Certified Photogrammetrist Exam — Questions and Answers

Question 1: What are the three rotation angles used to describe camera orientation in standard photogrammetric convention?

Omega, phi, kappa (Correct answer)
Azimuth, elevation, bank
Roll, pitch, yaw
Alpha, beta, gamma

Correct answer: Omega, phi, kappa

In photogrammetry, the three rotation angles omega (ω), phi (φ), and kappa (κ) define the rotational orientation of the camera relative to the ground coordinate system.

Question 2: What is 'ground sample distance' (GSD) in digital photogrammetry?

The distance between GPS ground control points
The real-world size represented by one pixel in the image (Correct answer)
The spacing between flight lines
The minimum detectable elevation difference

Correct answer: The real-world size represented by one pixel in the image

GSD (Ground Sample Distance) is the real-world dimension represented by a single pixel in the image, determining the spatial resolution of the final mapping products.

Question 3: What is the purpose of a reseau grid (reseau plate) in analog aerial cameras?

To provide reference marks for detecting and correcting film deformation (Correct answer)
To improve image sharpness at the corners of the frame
To filter ultraviolet radiation from sunlight
To record the exact time of each exposure

Correct answer: To provide reference marks for detecting and correcting film deformation

A reseau grid contains precisely positioned crosses or dots imaged onto the film, allowing detection and correction of film deformation that may occur during processing or scanning.

Question 4: Identifying a building as a high school because it is adjacent to a running track and football field uses which interpretation element?

Association (Correct answer)
Size
Pattern
Tone

Correct answer: Association

Association uses related nearby features to identify an object.

Question 5: What is 'stereoscopic exaggeration' in photogrammetric viewing?

The perceived amplification of vertical relief when the eye base is larger relative to the B/H ratio than normal human vision (Correct answer)
The enhancement of image contrast in stereo viewing systems
The distortion introduced by incorrect lens calibration
The color enhancement applied to improve feature discrimination

Correct answer: The perceived amplification of vertical relief when the eye base is larger relative to the B/H ratio than normal human vision

Stereoscopic exaggeration is the perceived amplification of terrain relief when the base-to-height ratio exceeds that of normal human stereo vision (approximately 1/30), making slopes appear steeper than they are.

Question 6: Which type of camera is commonly used in aerial photogrammetry?

Film projector
Metric camera (Correct answer)
Handheld DSLR
Phone camera

Correct answer: Metric camera

A metric camera is specifically designed for photogrammetric applications due to its high geometric stability and precisely calibrated internal parameters. Unlike consumer cameras, metric cameras minimize lens distortions and provide accurate focal length and principal point information, which are essential for precise measurements and mapping. This ensures the geometric integrity required for photogrammetric processing.

Question 7: In photogrammetric software, what does 'tie point extraction' (e.g., SIFT, SURF) accomplish?

Extracting control points from a GIS database automatically
Extracting building rooftops from aerial images using AI
Detecting distinctive image features and matching them across overlapping images for use in bundle adjustment (Correct answer)
Scanning film negatives to produce digital images

Correct answer: Detecting distinctive image features and matching them across overlapping images for use in bundle adjustment

Algorithms like SIFT and SURF detect distinctive keypoints in images and match them across overlapping photos, creating the tie points used in bundle adjustment.

Question 8: What is the collinearity condition in photogrammetry?

Three ground control points must form a right triangle
Parallel flight lines must be equidistant
The object point, perspective center, and image point all lie on a straight line (Correct answer)
All tie points must be visible in at least three photos

Correct answer: The object point, perspective center, and image point all lie on a straight line

The collinearity condition states that the object point, the camera's perspective center, and the corresponding image point are collinear—forming the mathematical basis for photogrammetric equations.

Question 9: What is the 'y-parallax' in a stereopair, and what does excessive y-parallax indicate?

Residual vertical displacement after relative orientation; it indicates incomplete relative orientation (Correct answer)
The parallax introduced by atmospheric refraction
The horizontal parallax difference used to measure elevation
The vertical image displacement caused by relief; it indicates high terrain

Correct answer: Residual vertical displacement after relative orientation; it indicates incomplete relative orientation

Y-parallax is residual vertical displacement of conjugate points in a stereopair after relative orientation; excessive y-parallax indicates that the relative orientation is incomplete or incorrect.

Question 10: In digital orthophoto production, what causes 'smear' artifacts in urban areas?

Excessive JPEG compression during orthophoto tile generation
The use of a DTM (bare-earth) instead of a DSM (full surface) for rectification, causing building rooftops to smear across adjacent areas (Correct answer)
GPS positioning errors causing misalignment of adjacent photos
Atmospheric haze reducing image contrast in urban areas

Correct answer: The use of a DTM (bare-earth) instead of a DSM (full surface) for rectification, causing building rooftops to smear across adjacent areas

Smear artifacts in urban orthophotos occur when a bare-earth DTM is used for rectification, causing building rooftops—which are elevated above ground—to be incorrectly projected and smeared across adjacent areas.

Question 11: An aircraft flies at 60 m/s with a shutter speed of 1/500 s and no forward motion compensation. How far does the ground move during exposure?

0.03 m
0.12 m (Correct answer)
0.06 m
0.30 m

Correct answer: 0.12 m

Ground motion = 60 m/s × 0.002 s = 0.12 m.

Question 12: In a conformal projection grid, what does the convergence angle describe?

The scale distortion at a point
The angle between magnetic north and grid north
The angle between grid north and geodetic (true) north (Correct answer)
The difference between ellipsoid and orthometric heights

Correct answer: The angle between grid north and geodetic (true) north

Grid convergence is the angle between grid north and geodetic north, and it grows with distance from the central meridian.

