Unit II: Compass Survey (5 hrs)
2.1 Introduction, Uses, and Importance:
2.1. Introduction to Compass Survey:
- Compass survey is a traditional method of land surveying that relies on compasses to determine directions and angles. It is one of the fundamental techniques in surveying, especially in areas where access to advanced surveying instruments is limited. Compass surveys provide a cost-effective way to establish basic reference lines and directions.
2.1. Uses of Compass Survey:
- Compass surveys have several important applications, including:
- Preliminary Surveys: Compass surveys are often used to create a preliminary layout for more detailed surveys or construction projects.
- Property Boundary Determination: They are employed to locate and demarcate property boundaries and land parcels.
- Orientation of Maps and Plans: Compass surveys help align maps and plans with the true geographic north, ensuring accurate representations.
- Simple Topographic Mapping: They can be used to create basic topographic maps of an area, including elevation contours.
2.1. Importance of Compass Survey:
- Compass surveys are important for several reasons:
- Accessibility: Compasses are relatively simple instruments and do not require advanced technology, making them accessible in remote or less-developed areas.
- Cost-Effective: Compass surveys are cost-effective for small-scale surveys and boundary determinations, saving resources in comparison to more sophisticated methods.
- Foundational Knowledge: Compass surveys serve as the basis for understanding surveying principles, measurements, and directional systems.
2.1. Skills Acquired:
- Compass surveys provide valuable skills to surveyors and professionals in related fields. These skills include:
- Understanding and measuring directions using compasses.
- Working with bearings, angles, and reference meridians.
- Creating basic survey plans and sketches.
- Learning to adapt to various field conditions and challenges.
2.1. Safety Considerations:
- Safety is paramount in compass surveying, as it often involves working in various environments and terrains. Surveyors must be aware of potential hazards, including wildlife, difficult terrain, and weather conditions. Proper safety measures and equipment should be used to ensure the well-being of surveyors and field personnel.
This introduction to compass survey sets the stage for understanding the fundamental concepts, techniques, and practical applications in compass surveying. It provides the groundwork for subsequent topics within this unit.
2.2 Meridians, Bearings, and Angles in Survey:
In surveying, understanding meridians, bearings, and angles is essential for measuring directions and orientations. These concepts help surveyors determine the position and alignment of lines and features on the Earth's surface. Let's delve into each of these components:
**2.2.1 Meridians:**
- **Definition:** Meridians are imaginary lines that run from the North Pole to the South Pole on the Earth's surface, and they are part of the global coordinate system. The prime meridian, which runs through Greenwich, England, is commonly used as a reference meridian for longitude measurements in degrees. Meridians help establish the framework for measuring directions and angles in surveying.
- **Use in Surveying:** Surveyors use meridians as reference lines for measuring directions and angles. By specifying the meridian used in a survey, they can accurately determine the orientation of lines, boundaries, and features on the ground.
**2.2.2 Bearings:**
- **Definition:** Bearings are angular measurements that represent the direction of a line or feature relative to a reference meridian. Bearings are expressed in degrees, minutes, and seconds, and they indicate the angle between the line and the reference meridian. Bearings are typically measured clockwise from the reference meridian.
- **Common Bearings:** Bearings can be categorized into two common systems:
- **Whole Circle Bearing (WCB):** In the WCB system, bearings are measured in degrees from 0° to 360°, starting from the north direction and proceeding clockwise. A line pointing due east has a WCB of 90°.
- **Quadrantal Bearing (QB):** In the QB system, bearings are measured in degrees from 0° to 90°, starting from the nearest cardinal direction (N, E, S, W) and proceeding clockwise. A line pointing due east has a QB of 90°.
- **Use in Surveying:** Bearings are fundamental in surveying for describing the orientation of lines, property boundaries, and other features. They help surveyors create accurate survey plans and maps.
**2.2.3 Angles:**
- **Definition:** Angles are measurements used to specify the relationship between two lines or features. In surveying, angles are measured in degrees, with a full circle comprising 360°. For angles less than 360°, the measurement is taken in a clockwise direction from one line to another or from a reference direction.
