I85PREP
⌘ K
Engineer Surveying Geo-Spatial Information study materials
Engineer Surveying Geo-Spatial Information study resources

Engineer Surveying Geo-Spatial Information practice questions

One question at a time. Build your Engineer Surveying Geo-Spatial Information understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Surveying Fundamentals and Geodesy

In a geodetic reference frame, what does the semi-major axis of the reference ellipsoid represent?

  1. The equatorial radius of the ellipsoid Correct answer.
  2. The flattening ratio expressed in metres
  3. The polar radius of the ellipsoid
  4. The distance from the ellipsoid surface to the geoid

Explanation

The reference ellipsoid is defined by a semi-major axis a and a flattening f. The semi-major axis is the radius in the equatorial plane, so it equals the equatorial radius. The polar radius is the semi-minor axis b, computed from a and f.

Question 2Surveying Fundamentals and Geodesy

A survey line is measured as 248.360 m on a horizontal plane. Which statement describes a horizontal distance in geodetic surveying?

  1. The straight chord distance between the two points through space
  2. The distance along the terrain slope between the two points
  3. The distance measured along the curved reference surface between two points Correct answer.
  4. The vertical difference in height between the two points

Explanation

Horizontal distance in geodesy is the length measured along the level reference surface, following the curvature of the ellipsoid. The straight chord is shorter than the arc for long lines, and slope distance is measured along the ground.

Question 3Surveying Fundamentals and Geodesy

Which quantity expresses the angular difference between true north and grid north at a point on a map projection?

  1. Magnetic declination
  2. Grid convergence Correct answer.
  3. Azimuth
  4. Convergence angle of the vertical

Explanation

Grid convergence is the angle between true (geographic) north and grid north at a point, and it varies with position within the projection. Magnetic declination relates magnetic north to true north, which is a different reference.

Question 4Surveying Fundamentals and Geodesy

A total station measures a slope distance of 150.000 m to a target, and the zenith angle is 85°00'00". What is the horizontal distance, to the nearest millimetre?

  1. 149.429 m Correct answer.
  2. 149.430 m
  3. 149.431 m
  4. 149.428 m

Explanation

Horizontal distance equals slope distance multiplied by the sine of the zenith angle: 150.000 × sin(85°) = 150.000 × 0.9961947 = 149.4292 m, which rounds to 149.429 m. Using the sine of the zenith angle, rather than its cosine, is essential to get the correct reduction.

Question 5Surveying Fundamentals and Geodesy

In a closed traverse, the sum of the interior angles of a five-sided polygon is found to be 539°59'40". What is the angular misclosure?

  1. -20" Correct answer.
  2. -40"
  3. +20"
  4. +40"

Explanation

The theoretical sum of interior angles for an n-sided polygon is (n-2)×180°, which is 540°00'00" for five sides. The observed sum is 20" less than theory, so the misclosure is -20". Misclosure is observed minus theoretical, giving a negative sign here.

Question 6Surveying Fundamentals and Geodesy

Which statement correctly distinguishes a geoid from a reference ellipsoid?

  1. The geoid is an equipotential surface of gravity approximating mean sea level, while the ellipsoid is a mathematical surface Correct answer.
  2. The geoid is defined by two axes only, while the ellipsoid requires three
  3. The geoid is used only for cadastral mapping, while the ellipsoid is used only for navigation
  4. The geoid is a perfect sphere, while the ellipsoid is flattened at the equator

Explanation

The geoid is the equipotential surface of the gravity field that best fits mean sea level, and it is irregular. The reference ellipsoid is a smooth mathematical surface used as a computational basis. Heights above the ellipsoid and above the geoid differ by the geoidal undulation.

Question 7Surveying Fundamentals and Geodesy

A point has orthometric height 120.450 m and the geoidal undulation at that location is -32.180 m. What is its ellipsoidal height?

  1. 152.630 m
  2. 88.270 m Correct answer.
  3. -32.180 m
  4. 120.450 m

Explanation

Ellipsoidal height h equals orthometric height H plus geoidal undulation N, so h = 120.450 + (-32.180) = 88.270 m. The negative undulation means the geoid lies below the ellipsoid at this point.

