What is Linear Measurement in Surveying? Instruments For Linear Measurements

What is Linear Measurement?

Linear measurement is the process of measuring distances between points on a surface. This is typically done with a tape measure, but can also be done with other devices, like lasers.

Linear measurement is an important part of surveying, as it allows surveyors to plot out points and measure distances between them.

This information can be used to create maps and other surveying documents.

Linear surveying is the measurement of distances between points on the Earth’s surface. Linear surveying can be done using a variety of approaches, and the best one depends on the level of accuracy needed.

Surveyors are concerned with the measurement of vertical and horizontal distances and angles, as well as direct location, in the modern world.

As a result, these can be used in a number of ways in traversing, triangulation, trilateration, and other mixed-mode operations.

Types of Liner measurement surveying.

There are three main types of linear surveying methods:

• Direct Measurements.
• Measurement by optical means
• Electronic methods

Direct Measurements

Methods of linear measurement that fall under the direct technique include:

Pacing as a method of linear measurement

The pacing strategy is most commonly used in the early stages of a project. In this procedure, the surveyor is obligated to undertake a preliminary survey in a short period of time.

Using this method, you can also roughly compare the distance you’ve already determined.

This method involves keeping track of the distance traveled between the two locations on a line.

Helps determine how long a line is when you know how long the pace is on average. How fast you pace and how steep the terrain is all factor into how long your stride will be.

In order to estimate the length of one’s natural step, it is helpful to walk on somewhat level ground and walk over numerous lines of specified lengths. Slopes and rocky ground make pacing difficult to do properly.

Measurement with a Passometer

A Passometer is a pocket or leg-mounted gadget styled like a stopwatch.

The Passometer measures how many paces a person has walked while wearing it.

Afterward, the distance between the two end stations can be calculated by multiplying the number of paces by the average pace length.

Pedometer

Pedometers are similar to passometers in that they measure distance automatically. For measuring vertical distances, a pedometer is the best choice.

Odometer

An odometer is a device that counts how many times a wheel has turned. The total distance traveled is calculated by multiplying the number of wheel revolutions by the wheel’s circumference.

On a curved surface, this equipment does not give reliable findings. The vehicle’s speedometer can be used if the surface is flat.

Basically, Odometers are mounted on wheels that travel the desired distance along measuring lines. Odometer readings can be multiplied by the circumference of the wheel to get the distance traveled.

The instrument’s readings on the undulating ground are erroneous since it only records the length of the surface it has actually traversed. It is possible to approximate the distance traveled by using a car’s speedometer if the path is somewhat straight.

Chaining

When measuring distance, chaining is the most exact means of doing so, as it involves either the use of a chain or tape.

An ordinary chain can be utilized, although a tape or special bar can be used for work of better precision. Chaining is the primary method for determining distances in surveying.

However precise the measurement of angles may be, the survey is limited by the chaining.

Measurement by Optical Means

Observations are made through a telescope, and distances such as tachometer (stadia) or triangulation are calculated as a result of this method.

To swiftly determine a point’s horizontal distance and elevation, surveyors use a tachometer (also known as a “stadia” in the US).

Using a telescope with two or more horizontal cross wires in a predetermined spacing, Stadia observations can be obtained.

A graded rod is held vertically in the desired stage to read the apparent intercepted length between the bottom and top wires.

Using comparable triangles, the distance from the telescope to the rod is perceived as if it were a rectangle. 1/500 of this distance can be accurately measured with sufficient care.

Electronic Methods

Radio or light waves are used to estimate distances in these linear surveying methods, which rely on propagation and reflection.

The following are some examples of the numerous instruments employed by electrical methods:

• Geodimeter
• Tellurometer,
• Decca navigator, and
• Lambda position fixing system.

Based on the modified light waves’ propagation, geodimeters can estimate distances. Radio waves are used to determine distance in the other three instruments.

Electra-Magnetic Methods Overview:

Measurements of distance in electronic methods rely on radio or light waves for propagation and reflection and subsequent reception.

Geodimeter, Tellurometer, and Decca Navigator are some of the electronic equipment that can be used for this purpose.

For surveyors on site today, ‘complete station’ is the most important piece of equipment It’s a tool that combines the classic theodolite’s ability to measure angles with that of an electronic distance meter.

