Question 1

Baseline measurement corrections: which of the following standard corrections apply to a measured base of length L taken with a tape in geodetic work?

Accepted Answer

Introduction / Context: High-precision baseline measurement requires applying systematic corrections so that the reported length represents a horizontal, sea-level-reduced value under standard conditions. Given Data / Assumptions: Measured length L with a suspended or supported tape. Known tape weight per unit length w and applied pull P. End height difference h; mean elevation H above MSL. Concept / Approach: Key corrections include sag (catenary effect), slope (to convert to horizontal), and mean sea level (to project to reference surface). Typical forms are:C_s = (w^2 * L^3) / (24 * P^2)C_θ ≈ - h^2 / (2 * L) for small slopesC_msl = - L * (H / R) Step-by-Step Solution: Apply sag correction to remove lengthening due to tape sag.Apply slope correction to reduce to horizontal length.Reduce to MSL using site elevation and Earth radius. Verification / Alternative check: Geodetic surveying manuals present these standard corrections; refined forms exist for large slopes and temperature calibration but the above are canonical. Why Other Options Are Wrong: Each listed correction is required; omitting any leads to bias. Common Pitfalls: Confusing sign conventions; remember sag and MSL corrections are subtractive. Final Answer: all the above

Question 2

Using principal points for radial directions on tilted photos: if average ground relief is about 10% of the flying height, up to what photo tilt can principal points still be used as centers of radial directions for small-scale mapping?

Accepted Answer

Introduction / Context: Photo-grammetric plotting often assumes radial directions emanate from the principal point. With tilted photographs, this assumption introduces error, but may be tolerated within small angles depending on relief and scale. Given Data / Assumptions: Ground relief ≈ 10% of flying height. Small-scale mapping where minor planimetric error is acceptable. Concept / Approach: Empirical guidelines allow using the principal point as the radial center on slightly tilted photos when relief is small relative to flying height. For relief ≈ 0.1 H, tilts up to about 3° maintain acceptable accuracy. Step-by-Step Solution: Assess relief ratio r = relief / H ≈ 0.1.Adopt permissible tilt where radial error remains within plotting tolerance.Choose ≈ 3° as acceptable upper bound for small-scale mapping. Verification / Alternative check: Photogrammetry references cite 2–3° as a practical limit for using principal points as radial centers when relief is modest; here the higher bound 3° is applicable. Why Other Options Are Wrong: 1° and 2° are conservative but not the maximum permissible. 4° often exceeds acceptable planimetric accuracy under given relief. Common Pitfalls: Ignoring relief variations that can tighten the allowable tilt below the rule-of-thumb. Final Answer: 3°

Question 3

Star elevation at elongation: which relation correctly gives the elevation α of a circumpolar star at elongation in terms of latitude φ and declination δ?

Accepted Answer

Introduction / Context: Elongation of a circumpolar star occurs when its azimuth is extremal (east or west), i.e., the star lies on or near the prime vertical. Determining the star's elevation at this instant is a classic problem in spherical astronomy used in surveying reductions. Given Data / Assumptions: Observer's latitude = φ. Star's declination = δ (circumpolar). Elongation condition corresponds to extreme azimuth (prime vertical crossing). Concept / Approach: From spherical trigonometry for the astronomical triangle, the general altitude formula is: sin h = sin φ sin δ + cos φ cos δ cos H. At elongation on the prime vertical, the condition for extremal azimuth yields cos H = (sin φ cos δ) / (cos φ sin δ) = tan φ cot δ. Substituting back gives sin h = sin φ * (sin^2 δ + cos^2 δ) / sin δ = sin φ * cosec δ. Step-by-Step Solution: Write sin h = sin φ sin δ + cos φ cos δ cos H.Use elongation condition: cos H = tan φ cot δ.Substitute and simplify → sin h = sin φ cosec δ. Verification / Alternative check: Alternative derivations via azimuth differentiation (dA/dH = 0) lead to the same expression. Why Other Options Are Wrong: Other combinations (using secant with sin φ or cos φ) do not satisfy the elongation condition when substituted into the altitude formula. Common Pitfalls: Using H = 90° (cos H = 0) indiscriminately; the true elongation hour angle depends on φ and δ. Final Answer: sin α = sin φ cosec δ

Question 4

Celestial angles terminology: the angle between the direction of a star and Earth’s rotation axis (i.e., the pole–star angular separation) is called what?

