Question 1

Survey reference directions — why are true meridians generally preferred over magnetic meridians for establishing bearings and control?

Accepted Answer

Introduction / Context: Bearings are referenced either to the true (geographic) meridian or to the magnetic meridian. The choice affects long-term consistency of surveys, mapping, and the integration of different datasets. Understanding the advantages of using the true meridian is critical for geodetic control and cadastral work. Given Data / Assumptions: True meridian is the line through a point toward the geographic North Pole. Magnetic meridian aligns with the Earth’s magnetic field at a point and time. Survey networks may be used and compared over many years. Concept / Approach: The principal advantage of the true meridian is its long-term constancy for a given location (aside from small, well-modeled geodetic effects). Magnetic meridians suffer from secular variation, diurnal changes, magnetic storms, and local attraction (e.g., iron structures, rocks), causing bearings to drift with time or space. Using true meridians ensures that bearings remain comparable across epochs and independent of transient magnetic anomalies. Step-by-Step Solution: 1) Define reference: true north is astronomically/geodetically determined; magnetic north is field-dependent.2) Evaluate stability: true meridian is stable; magnetic meridian varies with time and local attraction.3) Prefer the stable reference to minimize re-adjustments and inconsistencies.4) Conclude that true meridians are preferred because they remain constant. Verification / Alternative check: National mapping agencies publish geodetic coordinates and grid systems tied to true/geodetic north, not to the magnetic meridian, reflecting this preference. Why Other Options Are Wrong: Converge to a point — true for all meridians at the poles but not the reason for preference. Change due to time — describes magnetic meridian behaviour; it is a disadvantage, not a reason for preference. None of these — incorrect because one option clearly states the correct rationale. Common Pitfalls: Assuming “grid north” and “true north” are identical everywhere; grid convergence may need correction, yet both are more stable than magnetic north for control. Final Answer: these remain constant.

Question 2

Chain surveying accuracy — offsets measured with an accuracy of 1 in 40 must meet a plotting tolerance of 0.05 cm at a scale of 1 cm = 20 m. Considering both angular and measurement errors, what is the maximum permissible length of an offset?

Accepted Answer

Introduction / Context: Offsets from a chain line carry two principal error sources: (i) error in setting the perpendicular direction and (ii) error in measuring the offset length. For a given drawing scale and allowable displacement on the plan, the maximum offset length must be limited so the combined positional error does not exceed the plotting tolerance. Given Data / Assumptions: Accuracy of offset measurement = 1 in 40 (i.e., length error ≈ L/40). Allowable displacement on plan = 0.05 cm. Scale = 1 cm : 20 m ⇒ 0.05 cm on plan corresponds to 1 m on ground. Angular and linear components are treated as orthogonal and combined by root-sum-square. Concept / Approach: Let L be the offset length (ground). With 1 in 40 accuracy, the standard deviation/limit of both the directional (from setting perpendicular) and the linear measurement components can be taken as ≈ L/40 each (conventional exam assumption when only a single accuracy figure is given). The resultant ground-position error ≈ √[(L/40)² + (L/40)²] = (L/40)√2. This must be ≤ 1 m (ground equivalent of 0.05 cm at the stated scale). Solve for L. Step-by-Step Solution: 1) Allowed ground error E = 0.05 × 20 = 1.0 m.2) Resultant error: E ≈ (L/40)√2.3) Set (L/40)√2 ≤ 1 ⇒ L ≤ 40/√2 ≈ 28.28 m.4) Hence, the maximum permissible offset length is about 28.28 m. Verification / Alternative check: Even if the two components do not exactly equal each other, using the combined error as above yields a conservative limit close to tabulated values in surveying texts for similar scales and accuracies. Why Other Options Are Wrong: 14.14 m — overly conservative (half of the allowable limit). 200 m — far exceeds the limit; plan displacement would be much larger than permitted. None of these — incorrect because 28.28 m satisfies the conditions. Common Pitfalls: Forgetting to convert the plotting tolerance to ground units; adding errors arithmetically instead of by root-sum-square when they are independent; ignoring the angular component altogether. Final Answer: 28.28 m

Question 3

Traverse geometry — if the whole-circle bearings of lines AB and BC are 146° 30′ and 68° 30′ respectively, compute the included interior angle ABC.