Question 13: The collinearity condition in photogrammetry states that:

Flight lines must be parallel for accurate triangulation
Control points must be evenly distributed across the image block
An object point, the camera perspective center, and its image point must lie on a single straight line (Correct answer)
Images in a strip must have uniform scale throughout

Correct answer: An object point, the camera perspective center, and its image point must lie on a single straight line

The collinearity condition states that an object point, the camera's perspective center, and the corresponding image point must lie on the same straight line, which is the fundamental geometric basis of the photogrammetric equations.

Question 14: The image scale (s) of a vertical aerial photograph with focal length f taken at flying height H above datum is expressed as:

s = f × H
s = H / f
s = f / H (Correct answer)
s = f + H

Correct answer: s = f / H

Image scale equals focal length divided by flying height above datum (s = f/H); a longer focal length or lower flying height produces a larger (more detailed) scale.

Question 15: What is the primary purpose of aerial triangulation in photogrammetry?

To generate color-balanced orthophotos automatically
To calculate the focal length of the camera
To determine the exterior orientation parameters of photographs without ground control at every photo (Correct answer)
To measure the altitude of the aircraft during flight

Correct answer: To determine the exterior orientation parameters of photographs without ground control at every photo

Aerial triangulation determines exterior orientation parameters by using a network of tie points and sparse ground control, eliminating the need for ground control at every photograph.

Question 16: What does exterior orientation of a photograph define?

The internal geometric parameters of the camera
The image coordinate system origin
The calibration parameters of the lens distortion
The position and rotational attitude of the camera at the moment of exposure (Correct answer)

Correct answer: The position and rotational attitude of the camera at the moment of exposure

Exterior orientation defines the six parameters — X, Y, Z position and omega, phi, kappa rotation angles — describing where the camera was and how it was oriented when the photo was taken.

Question 17: What causes decentering (tangential) lens distortion?

Curvature mismatch of the lens elements
Atmospheric refraction of light rays
Misalignment of optical elements from the optical axis within the lens system (Correct answer)
Temperature variations during flight operations

Correct answer: Misalignment of optical elements from the optical axis within the lens system

Decentering distortion is caused by the physical misalignment or decentering of lens elements from the optical axis, producing an asymmetric distortion pattern.

Question 18: In the State Plane Coordinate System, which projection is typically used for states with a predominantly east-west extent such as Tennessee?

Polyconic
Transverse Mercator
Oblique Mercator
Lambert Conformal Conic (Correct answer)

Correct answer: Lambert Conformal Conic

Lambert Conformal Conic minimizes distortion along east-west bands between its standard parallels.

Question 19: In AT processing, what is a 'pass point'?

A point measured in consecutive photos along a flight strip to pass geometry forward (Correct answer)
A point where two flight lines cross
A control point verified by the client
The nadir point directly below the aircraft

Correct answer: A point measured in consecutive photos along a flight strip to pass geometry forward

A pass point is measured in consecutive overlapping photographs along a strip to propagate (pass) the geometry from one model to the next.

Question 20: Which factor converts a measured horizontal ground distance to a State Plane grid distance?

Combined factor (grid scale factor times elevation factor) (Correct answer)
Inverse flattening
Grid convergence angle
Geoid separation alone

Correct answer: Combined factor (grid scale factor times elevation factor)

Multiplying ground distance by the combined factor first reduces it to the ellipsoid and then applies projection scale.

Question 21: Which type of coordinate system is typically used in spatial analysis for mapping features on Earth?

Color histogram scale
Geographic coordinate system (latitude and longitude) (Correct answer)
Thermal grid system
Atmospheric layer grid

Correct answer: Geographic coordinate system (latitude and longitude)

A Geographic Coordinate System uses latitude and longitude to define precise locations on the Earth's curved surface. This system is fundamental for mapping and spatial analysis, providing a universal and standardized way to reference geographic features. It allows for accurate positioning and analysis of data across the globe.

Question 22: What is 'parallax bar measurement' used for in analogue stereo photogrammetry?

Measuring x-parallax differences between points to compute relative elevations (Correct answer)
Measuring the principal distance of the analogue plotter
Measuring the y-parallax to detect relative orientation errors
Calibrating the stage movement of a comparator

Correct answer: Measuring x-parallax differences between points to compute relative elevations

A parallax bar measures x-parallax differences between conjugate points in a stereopair, allowing height differences between terrain points to be calculated using the parallax formula.

Question 23: What is the purpose of 'edge matching' in stereo compilation projects?

Aligning GPS trajectories from two different flight days
Connecting control points across different coordinate zones
Ensuring that map features compiled in adjacent stereomodels connect seamlessly at model boundaries (Correct answer)
Matching the color histogram of adjacent photographs

Correct answer: Ensuring that map features compiled in adjacent stereomodels connect seamlessly at model boundaries

Edge matching ensures that map features (roads, contours, building outlines) compiled in adjacent stereomodels align perfectly at the boundaries between models, maintaining topological continuity.

Question 24: What is the main purpose of a Low Distortion Projection (LDP)?

To keep grid and ground distances nearly equal across the project area (Correct answer)
To remove the need for a geoid model
To make rhumb lines straight
To preserve area for thematic mapping

Correct answer: To keep grid and ground distances nearly equal across the project area

An LDP is scaled and positioned at the project's ground elevation so grid distances closely match ground distances.

Question 25: Which process is performed to ensure survey measurements are consistent with known benchmarks?

Survey control (Correct answer)
Image classification
Data encryption
Cloud correction

Correct answer: Survey control

Survey control refers to the process of establishing a network of precisely known points, called benchmarks, whose positions and elevations are determined with high accuracy. This network serves as a reference framework to ensure that all subsequent survey measurements are consistent, accurate, and tied into a common datum. It is fundamental for maintaining the integrity and reliability of survey data across projects.

