GELE Photogrammetry & Cartography — Aerial Photography and Camera GeometryRevision Notes
Quick revision notes for Aerial Photography and Camera Geometry — the one-page refresher for GELE aspirants. Every item on this page has appeared in recent GELE Photogrammetry & Cartography papers, so revising these is the shortest path to a confident performance in Professional Regulation Commission (PRC) — Board of Geodetic Engineering's GELE 2026.
Exam context
On the GELE 2026, the Photogrammetry & Cartography subtest carries a "Core" weight in Professional Regulation Commission (PRC) — Board of Geodetic Engineering's pattern. Aerial Photography and Camera Geometry lands at position 1st out of 6 in the standard review order. Target score is 70% weighted average, no sub-test below 50%, and roughly a meaningful share of items come from Photogrammetry & Cartography on a typical GELE paper.
Aerial Photography and Camera Geometry - Revision Notes
Aerial photogrammetry is the science of extracting reliable measurements from aerial photographs. For the PRC Geodetic Engineer Licensure Examination, mastery of camera geometry, photo scale computation, ground coverage determination, and flight planning principles is essential. This chapter establishes the foundational geometry of a vertical aerial photograph — the building block for all subsequent photogrammetric operations including stereophotogrammetry, orthophoto production, and digital terrain modeling. Every formula in this chapter derives from simple similar-triangle (collinearity) relationships between the camera, the photograph, and the ground. Understanding these relationships thoroughly will allow you to solve any board-exam problem quickly and confidently.
Sections
Formulas
Example
Given f = 152 mm = 0.152 m, H = 1520 m above ground. Scale = 0.152 / 1520 = 1/10 000. The photo scale is 1:10 000.
Formula
Scale = f / H
Variables
f = calibrated focal length of the camera (m or mm, consistent units); H = flying height above the ground or terrain (same units as f converted to m)
Application
Fundamental photo scale formula for a vertical photograph over flat terrain. Gives the representative fraction (RF) of the photo.
Example
Two road intersections are 45 mm apart on the photo and 450 m apart on the ground. Scale = 0.045 m / 450 m = 1/10 000.
Formula
Scale = photo distance (d_photo) / ground distance (D_ground)
Variables
d_photo = measured distance between two image points (mm or m); D_ground = corresponding horizontal ground distance (m)
Application
Used when two identifiable points appear on the photo and their ground distance is known (or vice versa). Alternative way to determine or verify scale.
Example
A building measures 18 mm on a 1:8 000 photo. Ground length = 0.018 m × 8 000 = 144 m.
Formula
D_ground = d_photo × S
Variables
D_ground = ground distance (m); d_photo = photo distance (m or mm, convert to m); S = scale denominator (unitless)
Application
Convert a measured photo distance to the equivalent horizontal ground distance.
Example
A road 360 m long at scale 1:12 000. Photo distance = 360 / 12 000 = 0.030 m = 30 mm.
Formula
d_photo = D_ground / S
Variables
d_photo = photo distance (m); D_ground = ground distance (m); S = scale denominator
Application
Determine what size a ground feature will appear on the photo — useful for checking plotability.
Exam Tips
- Memorize Scale = f/H. Every camera geometry question reduces to this or its algebraic rearrangement.
- When H is given as 'altitude above MSL' and a mean ground elevation is given, always compute H_above_ground = H_MSL − mean_elevation first.
- If a question gives a map scale (e.g., 1:50 000) and asks for a photo scale with a given f, the map scale is a distractor unless it involves computing a ground distance.
- Always double-check unit consistency before computing — focal length must be in meters when H is in meters.
Key Points
- A metric aerial camera has a precisely calibrated focal length (f) and a fixed, known format size — the standard is 230 mm × 230 mm (9 in × 9 in).
- The optical axis is the line through the lens center perpendicular to the image plane.
- The principal point (PP) is the foot of the perpendicular from the lens center to the image (photo) plane — it is the center of the format for a well-calibrated camera.
- The nadir point (N) is the ground point directly below the camera center (plumb point).
- For a truly vertical photograph, the optical axis is vertical, so the principal point and nadir coincide on both the photo and the ground.
- The interior orientation of the camera is defined by: focal length f, principal point coordinates (x₀, y₀), and lens distortion parameters.
- Flying height H is always measured above the ground (or mean terrain elevation for average scale), NOT above mean sea level (MSL) unless stated otherwise.
- The camera station (perspective center) is at height H above the ground datum.