Question 8Surveying Fundamentals and Geodesy

Which coordinate system uses latitude, longitude, and ellipsoidal height referenced to a named geodetic datum?

  1. Geocentric Cartesian coordinates
  2. Map grid coordinates
  3. Geodetic coordinates Correct answer.
  4. Local topocentric coordinates

Explanation

Geodetic coordinates are latitude, longitude, and ellipsoidal height referred to a specified datum and ellipsoid. Geocentric Cartesian coordinates give X, Y, Z from the Earth's centre, and grid coordinates give eastings and northings on a projection.

Question 9Surveying Fundamentals and Geodesy

Two points lie 12 km apart along a level surface. What is the approximate effect of Earth curvature on the difference between the chord and the arc, using R = 6371 km?

  1. About 2.8 m Correct answer.
  2. About 28 m
  3. About 11 m
  4. About 0.28 m

Explanation

The sagitta, or arc-to-chord difference, is approximately d²/(8R). With d = 12 km and R = 6371 km, that is 144/(50968) km, about 0.00283 km, or roughly 2.8 m. This shows why curvature corrections matter over distances of several kilometres.

Question 10Surveying Fundamentals and Geodesy

Which statement best describes the role of a geodetic datum transformation?

  1. It converts slope distances to horizontal distances
  2. It converts magnetic bearings to true bearings
  3. It converts coordinates expressed in one reference frame to another using defined parameters Correct answer.
  4. It removes refraction effects from observed vertical angles

Explanation

A datum transformation applies translation, rotation, and scale parameters to convert coordinates between reference frames. It does not perform observational corrections such as refraction or slope reduction.

Question 11Surveying Fundamentals and Geodesy

A level is set midway between two points A and B, 80 m apart. The rod readings are 1.452 m at A and 1.208 m at B. What is the height difference, and what advantage does the midway setup give?

  1. A is 0.244 m higher than B, and rod scale error is removed
  2. A is 0.244 m higher than B, and collimation error is eliminated
  3. B is 0.244 m higher than A, and curvature and refraction errors largely cancel Correct answer.
  4. B is 0.244 m higher than A, and the effect of Earth curvature is doubled

Explanation

The height difference is the back sight minus the fore sight: 1.452 - 1.208 = 0.244 m, so B is higher than A. With equal sight lengths, curvature, refraction, and residual collimation errors act almost equally on both readings and cancel in the difference.

Question 12Surveying Fundamentals and Geodesy

Which statement about a projected map grid is correct for a conformal projection such as a Transverse Mercator?

  1. Scale is constant across the entire grid
  2. Areas are preserved exactly everywhere on the grid
  3. Angles are preserved locally, but scale varies with position Correct answer.
  4. Bearings are true everywhere without convergence correction

Explanation

A conformal projection preserves local angles and shapes at the expense of scale, which varies with distance from the central meridian. Area is not preserved, and grid bearings differ from true bearings by the convergence.

Question 13Surveying Fundamentals and Geodesy

What is the primary purpose of a trilateration network in geodetic surveying?

  1. To determine positions only from measured horizontal angles
  2. To determine positions from measured distances between stations Correct answer.
  3. To measure gravity differences between stations
  4. To determine orthometric heights by spirit levelling

Explanation

Trilateration determines coordinates from measured distances between stations, usually with electronic distance measurement. Triangulation uses angles, and gravimetry and levelling serve other purposes.

Question 14Surveying Fundamentals and Geodesy

A bearing is recorded as S 42°15' W. What is the equivalent whole-circle azimuth measured clockwise from north?

  1. 137°45'
  2. 317°45'
  3. 42°15'
  4. 222°15' Correct answer.

Explanation

A southwest quadrant bearing converts to azimuth by adding 180°: 180° + 42°15' = 222°15'. The result lies in the third quadrant, consistent with a southwest direction.

Question 15Surveying Fundamentals and Geodesy

In a triangulation network, a triangle has observed angles of 48°12'10", 61°47'30", and 69°59'50". What is the angular misclosure before adjustment?

