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Interactive Audio Lesson
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Understanding Bearings
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Today, we are diving into the concept of bearings in surveying. Who can tell me what a bearing is?
Isn't it just the direction of one point to another?
Exactly! Bearings indicate the direction of a survey line with respect to a reference meridian. Now, can anyone tell me the types of meridians we use?
There are true meridian and magnetic meridian, right?
That's correct! The true meridian is established through astronomical observations while the magnetic meridian relates to where a magnetic needle points. This is key in obtaining accurate measurements. We can use a mnemonic like 'T for True, M for Magnetic' to remember these.
That's helpful! So, how do we actually measure these bearings?
Great question! Bearings can be measured either as Whole Circle Bearings or Reduced Bearings. Let's focus on Whole Circle Bearings first.
Types of Bearings
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Whole Circle Bearings (WCB) are measured clockwise from north. Can someone tell me its range?
0 to 360 degrees!
That's right! Now, about Reduced Bearings. Does anyone know how they are measured?
They are measured from the north or south towards the east or west, and can never exceed 90 degrees.
Exactly! We use letters N and S for north and south, and E and W for east and west. For instance, we might write a bearing as N30°15'E. Can we think of an acronym to help us remember how to notate Reduced Bearings?
How about 'NSEW' for North, South, East, West?
Perfect! It’s essential to understand these classifications in order to accurately communicate directions during surveys.
Magnetic Compasses
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Moving on to measurement tools, what kind of compasses are used in surveying?
I believe there are prismatic compasses and surveyor’s compasses?
Correct! The prismatic compass is popular for portability and ease. Can anyone tell me how its design helps in measuring bearings?
It has a prism that allows you to see the reading on the graduated ring while sighting a target.
Exactly! This design minimizes parallax errors. Remember, good technique is vital for accurate measurements. Can anyone provide a memory aid for using a compass?
How about 'Level, Align, Read' as a step reminder?
Great mnemonic! Keep practicing that, as precise usage will improve your surveying skills!
Effects on Measurements
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Last but not least, what are some factors that can affect our bearing measurements?
Local attraction can interfere with compass readings, right?
Exactly! Local attraction can cause errors due to nearby magnetic materials or objects. It’s crucial to check the difference between your fore bearing and back bearing to detect any issues.
What’s the significance of magnetic declination then?
Magnetic declination is the angle difference between true north and magnetic north. Remember to adjust for it as it varies by location and time. A quick way to recall it would be: 'Declination Direction Depends on Location.'
I see how understanding these factors is vital for accurate surveying!
Absolutely! Always stay aware of these influencing elements to ensure accuracy in your work.
Introduction & Overview
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Quick Overview
Standard
This section explains bearings as the directions of survey lines concerning meridians. It introduces the true and magnetic meridians, types of bearings, magnetic compasses for measurements, and considerations like magnetic declination and local attraction that affect the accuracy of bearings.
Detailed
Measurement of Bearings
In surveying, bearings refer to the direction of survey lines concerning a reference meridian. There are two main types of meridians: true meridian, based on astronomical observations, and magnetic meridian, derived from a freely suspended magnetic needle. Bearings can be classified into two types: Whole Circle Bearing (WCB), which is measured in a clockwise direction from north, and Reduced Bearing (RB), which measures angles from the north or south towards the east or west. This section also highlights different magnetic compasses used in surveying, discusses associated factors like magnetic declination and local attraction, and emphasizes their impact on measurement accuracy. Understanding bearings is crucial for accurate surveying, especially during traverses.
Audio Book
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Definition of Bearing
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Bearing is the direction of each survey line with respect to a reference meridian direction. Bearing of a line can be defined as the angle measured in clockwise direction from a given reference.
Detailed Explanation
A bearing indicates the direction of a line compared to a defined reference point, known as the meridian. It helps surveyors determine the orientation of a path in relation to the true north. When we talk about the bearing, we specifically mention how we measure this direction in a clockwise fashion from the reference meridian.
Examples & Analogies
Imagine using a GPS; when you want to navigate, it typically provides instructions based on directions from a fixed point (like north). Similarly, bearings help surveyors understand which way to go by giving a directional angle based on a north reference.
Types of Meridians
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Meridian direction can be divided into two main directions; (a) True meridian, and (b) Magnetic meridian.
Detailed Explanation
There are two types of meridian used in surveying. The true meridian is the geographical line that runs from the north to the south pole at a specific location. In contrast, the magnetic meridian is the direction indicated by a magnetic needle, which shows magnetic north. These two types of meridians may not always align, especially due to various magnetic influences in the area.
Examples & Analogies
If you think of a map showing true north, it’s like pointing to the top of a globe directly to the North Pole. On the other hand, using a compass is like a treasure hunt where the needle points you a bit off from true north due to magnetic influences—kind of like the magnetic pull can mislead you slightly from the true path.
Whole Circle Bearing (WCB) and Reduced Bearing (RB)
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Bearings are measured in two ways: 1. Whole circle bearing (WCB) 2. Reduced bearing (RB) or Quadrantal bearing (QB).
Detailed Explanation
Whole Circle Bearing (WCB) measures angles from a reference direction (like magnetic north) all the way around in a circular measure. It ranges from 0° to 360°. Reduced Bearing (RB), however, gives angles based on the closest cardinal direction, either north or south, and measures into the east or west quadrants. This simplifies calculations, especially in trigonometry.