Accepted Answer

Introduction / Context: Describing positions on the celestial sphere uses declination, right ascension, and related complements. Understanding the complement angles is key to interpreting star positions relative to the pole. Given Data / Assumptions: Earth’s rotation axis defines the celestial poles. The angular separation between a star and the pole is sought. Concept / Approach: Declination (δ) is measured from the celestial equator. Its complement with respect to 90 degrees is the co-declination (90° − δ), which equals the angular distance of the star from the nearest pole (pole distance). Step-by-Step Solution: Define declination δ.Compute co-declination = 90° − δ.Interpret as the angle between star direction and Earth’s axis (pole distance). Verification / Alternative check: Star charts label pole distance as 90° − δ, confirming that co-declination is the required quantity. Why Other Options Are Wrong: Co-latitude refers to 90° − φ (observer’s latitude), not a stellar coordinate. Declination itself is measured from the equator, not from the axis. Latitude pertains to Earth locations, not stellar angular distances. Common Pitfalls: Confusing co-latitude with co-declination due to similar naming. Final Answer: co-declination

Question 5

Astronomical surveying: which coordinate pairs can fully specify the position of a celestial body on the celestial sphere for an observer on Earth?

Accepted Answer

Introduction / Context: In astronomical surveying and navigation, we describe the position of a heavenly body on the celestial sphere using angular coordinates. Several coordinate systems are in common use, each suited to a different observational or computational task, but any complete pair from a standard system uniquely fixes the body’s apparent position at a given time. Given Data / Assumptions: The observer is at a fixed location on Earth at a given instant. Standard spherical coordinate systems are well defined. Refraction and parallax are neglected for the core concept of coordinate specification. Concept / Approach: Three principal systems are relevant: (1) the horizontal (altitude–azimuth) system tied to the observer’s horizon; (2) the equatorial (declination–hour angle) system tied to the local meridian; and (3) the equatorial (declination–right ascension) system tied to the celestial equator and vernal equinox. Any complete pair from one system specifies a unique point on the celestial sphere. Step-by-Step Solution: Alt–Az: altitude is angular height above the horizon; azimuth is bearing along the horizon. Together they fix the line of sight.Dec–HA: declination is north/south of the celestial equator; hour angle measures how far west the object is from the observer’s meridian.Dec–RA: declination paired with right ascension (measured from the vernal equinox) gives a time-independent sky map coordinate; local sidereal time converts RA to hour angle. Verification / Alternative check: Given any one pair, the other pairs are convertible through known transformations involving the observer’s latitude and local sidereal time, confirming their completeness. Why Other Options Are Wrong: “None of these” is incorrect because each listed pair is indeed sufficient. Common Pitfalls: Confusing right ascension with hour angle (they differ by local sidereal time), or assuming altitude–azimuth are global rather than local coordinates. Final Answer: All the above

Question 6

Stereoscopic plotting: when the z-column of the right projector is raised, at which instrument positions does the model exhibit maximum y-parallax?