  1. +30"
  2. -10"
  3. -30" Correct answer.
  4. +10"

Explanation

The angles of a plane triangle must sum to 180°00'00". The observed sum is 179°59'30", which is 30" short of theory, giving a misclosure of -30". Spherical excess is negligible for small triangles.

Question 16Surveying Fundamentals and Geodesy

Which statement correctly describes the deflection of the vertical?

  1. It is the angle between the ellipsoid normal and the direction of gravity at a point Correct answer.
  2. It is the angle between the geoid and mean sea level
  3. It is the angle between true north and magnetic north
  4. It is the change in gravity with latitude

Explanation

The deflection of the vertical is the angular difference between the ellipsoid normal and the gravity vector at a point. It links astronomical observations to geodetic coordinates and is not a magnetic or tidal quantity.

Question 17Surveying Fundamentals and Geodesy

A GNSS receiver reports an ellipsoidal height of 205.300 m, and the local geoid model gives N = +27.450 m. What is the orthometric height?

  1. 177.850 m Correct answer.
  2. 232.750 m
  3. 27.450 m
  4. 205.300 m

Explanation

Orthometric height equals ellipsoidal height minus geoidal undulation: 205.300 - 27.450 = 177.850 m. This reduction is essential when GNSS heights must be related to a levelling datum.

Question 18Surveying Fundamentals and Geodesy

Which property of a Universal Transverse Mercator zone limits distortion within each zone?

  1. Each zone uses a different unit of length
  2. Each zone uses a different ellipsoid
  3. Each zone is centred on the equator
  4. Each zone spans a narrow band of longitude with its own central meridian Correct answer.

Explanation

UTM divides the globe into narrow longitude zones, each with its own central meridian and a scale factor to control distortion. This keeps scale error small within a zone. The ellipsoid, units, and reference latitude are not varied per zone.

Question 19Surveying Fundamentals and Geodesy

What does the scale factor at a point on a map projection express?

  1. The angular difference between true and grid north
  2. The ratio of grid distance to ellipsoidal distance at that point Correct answer.
  3. The elevation of the projection surface above the geoid
  4. The ratio of map distance to ground distance along the terrain

Explanation

The point scale factor is the ratio of an infinitesimal grid distance to the corresponding ellipsoidal distance. It differs from map-to-ground ratio, which also involves elevation and terrain reduction.

Question 20Surveying Fundamentals and Geodesy

In spirit levelling, which error is largely eliminated by keeping back and fore sights equal in length?

  1. Magnetic declination
  2. Atmospheric refraction over the whole route
  3. Collimation error of the instrument Correct answer.
  4. Rod zero error

Explanation

Equal sight lengths make the systematic collimation error act equally on back and fore readings, so it cancels in the height difference. Rod zero error does not cancel unless the same rod is used both ways, and refraction is not removed by equal sights alone.

Question 21Surveying Fundamentals and Geodesy

Which statement about the relationship between geodetic and astronomical latitude is correct?

  1. They are always identical at every point on the Earth
  2. They differ by the grid convergence
  3. They differ by the component of the deflection of the vertical in the meridian plane Correct answer.
  4. They differ by the geoidal undulation expressed in seconds

Explanation

Geodetic latitude refers to the ellipsoid normal, while astronomical latitude refers to the gravity vector. Their difference is the meridian component of the deflection of the vertical.

Question 22Surveying Fundamentals and Geodesy

Which instrument is specifically designed to measure gravity differences for geodetic purposes?

  1. Digital level
  2. Total station
  3. Gravimeter Correct answer.
  4. Theodolite

Explanation

A gravimeter measures local gravity acceleration, which supports geoid modelling and height-system definition. Theodolites measure angles, total stations measure angles and distances, and digital levels measure height differences.

Question 23Surveying Fundamentals and Geodesy

A traverse leg has a bearing of 118°30' and a horizontal length of 245.000 m. What are the departure and latitude, respectively?

  1. -117.13 m and -215.30 m
  2. +117.13 m and +215.30 m
  3. +215.30 m and -117.13 m Correct answer.
  4. -215.30 m and +117.13 m

Explanation

Departure equals length times sine of bearing, and latitude equals length times cosine of bearing. For 118°30', sin is about 0.8788 and cos is about -0.4772, giving departure +215.30 m and latitude -117.13 m.

