Units of Measurement in Surveying
In the field of surveying, accurate measurements are crucial for precise mapping, construction, and land management. Surveyors use various units of measurement, primarily falling into two categories: linear measures and angular measures. Understanding these units and their conversions is essential for professionals and students alike.
Historically, two main systems of measurement have been used in surveying:
- Metric System: Introduced in India in 1956 through the Standards of Weight and Measure Act, this system is now widely used globally. It's based on units of 10 and includes measures for length, area, and volume.
- Foot-Pound-Second (FPS) System: Also known as the British Imperial System, this was commonly used before 1956 and is still prevalent in some countries. It includes units like feet, yards, and acres.
Surveyors often need to convert between these systems, especially when working with historical data or in regions that use different measurement standards. The following tables provide comprehensive information on various units of measurement and conversion factors used in surveying.
These tables cover:
- Basic units of length, area, and volume in both metric and FPS systems
- Conversion factors for lengths, areas, and volumes
- Specialized units used in land surveying and nautical measurements
Understanding these units and their relationships is fundamental for accurate surveying work and effective communication in the field.
Basic units of length in metric system
| Unit | Equivalent |
|---|---|
| 10 millimetres | 1 centimetre |
| 10 centimetres | 1 decimetre |
| 10 decimetres | 1 metre |
| 10 metres | 1 dekametre |
| 10 dekametres | 1 hectametre |
| 10 hectametres | 1 kilometre |
| 1.852 kilometres | 1 nautical mile |
Basic units of area in metric system
| Unit | Equivalent |
|---|---|
| 100 sq. metres | 1 are |
| 10 ares | 1 deka-are |
| 10 deka ares | 1 hecta-are |
Basic units of volume in metric system
| Unit | Equivalent |
|---|---|
| 1000 cub. millimetres | 1 cub. centimetre |
| 1000 cub. centimetres | 1 cub. decimetre |
| 1000 cub. decimetres | 1 cub. metre |
Basic units of length in F.P.S. System
| Unit | Equivalent |
|---|---|
| 12 inches | 1 foot |
| 3 feet | 1 yard |
| 5.5 yards | 1 rod, pole or 1 sq. perch |
| 4 poles | 1 chain (66 feet) |
| 10 chains | 1 furlong |
| 8 furlongs | 1 mile |
| 6 feet | 1 fathom |
| 120 fathoms | 1 cable length |
| 6080 feet | 1 nautical mile |
Basic units of area in F.P.S. System
| Unit | Equivalent |
|---|---|
| 144 sq. inch | 1 sq. foot |
| 9 sq. feet | 1 sq. yard |
| 30.25 sq. yard | 1 sq. rod or pole |
| 40 sq. rods | 1 rood |
| 4 roods | 1 acre |
| 640 acres | 1 sq. mile |
| 484 sq. yards | 1 sq. chain |
| 10 sq. chains | 1 acre |
Basic units of volume in F.P.S. System
| Unit | Equivalent |
|---|---|
| 1728 cu. inches | 1 cu. foot |
| 27 cu. feet | 1 cu. yard |
Conversion Factors for Lengths
| Metres | Yards | Feet | Inches |
|---|---|---|---|
| 1 | 1.0936 | 3.2808 | 39.37 |
| 0.9144 | 1 | 3 | 36 |
| 0.3048 | 0.3333 | 1 | 12 |
| 0.0254 | 0.0278 | 0.0833 | 1 |
Conversion Factors for Areas
| Sq. metres | Sq. yards | Sq. feet | Sq. inches |
|---|---|---|---|
| 1 | 1.196 | 10.7639 | 1550 |
| 0.8361 | 1 | 9 | 1296 |
| 0.0929 | 0.1111 | 1 | 144 |
| 0.00065 | 0.00077 | 0.0069 | 1 |
Conversion Factors for Areas (Ares, acres and sq. yards)
| Ares | Acres | Sq. metres | Sq. yards |
|---|---|---|---|
| 1 | 0.0247 | 100 | 119.6 |
| 40.469 | 1 | 4046.9 | 4840 |
| 0.01 | 0.000247 | 1 | 1.196 |
| 0.0084 | 0.00021 | 0.8361 | 1 |
Conversion Factors for Volumes
| Cub. metres | Cub. yards | Gallons (Imps) |
|---|---|---|
| 1 | 1.308 | 219.969 |
| 0.7645 | 1 | 168.178 |
| 0.00455 | 0.00595 | 1 |
Angular Measures in Surveying
Angular measurements are fundamental in surveying for determining directions, orientations, and the relative positions of points on Earth's surface. An angle is defined as the amount of rotation between two intersecting lines around their common point of intersection.