Accepted Answer

Introduction / Context: Analog stereo-plotters generate a three-dimensional model from overlapping aerial photographs. Adjustments of projector columns (x, y, z) control relative orientation and parallax. Understanding where y-parallax maximizes helps the operator diagnose orientation errors and perform accurate model set-ups. Given Data / Assumptions: A standard two-projector stereo-plotter is used. The right projector’s z-column is raised slightly from the relative-orientation condition. Instrument “positions” refer to standard checking locations around the model where parallax is assessed. Concept / Approach: Raising the z-column alters the image scale in the right projector, creating a differential vertical magnification that manifests primarily as y-parallax (parallax perpendicular to the air base). This effect is not uniform across the model and is known to peak at symmetric positions along the principal line away from the nadir, commonly noted as positions 4 and 6 in classical test patterns. Step-by-Step Solution: Start from correct relative orientation → y-parallax ideally zero at control points.Introduce a small +Δz on right projector → scale difference between left and right images.Scale difference translates predominantly to y-parallax that varies with location on the model.Empirically and from geometry, maxima are observed at the designated check points “4” and “6”. Verification / Alternative check: Operators verify by measuring y-parallax across a six-point pattern; largest values appear at 4 and 6 for a pure z-column perturbation. Why Other Options Are Wrong: Positions 1 or 2 alone do not capture the peak y-parallax created by a z-column change; single-position options (4 or 6 only) are incomplete. Common Pitfalls: Confusing x-parallax (related to base and height) with y-parallax (primarily tilt/scale differential); mixing up projector x/y/z adjustments. Final Answer: Position 4 and 6

Question 7

Fundamental astronomy: the angle between the plane of the Earth’s equator and the plane of the ecliptic is called the obliquity of the ecliptic. What is its standard value used in surveying calculations?

Accepted Answer

Introduction / Context: The obliquity of the ecliptic (ε) is the tilt of Earth’s rotational axis relative to the normal of its orbital plane. This tilt underlies the seasons and is a fundamental constant in spherical astronomy, navigation, and geodetic computations that reference celestial coordinates. Given Data / Assumptions: Standard surveying and navigation tables adopt a representative obliquity value. Secular variations are small over human timescales and do not affect routine problems. Concept / Approach: Obliquity links equatorial and ecliptic coordinate systems. A commonly used mean value for many engineering purposes is about 23° 27′, sufficiently accurate for computations like converting between right ascension/declination and ecliptic longitude/latitude. Step-by-Step Solution: Identify definition: ε = angle between equator's plane and ecliptic plane.Use standard mean value used in tables: ≈ 23° 27′.Select the matching option. Verification / Alternative check: Modern precise values vary slightly (~23° 26′…), but 23° 27′ is the conventional rounded constant used in many textbooks and exams. Why Other Options Are Wrong: 22° 30′ and 24° 0′ are too far; 23° 30′ is close but less standard than 23° 27′ for conventional problems. Common Pitfalls: Confusing mean obliquity with instantaneous or obliquity of date; rounding inconsistently across problems. Final Answer: 23° 27'

Question 8

Photogrammetry (relief displacement): a minar 72 m high shows 7.2 mm of relief displacement on the photograph, and its top lies 10 cm from the principal point. Estimate the flying height of the camera.

Accepted Answer

Introduction / Context: Relief displacement is the apparent radial shift of an elevated point on a vertical aerial photograph. It depends on the object height, its radial distance from the principal point, and the flying height above the datum. This relationship is frequently used to estimate flying height or to determine object elevation. Given Data / Assumptions: Object height h = 72 m. Measured relief displacement d (on photo) = 7.2 mm = 0.0072 m. Radial distance of the top from principal point r = 10 cm = 0.10 m (on photo). Vertical photograph; small tilt and lens distortion neglected. Concept / Approach: The first-order relation for vertical photography is: d = (r * h) / H, where H is the flying height above the same datum used for h. Rearranging gives H = (r * h) / d. Step-by-Step Solution: Write the formula: d = (r * h) / H.Rearrange: H = (r * h) / d.Insert values: H = (0.10 * 72) / 0.0072.Compute numerator: 0.10 * 72 = 7.2.Compute division: 7.2 / 0.0072 = 1000.Thus, H ≈ 1000 m. Verification / Alternative check: Proportionality check: doubling r or h would double d for a fixed H; the numbers scale consistently. Units also cancel properly, yielding metres. Why Other Options Are Wrong: 500 m and 800 m underestimate the height (they would produce larger d); 1500 m and 2000 m are too large for the observed displacement at r = 10 cm and h = 72 m. Common Pitfalls: Mixing ground units with photo units or using object ground distance instead of photo radial distance r; forgetting to keep d and r in the same (photo) length units. Final Answer: 1000 m

Question 9

Sidereal vs. solar days: in one tropical year, is the number of sidereal days less than, equal to, or greater than the number of mean solar days?