Question 24Surveying Fundamentals and Geodesy

Which statement correctly describes the difference between a geocentric datum and a local (regional) datum?

  1. A geocentric datum uses only plane coordinates, while a local datum uses latitude and longitude
  2. A local datum has no ellipsoid associated with it
  3. A geocentric datum is aligned to the Earth's centre of mass, while a local datum is fitted to a region Correct answer.
  4. A geocentric datum is always more accurate for local surveys than any local datum

Explanation

A geocentric datum is oriented so its ellipsoid centre coincides with the Earth's centre of mass, supporting global consistency. A local datum positions the ellipsoid to best fit a region, which can improve local accuracy but shifts relative to the global frame.

Question 25Surveying Fundamentals and Geodesy

A closed-loop levelling run of four legs has height differences of +1.240 m, -0.860 m, +2.115 m, and -2.505 m. What is the misclosure?

  1. -0.020 m
  2. -0.010 m Correct answer.
  3. +0.010 m
  4. +0.020 m

Explanation

In a closed loop the algebraic sum of height differences should be zero. Summing gives 1.240 - 0.860 + 2.115 - 2.505 = -0.010 m, so the loop closes 10 mm low.

Question 26Surveying Fundamentals and Geodesy

In a geodetic survey, a distance measured along the ellipsoid between two points must be reduced before it can be compared with a grid distance. Which reduction sequence is applied, in order, to convert a horizontal ground distance to a grid distance?

  1. Reduce to the horizontal plane through the instrument station, then multiply by the cosine of the grid convergence.
  2. Apply the combined curvature and refraction correction, then divide by the line scale factor to obtain the grid distance.
  3. Reduce to the ellipsoid using the ellipsoidal height and curvature terms, then multiply by the point scale factor to obtain the grid distance. Correct answer.
  4. Multiply by the point scale factor first, then apply the sea-level reduction using the mean orthometric height of the line.

Explanation

Grid distances are obtained by first projecting the measured horizontal distance down onto the reference ellipsoid (allowing for height above the ellipsoid and the curvature of the line), and then applying the map projection scale factor. The sea-level or ellipsoid reduction and the scale-factor multiplication are two distinct steps and must be applied in that order.

Question 27Surveying Fundamentals and Geodesy

A surveyor must state the accuracy of a baseline measured with a total station under field conditions. Which statement correctly describes the meaning of a relative precision quoted as 1:50 000 for that baseline?

  1. The baseline may contain a random error of about 1 mm for every 50 000 m measured, regardless of the length actually observed.
  2. The misclosure of the baseline may not exceed 50 000 mm over the whole network, independent of the leg length.
  3. The standard error of the measured length is about 1/50 000 of the length, so a 2 km baseline carries a standard error of roughly 40 mm. Correct answer.
  4. The baseline must be measured 50 000 times before the result can be accepted for geodetic use.

Explanation

Relative precision expresses the random error as a fraction of the measured length, so 1:50 000 means a standard error of about 0.02 m per kilometre. The absolute uncertainty therefore grows in proportion to the length of the line, which is why long baselines demand more rigorous methods.

Question 28Surveying Fundamentals and Geodesy

A survey control point is observed by GNSS in static mode for 45 minutes using a single-frequency receiver, and the baseline is processed against a reference station 38 km away. Which factor most limits the achievable accuracy of this baseline?

  1. The ionospheric delay decorrelation between the two ends of the long baseline, which single-frequency data cannot fully remove. Correct answer.
  2. The number of satellites visible above the receiver horizon at the mid-point of the session.
  3. The rate at which the receiver logs the carrier phase, provided it is at least 1 Hz.
  4. The height of the antenna above the ground marker at the reference station.

Explanation

Over baselines of tens of kilometres the ionosphere differs appreciably at the two ends, and single-frequency observations cannot form the ionosphere-free combination that removes this delay. The residual ionospheric error therefore dominates the baseline accuracy budget in this configuration.

Question 29Surveying Fundamentals and Geodesy

In a closed traverse, the angular misclosure is computed by comparing the sum of the observed interior angles with the theoretical sum. For a closed polygon traverse with seven stations, what is the theoretical sum of the interior angles?