- **Use in Surveying:** Angles are employed to determine the relative orientation of lines, calculate the bearing between two points, and establish angles of intersection, deflection, or convergence. Surveyors use angles extensively to create detailed survey plans and to calculate distances between points.
Understanding meridians, bearings, and angles is foundational for surveyors as they work to establish directions and positions on the Earth's surface. These concepts help ensure accurate and consistent measurements in surveying, whether for property boundary determination, topographic mapping, or construction layout. Properly accounting for meridians and working with bearings and angles is essential to the success of surveying projects.
Unit II: Compass Survey (5 hrs)
**2.3 Designation of Bearings, Whole Circle and Quadrantal System, and Conversions:**
**2.3.1 Designation of Bearings:**
- In compass surveying, the designation of bearings is crucial for representing the direction of lines, features, or boundaries. Bearings are usually expressed in degrees, minutes, and seconds, and they indicate the angle between the direction of the line and a reference meridian. This angle is measured clockwise from the reference meridian.
**2.3.2 Whole Circle Bearing (WCB):**
- Whole Circle Bearing (WCB) is a system of designating bearings that uses the full 360-degree circle. In the WCB system, bearings are measured clockwise from the north direction (0°) all the way around the circle to 360°. This means that a line pointing due east has a WCB of 90°, a line pointing south has a WCB of 180°, and so on. The compass bearing is indicated in degrees, minutes, and seconds.
**2.3.3 Quadrantal System (QB):**
- The Quadrantal System is another system used for designating bearings in compass surveying. In this system, the circle is divided into four quadrants, with each quadrant starting from a cardinal direction (North, East, South, West) and extending up to 90° clockwise.
- The QB system is typically used for simplifying bearings. For example:
- A line pointing due east has a QB of 90°.
- A line pointing due south has a QB of 180°.
- A line pointing due west has a QB of 270°.
- A line pointing due north has a QB of 0° or 360° (since the circle wraps around).
**2.3.4 Conversions:**
- Conversions between Whole Circle Bearing (WCB) and Quadrantal Bearing (QB) are essential for understanding and working with compass bearings effectively. Here are the main conversion principles:
- To convert WCB to QB:
- Subtract the WCB from 90° for lines in the first quadrant.
- Subtract the WCB from 180° for lines in the second quadrant.
- Subtract the WCB from 270° for lines in the third quadrant.
- Subtract the WCB from 360° for lines in the fourth quadrant.
- To convert QB to WCB:
- Add 90° to QB values in the first quadrant.
- Add 180° to QB values in the second quadrant.
- Add 270° to QB values in the third quadrant.
- Add 360° to QB values in the fourth quadrant.
- Conversions are necessary to ensure consistency and understanding when working with bearings in both systems. Surveyors must be proficient in making these conversions for accurate record-keeping and data analysis.
Understanding the designation of bearings, both in the Whole Circle Bearing (WCB) and Quadrantal Bearing (QB) systems, and being able to convert between them is a fundamental skill in compass surveying. It allows surveyors to accurately represent directions and angles on compass surveys and maps.
Unit II: Compass Survey (5 hrs)
**2.4 Fore Bearing and Back Bearing:**
**2.4.1 Fore Bearing:**
- The fore bearing is an important concept in compass surveying. It refers to the angle measured from a reference meridian (usually true north) to the direction of a line, feature, or boundary being surveyed. The fore bearing is measured in a clockwise direction.
- Key points regarding the fore bearing:
- It indicates the forward direction along the line being surveyed.
- It is typically measured in degrees, minutes, and seconds.
- The reference meridian is usually true north, but it can also be magnetic north in some cases.
- Fore bearings are crucial for creating survey plans and drawings. They provide the orientation of lines and features with respect to the reference meridian and help in mapping and boundary demarcation.
**2.4.2 Back Bearing:**
- The back bearing is the opposite of the fore bearing. It is the angle measured from the reference meridian to the direction that is exactly opposite to the fore bearing. In other words, the back bearing is 180 degrees (a half circle) different from the fore bearing.
