- 2062 Baisakh · 8 marks
Intersection versus resection in plane tabling
Short answer
Intersection locates an object by forward rays from two plotted stations using only the measured base line, useful for inaccessible points. Resection locates the table station by backward rays from plotted points without measuring distances, employing two‑point or three‑point problem solutions.
Distinguish between intersection and resection methods of plane table survey.
Intersection is the method in which a point is located by drawing rays to it from two known plotted stations. Resection is the method in which the table station itself is located on the sheet by drawing rays back from known plotted points to the station.
| Basis | Intersection | Resection |
|---|---|---|
| What is located | The point sighted (object) | The table position (instrument station) |
| Known data | Two stations plotted; base line known | Two or three well-defined points plotted |
| Rays drawn | From a and b forward towards the object | From a, b, c backward towards the table position |
| Table set at | The known stations A and B | The unknown station P |
| Orientation | By back-sighting along the base line | By back-sighting or by trial; must be correct for the rays to meet |
| Distance measured | Only the base line | None |
| Typical use | Inaccessible or far objects | Locating a new, convenient table station from already plotted points, e.g. to fill in details |
| Types / problems | No special problem | Two-point and three-point problems; triangle of error |
| Check | A third ray from another station | A fourth point sighted from the located station |
INTERSECTION RESECTION
p (to be found) a b c (known)
/\ \ | /
/ \ \ | /
a----b (known) \ | /
p (to be found)
In intersection the unknown is where the rays meet forward, while in resection the unknown is where the rays meet backward from known points.
✓ Answer checked by Claude Opus 5.5 (high effort)
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