Accepted Answer

Introduction / Context: A sidereal day measures Earth’s rotation relative to distant stars; a mean solar day measures rotation relative to the Sun. Because Earth orbits the Sun while rotating, there is a subtle difference in counts over the course of a year. Given Data / Assumptions: Length of the tropical year ≈ 365.2422 mean solar days. Length of one sidereal day ≈ 23 h 56 m 4 s (≈ 0.99727 mean solar days). Concept / Approach: Each day, Earth turns a bit more than 360° relative to the stars to bring the Sun back to the local meridian. Over one complete revolution around the Sun, this amounts to roughly one additional full rotation relative to the stars. Step-by-Step Solution: Number of sidereal days per year ≈ (length of year in solar days) / (length of one sidereal day in solar-day units).≈ 365.2422 / 0.99727 ≈ 366.24.Thus the count exceeds the number of solar days by ~1. Verification / Alternative check: Geometric reasoning: one extra star-relative rotation is needed each year to compensate for Earth’s orbital progression. Why Other Options Are Wrong: “Equal” and “one less” contradict the orbital geometry; “two more” is far too large. Common Pitfalls: Confusing “length of a sidereal day” with “number of sidereal days per year.” Final Answer: One more than mean solar days

Question 10

Pole star (Polaris) motion: at western elongation, in which cardinal sense does the pole star appear to move around the celestial pole for a northern observer?

Accepted Answer

Introduction / Context: Polaris (the pole star) traces a small circle around the North Celestial Pole due to Earth’s rotation. Understanding its apparent motion at key positions—upper and lower culmination, eastern and western elongations—is useful in field astronomy and azimuth determinations. Given Data / Assumptions: Northern hemisphere observer looking toward the north. “Western elongation” means Polaris is at its maximum angular distance west of the meridian (on the west side of the circle around the pole). Apparent stellar motion is counterclockwise around the pole when viewed from the northern hemisphere. Concept / Approach: Stars appear to rotate counterclockwise about the North Celestial Pole. At the westernmost point of the circular path (western elongation), the instantaneous direction of motion is tangential and points generally toward the north (upward in the sky diagram), whereas at eastern elongation it is toward the south. Step-by-Step Solution: Draw the small circle of Polaris around the pole.Mark W (left), E (right), N (top), S (bottom) relative to the pole in the sky diagram.Follow counterclockwise motion: at the westernmost point, the tangent points upward (northward).Hence, at western elongation, Polaris is moving northward. Verification / Alternative check: Symmetry: at eastern elongation it moves southward; at upper culmination it moves eastward; at lower culmination it moves westward—consistent with a counterclockwise circular track. Why Other Options Are Wrong: Southward is the direction at eastern elongation; eastward or westward correspond to culminations rather than elongations. Common Pitfalls: Mistaking cardinal directions on the sky diagram or assuming clockwise motion. Final Answer: Northward

Question 11

Culmination geometry: for latitude θ and declination δ, the upper culmination of a body is south of the zenith if its zenith distance z equals which expression?

