an assistant and they would be called a chainman. The term is still in use today, although it is becoming rarer.
The use of the chain also is evident in the measurement term chainage. Surveyors will use the term chainage as a distance measurement along a road or a railway. Chainages usually start at zero and follow the centreline of the road or railway and be referenced with 10m intervals.
With the advent of modern surveying equipment, chains are no longer used. Surveyors will now use laser tape measures or Total Stations for measuring larger distances. The Total Station allows the very accurate measurement of very long distances. The Total Station can achieve millimetre accuracy over distances of 300metres plus. For even greater distance measurements the surveyor may well choose to use GPS Surveying Equipment. GPS Surveying Equipment is ideal for measuring distance that are over half a mile or about 800m.
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What equipment does a surveyor use?
Surveyors will use a wide range of measuring devices. The type of measurement instrument will depend on the task the surveyor is undertaking. Choosing the right surveying equipment for the task at hand is one of the skills a surveyor must possess.
The job of a surveyor is to accurately record the dimensions of a given building or site. The measurements a surveyor needs to record accurately will vary from exceedingly small measurements to areas that can span for miles.
As the dimensions that a surveyor needs to measure can differ greatly, they must choose the right measuring instrument for the task at hand. The surveyor must also choose a measurement instrument that will give the required accuracy for the task being undertaken. If a surveyor is measuring distances that are greater than a mile, the accuracy of the equipment could be within either a yard or a metre. But if the surveyor is measuring a room in a building then the measuring equipment would want to be accurate to the millimetre or thousandth of an inch.
What are the types of surveying instruments?
There are several types of surveying instruments a surveyor would use. The instrument used would depend on the task being undertaken. Here is a list of the common surveying instruments that a surveyor would use today.
- Laser Tape Measure.
- Automatic or Digital Level.
- Theodolite.
- Total Station.
- GPS Surveying Equipment.
- 3D Scanner
- Drone Surveying Equipment.
What is a Laser Tape Measure?
A Laser Tape Measure does the same job as a standard Tape Measure, but it uses a laser to measure the distance instead of the physical steel or fibre of a traditional graduated tape measure. They use the same technology found in reflectorless total stations. By emitting a beam of laser light and measuring the time it takes to be reflected back off a surface the Laser Tape Measure can work out the distance accurately.
You can find more information on laser tape measures here on this site. I consider the Leica Disto D2 Laser Tape measures as one of the best on the market today. Read my review of the Leica Disto D2 here.
What is an Automatic Level?
An Automatic Level is a specialist piece of survey equipment used to obtain accurate levels over long distances. It is an optical device that can be setup easily with the line of sight perpendicular to the force of gravity. The line of sight observed is horizontal relative to the position that the automatic level is positioned.
The Automatic Level is most used by construction professionals and surveyors who need accurate levels. These accurate levels are usually over hundreds of metres.
To find out how an Automatic Level works I took one apart to show all the internals and explain how it works. The reason it is called the Automatic Level is because of the automatic compensator it has. Find out how the automatic level works here.
What is a Digital Level?
A Digital Level is like the Automatic Level. The digital level measures differences in height just like the Automatic Level, but it uses a special measuring staff called an Invar Staff. The Invar Staff has barcode type lines on it which enables the digital level to take readings. The digital level is much more accurate for taking levels than the Automatic Level.
The digital level is used by Surveyors who need accurate levels, maybe over long distances. The digital level is ideal for tasks such as monitoring for settlement or establishing control station levels.
What is a Theodolite?
A Theodolite is a precision piece of Surveying Equipment. The theodolite is used by surveyors to measure angles. These angles can be either on the horizontal plane or the vertical plane. These angles are read from the horizontal circle and the vertical circle that are etched glass within the theodolite.
The modern theodolite has a telescope that can move around two perpendicular axes. The horizontal axis is known as the trunnion axis. The vertical axis is just known as the vertical circle. These two axes must be perpendicular otherwise an error will be present in the horizontal axis.
Follow this guide on how to check a Theodolite.
What is a Total Station?
A Total Station is a theodolite with the ability to measure distances from the telescope. Early Total Stations were theodolites with an Electromagnetic Distance Measurement (EDM) device attached above the telescope. Advances in technology soon meant that the EDM was incorporated into the telescope and this would be the first true Total Station. The total station has the ability to measure horizontal angles, vertical angles and distances all at the same time.
Most total stations used by surveyors these days are know as robotic or one-man total stations. These total stations can search for and lock on to prisms, with the instrument readings being transmitted to the surveyor that can now be holding the detail pole and prism. These robotic total stations means that the chainman is no longer needed for surveys.
Follow this guide on how to check total stations for accuracy.
What is GPS Surveying Equipment?
GPS Surveying Equipment uses the signals from the NAVSTAR, GLONASS and Galileo Satellite systems to triangulate a position. For Surveyors, this position will be invariable the surface of the earth. Most GPS devices will give an accuracy to about 5metres. But with more sophisticated GPS Surveying Equipment we can achieve relative accuracy to within a few millimetres.
One of the main advantages with GPS Surveying Equipment is that no clear line of sight is needed, as is the case with automatic levels, theodolites and total stations. However, a clear view of the sky is essential for good accuracy. To be able to achieve millimetre accuracy from the GPS Surveying Equipment we need to be able to receive signals from at least 5 different satellites.
What is a 3D Scanner?
A 3D Scanner captures 3 dimensional points from surfaces that can reflect enough light back to the scanner instrument. 3D scanners use LiDAR. LiDAR is an acronym for Light Detection and Ranging. 3D scanners will produce a point cloud of the scanned area. The point cloud will have many thousands of individual points that the scanned area should be instantly recognisable.
With so many points being available, specialist software is usually required to manipulate the data. Most surveyors are concerned with dimensions between specific details, for example the distance between two buildings. For this reason 3D scanners are usually only found with a few specialist surveyors.
What is Drone Surveying Equipment?
Drones have become extremely popular over the last few years. And with them being fitted with powerful cameras, LiDAR scanners and GPS positioning systems drones can be particularly useful surveying tools. Drone Surveying Equipment is particularly useful for surveying large areas of land.
Drones can cover a larger area than a surveyor can on foot or by vehicle. They can also pick up more points during the flight than a surveyor can on foot. This will give a denser point information which in turn can lead to a more accurate survey. However, the more points that a surveyor has means more processing of information. This can increase the workload for the surveyor.
The prices of drones are falling all the time, so they are becoming more affordable. The popular drones with surveyors currently are the DJI drones. Check out the latest prices for DJI Drones on Amazon.
Conclusion
With a multitude of measurement instruments available to the modern-day surveyor, getting accurate measurements has never been so easy. Yet knowing how to use all the instruments available can be daunting. No matter how easy these instruments can make taking accurate measurements, it is still easy to make mistakes and get the distance measurement. Knowing whether the measurements that have been taken are right or wrong is due to the skill of the surveyor.