Question 26: The Modulation Transfer Function (MTF) in optical and sensor systems is used to measure:

The sensor dark current noise level
The radial lens distortion profile
The ability of the system to resolve and transfer spatial frequency detail (Correct answer)
The accuracy of onboard GPS position measurements

Correct answer: The ability of the system to resolve and transfer spatial frequency detail

MTF quantifies how well an optical system transfers contrast from the scene to the image at different spatial frequencies, characterizing the overall resolving power and sharpness of the system.

Question 27: Regularly spaced rows of trees that identify an orchard are an example of which interpretation element?

Pattern (Correct answer)
Shadow
Shape
Tone

Correct answer: Pattern

Pattern is the spatial arrangement of objects, such as the grid spacing of orchard trees.

Question 28: What is chromatic aberration in photogrammetric camera lenses?

The failure of a lens to focus different wavelengths of light at the same focal point (Correct answer)
Vignetting (light falloff) at the edges of the image frame
Motion blurring caused by aircraft vibration during exposure
Distortion caused by temperature-induced changes in the lens

Correct answer: The failure of a lens to focus different wavelengths of light at the same focal point

Chromatic aberration occurs when a lens fails to focus all wavelengths of light at exactly the same focal point, causing color fringing or reduced sharpness, particularly visible at high-contrast edges.

Question 29: In a weighted least squares adjustment, how is the weight of an observation related to its standard deviation?

Inversely proportional to the variance (Correct answer)
Directly proportional to the standard deviation
Independent of the standard deviation
Equal to the standard deviation

Correct answer: Inversely proportional to the variance

Weights are taken as inversely proportional to variance, so more precise observations carry more influence.

Question 30: In side-looking SAR imagery, layover occurs when which condition is met?

The backslope is steeper than the depression angle
The slope facing the radar is steeper than the local incidence angle (Correct answer)
The terrain is perfectly flat
The radar wavelength is shorter than the surface roughness

Correct answer: The slope facing the radar is steeper than the local incidence angle

When foreslope exceeds the incidence angle, the top returns before the base and is imaged closer to the sensor.

Question 31: What scale factor is applied at the central meridian of every UTM zone?

0.9999
1.0004
1.0000
0.9996 (Correct answer)

Correct answer: 0.9996

UTM uses a central meridian scale factor of 0.9996 to balance distortion across the 6-degree zone.

Question 32: What is the scale factor along the central meridian of a Universal Transverse Mercator (UTM) zone?

0.9996 (Correct answer)
0.9999
1.0004
1.0000

Correct answer: 0.9996

UTM uses a central meridian scale factor of 0.9996 to balance distortion across the 6-degree zone.

Question 33: Geodetic latitude is defined as the angle between the equatorial plane and which line?

The ellipsoid normal at the point (Correct answer)
The plumb line (direction of gravity)
The line to the celestial pole
The radius vector to Earth's center

Correct answer: The ellipsoid normal at the point

Geodetic latitude uses the ellipsoid normal, geocentric latitude uses the radius vector, and astronomic latitude uses the plumb line.

Question 34: What is the purpose of a GNSS base station within roughly a limited baseline distance of an airborne mapping project?

To control the aircraft autopilot
To measure atmospheric humidity
To provide differential corrections for precise aircraft trajectory computation (Correct answer)
To trigger the camera shutter

Correct answer: To provide differential corrections for precise aircraft trajectory computation

Short baselines to a base station enable reliable carrier-phase ambiguity resolution for the trajectory.

Question 35: Which vertical datum is the current official datum for orthometric heights in the conterminous United States?

NGVD 29
NAVD 88 (Correct answer)
NAD 27
IGLD 85

Correct answer: NAVD 88

NAVD 88 is the official vertical datum for CONUS until replaced by NAPGD2022.

Question 36: A camera with a 150 mm focal length is flown at 3,000 m above ground level. What is the approximate nominal image scale?

1:20,000 (Correct answer)
1:2,000
1:200,000
1:200

Correct answer: 1:20,000

Image scale = f/H = 0.150 m / 3,000 m = 1/20,000, giving a scale of 1:20,000.

Question 37: What enables Real-Time Kinematic (RTK) GNSS to achieve centimeter-level positioning?

Use of the SBAS satellites alone
Code-only pseudoranges averaged over a long session
Carrier-phase measurements with corrections from a nearby base station (Correct answer)
Single-frequency autonomous positioning

Correct answer: Carrier-phase measurements with corrections from a nearby base station

RTK resolves carrier-phase integer ambiguities using real-time corrections from a reference receiver.

Question 38: The US survey foot, deprecated by NIST and NGS at the end of 2022, is defined as exactly:

3937/1200 m
1200/3937 m (Correct answer)
0.3048 m
0.304801 m

Correct answer: 1200/3937 m

The US survey foot equals 1200/3937 m (about 0.3048006 m), while the international foot is exactly 0.3048 m.

Question 39: About how much ground distance does one arc-second of latitude cover?

About 111 m
About 30.9 m (Correct answer)
About 1.85 m
About 308 m

Correct answer: About 30.9 m

One degree of latitude is about 111 km, so one arc-second is about 111,000 / 3,600, or roughly 30.9 m.

Question 40: To obtain a photo scale of 1:12,000 with a 152.4 mm focal length camera, what flying height above average terrain is required?

1,524 m
1,829 m (Correct answer)
2,286 m
1,219 m

Correct answer: 1,829 m

H = f × scale denominator = 0.1524 m × 12,000 = 1,828.8 m.