Accepted Answer

Introduction / Context: Included angles in traverses are often derived from line bearings. Converting between forward and back bearings and then taking appropriate differences ensures consistency in traverse adjustment and plotting. This problem reinforces the method for computing an interior angle at a station using whole-circle bearings (WCBs). Given Data / Assumptions: Bearing of AB (WCB) = 146° 30′. Bearing of BC (WCB) = 68° 30′. Included angle ABC is the angle from BA to BC, measured inside the traverse at station B. Concept / Approach: First find the back bearing of AB to get the direction of BA at station B. Back bearing = forward bearing ± 180°. Then, the interior angle at B is the clockwise (or suitable) angle from BA to BC, accounting for 0–360° wrap-around. The smaller of the two possible angles consistent with the traverse direction is taken as the interior angle when the traverse proceeds A→B→C. Step-by-Step Solution: 1) Back bearing of AB (i.e., bearing of BA) = 146° 30′ + 180° = 326° 30′ (mod 360).2) Bearing of BC = 68° 30′.3) Angle from BA (326° 30′) to BC (68° 30′) going forward across 360°: (360° − 326° 30′) + 68° 30′ = 33° 30′ + 68° 30′ = 102°.4) Therefore, the included interior angle ABC = 102°. Verification / Alternative check: Graphical sketching with a protractor or computing the smaller angular difference between directions confirms 102° as the interior angle at B. Why Other Options Are Wrong: 78° or 45° — arise from incorrect difference order or omission of wrap-around at 360°. None of these — incorrect because 102° is correct. Common Pitfalls: Forgetting to convert to the back bearing at B; subtracting in the wrong order; ignoring the 0–360° wrap when crossing north. Final Answer: 102°

Question 4

Highway and railway design — which profile information is required for construction setting-out and earthwork computation?

Accepted Answer

Introduction / Context: Setting out highways and railways requires accurate representations of the terrain and the designed alignment. Two complementary forms of profile information—longitudinal sections and cross sections—are indispensable for geometric design, earthwork estimation, drainage planning, and quantity measurement. Given Data / Assumptions: Longitudinal section (L-section) follows the centerline (or reference line) of the alignment. Cross sections (C-sections) are taken at right angles to the alignment at specified intervals and at critical points. Earthworks (cut and fill) must be computed accurately for cost and scheduling. Concept / Approach: The L-section provides an elevation profile along the route, facilitating vertical alignment (gradients, vertical curves), sight distance checks, and drainage gradient design. Cross sections furnish transverse ground shapes and enable calculation of cut/fill areas for each station, which integrate over chainage to yield earthwork volumes. Together, they also assist in staking out formation widths, side slopes, ditches, and structures (culverts, retaining walls). Step-by-Step Solution: 1) Survey and plot the L-section along the proposed centerline, showing ground and designed grade lines.2) At suitable intervals (e.g., 10–30 m in urban, 30–100 m in rural) and at changes in terrain, take and plot cross sections.3) Compute cross-sectional areas and multiply by the spacing to estimate earthwork using end-area or prismoidal rules.4) Use both sets of data for setting out and quantity control during construction. Verification / Alternative check: Contract documents and standard specifications invariably require both L- and C-sections for design approval and payment measurement, confirming dual necessity. Why Other Options Are Wrong: L-section only — misses volumetric data across formation width. C-sections only — lacks grade control and vertical curve design context. None — contradicts basic practice in linear infrastructure projects. Common Pitfalls: Taking cross sections too widely spaced in variable terrain; failing to update L-section after alignment shifts. Final Answer: both longitudinal and cross sections are required

Question 5

Directional terminology — in plane surveying, the bearing of a line is also referred to as which of the following?

Accepted Answer

Introduction / Context: Surveyors use several terms to describe the direction of a line relative to a reference meridian. While nuances exist among systems, many exam questions equate the general term “bearing” with “azimuth” when measured from a meridian over a 0°–360° range. Clarifying these definitions avoids confusion when reading field notes or plotting directions. Given Data / Assumptions: Bearing: direction of a line with respect to a reference meridian. Azimuth: angle measured clockwise from a reference meridian, typically 0°–360°. Reduced bearing (RB): quadrant bearing measured from N/S toward E/W. Concept / Approach: In many surveying contexts, the term “bearing” is used broadly, and when it is a whole-circle value from north (0°–360°), it is synonymous with azimuth. Magnetic bearing and true bearing specify which meridian (magnetic or true) is used; they still may be expressed as azimuths or as reduced bearings depending on convention. Since the question asks for an alternate name for the bearing of a line in a general sense, “azimuth” is the best match. Step-by-Step Solution: 1) Recognize that bearings reference a meridian.2) Identify that azimuths are bearings expressed 0°–360° clockwise from north.3) Distinguish from “reduced bearing,” which is a quadrant format.4) Choose “azimuth” as the general alternate term. Verification / Alternative check: Textbooks often state: “Azimuth is the whole-circle bearing of a line,” confirming the equivalence when the bearing is not reduced to quadrants. Why Other Options Are Wrong: Magnetic bearing / true bearing — specify reference meridian type, not an alternate name. Reduced bearing — a different notation (quadrantal), not synonymous with whole-circle bearing. Common Pitfalls: Mixing RB and WCB systems; forgetting to convert when combining datasets from different notations. Final Answer: azimuth