Definitions
Term
Principal Point (PP)
Definition
The point on the photograph where the optical axis of the lens intersects the image plane; it is the geometric center of the photo format for a calibrated camera.
Importance
Defines the origin of the photo coordinate system. On a vertical photo, it coincides with the nadir point.
Term
Nadir Point
Definition
The point on the ground directly below the camera (the plumb point). On the photo, the nadir is where the vertical through the camera center intersects the image plane.
Importance
For a vertical photo, nadir = principal point. Displacement from nadir causes relief displacement in non-vertical (tilted) photos.
Term
Focal Length (f)
Definition
The perpendicular distance from the rear nodal point of the lens to the image plane when focused at infinity. For metric cameras, this is precisely calibrated and reported in the camera calibration certificate.
Importance
Directly determines photo scale: Scale = f/H. Common values: 88 mm (wide angle), 152 mm (normal), 210 mm (narrow angle).
Term
Flying Height (H)
Definition
The vertical distance from the camera (perspective center) to the ground datum or mean terrain elevation, measured above the ground surface — not above MSL unless the two coincide.
Importance
Must be height above terrain for scale computation. H_above_MSL minus mean_ground_elevation = H above ground.
Term
Interior Orientation
Definition
The set of camera calibration parameters that define the geometry of the camera itself: focal length (f), principal point coordinates, and lens distortion coefficients.
Importance
Required for all photogrammetric restitution; provided in the camera calibration certificate.
Term
Vertical Photograph
Definition
An aerial photograph taken with the camera axis intentionally vertical (or as nearly vertical as the aircraft permits, typically within 3° of true vertical).
Importance
Simplifies geometry to similar triangles; all board-exam problems assume truly vertical unless stated.
Section Title
1. The Metric Aerial Camera — Components and Geometry
Common Mistakes
- Using H above MSL instead of H above ground when computing scale — always subtract mean terrain elevation from aircraft altitude.
- Mixing units: focal length in mm and flying height in m without converting. Always use consistent units (both in meters) before dividing.
- Confusing principal point with nadir — they coincide ONLY on a truly vertical photo.
- Using the wrong format size — the standard metric camera format is 230 mm × 230 mm, not 200 mm or 300 mm.
Formulas
Example
Aircraft at 3 500 m MSL, f = 0.152 m, mean ground elevation = 500 m MSL. H_above_ground = 3 500 − 500 = 3 000 m. Scale_avg = 0.152/3 000 = 1/19 737 ≈ 1:19 700.
Formula
Scale_avg = f / (H_aircraft − h_mean)
Variables
H_aircraft = aircraft altitude above datum (m MSL); h_mean = mean ground elevation above datum (m MSL); f = focal length (m)
Application
Computes the average representative photo scale over a project area with variable terrain.
Example
At a hilltop where h_A = 800 m MSL, aircraft at 3 500 m MSL, f = 0.152 m. Scale_A = 0.152/(3 500 − 800) = 0.152/2 700 = 1:17 763.
Formula
Scale_A = f / (H_aircraft − h_A)
Variables
h_A = ground elevation at point A above the same datum as H_aircraft
Application
Local scale at a specific terrain point A, used to convert a photo measurement at that point to a ground distance.
Exam Tips
- In board exams, if both aircraft altitude (MSL) and ground elevation are given, the effective H = aircraft altitude − ground elevation.
- Scale fraction: larger numerator in f/H means larger scale (more detail). Lower ground = larger H = smaller scale.
- If the problem says 'flat terrain' or 'sea level,' then H above ground = H above MSL — no subtraction needed.
Key Points
- Photo scale is constant everywhere only over perfectly flat terrain at a uniform elevation.
- Over varying terrain, the scale changes because H (height above ground) changes from point to point.
- Points at higher elevations are closer to the camera → smaller H → larger scale (appear larger on photo).
- Points at lower elevations are farther from the camera → larger H → smaller scale (appear smaller on photo).
- Average (nominal) scale uses the mean ground elevation: Scale_avg = f / (H_aircraft − elevation_mean).
- Scale at a specific point: Scale_point = f / (H_aircraft − elevation_point).
- The scale denominator S = H / f; ground distance = photo distance × S.
Definitions
Term
Average (Nominal) Photo Scale
Definition
The scale computed using the mean terrain elevation of the project area. Used for general flight planning, ground coverage estimation, and map production specifications.
Importance
Standard basis for specifying a photogrammetric project — e.g., 'photos at 1:10 000 average scale'.