  1. 1260°00'00"
  2. 900°00'00" Correct answer.
  3. 720°00'00"
  4. 1080°00'00"

Explanation

The interior angles of a closed polygon with n sides sum to (n − 2) × 180°. For seven stations the sum is 5 × 180° = 900°, and any departure from this value is the angular misclosure to be distributed.

Question 30Surveying Fundamentals and Geodesy

A surveyor must choose between a conformal projection and an equal-area projection for a national topographic mapping series in which local shape and direction must be preserved for engineering survey work. Which statement justifies the choice correctly?

  1. An equal-area projection preserves shape locally because it keeps the scale identical in all directions while allowing area to vary.
  2. A conformal projection keeps both shape and area correct everywhere, so no scale factor correction is needed for survey work.
  3. A conformal projection preserves shape at every point by keeping the scale the same in all directions there, although areal scale varies across the map. Correct answer.
  4. An equal-area projection preserves all angles between mapped lines, so bearings can be used directly without convergence correction.

Explanation

Conformality means the scale at a point is the same in every direction, so small shapes and the angles between lines are preserved; the price is that areal scale departs from unity away from the standard line. Equal-area projections do the opposite, preserving area while distorting shape and angular relationships.

Question 31Geospatial Data Acquisition and Measurement

In GNSS positioning, which observable is formed by differencing the carrier-phase measurements of two receivers observing the same satellite at the same epoch?

  1. Triple difference
  2. Single difference Correct answer.
  3. Double difference
  4. Ionosphere-free linear combination

Explanation

A single difference subtracts simultaneous observations of the same satellite from two receivers, removing satellite clock error and largely cancelling atmospheric effects common to both ends. Double differencing goes one step further by differencing across two satellites, and triple differencing adds a time difference between epochs.

Question 32Geospatial Data Acquisition and Measurement

What does the horizontal dilution of precision (HDOP) value primarily describe about a GNSS position solution?

  1. The residual tropospheric delay after modelling
  2. The number of satellites rejected during processing
  3. The vertical accuracy after ambiguity resolution
  4. The geometric strength of the satellite constellation in the horizontal plane Correct answer.

Explanation

DOP factors are derived from the geometry matrix of the satellite-receiver line-of-sight vectors and express how satellite geometry amplifies ranging errors. HDOP specifically reflects the horizontal component, with smaller values indicating better geometry.

Question 33Geospatial Data Acquisition and Measurement

A total station measures a slope distance of 150.000 m to a target, and the vertical angle from horizontal is 10 degrees. Ignoring instrument and target heights, what is the horizontal distance?

  1. 147.721 m Correct answer.
  2. 26.047 m
  3. 152.318 m
  4. 148.482 m

Explanation

The horizontal distance equals the slope distance multiplied by the cosine of the vertical angle: 150.000 x cos(10 degrees) = 150.000 x 0.98481 = 147.721 m. The sine of the angle would give the height difference instead.

Question 34Geospatial Data Acquisition and Measurement

In a levelling survey, what is the purpose of taking backsight and foresight readings on a change point?

  1. To calibrate the circular bubble of the level
  2. To transfer the reduced level from one instrument setup to the next Correct answer.
  3. To determine the magnetic bearing of the levelling line
  4. To measure the horizontal angle between two traverse legs

Explanation

A change point is a stable staff position observed as a foresight from one setup and as a backsight from the next, allowing the height datum to be carried forward. The difference between the two readings gives the height change between setups.

Question 35Geospatial Data Acquisition and Measurement

Which statement correctly describes the difference between a geoid and an ellipsoid in geospatial measurement?

  1. The geoid is an equipotential surface of gravity, while the ellipsoid is a mathematical reference surface Correct answer.
  2. The geoid defines magnetic north, while the ellipsoid defines grid north
  3. The geoid is a mathematical surface, while the ellipsoid follows mean sea level
  4. The geoid and ellipsoid are identical surfaces used only for map projection

Explanation

The geoid is the equipotential surface of the Earth's gravity field that best approximates mean sea level, and it is irregular. The reference ellipsoid is a smooth mathematical surface used as the basis for horizontal coordinates and ellipsoidal heights.

