In surveying, accurate measurements of distances are crucial for creating precise maps and plans. There are several methods available for linear measurements in surveying, each with its own advantages and limitations. In this blog post, we will explore common methods used for linear measurements in surveying by direct method.
1. Pacing Method
The pacing method is one of the simplest and oldest methods for measuring distances in surveying. It involves counting the number of steps taken to cover a certain distance. This method is best suited for rough estimates and short distances, as it may not provide high accuracy.
2. Instrumental Method
The instrumental method involves using surveying instruments, such as theodolites or total stations, to measure distances. These instruments use various techniques, such as triangulation or electronic distance measurement, to calculate distances accurately. The instrumental method is highly precise and is commonly used in professional surveying.
3. Judging Distance Method
The judging distance method relies on the surveyor’s visual estimation of distances. It involves comparing the target distance with known reference distances or objects. This method requires experience and skill to achieve accurate measurements and is often used in situations where instruments are not available.
4. Time Measurement Method
The time measurement method is based on the principle that the speed of sound is constant. In this method, a sound signal is generated at the starting point, and the time taken for the sound to reach the receiver at the endpoint is measured. By knowing the speed of sound, the distance can be calculated. This method is suitable for measuring long distances but may be affected by environmental factors.
5. Chaining Method
The chaining method is a traditional method that involves using a chain or tape to measure distances. The chain or tape is laid along the ground, and the distance is measured by counting the number of chain or tape lengths. This method is relatively accurate and is commonly used in land surveying.
To perform linear measurements by the direct method, surveyors use a variety of equipment:
1. Tape Measure
A flexible tape measure is used for measuring shorter distances, typically up to 100 feet. It is made of steel or fiberglass and is available in various lengths.
2. Steel Band
For longer distances, a steel band is used. It is more rigid than a tape measure and can measure distances up to several hundred feet.
3. Electronic Distance Measuring (EDM) Device
In modern surveying, electronic devices are used to measure distances with high precision. These devices use laser or electromagnetic waves to determine distances.
The direct method of linear measurement involves the following steps:
1. Selecting Reference Points
Surveyors choose two reference points, such as the corners of a building or existing survey markers, to establish a baseline.
2. Setting Up the Equipment
The surveyor sets up the tape measure or steel band at one reference point and extends it to the other reference point.
3. Taking Measurements
The surveyor carefully measures the distance between the two reference points using the tape measure or steel band. They ensure the tape or band is straight and taut for accurate measurements.
4. Recording the Measurements
The measured distance is recorded in the surveyor’s field book or digital device.
Accuracy and Error Sources
While the direct method of linear measurement is relatively simple, it is important to consider potential sources of error:
1. Tape or Band Stretching
Over time, tape measures and steel bands can stretch, leading to inaccurate measurements. Regular calibration and maintenance are necessary to ensure their accuracy.
2. Temperature and Humidity
Environmental conditions can affect the length of a tape measure or steel band. Changes in temperature and humidity cause expansion or contraction, resulting in measurement errors.
3. Human Error
Surveyors must take measurements with precision and avoid parallax errors caused by viewing the tape or band from an angle. Training and experience are essential to minimize human errors.
Linear measurements in surveying by direct method play a crucial role in creating accurate maps, plans, and land surveys. The choice of measurement method depends on factors such as the required accuracy, distance, availability of instruments, and surveyor’s expertise. While the instrumental method provides the highest level of accuracy, other methods such as pacing, judging distance, time measurement, and chaining can also be effective for different surveying scenarios.
FAQs on Linear Measurements in Surveying by Direct Method
What is linear measurement in surveying?
Linear measurement in surveying refers to the process of measuring distances between two points on the ground. It is an essential part of surveying as it helps in determining the size, shape, and location of land or any other object.
What is the direct method of linear measurement?
The direct method of linear measurement in surveying involves physically measuring the distance between two points using various instruments such as a tape measure or an electronic distance measuring device (EDM). This method is commonly used for shorter distances and provides accurate results.
What instruments are used for linear measurement in surveying?
There are several instruments used for linear measurement in surveying. The most common ones include:
- Tape measure: A flexible measuring tape made of steel or fiberglass.
- Electronic distance measuring device (EDM): A device that uses laser or electromagnetic waves to measure distances.
- Optical instruments: Instruments such as theodolites and total stations that have built-in distance measuring capabilities.
What are the units of linear measurement in surveying?
The units of linear measurement in surveying vary depending on the country or region. The most commonly used units include meters, feet, and chains. In some cases, surveyors may also use kilometers or miles for larger distances.
How accurate are linear measurements in surveying?
The accuracy of linear measurements in surveying depends on various factors such as the instrument used, the skill of the surveyor, and the environmental conditions. In general, modern instruments can provide highly accurate measurements with an error margin of a few millimeters or less.
What are the challenges in linear measurement in surveying?
Linear measurement in surveying can be challenging due to several factors. Some of the common challenges include:
- Uneven terrain: Surveying in hilly or rugged terrain can make it difficult to obtain accurate measurements.
- Obstacles: The presence of trees, buildings, or other obstacles can obstruct the direct measurement between two points.
- Weather conditions: Adverse weather conditions such as rain, fog, or strong winds can affect the accuracy of measurements.
Why is linear measurement important in surveying?
Linear measurement is important in surveying as it forms the basis for creating accurate maps, determining property boundaries, and planning construction projects. It helps in ensuring that the measurements are precise and consistent, allowing for proper decision-making and analysis.