Accepted Answer

Introduction / Context: At upper culmination (meridian transit), a celestial body attains its greatest altitude for that day. Whether it passes south or north of the zenith depends on the observer’s latitude θ and the body’s declination δ. This relation is fundamental in astro-navigation and field astronomy. Given Data / Assumptions: Observer is in the same hemisphere as the body (typical surveying cases). Upper culmination occurs on the local meridian. Refraction is negligible for the conceptual discussion. Concept / Approach: For an object culminating on the meridian, the zenith distance is z = |θ − δ|. If δ < θ (typical mid-latitudes with small declinations), the body lies south of the zenith at culmination and z = θ − δ (a positive angle). If δ > θ, the body passes north of the zenith and z = δ − θ. Step-by-Step Solution: Use meridian altitude formula: altitude at upper culmination a = 90° − |θ − δ|.Hence z = 90° − a = |θ − δ|.For “south of zenith” in the common case δ < θ → z = θ − δ.Therefore the required expression is θ − δ. Verification / Alternative check: Example: θ = 30°, δ = 10° → z = 20° (body is 20° south of zenith). If δ = 40° > θ, the body passes north of zenith with z = 10° but oriented to the north side. Why Other Options Are Wrong: θ + δ is not a zenith-distance expression; δ − θ would be negative for δ < θ (the south-of-zenith case); parentheses do not change the value. Common Pitfalls: Forgetting the absolute value in z = |θ − δ| and mixing “north of zenith” with “south of zenith.” Final Answer: θ − δ

Question 12

Definition check: latitude of a place is defined as which angular distance on the Earth, measured in the proper geometric sense?

Accepted Answer

Introduction / Context: Clear definitions matter in geodesy and cartography. Latitude and longitude are angular coordinates on Earth used to specify positions relative to the equator and the Greenwich meridian, respectively. Misstatements can cause conceptual errors in fieldwork and computations. Given Data / Assumptions: Assume a reference ellipsoid approximating Earth. Latitude is measured along a meridian (a great ellipse on the ellipsoid) from the equator. Concept / Approach: Latitude (φ) is the angle between the equatorial plane and the normal to the ellipsoid at the point (geodetic latitude). For simplified spherical definitions used in elementary surveying, it is the angular distance of the place north or south from the equator, measured along the meridian passing through that place, up to the nearer pole direction. Step-by-Step Solution: Eliminate longitude-related option: “from Greenwich to the place” defines longitude, not latitude.Recognize that latitude must be tied to the local meridian (the north–south great circle through the place).Thus, the correct detailed wording is: from the equator to the nearer pole along the meridian of the place. Verification / Alternative check: Any atlas or geodesy text defines latitude as an angular distance from the equator along a meridian; longitude is measured east or west from Greenwich. Why Other Options Are Wrong: “Equator to the poles” is incomplete and not localized; “equator to the nearer pole” is still incomplete without “along the meridian.” Common Pitfalls: Confusing geocentric with geodetic latitude; ignoring that measurement follows the meridian through the point. Final Answer: From the equator to the nearer pole along the meridian of the place

Question 13

Triangulation adjustments: which geometric angle-sum conditions must hold for stations, triangles, and braced quadrilaterals in a properly adjusted network?

Accepted Answer

Introduction / Context: Triangulation provides horizontal control for mapping and engineering works. Geometric constraints are used during adjustment to distribute observational errors consistently across the network and to ensure closure conditions are satisfied. Given Data / Assumptions: Angles are reduced to a common datum (e.g., station mark, horizon, etc.). Plane-triangle approximations are applied where appropriate. Braced quadrilaterals are used to strengthen networks and provide checks. Concept / Approach: Closure and angle-sum checks safeguard the internal consistency of observed angles. Around a station, all angles subtend the full circle (360°). In plane geometry, triangle angles sum to 180°. In a braced quadrilateral, angle arrangements yield specific total sums (commonly the sum of eight selected angles equals 360°) providing a powerful redundancy check. Step-by-Step Solution: Station closure: confirm angles around a station total 360°.Triangle closure: enforce 180° for each triangle; distribute small misclosures by least squares or proportional rules.Braced quadrilateral checks: verify prescribed angle sums (e.g., selected eight angles) equal 360°; reconcile misclosures in adjustment. Verification / Alternative check: These relationships are standard and appear in triangulation specifications and adjustment textbooks as primary geometry checks. Why Other Options Are Wrong: Individual statements (a)–(c) are correct; therefore the most complete answer is “All the above.” Common Pitfalls: Neglecting to convert repeated or oriented angles to a consistent reference; omitting refraction and curvature corrections when necessary. Final Answer: All the above

Question 14

Applications of triangulation surveys: for which purposes are triangulation networks commonly executed in civil and geodetic practice?