Question 36Geospatial Data Acquisition and Measurement

Which coordinate system is defined by an origin at the Earth's centre of mass with axes fixed relative to the rotating Earth?

  1. Astronomical horizon system
  2. Earth-Centred, Earth-Fixed (ECEF) Correct answer.
  3. Local tangent plane
  4. Universal Transverse Mercator grid

Explanation

An ECEF system places the origin at the Earth's centre of mass and rotates the axes with the Earth, so a fixed ground point keeps constant coordinates. This makes it the natural frame for GNSS broadcast ephemerides and Cartesian position output.

Question 37Geospatial Data Acquisition and Measurement

What is the primary reason for observing a closed traverse loop in a control survey?

  1. To eliminate the need for any known control points
  2. To provide a check on angular and linear misclosure before adjustment Correct answer.
  3. To increase the number of redundant satellite observations
  4. To convert ellipsoidal heights to orthometric heights

Explanation

Closing the traverse back on a known point or on the starting station yields a misclosure that reveals gross errors and random error accumulation. The misclosure is then distributed by a recognised adjustment method.

Question 38Geospatial Data Acquisition and Measurement

Which instrument is specifically designed to measure horizontal and vertical angles with high precision using a graduated circle read by optical or electronic means?

  1. Clinometer
  2. Planimeter
  3. Barometer
  4. Theodolite Correct answer.

Explanation

A theodolite measures horizontal and vertical angles precisely through graduated circles and a telescope, and it is the classic angular instrument in control surveys. Modern total stations combine a theodolite with an electronic distance meter.

Question 39Geospatial Data Acquisition and Measurement

A GNSS receiver reports an ellipsoidal height of 120.000 m at a site where the geoid undulation is +35.000 m. What is the orthometric height, using h = H + N?

  1. 35.000 m
  2. 155.000 m
  3. 85.000 m Correct answer.
  4. 120.000 m

Explanation

The relation h = H + N links ellipsoidal height h, orthometric height H and geoid undulation N. Rearranging gives H = h - N = 120.000 - 35.000 = 85.000 m.

Question 40Geospatial Data Acquisition and Measurement

Two GNSS stations 20 km apart are processed in relative static mode. Which error is most effectively reduced by this approach?

  1. Receiver internal noise
  2. Satellite orbit and atmospheric errors common to both stations Correct answer.
  3. Multipath at the rover antenna
  4. Antenna phase centre variation

Explanation

Relative processing differences observations between a base and rover, so errors that are spatially correlated over short baselines, such as orbit error and much of the atmospheric delay, largely cancel. Errors local to one antenna, such as multipath, do not cancel.

Question 41Geospatial Data Acquisition and Measurement

In a resection (free station) setup, a total station measures angles and distances to several known control points. What is the minimum information required to determine the instrument position and orientation uniquely?

  1. Two known points observed with one horizontal angle only
  2. Two known points observed with both angles and distances, or three points with angles only Correct answer.
  3. One known point observed with a distance only
  4. Any number of points observed with vertical angles only

Explanation

Resection requires enough independent observations to solve the two position coordinates and the orientation. Two fully observed points supply a distance-distance plus angle solution, while three points with horizontal angles alone provide the necessary angular redundancy.

Question 42Geospatial Data Acquisition and Measurement

A line measured on a map at a scale of 1:2500 has a length of 84.0 mm. What is the corresponding ground distance?

  1. 8.4 m
  2. 21 m
  3. 210 m Correct answer.
  4. 2100 m

Explanation

Ground distance equals map distance multiplied by the scale denominator: 84.0 mm x 2500 = 210000 mm = 210 m. Unit conversion from millimetres to metres is the step most often missed.

Question 43Geospatial Data Acquisition and Measurement

Which statement best explains why a projection such as UTM uses a secant cylinder rather than a tangent one?