For all base-line measurements, the use of tape measures has been deemed obsolete.

All terrain conditions can now be taken into consideration when determining the distance.

There are algorithms in modern total stations, as shown in fig. 2 and fig. 3, that reduce the slope distance to its horizontal and vertical components.

Today, total stations with built-in data logging are commonplace on construction sites for conducting surveys of various kinds.

Distance measurements typically take between 1.5 and 3 seconds. Measurements can be repeated automatically in difficult weather circumstances to increase accuracy.

Measurements from a distance are repeated multiple times a second in tracking modes. Total stations with built-in EDM enable the following:

The ability to traverse large distances while maintaining a high degree of control over swing faults.

Triangulation has been outmoded by control networks that include more measured lengths. In the end, this leads in a significantly larger control scale mistake

Large expanses of land were surveyed and controlled by polar coordinates from a single baseline.

EDMs like the Mekometer ME5000 can be used to measure deformation to sub-millimeter accuracies.

This device has a range of 8 kilometers and an accuracy of 0.2 mm 0.2 mm/km of the distance recorded excluding un-modelled refraction effects.

Instruments For Linear Measureements

Different instruments can be used to perform linear measurements. These are some examples:

Chain

The chain is made up of 100 or 150 links made of galvanized mild steel wire that are connected together with oval rings and handles at both ends. The area is divided into a network of triangles, and the sides of different triangles are measured directly in the field with a chain or tape.

Tape

Tapes are used to take more precise measurements. Cloth or linen tape, Fiber tape, Metallic tape, Steel tape, and Invar tape are the materials from which the tapes are made.

Arrows

Arrows are used to make chains and tape easier to use. They’re used to indicate the end of a chain. The one-pointed end of an arrow is embedded in the ground, and the other is secured with a ring.

Ranging rod

Ranging Rods are vertical rods with a height of 2-3 meters that are used to mark survey stations. It is painted with 20 cm wide red and white bars. These rods are used to range survey intermediate sites.

Tacheometer

The tachometer is a device that measures the vertical and horizontal distance between two locations.

Electro-Magnetic Distance Measuring Device

The following characteristics are seen in EDM devices:

• Absolute circle reading
• Laser plummet
• Never-ending drives
• 30 x magnifications,
• High-resolution LCD display.

It is an extremely accurate approach that works on electromagnetic waves and is not affected by geography. A pulse of radiation of a specific wavelength is transmitted.

Importance of Linear Measurement in Surveying

Linear Measurement is the process of measuring distance in units of length. The surveyor uses a measuring tape to measure this distance by walking along the ground and recording the distances.

The following are some reasons why linear measurement is used in surveying:

• Accurate determination of the distance
• Relatively low cost of equipment
• No need to convert data into three dimensions (survey on flat or regular terrain)
• Relatively easy to use with basic training.

Linear measurements are a very useful tool of surveyors. With the aid of distance measuring devices, the job has become more efficient and less time consuming.

A majority of surveying instruments can be used to measure distance.

Errors in linear measurement in surveying

Length other than standard

Tape makers do not guarantee that 100 ft steel tapes are exactly 100.00 ft in length. Every time the tape is used, an error due to the improper length occurs.

Temperatures that are not typical

Steel tapes are standardized at a temperature of 68° F (20° C).

The length of the tape will alter when the temperature rises or falls. The temperature of the tape can differ significantly from the temperature of the measured air.

Tension

If the strain is higher than normal, the tape will stretch. When less than standard tension is used, the tape will be shorter than usual.

Sag

A tape that is not supported all the way along its length will sag. Sag can be reduced by applying the proper tension.

Inadequate alignment

This error occurs when one end of the tape is disconnected or when there is an impediment in the path. The real distance will be shorter than the measured distance.

Inaccurate marking

This issue occurs at random as a result of incorrectly placed chaining pins. Errors can be reduced by carefully placing chaining pins and then double-checking the measurement.

Improper reading or interpolation

When reading or noting the measurement clearly or in a hurry, inaccuracy occurs. Errors can be reduced by reading carefully and using a tiny scale to obtain the final value.

Challenges of Linear Measurement in Surveying

In most cases, problems related to linear measurement occur in three areas: location and construction of intermediate sites, location probes, and survey control loops.