Question 6

Vertical alignment — an ideal vertical curve for smoothly joining two different gradients in highways and railways is of which mathematical form?

Accepted Answer

Introduction / Context: Vertical curves provide a smooth transition between ascending and descending grades in road and rail profiles. The choice of curve affects riding comfort, sight distance, and drainage. Designers typically use a mathematical form that ensures a constant rate of change of gradient, which corresponds to a constant vertical acceleration for a vehicle moving at constant speed. Given Data / Assumptions: The objective is uniform comfort and predictable sight distance along the curve. Gradients change from g1 to g2 over a defined length. Vehicle travels at approximately constant speed over the curve. Concept / Approach: A parabolic profile (typically a simple quadratic y = ax² + bx + c) yields a constant rate of change of slope (second derivative constant). This means the vertical acceleration experienced at constant speed is uniform along the curve, minimizing jerk and improving comfort. The parabola also simplifies computation: offsets from tangents vary with the square of chainage, and sight distance calculations become tractable. Step-by-Step Solution: 1) Define desired property: constant change of gradient across the curve length.2) Recognize that a parabola has constant second derivative → constant rate of grade change.3) Conclude that a parabolic curve best meets geometric and comfort criteria.4) Select “parabolic.” Verification / Alternative check: Design manuals (highways/railways) specify parabolic vertical curves for crest and sag transitions; circular arcs are reserved primarily for horizontal alignment. Why Other Options Are Wrong: Circular — constant curvature suits horizontal curves, not ideal for vertical grade transitions. Elliptical/hyperbolic — unnecessary complexity and do not ensure constant rate of grade change. Common Pitfalls: Confusing vertical with horizontal design practice; assuming any smooth curve suffices without considering acceleration (jerk) control. Final Answer: parabolic

Question 7

Chain surveying — the overall accuracy of measurement in a chain survey does not depend on which one of the following considerations?

Accepted Answer

Introduction / Context: Accuracy in chain surveying depends on how measurements are taken and controlled so that plotting errors stay within acceptable limits. Several factors influence this, including the layout of chain lines, the size of offsets, and the plotting scale. However, some considerations affect only the amount of detailing effort, not the measurement accuracy itself. Given Data / Assumptions: Offsets must be short enough to stay within positional tolerances at the chosen scale. Chain line layout should minimize cumulative error and provide good checks (tie lines, check lines). Plotting scale converts ground errors into plan displacements. Concept / Approach: Accuracy hinges on geometric control and measurement precision. Long offsets amplify perpendicular-setting errors; poor chain-line layout can magnify cumulative errors; a small plotting scale tightens tolerances. The importance of features (e.g., whether a fence is critical or minor) influences how frequently you observe and plot details, but it does not change the underlying accuracy of measurement process or the permissible errors dictated by scale and method. Step-by-Step Solution: 1) Identify variables that affect numeric error limits: scale, offset length, and chain-line geometry.2) Note that “importance” affects the decision to include more or fewer details, not accuracy per se.3) Conclude that measurement accuracy does not depend on feature importance.4) Select the corresponding option. Verification / Alternative check: Surveying guidance relates limiting offset lengths and check-line frequencies to scale and layout—not to subjective feature importance. Why Other Options Are Wrong: Length of offset — directly affects perpendicular error magnitude. Scale of plotting — sets plan tolerance for ground errors. General layout — impacts error propagation and ability to detect/correct mistakes. Common Pitfalls: Allowing “important” features to bias instrument precision expectations; accuracy must be maintained uniformly across the sheet to ensure consistency. Final Answer: importance of the features

Question 8

Chain surveying—alignment error: If a 30 m chain (tape) is laid with its line diverging by a constant perpendicular offset d from the correct alignment, what is the error in the measured length along the intended line?