Accepted Answer

Introduction / Context: Triangulation—establishing a framework of intervisible stations measured by angles and selected distances—has long been a backbone of control surveying. Even with modern GNSS, triangulation concepts inform network design, redundancy, and quality assurance. Given Data / Assumptions: Large-area mapping requires a control skeleton. Photogrammetry needs ground control for absolute orientation. Engineering projects demand precise positioning of critical points. Concept / Approach: By forming a connected network of triangles (often strengthened by braced quadrilaterals), triangulation yields precise coordinates of control points. These control points support topographic mapping, aerial triangulation in photogrammetry, and the layout of linear infrastructure (tunnels, bridges, pipelines) where opposing works must meet with minimal positional error. Step-by-Step Solution: Large-area control: triangulation densifies a national datum into regional/local frameworks.Photogrammetry: control points tie aerial photos to ground, enabling accurate stereo-compilation.Engineering works: fixed control enables transfer of alignment and grade over long distances and through difficult terrain. Verification / Alternative check: Historical and current surveying standards list these as principal uses; many agencies still specify triangulation-derived or GNSS-supported control prior to mapping and construction. Why Other Options Are Wrong: Each listed application is valid; restricting to a subset would be incomplete. Common Pitfalls: Assuming GNSS removes the need for geometric checks; in practice, hybrid networks improve reliability. Final Answer: All the above

Question 15

In global navigation and astronomical surveying, where is the International Date Line conventionally located on the Earth’s surface?

Accepted Answer

Introduction / Context: The International Date Line is a crucial construct in navigation, cartography, and timekeeping. It is the notional line on the Earth’s surface where calendar dates change by one day when crossed. Understanding its conventional position helps surveyors, navigators, and GIS professionals interpret time-zone data and manage east–west travel logistics. Given Data / Assumptions: The International Date Line is a convention, not a geophysical boundary. It is commonly associated with a specific meridian but deviates around landmasses and political boundaries. We assume standard geodetic understanding of meridians and parallels. Concept / Approach: Meridians are lines of constant longitude; the prime reference is the Greenwich meridian (0°). The dateline is placed approximately halfway around the globe from Greenwich to create a logical date-change boundary. This is conventionally the 180° meridian, which is opposite Greenwich on a spherical Earth model. Step-by-Step Solution: Identify the meridian opposite to 0° → 180° longitude.Recognize that a date-change boundary must be continuous and minimally disruptive to inhabited regions.Note that the actual line zigzags to avoid splitting nations or island groups, but it is still described as being ‘‘along 180° longitude’’ by convention. Verification / Alternative check: Global time-zone maps and nautical charts depict the International Date Line closely tracking the 180° meridian with localized deviations near the Bering Strait, Kiribati, Samoa, and Fiji. Why Other Options Are Wrong: Standard meridian: vague and not uniquely defined globally. Greenwich meridian: defines 0° longitude, not the date-change line. Equator: a latitude circle, not a date-change meridian. None of these: incorrect because 180° longitude is the accepted convention. Common Pitfalls: Assuming the line is a perfectly straight 180° meridian; it bends to accommodate political boundaries. Confusing time-zone borders with the dateline; they are related but not identical. Final Answer: 180° longitude

Question 16

In surveying and observations, which statements correctly describe accidental (random) errors in measurements?