- Key points regarding the back bearing:
- It indicates the backward direction along the same line that was surveyed.
- It is typically used in traversing and boundary surveying to check for closure and accuracy.
- The back bearing is essential for detecting blunders or errors in compass surveys. It should match the fore bearing if there are no errors in the measurements.
- The relationship between the fore bearing and the back bearing is simple: The sum of the fore bearing and the back bearing should be equal to 360 degrees. This relationship ensures that the measurements form a closed traverse or circuit.
**2.4.3 Practical Significance:**
- In compass surveying, fore bearings and back bearings are essential for various purposes:
- They help in closing survey loops and circuits, ensuring that the measurements are accurate.
- Back bearings are used to verify the consistency and accuracy of compass measurements. A significant difference between fore and back bearings may indicate errors in the survey.
- For example, when conducting a compass traverse to determine property boundaries, the back bearing for the last line surveyed should match the fore bearing of the first line. If they do not match, it suggests that errors have been made in the survey, and corrections are needed.
- Back bearings are also useful when plotting surveys on maps or plans, as they provide a reference for accurately representing the direction of lines and features in relation to a reference meridian.
Understanding fore bearings and back bearings is crucial for compass surveyors to ensure the accuracy and reliability of their survey data. They play a significant role in checking for errors, closing surveys, and maintaining consistency in compass measurements.
Unit II: Compass Survey (5 hrs)
**2.5 Types of Compass:**
Compasses are essential tools in compass surveying, used to determine directions, bearings, and angles. There are different types of compasses, each with specific features and applications. Here are some of the common types of compasses used in compass surveying:
**1. Magnetic Compass:**
- The magnetic compass is the most basic and widely recognized type of compass. It operates based on the Earth's magnetic field and consists of a magnetic needle that aligns itself with the Earth's magnetic poles. The compass card usually displays the cardinal directions (N, S, E, W) and degrees.
- Use: Magnetic compasses are suitable for basic orientation tasks, such as determining the north direction and magnetic bearings.
**2. Prismatic Compass:**
- A prismatic compass is an advanced version of the magnetic compass. It includes a prism or prism system that allows surveyors to read the compass card directly from the sighting line. Prismatic compasses provide more accurate readings compared to standard magnetic compasses.
- Use: Prismatic compasses are used for more precise compass surveying, especially when higher accuracy is required.
**3. Surveyor's Compass:**
- A surveyor's compass is a specialized compass designed for surveying tasks. It often includes additional features such as a clinometer to measure vertical angles, a leveling bubble to ensure the compass is horizontal, and a telescope for sighting distant points.
- Use: Surveyor's compasses are used in compass surveys for measuring both horizontal and vertical angles, making them suitable for more advanced surveying tasks.
**4. Clinometer Compass:**
- A clinometer compass, also known as a clinometer or inclinometer compass, is designed to measure vertical angles. It usually includes a dial or card for reading angles and a leveling bubble for ensuring that it's held in a level position.
- Use: Clinometer compasses are valuable for measuring slopes, elevations, and vertical angles in topographic surveys.
**5. Gyrocompass:**
- A gyrocompass is a highly specialized and precise compass that uses a rapidly spinning gyroscope to determine true north. It is unaffected by magnetic fields, making it suitable for use on ships, airplanes, and in other environments where magnetic compasses may not be reliable.
- Use: Gyrocompasses are primarily used in marine and aviation navigation rather than land surveying.
**6. Geological Compass:**
- Geological compasses are designed for use in geological and geophysical surveys. They often include features such as an inclinometer, a clinometer, and a compass card. They are essential for measuring the orientation of rock layers, faults, and other geological structures.
- Use: Geological compasses are primarily used in geology and earth sciences.
Each type of compass has specific advantages and applications. The choice of compass depends on the surveying task at hand, the level of accuracy required, and the specific conditions of the surveying environment. Surveyors select the most appropriate compass based on the project's needs and the desired level of precision.