  1. It eliminates convergence of meridians
  2. It distributes scale error so that the central meridian has a scale factor slightly less than one Correct answer.
  3. It makes the projection conformal at all latitudes
  4. It removes the need for a false easting

Explanation

A secant cylinder intersects the ellipsoid along two standard lines, giving a central scale factor of 0.9996 in UTM. Scale error is thus spread across the zone, keeping distortion within acceptable limits rather than growing monotonically from the central meridian.

Question 44Geospatial Data Acquisition and Measurement

During a precise levelling run, the staff is read at 1.532 m as a backsight and 1.786 m as a foresight. If the backsight station has a reduced level of 45.000 m, what is the reduced level at the foresight station?

  1. 43.468 m
  2. 45.254 m
  3. 46.786 m
  4. 44.746 m Correct answer.

Explanation

The height difference is backsight minus foresight: 1.532 - 1.786 = -0.254 m. Adding this to the backsight reduced level gives 45.000 - 0.254 = 44.746 m.

Question 45Geospatial Data Acquisition and Measurement

What is the main effect of atmospheric refraction on a total station distance measurement made with a modulated light beam?

  1. It changes the propagation speed, so the measured distance is scaled unless corrected Correct answer.
  2. It shifts the target prism constant
  3. It rotates the horizontal circle reading
  4. It alters the vertical axis tilt of the instrument

Explanation

The distance is derived from the travel time or phase of the beam, which depends on the refractive index of air along the path. Temperature and pressure changes alter that index, so the instrument applies atmospheric corrections to scale the range.

Question 46Geospatial Data Acquisition and Measurement

Which statement correctly distinguishes a ground sample distance (GSD) from image resolution in aerial photogrammetry?

  1. GSD depends only on flight altitude, while resolution depends only on the lens
  2. GSD and resolution are identical quantities expressed in different units
  3. GSD is measured in pixels, while resolution is measured in metres on the ground
  4. GSD is the ground spacing represented by one pixel, while resolution describes the sensor's ability to record fine detail Correct answer.

Explanation

GSD expresses the ground footprint of a single pixel and depends on flying height, focal length and pixel size. Image resolution refers to the sensor's capability to resolve detail, which also involves optics and sampling, so the two are related but not identical.

Question 47Geospatial Data Acquisition and Measurement

In laser scanning, what does registration of multiple scans achieve?

  1. It converts point intensity values into reflectance
  2. It increases the angular resolution of each scanner
  3. It removes the need for any control points in the survey
  4. It transforms all scans into a common coordinate frame so overlapping data align Correct answer.

Explanation

Registration estimates the transformation parameters that align overlapping scans into a single reference frame, often using targets or feature matching. Without it, individual scan coordinate systems would remain unrelated.

Question 48Geospatial Data Acquisition and Measurement

A GNSS baseline is processed using broadcast ephemerides rather than precise ephemerides. What is the expected consequence?

  1. An increase in the number of visible satellites
  2. A larger orbit error component, which limits accuracy on long baselines Correct answer.
  3. A complete loss of carrier-phase ambiguity fixing
  4. A reduction in the receiver clock offset

Explanation

Broadcast orbits have metre-level errors, and their effect on the baseline grows with baseline length because the error is not fully common to both stations. Precise ephemerides reduce this orbit error and are preferred for long baselines and high accuracy.

Question 49Geospatial Data Acquisition and Measurement

Which quantity does the prism constant of a reflector correct in an electro-optical distance measurement?

  1. The offset between the electrical and mechanical centre of the reflector Correct answer.
  2. The collimation error of the theodolite
  3. The refractive index of the atmosphere along the line
  4. The scale error of the horizontal circle

Explanation

The measured range refers to a specific optical point inside the prism, which differs from the mounting point or plumb line. The prism constant compensates for this fixed offset so that the distance refers to the correct physical point.

Question 50Geospatial Data Acquisition and Measurement

In a network adjustment, what does the a posteriori reference variance indicate?

  1. The convergence of the map projection used for the coordinates
  2. The number of redundant observations in the network
  3. Whether the stochastic model assumed for the observations is consistent with the residuals Correct answer.
  4. The exact coordinates of the fixed control points

Explanation

The a posteriori variance factor compares the weighted residuals with the assumed observation variances. A value close to one suggests the stochastic model is realistic, while values far from one indicate over- or under-estimated observation precision.