Accepted Answer

Introduction / Context: In chain (tape) surveying, accurate linear measurement assumes the tape is laid exactly along the intended straight alignment. If, however, the tape is displaced sideways by a constant perpendicular distance d, the measured length becomes the hypotenuse of a small right triangle rather than the required horizontal projection along the true line. This creates a systematic alignment (sagitta)-type error even when the tape is otherwise correct and straight. Given Data / Assumptions: Tape length L = 30 m. Perpendicular divergence from true line = d (constant over the measured length). Flat ground and negligible slope, sag, or temperature errors so we isolate alignment error only. Concept / Approach: If the tape is offset by d, the measured straight line is the hypotenuse, while the true length along alignment is the adjacent side. For a short constant offset, the true projection is D = √(L² − d²). The error in length (measured minus true) is therefore c = L − √(L² − d²). Using a binomial expansion, this simplifies to the well-known approximation c ≈ d²/(2L) for small d/L. Step-by-Step Solution: 1) True projected distance: D = √(L² − d²).2) Error: c = L − D = L − √(L² − d²).3) For small d/L, expand √(1 − x) ≈ 1 − x/2: c ≈ L[1 − (1 − d²/(2L²))] = d²/(2L).4) Substitute L = 30 m → c ≈ d²/(2×30) = d²/60. Verification / Alternative check: Numerical illustration: With d = 0.3 m, c ≈ 0.3²/60 = 0.09/60 = 0.0015 m (1.5 mm), which matches calculator results to within rounding for such small offsets. Why Other Options Are Wrong: d²/30: doubles the correct error; it ignores the 1/2 factor from the binomial expansion. d/30 and 30 d²: dimensionally inconsistent or grossly incorrect magnitude. Zero: alignment divergence always produces a positive error. Common Pitfalls: Treating the offset as a random error; it is systematic if the divergence is constant. Confusing alignment error with slope or sag corrections, which require different formulas. Final Answer: d² / 60

Question 9

Topographic surveying—definitions: An imaginary line that joins points on the Earth's surface having exactly the same elevation (reduced level) is called what?

Accepted Answer

Introduction / Context: Contour mapping is central to civil engineering design for roads, canals, embankments, and drainage. Understanding the precise meaning of contour-related terms helps in interpreting maps and preparing longitudinal and cross sections for earthwork computations. Given Data / Assumptions: The question asks specifically for the term describing a line joining points of equal elevation (reduced level) on a plan or map. Standard plane surveying conventions apply. Concept / Approach: A contour line is the locus of points with the same elevation relative to a chosen datum (e.g., mean sea level). On maps, these lines depict terrain relief; close spacing means steep slopes, while wide spacing indicates gentle slopes. By contrast, a contour surface is the three-dimensional surface itself; a contour gradient is a line with a constant slope on the ground; and a level line is a line everywhere perpendicular to the direction of gravity (equipotential) and, strictly speaking, curved with the Earth. Step-by-Step Solution: 1) Identify the required entity: a line on the plan joining equal RLs.2) Match to terminology: ‘‘contour line’’ satisfies the definition.3) Exclude related but different terms (surface, gradient, level line). Verification / Alternative check: Any standard topographic sheet shows multiple contour lines labeled by elevations; interpolating between them estimates ground levels and slopes. Why Other Options Are Wrong: Contour surface: 3D surface, not a map line. Contour gradient: constant-slope line on ground between two contours. Level line: line of equal potential, not a mapping locus of equal elevation points across varying plan positions. None: incorrect because the proper term exists. Common Pitfalls: Confusing level lines (which are truly horizontal) with contour lines (which follow the ground on a plan). Final Answer: contour line

Question 10

Traverse adjustment—Transit Rule: If the arithmetic sum of the latitudes of a closed traverse is ∑Lat and the closing error in latitude is denoted by dx, what is the correction (to be applied to latitude) for a side whose computed latitude is l acco…