Question 41: What is a key advantage of active remote sensing systems like LiDAR?

They function in any lighting conditions (Correct answer)
They require daylight to operate
They only measure air temperature
They depend on visible light reflection

Correct answer: They function in any lighting conditions

A key advantage of active remote sensing systems, such as LiDAR or radar, is their ability to emit their own energy (e.g., laser pulses or microwaves) and measure the reflected signal. This independence from external light sources allows them to collect data effectively during both day and night, and often through atmospheric conditions like clouds or haze, ensuring consistent data acquisition.

Question 42: What is a 'metadata report' required to accompany photogrammetric deliverables?

Documentation describing data acquisition parameters, processing methods, datum/projection, accuracy, and data quality information (Correct answer)
A list of all software licenses used in production
A financial invoice detailing all project costs
A photographic log of the camera operator's activities

Correct answer: Documentation describing data acquisition parameters, processing methods, datum/projection, accuracy, and data quality information

Metadata reports document all relevant information about data acquisition and processing—including flight parameters, camera calibration, datum, projection, accuracy statistics, and lineage—enabling proper use and archiving of deliverables.

Question 43: Strip deformation in aerial triangulation typically appears as what type of systematic error?

Rotation of the entire block around the Z-axis
A 'bow' or 'banana' shape bending along the flight strip (Correct answer)
Uniform scale error across the entire block
Random noise on individual image measurements

Correct answer: A 'bow' or 'banana' shape bending along the flight strip

Strip deformation manifests as a systematic bow or banana-shaped bending along a flight strip, caused by accumulated errors in relative orientation between successive stereomodels.

Question 44: In an Earth-Centered, Earth-Fixed (ECEF) Cartesian system, the X-axis points toward which location?

The intersection of the equator and the prime meridian (Correct answer)
The conventional North Pole
The vernal equinox
The intersection of the equator and 90 degrees E

Correct answer: The intersection of the equator and the prime meridian

In ECEF, X points to 0 degrees latitude and 0 degrees longitude, Z points to the reference pole, and Y completes a right-handed system.

Question 45: What false easting is assigned to the central meridian of every UTM zone?

500,000 m (Correct answer)
10,000,000 m
0 m
2,000,000 m

Correct answer: 500,000 m

A 500,000 m false easting keeps all eastings within a zone positive.

Question 46: What is the effect of using too few ground control points in a large photo block?

Reduced number of tie points required
Systematic deformations and poor absolute accuracy of the final product (Correct answer)
Shorter processing time with no accuracy impact
Increased pixel resolution in the output orthophoto

Correct answer: Systematic deformations and poor absolute accuracy of the final product

Insufficient ground control allows systematic block deformations to go uncorrected, degrading the absolute accuracy of the final mapping products.

Question 47: In aerial photography, fiducial marks are used primarily to:

Measure ground control points
Define the image coordinate system (Correct answer)
Calibrate the onboard GPS receiver
Determine the aircraft flight altitude

Correct answer: Define the image coordinate system

Fiducial marks are reference points etched into the camera's focal plane that define the image coordinate system and allow transformation from scanner to image coordinates.

Question 48: What does interior orientation define in photogrammetry?

The position and attitude of the camera in the world coordinate system
The transformation from pixel to ground coordinates
The geometric relationship between the image plane and the perspective center (Correct answer)
The spatial relationship between overlapping images

Correct answer: The geometric relationship between the image plane and the perspective center

Interior orientation defines the geometric relationship between the image coordinate system and the perspective center, including focal length, principal point location, and lens distortion parameters.

Question 49: What is the 'sigma naught' (σ₀) in bundle adjustment output?

The number of iterations to convergence
The RMS flight altitude deviation
The nadir angle of the camera
The standard deviation of unit weight, indicating overall solution quality (Correct answer)

Correct answer: The standard deviation of unit weight, indicating overall solution quality

Sigma naught (σ₀) is the standard deviation of unit weight from the least-squares solution, providing an overall indicator of the internal consistency and quality of the adjustment.

Question 50: What is the principal point in camera calibration?

The geometric center of the image frame
The projection center of the lens
The midpoint between two fiducial marks
The point where the optical axis intersects the image plane (Correct answer)

Correct answer: The point where the optical axis intersects the image plane

The principal point is where the optical axis intersects the image plane, representing the foot of the perpendicular from the perspective center to the image plane.

Question 51: What causes 'layover' in radar imagery, and can it affect photogrammetric products?

Layover in photogrammetry refers to GPS signal multipath errors
In radar, layover occurs when tall objects lean toward the sensor; in photogrammetry, the analogue is relief displacement (Correct answer)
Layover is caused by atmospheric haze and degrades photogrammetric accuracy uniformly
Layover is exclusive to multispectral sensors and does not affect photogrammetric products

Correct answer: In radar, layover occurs when tall objects lean toward the sensor; in photogrammetry, the analogue is relief displacement

Radar layover occurs when tall objects appear to lean toward the sensor due to the near-range compression of elevated objects; the photogrammetric analogue is relief displacement, where objects appear displaced from their true position.

Question 52: In image interpretation, 'texture' is best defined as what?

The spatial arrangement of repeated objects
The overall color of an object
The geographic location of a feature
The frequency of tonal change within an area (Correct answer)

Correct answer: The frequency of tonal change within an area

Texture describes the fineness or coarseness produced by tonal variation too small to discern individually.

Question 53: What is 'multi-ray' matching in photogrammetric dense reconstruction?