Location of Intermediate Sites

Problems in location of intermediate sites can be reduced by using a tacheometer, as it relies only on the distance between two measuring points.

Location Probes

The errors in the construction of location probes can be reduced with use of an indicator or an arrow that represents where the next probe should be placed. The error due to not using such indicators is very high.

Survey Control Loops

The errors in this case occur due to insufficiencies in the measurement of the distance between control points. These errors can be reduced by making different measurements, plotting and tracing surveys and adjusting distance measuring devices.

Measurement Limitations

Linear measurements are not exactly accurate. At most, they are accurate within 2 cm (1/4 inch). In fact, the standard deviation of linear measurements is 1 cm (1/8 inch).

Generally, linear measurements are accurate enough for fieldwork. However, they may not be accurate enough if the surveyor is trying to make a point measurement that is less than 1/8 inch (3.1 mm).

 Linear Measurements FAQs

What is Linear Measurement in Surveying?

Linear measurement is the process of measuring distance in units of length. The surveyor uses a measuring tape to measure this distance by walking along the ground and recording the distances.

The most common tool used to measure linear distances is a tape measure, but other types of instruments can also be used, such as chains, rods, and lasers.

What are some problems with linear measurement?

• Length other than standard
• Tape makers do not guarantee that 100 ft steel tapes are exactly 100.00 ft in length. Every time the tape is used, an error due to the improper length occurs.
• Temperatures that are not typical
• Steel tapes are standardized at 68° F (20° C).

What is a linear string?

Linear strings are lines of string that are used to determine distances in linear measurement surveys. They measure distances along a straight line. Each piece is taken at a specific distance between two points that were determined by triangulation or coordinates.

How much time does it take to perform one linear measurement?

It takes approximately one minute to make one linear measurement while walking at a velocity of 1 yard per second.

How far do surveyors move during one linear measurement?

Surveyors can walk anywhere from 400 to 1000 yards for one linear measurement depending on the terrain, density of angular points and the accuracy required.

What is linear measurement?

Linear measurement is the process of measuring distance in units of length. The surveyor uses a measuring tape to measure this distance by walking along the ground and recording the distances.

How do you find the linear measurement?

The distance between two specified points or objects is measured linearly. Thus, length can be defined as “the total distance measured between the leftmost and rightmost ends of an item in the specified system of units.” Using tape to measure the length of a banana

What equipment is used in a linear survey?

Linear measurement can be performed by surveying instruments such as the compass, bubble level and calipers. They are required to locate a starting point and two survey points that can be determined by triangulation.

The sequence of measurements will determine the amount of accuracy required to find the linear distance.

What are the types of measurements in surveying?

Horizontal distances and angles, vertical distances and angles, and slope distances are the five most prevalent forms of survey measures.

Angles and distances are calculated relative to a horizontal or vertical plane.

What are the two types of linear measuring instruments?

Linear measuring instruments are classified based on their precision. There are two types of instruments: non-precision instruments and precision instruments.

Steel rule, caliper divider, and telescopic gauge are non-precision tools used to measure to the line graduations of a rule.

What is the objective of linear surveying?

The objective of linear surveying is to establish a series of specific distances that can be used for the project.

Linear measurements are used to determine the minimum, maximum, and average distances (distance between two points).

What is linear accuracy?

There are several approaches for progressively positioning a user payload along a linear axis. The degree to which commanded moves match globally recognized units of length is simply referred to as linear positioning accuracy.

What is the linear error?

Linear error is a measure of inaccuracy that occurs during a survey because of an error in the measurements. Linear errors are expressed in terms of ‘ x.

What are the advantages of linear measurement?

Linear measurements are a very useful tool for surveyors. With the aid of distance measuring devices, the job has become more efficient and less time-consuming.

Consequently, it is considered one of the most important parts of surveying.

What are the disadvantages of linear measurement?

Prospective surveyors need to consider the disadvantages of linear measurement.

For one, measuring is a slow process unlike other forms of surveying such as triangulation. Training is also needed, as well as updated knowledge on current guidelines and regulations in the field of surveying.

What is a survey primer? 

A survey primer outlines the fundamentals of surveying so that novices can grasp the basic concepts around this particular field.