**2.6 Magnetic Declination:**
Magnetic declination, also known as magnetic variation, is a significant factor in surveying and navigation. It represents the angle between true north (geographic north) and magnetic north, which is the direction indicated by a magnetic compass. Understanding magnetic declination is crucial for accurate orientation, especially when using magnetic compasses in surveying. Here's a more detailed explanation:
**1. Definition:** Magnetic declination is the angle, in degrees, between true north and magnetic north at a specific location on the Earth's surface. It occurs because the Earth's magnetic field is not perfectly aligned with the geographic north pole.
**2. Variation by Location:** Magnetic declination is not constant and varies depending on your geographic location. Different regions on Earth have different magnetic declination values. Some areas have no magnetic declination (i.e., magnetic north aligns with true north), while in other regions, the magnetic compass can deviate significantly from true north.
**3. Causes of Magnetic Declination:**
- **Geographic Variation:** Earth's magnetic field is generated by the movement of molten iron in its core. As this molten iron flows, it generates a magnetic field that is not perfectly aligned with the Earth's axis of rotation, leading to magnetic declination.
- **Local Variation:** Magnetic declination can also be influenced by local geological features, such as underground ore deposits or magnetic anomalies.
**4. Use in Surveying:**
- Surveyors need to account for magnetic declination when using a magnetic compass for orientation. Ignoring magnetic declination can lead to significant errors in direction and measurement.
- To correct for magnetic declination, surveyors apply the declination value to their compass measurements. They either add or subtract the appropriate number of degrees to align the compass reading with true north. The direction of adjustment depends on whether the magnetic north is east (positive declination) or west (negative declination) of true north.
**5. Measuring Magnetic Declination:**
- Magnetic declination values can change over time due to fluctuations in Earth's magnetic field. Surveyors and navigators can obtain current magnetic declination values for a specific location from government agencies, magnetic observatories, or online resources.
- Declination values are typically expressed in degrees and minutes east or west, relative to true north. For example, a declination of "10° 30' E" means that magnetic north is 10 degrees and 30 minutes east of true north.
In conclusion, magnetic declination is a critical consideration in surveying and navigation, especially when using magnetic compasses. Surveyors must account for magnetic declination to ensure accurate orientation and measurement. Understanding local declination values and applying corrections is essential for precise survey work, ensuring that survey data aligns correctly with true geographic directions.
**2.7 Local Attraction:**
Local attraction, in the context of surveying, refers to the magnetic influence or interference that can affect the readings of a magnetic compass or other magnetic instruments used for measuring directions and angles. This interference can be caused by nearby magnetic objects, mineral deposits, or geological features and may lead to inaccurate compass measurements. Here's a more detailed explanation of local attraction in surveying:
**1. Causes of Local Attraction:**
Local attraction can be caused by a variety of factors, including:
- **Magnetic Objects:** Nearby magnetic objects, such as vehicles, metal structures, power lines, and equipment, can create magnetic fields that affect the operation of a magnetic compass. These magnetic objects can deflect the compass needle and result in erroneous readings.
- **Mineral Deposits:** Areas with significant underground mineral deposits, particularly those containing magnetic minerals like iron ore, can influence the magnetic field in the vicinity. This, in turn, can affect the behavior of magnetic instruments.
- **Geological Features:** Certain geological formations, such as basalt, which contains magnetic minerals, can influence the magnetic field locally. These formations can lead to local magnetic anomalies and impact compass readings.
**2. Detecting and Correcting Local Attraction:**
Surveyors need to be aware of the potential for local attraction and take steps to detect and correct it:
- **Detection:** Detecting local attraction involves conducting checks and tests to identify compass disturbances. Common techniques include comparing compass readings at different locations, using multiple compasses, and checking the consistency of compass readings over time.
- **Correction:** Correcting local attraction requires identifying the sources of magnetic interference and taking measures to mitigate their effects. Correction methods may include:
- Moving away from magnetic objects or sources of interference.