A method for connecting flight strips using cross-tie points
A technique for matching features across different spectral bands
Matching image features using only two overlapping images (stereopair)
Simultaneously using three or more overlapping images to improve matching reliability and accuracy (Correct answer)

Correct answer: Simultaneously using three or more overlapping images to improve matching reliability and accuracy

Multi-ray matching uses three or more overlapping images simultaneously to verify and improve the reliability of matched points, reducing errors compared to stereopair-only matching.

Question 54: In digital photogrammetry, pixel size of the sensor is most directly related to:

The focal length of the camera lens
The lens radial distortion magnitude
The ground sample distance (GSD) (Correct answer)
The shutter speed setting

Correct answer: The ground sample distance (GSD)

Pixel size directly determines the ground sample distance (GSD) for a given flying height and focal length; GSD defines the smallest ground detail that can be resolved.

Question 55: Why does a 12-bit or 14-bit sensor offer an advantage over an 8-bit sensor in aerial imaging?

Faster frame rates
Greater radiometric resolution to capture detail in shadows and highlights (Correct answer)
Higher spatial resolution
Smaller file sizes

Correct answer: Greater radiometric resolution to capture detail in shadows and highlights

More bits per pixel record finer brightness gradations across a wider dynamic range.

Question 56: A 7-parameter Helmert (similarity) transformation between datums consists of which parameters?

3 translations, 3 rotations, 1 scale (Correct answer)
6 translations, 1 scale
4 translations, 2 rotations, 1 scale
3 translations, 2 rotations, 2 scales

Correct answer: 3 translations, 3 rotations, 1 scale

The Helmert transformation uses three shifts, three axis rotations, and one uniform scale factor.

Question 57: Each photo covers 2,000 m on the ground in the flight direction and the plan calls for 60% endlap. What is the air base between exposures?

800 m (Correct answer)
600 m
1,400 m
1,200 m

Correct answer: 800 m

Air base = (1 − 0.60) × 2,000 m = 800 m.

Question 58: Which type of aerial camera lens has an angular field of view greater than 100 degrees and is used for small-scale mapping?

Telephoto lens (about 30°)
Superwide-angle lens (about 120°) (Correct answer)
Normal-angle lens (about 60°)
Wide-angle lens (about 90°)

Correct answer: Superwide-angle lens (about 120°)

Superwide-angle lenses have angular fields of view greater than 100 degrees (typically ~120°), covering large ground areas per photograph, making them suited for small-scale topographic mapping.

Question 59: Which tool is typically used for capturing highly accurate GNSS-based location data?

GNSS receiver (Correct answer)
Rain gauge
Barometer
Anemometer

Correct answer: GNSS receiver

A GNSS (Global Navigation Satellite System) receiver is a specialized electronic device that receives signals from satellites to determine its precise location on Earth. Professional-grade GNSS receivers are designed for high accuracy, making them essential tools for capturing reliable location data in surveying, mapping, and other applications requiring precise positioning. The other options are unrelated measurement tools.

Question 60: In digital aerial cameras, what component replaces the photographic film at the focal plane?

The lens system
The CCD or CMOS image sensor (Correct answer)
The shutter mechanism
The viewfinder assembly

Correct answer: The CCD or CMOS image sensor

In digital cameras, the CCD or CMOS sensor array is positioned at the focal plane to capture light, directly replacing the role of photographic film as the image recording medium.

Question 61: What is the ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) Class 1 horizontal accuracy for 1 cm GSD imagery?

RMSEx and RMSEy ≤ 0.5 cm, with 95% confidence radius ≤ 0.9 cm
RMSEx and RMSEy ≤ 2.5 cm, with 95% confidence radius ≤ 4.3 cm
RMSEx and RMSEy ≤ 1.0 cm, with 95% confidence radius ≤ 1.7 cm (Correct answer)
RMSEx and RMSEy ≤ 5.0 cm, with 95% confidence radius ≤ 8.6 cm

Correct answer: RMSEx and RMSEy ≤ 1.0 cm, with 95% confidence radius ≤ 1.7 cm

Under ASPRS 2014 standards, Class 1 horizontal accuracy for 1 cm GSD specifies RMSEx and RMSEy ≤ 1.0 cm (equal to the GSD), with a 95% radial confidence of ≤ 1.7 cm.

Question 62: To convert a horizontal ground distance to a State Plane grid distance, the ground distance is multiplied by which factor?

The geoid separation
The combined factor (grid scale factor times elevation factor) (Correct answer)
The convergence angle
The elevation factor only

Correct answer: The combined factor (grid scale factor times elevation factor)

The combined factor accounts for both reduction to the ellipsoid and projection scale distortion.

Question 63: In digital photogrammetry, what is 'epipolar geometry' used for?

Converting pixel coordinates to geographic coordinates
Defining the flight line spacing for a project
Constraining image matching to a 1D search along epipolar lines, reducing computation and false matches (Correct answer)
Correcting color balance between adjacent strips

Correct answer: Constraining image matching to a 1D search along epipolar lines, reducing computation and false matches

Epipolar geometry constrains the search for corresponding points to a one-dimensional line (epipolar line) in the second image, dramatically reducing computation and eliminating many false matches.

Question 64: In photogrammetric sensor calibration, what is meant by 'self-calibration'?

Calibration performed using only onboard GPS/IMU data without ground control
Camera interior orientation parameters are solved simultaneously with exterior orientation during bundle adjustment using object-space control (Correct answer)
The manufacturer pre-calibrates the sensor before delivery to the client
The camera automatically adjusts its parameters during flight

Correct answer: Camera interior orientation parameters are solved simultaneously with exterior orientation during bundle adjustment using object-space control

Self-calibration (on-the-job calibration) simultaneously solves for interior orientation parameters and exterior orientation parameters within the bundle adjustment, using highly redundant imagery and ground control points.