Examples & Analogies
Think about a round clock. The WCB is like telling the time from 12 o'clock (0° for north) all the way around to 6 o'clock (180°). Reduced Bearings are more like saying, 'It’s quarter past 3'—where you’ve defined it in reference to north or south.
Types of Magnetic Compasses
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The magnetic compasses used in surveying may be classified as: 1. Prismatic Compass 2. Surveyor's Compass 3. Trough Compass 4. Tubular Compass.
Detailed Explanation
Surveys use different types of magnetic compasses for different needs. The Prismatic Compass is versatile and provides clear readings, while the Surveyor's Compass is not as commonly used. Trough and Tubular compasses serve as accessories to various instruments, focusing on indicating direction rather than detailed measurements.
Examples & Analogies
Think of these compasses like different types of smartphones. The Prismatic Compass is like a smartphone with excellent camera features, perfect for versatile use. Meanwhile, the Trough or Tubular Compass is like a simple mobile device that just serves the primary function of making calls—very useful, yet limited in its capabilities.
Fore Bearing and Back Bearing
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Fore bearing and back bearing of a line AB are to be measured. Set the compass at station A, bisect station B.
Detailed Explanation
When surveying, fore bearings are measured when you face a particular direction first (e.g., from A to B), while back bearings are measured the opposite way (from B to A). This helps verify that the measurements taken are accurate, as both bearings from two points should differ by a specific angle, typically 180°.
Examples & Analogies
Imagine you're running a relay race where one runner passes the baton to the next. The fore bearing represents the first runner's direction towards the finish line, while the back bearing indicates where that runner came from. Just like in survey methods, checking these routes ensures that the baton was passed correctly without any mistakes.
Magnetic Declination
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The horizontal angle between magnetic meridian and true meridian is known as magnetic declination.
Detailed Explanation
Magnetic declination occurs because the magnetic north pole does not perfectly align with the geographic north pole. Depending on where you are, this angle can affect how accurate a compass reading is when determining true bearings. Knowing the degree of declination allows surveyors to adjust their measurements.
Examples & Analogies
Think about it like adjusting your view while navigating using Google Maps. The maps are accurate, but if there is interference (a detour, for instance), you must know how to navigate around that issue, similar to adjusting for magnetic declination when using a compass.
Local Attraction
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Deviation in reading caused by nearby magnetic objects is called local attraction.
Detailed Explanation
In surveying, local attraction happens when nearby magnetic materials influence the compass needle, leading to incorrect readings. This can arise from things like power lines, pipelines, or even metallic objects on-site. Surveyors must be aware of these influences to ensure accuracy in their measurements.
Examples & Analogies
Imagine being at a party with friends trying to find someone in a crowd. If your friend stands too close to a magnet (like wearing metallic clothing), it might distort your view of them. Similarly, magnetic items nearby can distort the compass reading, leading surveyors astray.
Computation of Included Angles
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In a closed traverse, bearings of lines may be calculated if bearing of one of the line and the included horizontal angles between various lines are known.
Detailed Explanation
To find the bearing of a line in a closed traverse, you can start with one known bearing and add the included angles between that line and the others. This method helps in calculating the geometrical relationships between different lines when surveying.
Examples & Analogies
Think of it as piecing together a jigsaw puzzle. You have one corner piece (the known bearing), and as you fit in the angles that connect to other pieces (the included angles), it tells you the full picture of how the lines interact with each other.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Bearings: Directions measured relative to meridians in surveying.
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True Meridian: The north-south direction obtained through astronomical observations.
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Magnetic Meridian: Direction indicated by a magnetic needle.
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Whole Circle Bearing: A complete circle of measurement from 0° to 360°.
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Reduced Bearing: A measurement not exceeding 90° related to north or south.
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Magnetic Declination: The angle between magnetic and true north.
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Local Attraction: Magnetic interference that can affect accuracy.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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A survey line has a bearing of N45°30'E, meaning it is measured 45 degrees 30 minutes east of north.
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If the magnetic declination at a point is 5° east, the true bearing of a line with a magnetic bearing of 100° is calculated as 100° + 5° = 105°.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Bearings are neat, in a circle we show, North to South, and East to West flow.
📖 Fascinating Stories
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Imagine a traveler who always consults their compass, turning first to the true north, then adjusting for the magnetic pull they feel from the compass needle. This story illustrates how bearings guide them safely as they navigate.
🧠 Other Memory Gems
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To remember the types of bearings: 'W for Whole, R for Reduced.'
🎯 Super Acronyms
Use 'TAKE NOTE' to recall
- True and Magnetic
- Adjust for Declination
- Keep an Eye on Local Attraction!
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Bearing
Definition:
The direction or angle of a survey line with respect to a reference meridian.
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Term: True Meridian
Definition:
The direction established by the geographic north and south poles, based on astronomical observations.
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Term: Magnetic Meridian
Definition:
The direction indicated by a freely suspended magnetic needle at a specific location.
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Term: Whole Circle Bearing (WCB)
Definition:
An angle measured clockwise from the magnetic north, ranging from 0° to 360°.
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Term: Reduced Bearing (RB)
Definition:
The angle between a survey line and the north or south direction, always less than 90°.
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Term: Magnetic Compasses
Definition:
Instruments used to determine magnetic bearings, including different types like prismatic and surveyor's compass.
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Term: Magnetic Declination
Definition:
The angle difference between the magnetic north and the true north.
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Term: Local Attraction
Definition:
Errors in compass readings caused by nearby magnetic materials or objects.