Accepted Answer

Introduction / Context: Every measurement contains error. In surveying and geodesy, it is essential to distinguish between systematic errors (bias) and accidental or random errors to ensure correct data adjustment and quality control. Understanding the behavior of accidental errors guides the use of statistical methods for precision estimation. Given Data / Assumptions: Accidental errors arise from small, uncontrollable variations in observation conditions and human/ instrument limitations. They vary in sign and magnitude and tend to cancel out over many observations. We consider standard field conditions without gross mistakes (blunders). Concept / Approach: Systematic errors can be modeled and corrected. Accidental errors, however, cannot be eliminated by deterministic corrections and are evaluated statistically (mean, variance). In classical surveying pedagogy they are often termed ‘‘compensating errors’’ because positive and negative deviations tend to offset each other over repeated measurements. Step-by-Step Solution: Recognize that accidental errors arise unpredictably → not removable by fixed correction.Their magnitudes are typically small compared to systematic effects in well-run observations.Because signs vary, multiple observations reduce their effect on the mean (hence ‘‘compensating’’). Verification / Alternative check: Least-squares adjustment theory treats residuals as random; precision improves with the square root of the number of observations, indicating compensatory behavior. Why Other Options Are Wrong: Each individual statement characterizes accidental errors in standard textbooks; therefore the combined choice ‘‘all the above’’ is appropriate. Common Pitfalls: Confusing accidental errors with systematic bias (which can be modeled and corrected). Assuming a single reading is ‘‘true’’; precision demands repetition and averaging. Final Answer: all the above

Question 17

During astronomical observations with a theodolite or transit, which directional references are the observer primarily concerned with?

Accepted Answer

Introduction / Context: Astronomical observations in surveying (e.g., determining azimuths, latitude, and time) require careful orientation of the instrument and a clear understanding of reference directions in the celestial sphere. Correctly aligning these directions ensures that observed angles reduce to meaningful geodetic quantities. Given Data / Assumptions: The observer uses a precise instrument (theodolite, transit, or total station with astronomical capability). The celestial sphere model is employed: poles, equator, zenith, and nadir. Local vertical is established by the instrument’s leveling (plumb line or spirit/tilt sensors). Concept / Approach: Three directional references matter simultaneously: (1) the local vertical, defining the sensible horizon and the instrument’s rotation axis; (2) the celestial poles, aligning with Earth’s rotation axis and enabling conversion between hour angle and azimuth; and (3) the line of sight to the star, defining the observed altitude and azimuth of the body. Step-by-Step Solution: Establish the vertical by careful leveling to set the instrument’s axis.Relate the instrument orientation to the celestial poles (north/south) for azimuth reference.Sight the target star; record the star’s direction (altitude/azimuth or hour angle/declination). Verification / Alternative check: Reduction formulas for astronomical azimuth rely on the instrument’s vertical orientation, pole direction, and the star’s observed direction; all three must be known or inferred. Why Other Options Are Wrong: Each individual direction is necessary; the correct comprehensive answer is therefore ‘‘all the above.’’ Common Pitfalls: Neglecting instrument leveling causes azimuth and altitude errors. Failing to account for polar reference (latitude) leads to incorrect reductions. Final Answer: all the above

Question 18

In positional astronomy for surveying, the angle between Earth’s rotation axis and the local vertical at the observation station is termed what?

Accepted Answer

Introduction / Context: Precise terminology in spherical astronomy helps convert celestial observations into terrestrial coordinates. The relationships among latitude, co-latitude, and the local vertical are fundamental for geodetic work and astro-orientation. Given Data / Assumptions: The local vertical is the line through the observer’s zenith and nadir. Earth’s rotation axis defines the celestial poles. Astronomical latitude (φ) is the angle between the local vertical and the equatorial plane. Concept / Approach: The angle between Earth’s axis and the local vertical equals the complement of the astronomical latitude, i.e., co-latitude (90° − φ). Since the axis is 90° from the equatorial plane, the vertical-to-axis angle must be 90° − φ. Step-by-Step Solution: Define astronomical latitude φ as the angle between the equatorial plane and local vertical.Recognize that the angle between the vertical and the axis = 90° − φ.Therefore the required term is ‘‘astronomical co-latitude.’’ Verification / Alternative check: Star elevation at the pole equals φ; consequently, pole distance from the zenith is 90° − φ, matching the vertical–axis angle. Why Other Options Are Wrong: Astronomical latitude is φ, not the complement. Co-declination and declination refer to a star's position, not the station's orientation. Common Pitfalls: Confusing star-based quantities (declination) with site-based quantities (latitude/co-latitude). Final Answer: astronomical co-latitude