- Physically shielding the compass from magnetic influences.
- Applying mathematical corrections to compass measurements based on observed local attraction effects.
- **Field Notes:** Surveyors should document instances of local attraction in their field notes, along with the corrective measures applied. This information is critical for ensuring the accuracy and reliability of survey data.
**3. Importance of Addressing Local Attraction:**
Addressing local attraction is essential in surveying for several reasons:
- **Accuracy:** Local attraction can lead to significant errors in compass measurements, which can have a cascading effect on the entire survey. Accurate direction and angle measurements are fundamental to reliable survey results.
- **Reliability:** Inaccurate readings due to local attraction can lead to disputes in boundary determinations and property surveys. To maintain the integrity and credibility of survey work, addressing local attraction is crucial.
- **Consistency:** Ensuring that compass readings are free from local attraction effects helps maintain consistency in survey data, especially when multiple surveyors are involved or when measurements are taken over an extended period.
In summary, local attraction is a potential source of error in compass surveying, and surveyors must be vigilant in detecting and addressing its effects. By understanding the causes and implementing appropriate correction measures, surveyors can ensure the accuracy and reliability of their compass measurements and the overall quality of their survey work.
**2.8 Closing Error and Adjustments (Graphical and Analytical):**
In surveying, closing errors can occur when conducting traverse surveys or measurements of closed loops. Closing errors are discrepancies between the initial and final measurements of a survey, often due to a combination of systematic and random errors. These errors can lead to misalignment, inaccuracies in data, and inconsistencies in survey results. Surveyors use two main methods to address closing errors: graphical adjustments and analytical adjustments.
**1. Closing Error:**
- A closing error, also known as a closing mistake or discrepancy, is the difference between the calculated or measured initial position and the position obtained by completing a closed traverse or loop. It is expressed as both the horizontal and vertical error components, and it indicates how well the measurements conform to the principles of closure in surveying.
**2. Graphical Adjustments:**
- **Graphical adjustments** involve manipulating and correcting the measured or calculated survey data using graphical techniques. Surveyors make adjustments to ensure that the traverse closes correctly and conforms to the principles of closure.
- **Common techniques used in graphical adjustments include:**
- **Bowditch Method:** The Bowditch method involves adjusting traverse measurements by distributing the error proportionally to each line or angle based on the algebraic sign of the discrepancy.
- **Transit Rule:** The transit rule is a graphical adjustment technique that applies corrections to angles or directions based on their discrepancies, with the primary goal of closing the traverse.
- **Graphical Resection:** Graphical resection is used when adjusting the position of a station to fit the observed angles and distances while maintaining other fixed positions.
**3. Analytical Adjustments:**
- **Analytical adjustments** involve mathematical computations to correct the survey data, ensuring that the traverse closes within acceptable limits. These adjustments are often applied using specific adjustment procedures.
- **Common analytical adjustment methods include:**
- **Compass Rule:** The compass rule is an adjustment technique that uses mathematical principles to calculate the necessary corrections to traverse measurements. It adjusts both distances and directions to close the traverse.
- **Crandall's Rule:** Crandall's rule is a modification of the compass rule that incorporates distance corrections while minimizing angular changes in the traverse.
**4. Importance of Closing Error and Adjustments:**
- Addressing closing errors and making appropriate adjustments is crucial for the following reasons:
- **Accuracy:** Accurate survey data is vital for land management, construction, mapping, and various engineering projects. Closing errors can lead to inaccurate measurements, affecting the quality of survey results.
- **Consistency:** Closing errors can introduce inconsistencies in survey data, potentially causing disputes in boundary determinations or legal surveys. Correcting these errors ensures consistent and reliable survey outcomes.
- **Professional Standards:** Surveyors are bound by professional standards and ethical guidelines. Addressing closing errors and making adjustments is a fundamental aspect of adhering to these standards and delivering trustworthy surveying services.