Question 65: What is the calibrated focal length (CFL) in photogrammetry?

The distance from the rear nodal point to the film plane
The focal length measured when focused at infinity
The focal length value that minimizes the overall effect of radial distortion across the image (Correct answer)
The manufacturer's nominal specified focal length

Correct answer: The focal length value that minimizes the overall effect of radial distortion across the image

The calibrated focal length is the value that minimizes the overall effect of radial lens distortion across the image format, and may differ slightly from the manufacturer's specification.

Question 66: What is a TIN (Triangulated Irregular Network) in 3D modeling?

A network of GPS base stations for differential correction
A surface model composed of irregular triangular facets connecting measured mass points and breaklines (Correct answer)
A raster grid interpolated from contour lines
A point cloud storage format for LiDAR data

Correct answer: A surface model composed of irregular triangular facets connecting measured mass points and breaklines

A TIN is a vector-based surface model made of irregular triangular facets connecting measured points and breaklines, faithfully representing terrain morphology including sharp features like ridges.

Question 67: What is the deflection of the vertical?

The angle between the plumb line and the ellipsoid normal (Correct answer)
The difference between magnetic and true north
The angle between two adjacent meridians
The angle between grid north and geodetic north

Correct answer: The angle between the plumb line and the ellipsoid normal

Deflection of the vertical is the angle between the direction of gravity (plumb line) and the ellipsoid normal at a point.

Question 68: Which distortion model parameter primarily describes symmetric radial lens distortion?

Decentering coefficient P1
Affinity coefficient
Principal point offset
K1 radial distortion coefficient (Correct answer)

Correct answer: K1 radial distortion coefficient

K1 is the primary radial distortion coefficient that describes symmetric, rotationally symmetric distortion measured from the lens center outward.

Question 69: A set of repeated distance measurements clusters tightly together but is consistently 0.15 m longer than the true value. How are these measurements best described?

Neither precise nor accurate
Both precise and accurate
Precise but not accurate (Correct answer)
Accurate but not precise

Correct answer: Precise but not accurate

Tight clustering indicates precision, while the consistent offset from truth indicates a lack of accuracy.

Question 70: A project sits at 1,000 m ellipsoid height. Using R = 6,371 km, what is the approximate ellipsoid distance for a 1,000.000 m ground distance?

1,000.157 m
1,000.000 m
999.843 m (Correct answer)
999.600 m

Correct answer: 999.843 m

Elevation factor = R/(R+h) = 6,371,000/6,372,000 = 0.999843, so 1,000 m becomes about 999.843 m.

Question 71: Which laboratory calibration method uses precision optical collimators to simulate distant targets at infinity?

Test field calibration
On-the-job self-calibration
Goniometer calibration (Correct answer)
Stellar calibration

Correct answer: Goniometer calibration

Goniometer calibration uses a precision instrument with collimators to project parallel rays simulating targets at infinity, enabling measurement of angular relationships and lens distortion in a controlled lab environment.

Question 72: NAVD 88 was held fixed at a single tide-gauge benchmark located where?

Galveston, Texas
Father Point/Rimouski, Quebec (Correct answer)
San Francisco, California
Sandy Hook, New Jersey

Correct answer: Father Point/Rimouski, Quebec

NAVD 88 was a minimally constrained adjustment fixed at the Father Point/Rimouski benchmark in Quebec.

Question 73: In 3D city modeling, what is 'Level of Detail' (LOD) as defined by CityGML?

The number of control points used in the block adjustment
A measure of image resolution used for acquisition planning
A hierarchical scale of model complexity, from simple block models (LOD1) to fully textured models with interior detail (LOD4) (Correct answer)
The output file size of the 3D model

Correct answer: A hierarchical scale of model complexity, from simple block models (LOD1) to fully textured models with interior detail (LOD4)

CityGML defines LOD (Level of Detail) as a hierarchy from LOD0 (footprint) through LOD1 (block), LOD2 (roof structures), LOD3 (facades), to LOD4 (interior elements), reflecting increasing geometric complexity.

Question 74: The f-number (f/stop) of a photogrammetric camera lens is defined as:

The effective aperture diameter divided by the focal length
The focal length divided by the effective aperture (entrance pupil) diameter (Correct answer)
The ratio of image distance to object distance
The number of optical elements in the lens system

Correct answer: The focal length divided by the effective aperture (entrance pupil) diameter

The f-number is the ratio of the focal length to the effective aperture (entrance pupil) diameter, controlling the amount of light reaching the film or sensor plane.

Question 75: What is the spatial resolution of the panchromatic band on the Landsat 8/9 OLI sensor?

15 m (Correct answer)
10 m
30 m
60 m

Correct answer: 15 m

OLI band 8 (panchromatic) has 15 m resolution, while its multispectral bands are 30 m.

Question 76: Which camera calibration parameter corrects for non-orthogonality (shear) between the x and y axes of the image coordinate system?

Radial distortion coefficient K1
Affinity (shear) parameter (Correct answer)
Focal length correction
Principal point offset

Correct answer: Affinity (shear) parameter

The affinity or shear parameter corrects for non-orthogonality between the image coordinate axes, which can result from imperfect sensor geometry or digitizer scanning.

Question 77: What does 'logical consistency' mean in geospatial data quality standards (ISO 19157)?

The matching of feature attributes between different data sources
The consistency of radiometric values across the image mosaic
The degree to which a dataset conforms to its data model rules, including topological correctness and no invalid geometries (Correct answer)
The agreement between the dataset and ground truth check points

Correct answer: The degree to which a dataset conforms to its data model rules, including topological correctness and no invalid geometries

Logical consistency (ISO 19157) measures adherence to the data model's rules—such as polygon closure, no slivers, proper topology, and valid attribute values—independent of real-world accuracy.

