📚 CTEVT | Control Survey – Chapter 5: Resection and Intersection
(Full Notes + Practice Questions + Free PDF)
Resection and Intersection are important control point establishment techniques used in Control Survey (EG 2102 GE) when direct measurement of distances or angles is difficult or impossible.
Chapter 5 explains how unknown positions can be determined from known control points, making these methods especially useful in rough terrain, urban areas, hilltops, valleys, and inaccessible locations.
This chapter completes the Control Survey syllabus by introducing indirect but powerful positioning techniques.
🧩 Chapter Overview: Resection and Intersection
Resection and Intersection are surveying methods used to determine the position of an unknown point using observations from or to known points.
This chapter helps students understand:
✔️ Definition and basic principles
✔️ Difference between resection and intersection
✔️ Purpose and scope of both methods
✔️ Field procedures and observations
✔️ Computation and adjustment concepts
✔️ Practical applications in control surveys
These methods are widely used in triangulation densification, plane table surveying, and modern total station work.
📥 Download the Full Chapter 5 Notes (Free PDF)
🎥 Watch the Chapter 5 Video on YouTube
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👉 [Click Here to Watch Chapter 5 on YouTube]
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🔍 5.1 Resection
🔍 5.1.1 Definition of Resection
Resection is the method of determining the position of an unknown point by observing angles or directions from the unknown point to at least three known control points.
📌 In resection, the instrument is set up at the unknown station.
🔍 5.1.2 Principle of Resection
The basic principle is:
📌 If the directions or angles from an unknown point to known points are measured, the position of the unknown point can be computed.
Resection is based on:
✔️ Geometrical relationships
✔️ Angular observations
✔️ Intersection of lines drawn from known points
🔍 5.1.3 Purpose and Scope of Resection
Resection is used when:
✔️ Instrument station cannot be measured directly
✔️ Control points are visible but inaccessible
✔️ Working in hilly or congested areas
✔️ Extending or densifying control networks
Applications include:
🏔️ Hilltop surveys
🏙️ Urban control surveys
🗺️ Plane table and total station surveys
🔍 5.1.4 Methods of Resection (Conceptual)
Common resection concepts include:
✔️ Three-point resection
✔️ Resection by angle observation
✔️ Resection using bearings
✔️ Resection using total station
(Exact computational methods depend on instrument and field condition.)
🔍 5.2 Intersection
🔍 5.2.1 Definition of Intersection
Intersection is the method of fixing the position of an unknown point by observing directions or angles from two or more known control points.
📌 In intersection, the instrument is set up at known stations, and observations are taken towards the unknown point.
🔍 5.2.2 Principle of Intersection
The principle is:
📌 If directions or angles from known points to an unknown point are observed, the intersection of these lines gives the position of the unknown point.
Intersection is based on:
✔️ Angular measurement
✔️ Line intersection geometry
✔️ Known control coordinates
🔍 5.2.3 Purpose and Scope of Intersection
Intersection is used when:
✔️ The point to be fixed is inaccessible
✔️ Direct measurement is impossible
✔️ The point lies across rivers, valleys, or buildings
Applications include:
🌉 River-crossing surveys
🏗️ Tower and chimney positioning
🗻 Peak and mountain point fixing
🗺️ Control point densification
🔍 5.3 Field Operations for Resection and Intersection
Both methods follow systematic field procedures.
🔍 5.3.1 Reconnaissance
✔️ Identify known control points
✔️ Ensure intervisibility
✔️ Plan observation strategy
✔️ Check geometry for accuracy
🔍 5.3.2 Monumentation and Signaling
✔️ Mark control points permanently
✔️ Provide clear targets or signals
✔️ Ensure stability of stations
🔍 5.3.3 Observation
For Resection:
✔️ Observe angles/bearings from unknown point to known points
For Intersection:
✔️ Observe angles/bearings from known points to unknown point
Multiple observations are taken to improve accuracy.
🔍 5.3.4 Recording
✔️ Field observations recorded carefully
✔️ Proper sketches included
✔️ Station details clearly noted
🔍 5.3.5 Computation and Adjustment
✔️ Position computed using geometric or trigonometric methods
✔️ Errors checked by redundancy
✔️ Adjustments applied if necessary
Accuracy depends on:
📌 Geometry of points
📌 Observation precision
📌 Proper field procedure
🔍 5.4 Field Precautions
To obtain reliable results:
✔️ Select well-conditioned geometry
✔️ Avoid very acute or obtuse angles
✔️ Ensure accurate centering and leveling
✔️ Take repeated observations
✔️ Avoid long sight distances when possible
Good field practice significantly improves accuracy.
🧪 Practical Insights for Students (Chapter 5)
By studying resection and intersection, students learn:
✔️ How to fix inaccessible points
✔️ Difference between observing from unknown vs known stations
✔️ Importance of geometry in control surveys
✔️ Application of indirect positioning methods
✔️ Foundation for modern total station and GNSS work
These methods complement:
📌 Triangulation
📌 Trilateration
📌 Traverse Survey
📝 Short Questions
1️⃣ Define resection.
2️⃣ Define intersection.
3️⃣ State the principle of resection.
4️⃣ State the principle of intersection.
5️⃣ Where is resection used?
6️⃣ Where is intersection preferred?
7️⃣ What is the main difference between resection and intersection?
8️⃣ Mention any two field precautions.
📝 Long Questions
1️⃣ Explain the principle, purpose, and scope of resection.
2️⃣ Describe the principle and applications of intersection.
3️⃣ Compare resection and intersection methods.
4️⃣ Explain field procedures for resection and intersection.
5️⃣ Write notes on errors and precautions in resection and intersection surveys.
🎯 Key Takeaways
✔️ Resection fixes an unknown point from known points.
✔️ Intersection fixes an unknown point by observing from known stations.
✔️ Both are indirect positioning methods.
✔️ Geometry plays a key role in accuracy.
✔️ These methods are vital in inaccessible terrain surveys.
📂 Download Free PDF Notes – Chapter 5: Resection and Intersection
🔽 [Download Notes – Chapter 5 (PDF)]
🎥 Watch the Full Chapter 5 Video
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📂 Download Control Survey PDF
📘 SYLLABUS – Download PDF
📘 Unit 1: Levelling – Download PDF
📘 Unit 2: Traverse – Download PDF
📘 Unit 3: Triangulation – Download PDF
📘 Unit 4: Trilateration – Download PDF
📘 Unit 5: Resection & Intersection – Download PDF
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