Question 19

Principles behind stereo-plotting instruments: which foundational projection mechanisms are commonly used in their manufacture and operation?

Accepted Answer

Introduction / Context: Stereo-plotting instruments transform paired aerial photographs into measurable 3D models for mapping. Understanding the mechanisms behind these instruments aids in selecting and operating equipment for photogrammetric compilation. Given Data / Assumptions: Stereo viewing requires accurate geometry between left and right photos. Instruments may implement projection through optics, precision mechanics, or combinations of both. Modern systems may also incorporate digital/analytic components, but the core principles echo earlier analog designs. Concept / Approach: Analog stereo-plotters use optical projection (e.g., projectors, lenses) to recreate the geometry of the air photos; mechanical linkages maintain conjugacy and orientation (mechanical projection). Hybrid ‘‘optical-mechanical’’ designs integrate both to maintain parallax relationships as the operator traces features, forming the stereoscopic model for plotting contours and planimetry. Step-by-Step Solution: Align and orient photo pair to satisfy relative and absolute orientation.Use optical projection to form a stereoscopic image pair.Employ mechanical or opto-mechanical linkages so model motions correspond to ground motions, enabling accurate plotting. Verification / Alternative check: Classic instruments (e.g., Wild A-series, Zeiss stereoplanigraphs) demonstrate optical and mechanical projection principles; analytic plotters later replicated these with computation. Why Other Options Are Wrong: Each mechanism plays a role; therefore the comprehensive choice ‘‘all the above’’ best describes real instruments. Common Pitfalls: Assuming only optical or only mechanical methods; many designs are hybrid. Overlooking the necessity of correct relative/absolute orientation for accurate parallax reproduction. Final Answer: all the above

Question 20

Great-circle navigation: the shortest surface distance between two locations on the Earth is equal to which of the following?

Accepted Answer

Introduction / Context: In geodesy, navigation, and aviation, the shortest route over the Earth’s surface is fundamental for route planning and distance computation. On a sphere (or near-spherical ellipsoid), this path is the great-circle arc between the two points. Given Data / Assumptions: The Earth is approximated as a sphere for conceptual understanding (ellipsoidal refinements are small for many purposes). Two points (not antipodal) define a unique great circle. We compare distances along equator, parallels, and great circles. Concept / Approach: A great circle is any circle on the sphere whose center coincides with the sphere’s center. The geodesic (shortest surface path) between two points on a sphere lies along the great-circle arc joining them. Parallels (except the equator) are small circles and do not provide shortest paths unless the two points happen to lie on the equator itself. Step-by-Step Solution: Construct the unique great circle through the two points (and the center of the sphere).Measure the central angle Δσ between their position vectors.Surface distance = R * Δσ, which follows the great-circle arc. Verification / Alternative check: Airline ‘‘orthodrome’’ routes appear curved on Mercator projections but are shortest because they follow great circles. Rhumb lines (loxodromes) are longer except in special cases. Why Other Options Are Wrong: Equator segment is a great-circle arc only if both points lie on the equator. Parallels are small circles and generally longer than the great-circle route. ‘‘None of these’’ is incorrect since the great-circle arc is the standard result. Common Pitfalls: Misinterpreting map projection curves as physical path lengths. Confusing loxodromic (constant bearing) with geodesic (shortest) routes. Final Answer: length of the arc of the great circle passing through them

Advanced Surveying Questions