--- title: "Radiation and intersection methods" subject: "Surveying I" chapter: 6 key: "semester_3/surveying_i:radiation-and-intersection-methods" source: https://www.bctengineer.com/q/semester_3/surveying_i/radiation-and-intersection-methods site: BCT Engineering --- # Radiation and intersection methods Surveying I · Chapter 6: Plane Table Survey - Asked in: 2078 Kartik, 4 marks; 2069 Chaitra, 4 marks; 2066 Jestha, 8 marks; 2065 Shrawan, 6 marks (asked 4 times) - Video: [Plane Table Survey || Radiation Method || With Explanation](https://www.youtube.com/watch?v=boPrQFZEn9A) — Civil Samajh - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/surveying_i/radiation-and-intersection-methods - Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-6 ## Question Explain the radiation and intersection methods of plane table survey, with their suitability and sketches. ## Short answer Radiation method: the table is set at a single station, rays drawn to points, and distances measured and scaled; suitable for small open areas where all points are accessible. Intersection method: two stations with a measured base line are used; rays drawn to the point from both stations intersect to fix it; it is used for inaccessible points where distance cannot be measured, requiring only one linear measurement. ## Answer #### Radiation method The table is set up at one station O, from which all the points to be plotted are visible. 1. Level, centre and fix the sheet; mark the point **o** on the sheet for O. 2. Pivot the alidade on **o** and sight each station A, B, C, D in turn; draw a ray towards each. 3. Measure the distances OA, OB, OC, OD with a tape and mark them to scale along the rays to get a, b, c, d. 4. Join a, b, c, d to obtain the plan. ```text b c \ / \ ray / a ------- o (table) -------- d ``` **Suitability:** small areas with open ground, where all points can be seen from one station and distances can be measured easily. It is the base of detailing by plane table. #### Intersection method Two stations A and B (the ends of a base line) are chosen so that the point P to be located is visible from both. 1. Set the table at A, orient it by compass, and plot **a**. Sight B and draw the ray; measure AB and plot **b** to scale. 2. Sight P from a and draw the ray aP (also rays to the other points). 3. Shift to B, centre **b** over B, and orient the table by back-sighting A along the line ba. 4. Sight P again from b and draw the ray bP. The intersection of the two rays is the plotted point **p**. ```text p / | \ / | \ / | \ a ------------- b (stn A) base (stn B) ``` **Suitability / advantages:** - Used for locating inaccessible points (across rivers, hills, buildings, a far-away church spire, etc.) where distance cannot be measured. - Only one linear measurement (the base line) is needed; many points can be fixed quickly. - A third ray from another station checks the plotted point. - Good intersection angle (about 60 to 120 degrees) is needed for accuracy. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Radiation is best for: A. Small open areas where all points are visible from one station B. Locating the table station C. Inaccessible points across rivers D. Long traverses Answer: A. All points must be seen from one station and distances measurable. (Key point: Radiation suitability) 2. After drawing rays, how are points plotted? A. By angle measurement B. Distances are measured and marked to scale along the rays C. By a second ray D. By compass Answer: B. Plot a, b, c, d at scaled distances along the rays. (Key point: Radiation step) 3. At the second station B in intersection, how is the table oriented? A. It is not oriented B. By a third point C. By measuring distance D. By back-sighting A along line ba Answer: D. Back-sight along ba so the sheet keeps the same orientation. (Key point: Intersection orientation) 4. Why is intersection used? A. To locate inaccessible points needing only the base line measured B. Distances to every point are measured C. It is the most accurate for narrow angles D. Single station only Answer: A. Only the base line is measured; intersection angles of about 60 to 120 degrees give good accuracy. (Key point: Intersection advantage) ## Related in Surveying I - [Methods of plane table survey](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Amethods-of-plane-table-survey) — Surveying I, chapter 6, asked 6× - [Working principle of plane table survey](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aworking-principle-plane-table) — Surveying I, chapter 6 - [Reliable orientation; intersection over radiation](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aorientation-reliable-intersection-vs-radiation) — Surveying I, chapter 6 - [Intersection versus resection in plane tabling](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aintersection-vs-resection-plane-table) — Surveying I, chapter 6 - [Plane table principles; orientation by back sighting](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aorientation-back-sighting) — Surveying I, chapter 6, asked 4× - [Plane table principles; advantages, disadvantages](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aprinciples-adv-disadv-plane-table) — Surveying I, chapter 6, asked 2× ## Related in other subjects - [Coplanar lines, intersection point and plane](https://www.bctengineer.com/question.md?key=semester_2%2Fmathematics%3Acoplanar-lines-intersection-point-plane) — Mathematics, chapter 3, asked 2× - [Plane through intersection, perpendicular to plane](https://www.bctengineer.com/question.md?key=semester_2%2Fmathematics%3Aplane-through-intersection-perpendicular-plane) — Mathematics, chapter 3 - [Rankine's method table, 150° intersection, 3°](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Arankine-simple-curve-150-3deg) — Surveying II, chapter 6 - [Parametric line in 3D: point and plane intersection](https://www.bctengineer.com/question.md?key=semester_4%2Fcomputer_aided_design%3Aparametric-line-segment-plane) — Computer Aided Design, chapter 3