Question 78: A GNSS point has ellipsoid height h = 152.40 m and geoid height N = -30.10 m. What is its orthometric height H?

182.50 m (Correct answer)
152.40 m
-122.30 m
122.30 m

Correct answer: 182.50 m

H = h - N = 152.40 - (-30.10) = 182.50 m.

Question 79: What is a 'true orthophoto' as distinct from a standard orthophoto?

An orthophoto produced from satellite imagery rather than aerial photography
An orthophoto corrected for building lean using a surface model of all above-ground features (DSM), so building walls do not appear in the image (Correct answer)
An orthophoto produced using only ground control points without GPS assistance
A color-balanced orthophoto with radiometric corrections applied

Correct answer: An orthophoto corrected for building lean using a surface model of all above-ground features (DSM), so building walls do not appear in the image

A true orthophoto uses a full DSM (including buildings and trees) for differential rectification, eliminating building lean and wall visibility that appears in standard orthophotos orthorectified using only a DTM.

Question 80: What is 'noise filtering' in point cloud processing?

Removing radiometric speckle from raster images
Eliminating outlier points that do not represent actual surfaces (e.g., flying points) (Correct answer)
Removing duplicate image exposures from the project
Filtering GPS positions with poor PDOP

Correct answer: Eliminating outlier points that do not represent actual surfaces (e.g., flying points)

Noise filtering removes outlier or erroneous points—such as isolated flying points far from the main surface—that would degrade the accuracy of derived terrain models.

Question 81: What is the approximate combined curvature and refraction correction for a horizontal sight of 1 km?

0.0067 m
0.067 m (Correct answer)
0.67 m
6.7 m

Correct answer: 0.067 m

The combined correction is about 0.0675 K^2 m, giving roughly 0.067 m at 1 km.

Question 82: When terrain elevation varies greatly within a flight line, what happens to GSD and overlap if flying height above sea level is held constant?

Overlap is unaffected, only GSD changes
Over higher terrain, GSD gets larger and overlap increases
Both remain constant
Over higher terrain, GSD gets smaller and overlap decreases (Correct answer)

Correct answer: Over higher terrain, GSD gets smaller and overlap decreases

Higher terrain is closer to the camera, so ground coverage shrinks, reducing GSD and overlap.

Question 83: What is the purpose of 'thinning' or 'decimating' a point cloud?

Reducing point cloud size by removing redundant points while preserving surface representation (Correct answer)
Increasing point density through interpolation
Splitting a large point cloud into manageable tiles
Adding color attributes to uncolored points

Correct answer: Reducing point cloud size by removing redundant points while preserving surface representation

Point cloud thinning/decimation reduces the number of points by removing redundant ones while preserving the essential shape and detail of the surface, making processing more manageable.

Question 84: What does 'resampling' mean in the context of raster photogrammetric products?

Resampling GPS trajectories to a uniform time interval
The process of computing pixel values at new grid positions during geometric transformations (e.g., bilinear, cubic convolution) (Correct answer)
Collecting additional ground control points after initial triangulation
Re-flying an area to collect additional imagery

Correct answer: The process of computing pixel values at new grid positions during geometric transformations (e.g., bilinear, cubic convolution)

Resampling computes new pixel values during raster transformation using interpolation methods—nearest neighbor preserves sharp edges, bilinear smooths slightly, and cubic convolution provides the best quality at higher cost.

Question 85: Under FAA Part 107, what is the general maximum altitude for a small UAS flying a mapping mission away from structures?

1,000 ft AGL
500 ft AGL
200 ft AGL
400 ft AGL (Correct answer)

Correct answer: 400 ft AGL

Part 107 limits operations to 400 ft AGL unless within 400 ft of a structure.

Question 86: Which factor determines how frequently a satellite can revisit the same location?

Spectral resolution
Temporal resolution (Correct answer)
Cloud cover density
Radiometric resolution

Correct answer: Temporal resolution

Temporal resolution refers to how frequently a remote sensing system can acquire imagery of the same geographic area. It is determined by the satellite's orbital characteristics and sensor capabilities. This factor is crucial for monitoring dynamic phenomena like vegetation growth, disaster response, or land-use change over time, as it dictates the frequency of data updates.

Question 87: What is the role of a flight plan in aerial photogrammetry?

To document ground measurements
To monitor film development
To adjust image contrast
To define image coverage paths and overlaps (Correct answer)

Correct answer: To define image coverage paths and overlaps

A flight plan is a meticulously designed route that dictates the aircraft's path, altitude, and camera firing intervals over a project area. Its primary role is to ensure systematic and complete photographic coverage, defining the precise image locations and the required forward and side overlaps between images. This planning is critical for efficient data acquisition and successful subsequent photogrammetric processing.

Question 88: A GNSS observation session reports a PDOP of 1.8. What does this indicate?

Excessive ionospheric delay
Severe multipath at the site
Poor satellite geometry and weak positions
Strong satellite geometry favorable for positioning (Correct answer)

Correct answer: Strong satellite geometry favorable for positioning

Low PDOP values indicate well-distributed satellites and stronger position solutions.

Question 89: On a DEM, the elevation rises 15 m over a horizontal distance of 300 m. What is the percent slope?

20%
15%
2%
5% (Correct answer)

Correct answer: 5%

Percent slope is (rise / run) x 100 = (15 / 300) x 100 = 5%.

Question 90: What type of distortion is unavoidable when projecting Earth’s curved surface onto a flat map?