The basic unit of angular measurement is the radian, which is the angle subtended at the center of a circle by an arc equal to the radius of the circle. However, in practical surveying, two primary systems are used for angular measurements:
1. Sexagesimal System
The sexagesimal system, also known as the degree-minute-second (DMS) system, is the most widely used method for angular measurements in surveying. In this system:
- A full circle is divided into 360 degrees (360°)
- Each degree is subdivided into 60 minutes (60')
- Each minute is further divided into 60 seconds (60")
This system has been used since ancient times and is deeply ingrained in surveying practices. Most surveying instruments, such as theodolites and total stations, are graduated according to this system.
2. Centesimal System
The centesimal system, also known as the grad system, is an alternative method of angular measurement that's gaining popularity, especially in some European countries. In this system:
- A full circle is divided into 400 grads (400g)
- Each grad is divided into 100 centigrads
- Each centigrad is divided into 100 centicentigrads
The centesimal system offers advantages in computation and interpolation due to its decimal nature, making it easier to use with modern digital equipment.
Importance in Surveying
Angular measurements are crucial in various surveying applications, including:
- Triangulation and trilateration for establishing control networks
- Traversing for determining the positions of points
- Setting out curves in road and railway construction
- Calculating areas and volumes
- Astronomical observations for precise positioning
Surveyors must be proficient in both systems and understand how to convert between them, as different regions or projects may require the use of one system over the other. The choice between sexagesimal and centesimal systems often depends on local practices, the equipment available, and the specific requirements of the survey project.
Accuracy in angular measurements is paramount in surveying. Even small errors in angular measurements can lead to significant discrepancies over large distances. Therefore, surveyors use precise instruments and techniques to ensure the highest possible accuracy in their angular measurements.
Angular Measurement Systems
| System | Full Circle | Subdivision 1 | Subdivision 2 |
|---|---|---|---|
| Sexagesimal | 360 degrees (360°) | 1 degree = 60 minutes (60') | 1 minute = 60 seconds (60") |
| Centesimal | 400 grads (400g) | 1 grad = 100 centigrads | 1 centigrad = 100 centicentigrads |
Conversion Factors between Sexagesimal and Centesimal Systems
| Sexagesimal | Centesimal |
|---|---|
| 1° | 1.1111 grads |
| 0.9° | 1 grad |
| 1' | 0.0185 grads |
| 0.54' | 0.01 grads (1 centigrad) |
| 1" | 0.0003086 grads |
| 0.324" | 0.0001 grads (1 centicentigrad) |
Radian Measure
| Measure | Equivalent |
|---|---|
| 1 radian | 57.2958 degrees |
| 1 radian | 63.6620 grads |
| π radians | 180 degrees |
| 2π radians | 360 degrees (full circle) |
Conclusion
Understanding units of measurement is fundamental to the practice of surveying. This article has explored the two primary categories of measurements used in surveying: linear measures and angular measures.
Key takeaways include:
- Linear Measurements: We've examined both the metric system and the Foot-Pound-Second (FPS) system, highlighting their units for length, area, and volume. The ability to convert between these systems is crucial, especially when working with historical data or in regions using different standards.
- Angular Measurements: We've discussed the sexagesimal (degree-minute-second) and centesimal (grad) systems. While the sexagesimal system remains widely used, the centesimal system offers advantages in computation and is gaining popularity in some regions.
- Conversion Factors: The provided tables offer essential conversion factors between different units and systems, serving as a valuable reference for surveyors in their day-to-day work.
- Practical Application: Understanding these units and their conversions is not just academic; it's crucial for accurate mapping, construction, land management, and effective communication in the field of surveying.
As surveying technology continues to advance, the importance of understanding these fundamental units remains constant. Modern surveying instruments may automate many calculations, but a solid grasp of measurement units ensures that surveyors can verify results, communicate effectively with colleagues and clients, and adapt to various working environments.
Whether working with cutting-edge GPS technology or traditional theodolites, whether measuring vast tracts of land or precise engineering tolerances, the units of measurement discussed in this article form the backbone of surveying practice. Mastery of these units and their relationships is a hallmark of a skilled surveyor, enabling precise, reliable work across diverse projects and geographical areas.
As the field of surveying continues to evolve, staying updated with measurement standards and practices will remain an essential part of a surveyor's professional development. This knowledge not only ensures accuracy in current work but also allows for the interpretation and utilization of historical survey data, bridging past and present in the ongoing task of measuring and mapping our world.