Accepted Answer

Introduction / Context: Traverse adjustment distributes small misclosures so that the final figure satisfies ΣDeparture = 0 and ΣLatitude = 0. When angular work is relatively more precise than linear, the Transit Rule is preferred over Bowditch's rule, because it allocates corrections in proportion to the computed departures and latitudes themselves, not to side lengths. Given Data / Assumptions: Closed traverse with known closing error in latitude: dx. Arithmetic sum (taken without sign convention issues for scaling) denoted as ∑Lat. A particular side has computed latitude l (algebraic). Concept / Approach: The Transit Rule prescribes that corrections be proportional to the magnitudes of the components: Clatitude,i = − (li/∑Lat) × dx and Cdeparture,i = − (Di/∑Dep) × dy. The negative sign ensures that the applied corrections act opposite to the misclosure so that the adjusted sums become zero. This contrasts with Bowditch, which uses side length as the weighting parameter. Step-by-Step Solution: 1) Compute raw latitudes and departures from measured lengths and bearings.2) Determine closing errors: dx (latitude), dy (departure).3) Apply Transit Rule: CL(side) = −(l/∑Lat)×dx.4) Re-sum adjusted latitudes to confirm ΣL = 0. Verification / Alternative check: Check that ΣCL = −dx. If satisfied, the latitude misclosure has been fully compensated by the distributed corrections. Why Other Options Are Wrong: Positive sign would increase the misclosure. Using |l| or l² is not part of the Transit Rule definition. None of these is incorrect because the standard formula exists. Common Pitfalls: Confusing Transit Rule with Bowditch (length-proportional) adjustments. Mixing sign conventions; maintain consistent quadrants when computing l. Final Answer: − (l / ∑Lat) × dx

Question 11

Instrumental error and reversal: Which statements are correct concerning the use of reversal to diagnose/cancel systematic errors and how corrections are applied?

Accepted Answer

Introduction / Context: Many surveying instruments permit reversal—such as face left/right with a theodolite, fore/after transiting the telescope, or reversing the bubble vial. Reversal exposes certain systematic errors (index, collimation, eccentricity) because those errors change sign with instrument reversal, while the true value remains constant. Averaging the two readings can thus cancel the bias. Given Data / Assumptions: A reversible instrument (e.g., transit theodolite or tilting level) is available. Systematic error changes sign on reversal; random errors remain random. Observed discrepancy is the difference between the two reversed readings. Concept / Approach: When reversal changes the sign of an error, the observed discrepancy equals twice the actual error, since one reading has +e and the other −e. Therefore, the correction to the reading is half the observed discrepancy, with sign chosen to counteract the bias. Even a slightly defective instrument can yield acceptable results by taking both positions and averaging, thereby cancelling the reversible component of error. Step-by-Step Solution: 1) Observe quantity in position 1 and position 2 (reversed).2) Compute discrepancy Δ = R1 − R2 = (T + e) − (T − e) = 2e.3) Actual error e = Δ/2 → apply correction = −e = −Δ/2 to each reading or average the two readings. Verification / Alternative check: Repeat observations on multiple targets; if the averaged values converge and pass closure checks, the reversal method is functioning as intended. Why Other Options Are Wrong: Options A–C are all correct statements; choosing any one ignores the rest. Hence ‘‘all the above’’ is appropriate. Common Pitfalls: Applying half discrepancy with the wrong sign; the correction must oppose the bias. Assuming all errors reverse; some (e.g., scale graduation errors) may not cancel by reversal. Final Answer: all the above

Question 12

Chain surveying—purpose of tie lines: In a chained framework, tie lines (subsidiary lines) are primarily provided for which purpose?

Accepted Answer

Introduction / Context: Chain surveying uses a network of well-conditioned triangles formed by main survey lines. However, interior details (buildings, walls, ponds) often lie away from the main lines. Tie lines are short subsidiary lines introduced to conveniently fix these features without resorting to excessively long offsets that reduce accuracy. Given Data / Assumptions: Plan is controlled by a skeleton of main lines. Numerous interior details require measurement from a nearby reference line. Offsets should be reasonably short and perpendicular for precision. Concept / Approach: The primary purpose of a tie line is to provide an additional base from which offsets for detail can be taken—especially when details cannot be conveniently set out from the main lines. While tie lines can also help check plotting or reduce long offsets, these are secondary benefits; their central role is detail location within the framework. Step-by-Step Solution: 1) Identify interior features distant from the main line.2) Run a tie line connecting suitable points within the triangle.3) Take short, accurate offsets from the tie line to fix details. Verification / Alternative check: Plotting with tie lines reduces distortion and improves closure of small detail loops; check by resection if available. Why Other Options Are Wrong: Accuracy checks and avoiding long offsets are useful effects but not the principal reason. Increasing chain lines indiscriminately complicates the survey with no guaranteed accuracy benefit. Reducing sag errors is unrelated; sag is a taping issue, not a tie-line function. Common Pitfalls: Laying a tie line without ensuring it improves offset geometry (perpendicular, short). Final Answer: to take offsets for detail survey (locate interior features)

Question 13

Traverse bearings—probable error: The probable error of the adjusted bearing at the middle of a series of observations is best expressed as which of the following (r = probable error of a single observed bearing, n = number of observations)?