Only shape
All of the above (Correct answer)
Only area
Only distance

Correct answer: All of the above

It is mathematically impossible to flatten a curved surface, such as the Earth, onto a two-dimensional plane without introducing some form of distortion. Therefore, all map projections will inevitably distort at least one, and often a combination, of these properties: area, shape, distance, and direction. There is no perfect projection that can preserve all properties simultaneously.

Question 91: Using Wien's displacement law, an Earth surface at about 300 K has peak emission near which wavelength?

25 µm
3.0 µm
0.5 µm
9.7 µm (Correct answer)

Correct answer: 9.7 µm

Peak wavelength ≈ 2898 µm·K / 300 K ≈ 9.7 µm.

Question 92: Which atmospheric condition negatively impacts aerial photogrammetry quality?

Low humidity
Heavy cloud cover (Correct answer)
Clear skies
No wind

Correct answer: Heavy cloud cover

Heavy cloud cover severely obstructs the ground surface from the aerial camera's view. This prevents the acquisition of clear, complete, and usable imagery, leading to significant gaps in data and poor image quality. Without visible ground features, accurate photogrammetric processing, such as stereoscopic matching and 3D model generation, becomes impossible or highly unreliable.

Question 93: In photogrammetric project specifications, what does 'NVA' stand for and how is it defined?

Network Validation Algorithm — the software process for checking tie-point networks
Nominal Vector Accuracy — the positional accuracy of vector features
Normal Vertical Adjustment — the result of the bundle adjustment vertical component
Non-Vegetated Accuracy — the vertical accuracy of the DEM in open, bare-earth areas, reported at the 95% confidence level (Correct answer)

Correct answer: Non-Vegetated Accuracy — the vertical accuracy of the DEM in open, bare-earth areas, reported at the 95% confidence level

NVA (Non-Vegetated Vertical Accuracy) is the vertical accuracy of the DEM in open, non-vegetated areas assessed using check points, reported at the 95th percentile confidence level (≈ 1.9600 × RMSEz).

Question 94: Why do flight planners typically raise endlap to 80% or more for urban true-orthophoto projects?

To minimize occluded areas caused by tall buildings (Correct answer)
To lower the GSD without changing altitude
To eliminate the need for ground control
To reduce the number of flight lines

Correct answer: To minimize occluded areas caused by tall buildings

Higher overlap provides multiple views of each point so building lean and occlusions can be resolved.

Question 95: What accuracy class does ASPRS 2014 assign when RMSEz of a DEM equals 10 cm?

The DEM meets Class 2 specifications for 5 cm GSD products
The DEM is classified as a bare-earth DTM regardless of source GSD
The DEM meets Class 1 specifications for 1 m GSD products
The DEM meets accuracy for products with 10 cm Non-Vegetated Vertical Accuracy (NVA) (Correct answer)

Correct answer: The DEM meets accuracy for products with 10 cm Non-Vegetated Vertical Accuracy (NVA)

Under ASPRS 2014, a DEM with RMSEz = 10 cm has a Non-Vegetated Vertical Accuracy (NVA) of approximately 19.6 cm (95% confidence), placing it in the accuracy class for products with 10 cm NVA.

Question 96: What is 'photogrammetric restitution' in the context of digital mapping?

The process of extracting planimetric and topographic features from stereo imagery for map compilation (Correct answer)
Recovering deleted project files from backup storage
Reconstructing damaged photographs from partial data
The process of recovering financial costs from project overruns

Correct answer: The process of extracting planimetric and topographic features from stereo imagery for map compilation

Photogrammetric restitution is the process of extracting map features—planimetric (roads, buildings) and topographic (contours, elevation)—from oriented stereo imagery for map production.

Question 97: A steel tape standardized at 20 degrees C is used on a hot day without correction. What type of error results?

Systematic error (Correct answer)
Instrumental noise that averages out
Blunder
Random error

Correct answer: Systematic error

Thermal expansion follows a predictable physical law and biases every measurement in the same direction.

Question 98: Which term describes the interpretation of remotely sensed images to classify land cover?

Pixel smoothing
Raster compositing
Histogram equalization
Image classification (Correct answer)

Correct answer: Image classification

Image classification is the process of categorizing pixels in a remotely sensed image into different land cover or land use classes (e.g., forest, water, urban, agriculture). This is achieved by analyzing the spectral characteristics of pixels and assigning them to predefined categories, creating thematic maps that represent the distribution of various features on the Earth's surface.

Question 99: What is the term for the area captured in a single aerial photograph?

Viewport
Ground coverage (Correct answer)
Frame buffer
Pixel zone

Correct answer: Ground coverage

Ground coverage refers to the actual area on the Earth's surface that is captured within a single aerial photograph. This area is determined by factors such as the camera's focal length, the sensor size, and the flight altitude. Understanding ground coverage is essential for planning flight paths and ensuring complete area mapping.

Question 100: In stereo compilation, what does 'absolute orientation' accomplish?

It determines the interior orientation of each camera
It scales, rotates, and positions the stereomodel into a real-world coordinate system using ground control (Correct answer)
It removes y-parallax from the stereopair
It adjusts image contrast for better stereoscopic viewing

Correct answer: It scales, rotates, and positions the stereomodel into a real-world coordinate system using ground control

Absolute orientation transforms the relatively oriented stereomodel (which exists in an arbitrary coordinate system) into real-world coordinates using ground control points.

Certified Photogrammetrist Exam

This certification validates an individual's expertise in the science and art of making measurements from photographs, especially for recovering the exact positions of surface points.

100

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180 min

Time Limit

70%

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Sources & references

Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy

asprs.org — Test delivery, eligibility, fees, renewal, retake fee, retake policy, time limit, score validity, exam information · verified Nov 2026
prometric.com — Registration · verified Oct 2026