In summary, closing errors are common in traverse surveys, and surveyors use both graphical and analytical adjustments to correct these errors and ensure that survey data conforms to the principles of closure. By applying appropriate adjustments, surveyors maintain the accuracy, consistency, and reliability of their survey work, which is crucial for various applications in land management, construction, and cartography.
**2.9 Instruction on Field Works:**
Fieldwork is a critical component of surveying where surveyors collect data, measurements, and observations in the field to support various surveying tasks and projects. Proper fieldwork is essential to ensure the accuracy and reliability of survey data. Here are some key instructions for conducting fieldwork in surveying:
**1. Planning and Preparation:**
- **Site Visit:** Before beginning fieldwork, visit the survey site to familiarize yourself with the terrain, landmarks, and any potential challenges. Understanding the site's characteristics is crucial for planning the survey.
- **Research:** Conduct background research on the area, including existing survey records, property boundaries, legal considerations, and any historical data that might be relevant to your survey.
- **Equipment Check:** Ensure that all surveying instruments and equipment are in good working condition and properly calibrated. This includes levels, total stations, theodolites, GPS equipment, and compasses.
**2. Safety Measures:**
- **Safety First:** Prioritize safety in the field. Surveyors often work in varying conditions, including remote or hazardous areas. Use appropriate personal protective equipment (PPE), adhere to safety protocols, and be aware of potential risks.
- **Weather Considerations:** Be prepared for weather conditions, especially in outdoor fieldwork. Protect equipment from adverse weather, and ensure the safety of the surveying team during extreme conditions.
**3. Team Coordination:**
- **Roles and Responsibilities:** Clearly define the roles and responsibilities of each team member. Assign tasks based on each team member's skills and expertise.
- **Communication:** Maintain effective communication within the team. Establish a communication protocol to ensure that team members can relay information and observations accurately.
**4. Data Collection:**
- **Precision and Accuracy:** Pay meticulous attention to precision and accuracy during data collection. Measure multiple times if necessary to minimize errors. Record measurements consistently and legibly in field notes.
- **Environmental Factors:** Be aware of environmental factors that can affect measurements, such as temperature, wind, and atmospheric conditions. These factors can influence instrument accuracy.
- **Instrument Operation:** Ensure that instruments are set up and operated correctly. Follow established procedures for instrument use, leveling, and data recording.
**5. Field Notes and Documentation:**
- **Field Notes:** Maintain detailed field notes, which should include information about the survey location, date and time, weather conditions, instrument used, measurements taken, and any observations. Field notes should be organized and well-documented for future reference and analysis.
- **Sketches and Diagrams:** Create sketches and diagrams to document the survey area and any significant features, landmarks, or measurements. These visual aids can be valuable when interpreting data.
**6. Quality Control:**
- **Redundant Measurements:** Take redundant measurements for key points or features to verify their accuracy. Inconsistencies may indicate errors that need to be addressed.
- **Blunder Detection:** Implement procedures for blunder detection to identify measurement errors. This may involve scrutinizing measurements that seem inconsistent with expected values.
**7. Closure and Adjustment:**
- **Closure Checks:** After completing fieldwork, conduct closure checks to assess the accuracy of the measurements and to identify any closing errors. Use the appropriate adjustment methods (graphical or analytical) to correct any errors and ensure that the traverse or survey aligns correctly.
**8. Data Transfer:**
- **Data Storage:** Safely store and back up field data to prevent data loss. Use appropriate data transfer and storage methods to ensure data security and accessibility.
**9. Reporting:**
- **Report Generation:** Prepare clear and comprehensive survey reports. The report should include a summary of the fieldwork, the methods used, findings, and any recommendations.
**10. Post-Processing:**
- **Data Processing:** After fieldwork, process collected data using specialized software or tools. Verify data accuracy and consistency during post-processing.
- **Map and Plan Creation:** Use processed data to create maps, plans, and other deliverables as required by the project or survey specifications.
Proper fieldwork is crucial for the success of surveying projects. Following these instructions and best practices in the field will help surveyors collect accurate and reliable data, ensuring that survey results are of the highest quality and meet the project's objectives.