Accepted Answer

Introduction / Context: When repeated observations are combined to obtain an adjusted bearing (or any repeated measurement), random errors tend to cancel out. The spread of the mean (or adjusted value) decreases with the number of observations, a fundamental result from error theory used in surveying adjustments. Given Data / Assumptions: Each repeated observation of the bearing has the same precision (identical r). Errors are random, independent, and follow a normal distribution. We are interested in the probable error of the adjusted bearing (essentially the mean). Concept / Approach: For independent, equally precise observations, the dispersion of the mean is related to that of a single observation by the factor 1/√n. Thus the probable error (or standard error, up to a constant factor) of the average is r/√n. This is why surveyors repeat angle measurements and bearings in multiple sets; the precision of the adjusted value improves as the square root of the number of sets. Step-by-Step Solution: 1) Let each bearing observation have probable error r.2) Combine n observations → mean's dispersion scales as 1/√n.3) Therefore, probable error of adjusted (mean) bearing = r/√n. Verification / Alternative check: Compute the sample variance of repeated sets and compare against the expected 1/√n improvement; practical field data track this trend unless dominated by systematics. Why Other Options Are Wrong: r√n: would imply worse precision with more observations, contrary to statistics. r independent of n or n/r: ignore the averaging benefit. r/(n − 1): relates to an unbiased variance estimator, not probable error of the mean. Common Pitfalls: Assuming more observations always help: only true if errors are random and independent; systematics must still be controlled. Final Answer: r / √n

Question 14

Telescope optics—image location: For proper focusing and zero parallax, where must the real image formed by the objective lens lie with respect to the diaphragm of cross-hairs?

Accepted Answer

Introduction / Context: Eliminating parallax is essential for precise sighting. Parallax occurs when the image of the target and the cross-hair plane do not coincide; moving the eye then causes apparent relative motion between the two. Understanding where the objective's image must be formed ensures correct focusing procedure in levels and theodolites. Given Data / Assumptions: Standard Keplerian telescope with objective, cross-hair diaphragm, and eye-piece. Cross hairs are fixed at the focal plane of the eye-piece once initially focused. Observer can adjust both the eye-piece (for the reticle) and the objective (for the target image). Concept / Approach: First, focus the eye-piece until the cross hairs appear sharp—this places the cross-hair plane at the eye-piece focal plane. Then focus the objective so that the real image of the target is formed exactly in the plane of the cross hairs. Only then will both the target image and the cross hairs be conjugate to the eye, eliminating parallax. Step-by-Step Solution: 1) Focus eye-piece on cross hairs until crisp and black (reticle at eye-piece focus).2) Aim at target; adjust focusing screw so the target image coincides with the cross-hair plane.3) Verify by moving the eye laterally; absence of relative motion confirms no parallax. Verification / Alternative check: If parallax persists, repeat steps because either the eye-piece was not correctly set or the objective focus is off. Why Other Options Are Wrong: At the centre or optical centre are meaningless locations for image formation. Anywhere inside or slightly in front produces parallax and reading errors. Common Pitfalls: Focusing the objective before the eye-piece; always focus the eye-piece first. Final Answer: in the plane of cross hairs

Question 15

Inclined sight with tilted staff—error expression: If θ is the vertical angle of an inclined sight and δ is the angle of tilt of the staff from the vertical, the resulting error in the staff reading is best represented by which expression?

Accepted Answer

l (1 − cos δ) sec θ

Question 16

Highway/railway alignment—transition curve geometry: For a main circular curve of radius R with a transition curve of length L on each end and shift S, the total tangent length (from Point of Intersection to Point of Tangency) is given by which expr…

Accepted Answer

Introduction / Context: Transition (spiral) curves are used to provide a gradual change of curvature from a straight to a circular arc, improving comfort and safety by controlling lateral acceleration and jerk. Introducing spirals alters the geometry near the tangent points by a small shift S and by adding half the transition length to each tangent segment. Given Data / Assumptions: Main circular curve radius = R. Deflection (intersection) angle = θ (Δ). Transition length on each side = L/2, so total transition length = L. Shift S is the inward displacement of the circular arc due to the transition. Concept / Approach: For a simple circular curve (no transition), the tangent length is R tan(θ/2). With equal transitions, the circular arc is shifted inward by S, effectively replacing R by (R + S) in the tangent-length relation, and adding a linear component + L/2 because each tangent must extend by half the transition length from the tangent point to the beginning of curvature. Step-by-Step Solution: 1) Base tangent length (no spiral): T₀ = R tan(θ/2).2) Include shift: replace R by (R + S) → (R + S) tan(θ/2).3) Include transition contribution: + L/2 (since the tangent extends along the transition before the circular arc starts).4) Therefore, total tangent length T = (R + S) tan(θ/2) + L/2. Verification / Alternative check: Check limiting cases: If L → 0 and S → 0, the expression reduces to R tan(θ/2), the classic formula for a simple circular curve—confirming consistency. Why Other Options Are Wrong: Minus signs before L/2 would shorten the tangent contrary to geometric construction. Using (R − S) conflicts with the inward shift convention (spiral pushes the circular arc inward). cos(θ/2)-based expressions do not represent tangent geometry for this problem. Common Pitfalls: Confusing shift S with setback of the curve or misplacing L/2 to the wrong side. Forgetting that each end contributes L/2 along the tangent from PI. Final Answer: (R + S) tan (θ/2) + L/2

Question 17

Parallax test in levelling: When viewing through a level telescope and shifting the eye slightly causes relative movement between the staff image and the cross-hairs, the instrument condition is best described as what?

Accepted Answer

Introduction / Context: Parallax is a focusing error that introduces reading bias in levelling and angle measurements. It occurs when the real image formed by the objective lens does not coincide with the plane of the cross-hair diaphragm. Detecting and removing parallax is part of standard instrument setup before taking observations. Given Data / Assumptions: The observer slightly shifts the eye laterally while looking through the telescope. A relative motion between the staff image and the cross hairs is observed. Standard optical layout: objective → cross-hair diaphragm → eye-piece. Concept / Approach: If the target image and cross hairs lie in different planes, moving the eye changes the line of sight through the eye-piece, making the cross hairs appear to slide over the image (or vice versa). This is parallax. The cure is two-step focusing: first focus the eye-piece sharply on the cross hairs, then focus the objective until the target image snaps into the same plane, confirmed when no relative motion is seen upon eye movement. Step-by-Step Solution: 1) Focus eye-piece on cross hairs (black, crisp appearance).2) Focus objective on the staff until the image appears sharp.3) Move the eye slightly; if no relative motion occurs, parallax has been eliminated. Verification / Alternative check: Repeat the test at a different staff distance to ensure the condition persists; minor residual parallax at extreme distances may require small refocusing. Why Other Options Are Wrong: Correctly focussed / free from parallax: contradict the observed relative movement. Not correctly focussed: true in effect, but the technically precise description is that the instrument ‘‘has parallax’’; eliminating parallax achieves correct focus. Common Pitfalls: Focusing the objective before the eye-piece; always focus the eye-piece first to set the reticle plane. Final Answer: said to have parallax

Question 18

Plane table surveying — what is the typical accuracy of a 'fix' obtained by the two-point resection problem compared with the standard three-point method?

Accepted Answer

Introduction / Context: In plane table surveying, a 'fix' means determining the map position of an unknown instrument station by sighting known control points. The two-point problem uses only two known points to orient the table and obtain a fix, whereas the three-point problem uses three known points and is the standard, more stable method. This question asks about the accuracy and practical reliability of the two-point fix. Given Data / Assumptions: Only two well-defined control points are visible from the unknown station. Orientation must be obtained graphically (or with auxiliary station) before plotting the fix. No redundant geometric check is available from a third ray. Concept / Approach: With only two rays, many configurations are ill-conditioned: small sighting or plotting errors rotate the table and shift the computed position noticeably along the line of intersection. The two-point problem therefore lacks the inherent redundancy and error trapping of the three-point problem. While auxiliary-station techniques can improve matters, the general guidance remains that the two-point fix is inferior in reliability and should be avoided when a third point is available. Step-by-Step Solution: 1) Sight the first known point and draw the ray; sight the second and draw its ray.2) Orient the board by trial to make the rays pass through the plotted control points.3) Note that any tiny angular error rotates the board, moving the intersection a large amount.4) Conclude that the obtained fix is not reliable compared with a three-point resection. Verification / Alternative check: Textbook rules (e.g., Lehmann’s) emphasize the superiority of three-point resection for accuracy; two-point methods are reserved for constrained visibility or as preliminary orientation. Why Other Options Are Wrong: Good — overstates the accuracy; two-point lacks redundancy. Bad — ambiguous; 'not reliable' is the accepted characterization. Unique — false; geometry allows multiple near-fits due to rotation sensitivity. Common Pitfalls: Trusting a two-point fix without independent checks; ignoring poor geometry (points nearly collinear) which magnifies error. Final Answer: not reliable

Question 19

Tacheometry fundamentals — one of the two tacheometric instrument constants is the additive constant; identify the other fundamental constant used in staff intercept reduction.

Accepted Answer

Introduction / Context: Tacheometry determines horizontal distance and elevation differences from the staff intercept observed through a telescope fitted with stadia hairs. The distance formula involves two instrument constants that depend on the optics. Recognizing these constants is essential for reducing field observations accurately and checking instrument calibration. Given Data / Assumptions: Stadia method with fixed-hair telescope is used. The distance formula is typically D = k·s + c, where s is the staff intercept. Instrument has been factory-calibrated so that the constants are stable during normal use. Concept / Approach: In the stadia equation D = k·s + c, k is called the multiplying constant (often ≈ 100 for many instruments) and c is called the additive constant (≈ the distance from objective to instrument axis plus focusing offset). The multiplying constant scales the staff intercept to distance; the additive constant corrects for the fixed spacing between the instrument centre and the focal point. Field checks (e.g., observing a staff at two known distances) can be used to verify or re-determine these constants if needed. Step-by-Step Solution: 1) Recall stadia formula D = k·s + c.2) Identify c as the additive constant.3) Identify k as the multiplying constant linking s to distance.4) Conclude that the 'other' constant is the multiplying constant. Verification / Alternative check: Instrument manuals for tacheometers specify k and c explicitly; many are designed for k = 100 to simplify mental arithmetic. Why Other Options Are Wrong: Subtractive/dividing/indicative constants are not standard terms in stadia reduction. Common Pitfalls: Forgetting to apply the additive constant in short sights; using wrong units for s, leading to scaled errors in D. Final Answer: multiplying constant

Question 20

Geometrical optics — for a thin convex lens of focal length f, if f₁ and f₂ are the distances from the optical centre to two conjugate points P₁ and P₂ respectively, which relationship correctly relates f, f₁, and f₂?

Accepted Answer

Introduction / Context: Conjugate points P₁ and P₂ for a thin lens are a pair of object–image points that map into each other through the lens. For paraxial rays, their distances f₁ and f₂ from the optical centre obey the thin-lens formula. Remembering the correct algebraic relationship (with proper sign convention) is vital in the design and analysis of optical components used in surveying instruments such as levels and theodolites. Given Data / Assumptions: The lens is thin and centred; principal planes coincide with the optical centre. Distances f₁ and f₂ are measured along the principal axis with the usual sign convention. Small-angle (paraxial) approximation holds. Concept / Approach: The thin-lens equation is 1/f = 1/v + 1/u, where u and v are the algebraic object and image distances. If we denote these two conjugate distances as f₁ and f₂, the identical relation becomes 1/f = 1/f₁ + 1/f₂. This equation captures the reciprocal nature of conjugate distances. Newton’s form (x·x′ = f²) is equivalent when distances are measured from the principal foci instead of the optical centre, but with the current definition (from the optical centre), the reciprocal form is correct. Step-by-Step Solution: 1) Start with the thin-lens formula: 1/f = 1/v + 1/u.2) Identify f₁ ≡ |u| and f₂ ≡ |v| under the adopted sign convention.3) Substitute to obtain 1/f = 1/f₁ + 1/f₂.4) Conclude that option '1/f = 1/f₁ + 1/f₂' is correct. Verification / Alternative check: Using Newton’s form with x = u − f and x′ = v − f gives x·x′ = f²; rearrangement with u and v recovers the same reciprocal relation. Why Other Options Are Wrong: f = f₁ + f₂ — dimensionally inconsistent for conjugate distances. f = (f₁ f₂)/(f₁ + f₂) — this is the harmonic mean formula for equivalent focal length of two thin lenses in contact, not for object–image distances. None of these — incorrect because the standard lens formula applies. Common Pitfalls: Sign mistakes (treating one distance as positive instead of negative); mixing Newton’s and Gaussian forms without consistent reference points. Final Answer: 1/f = 1/f₁ + 1/f₂

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