Term
Local Scale
Definition
The actual scale at a specific terrain point, accounting for that point's actual elevation relative to the aircraft.
Importance
Needed for precise ground distance measurements at known elevations from the photo.
Section Title
2. Photo Scale — Variations Over Terrain
Common Mistakes
- Forgetting that higher ground = LARGER scale (smaller denominator), not smaller scale — the mountain top appears bigger.
- Using H above MSL directly in Scale = f/H without subtracting ground elevation.
- Assuming scale is uniform across the photo when terrain is undulating.
Formulas
Example
Format d = 0.230 m, scale 1:10 000. L_ground = 0.230 × 10 000 = 2 300 m = 2.3 km per side.
Formula
L_ground = d × S
Variables
L_ground = ground dimension covered per photo side (m); d = photo format side length (m); S = scale denominator
Application
Computes the linear ground dimension covered by one side of the aerial photo.
Example
d = 0.230 m, S = 10 000. A_ground = (0.230 × 10 000)² = 2 300² = 5 290 000 m² = 529 ha.
Formula
A_ground = (d × S)²
Variables
A_ground = total ground area covered by one photo (m²); d = format side (m); S = scale denominator
Application
Computes total ground area covered by a single vertical photo over flat terrain.
Example
d = 0.230 m, H = 3 000 m, f = 0.152 m. L_ground = 0.230 × (3 000/0.152) = 0.230 × 19 737 = 4 539.5 m ≈ 4.54 km.
Formula
L_ground = d × (H / f)
Variables
H = flying height above ground (m); f = focal length (m); d = format side (m)
Application
Alternative formula — substituting S = H/f into L_ground = d×S. Useful when H and f are given directly.
Exam Tips
- Always convert d to meters: 230 mm = 0.230 m. Then ground side = 0.230 × S gives answer directly in meters.
- Quick area conversion: divide m² by 10 000 to get hectares.
- If the question asks for the number of photos to cover a given area, divide total area by the effective (net) area per photo (after accounting for overlaps).
Key Points
- A standard metric camera has a square format: d = 230 mm = 0.230 m per side.
- At scale 1:S, the ground dimension covered by one side of the photo = d × S.
- Ground area covered by one photo = (d × S)² for a square format.
- Coverage increases as scale denominator S increases (higher altitude = more area per photo).
- Ground coverage is also expressed as: Ground side = f_ground × (H/f) where these are equivalent forms.
- Coverage in hectares: 1 ha = 10 000 m²; 1 km² = 100 ha.
- For a rectangular format (d₁ × d₂), ground area = (d₁ × S) × (d₂ × S).
Definitions
Term
Ground Coverage
Definition
The total area of ground terrain captured in a single aerial photograph, determined by the photo format size and the photo scale.
Importance
Essential for flight planning — determines the number of photos needed to cover a project area.
Term
Format Size
Definition
The physical dimensions of the photographic image on the film or sensor. Standard metric aerial cameras use 230 mm × 230 mm.
Importance
Fixed camera property used in all coverage and flight planning calculations.
Section Title
3. Ground Coverage — Format Size and Area Computation
Common Mistakes
- Forgetting to convert format size from mm to m before multiplying by S (in m units) — result will be off by a factor of 1 000.
- Reporting area in m² without converting to ha or km² as the question requires.
- Using diameter or radius instead of side length for format size.
Formulas
Example
L_ground = 2 300 m (from Example 2, 1:10 000 scale), p = 0.60. B = (1 − 0.60) × 2 300 = 0.40 × 2 300 = 920 m.
Formula
B = (1 − p) × L_ground
Variables
B = air base — ground distance between consecutive exposures (m); p = forward overlap as a decimal (e.g., 0.60 for 60%); L_ground = ground coverage per photo in the flight direction (m)
Application
Computes the required spacing between exposures along the flight line to achieve a specified forward overlap.
Example
L_ground = 2 300 m, q = 0.30. Strip spacing = (1 − 0.30) × 2 300 = 0.70 × 2 300 = 1 610 m.
Formula
Strip_spacing = (1 − q) × L_ground
Variables
Strip_spacing = distance between adjacent flight line centers (m); q = sidelap fraction (e.g., 0.30); L_ground = ground coverage in cross-track direction (m)
Application
Determines the lateral spacing between parallel flight lines to achieve the required sidelap.
Example
Project length = 10 000 m, B = 920 m. N = ceil(10 000/920) + 1 = ceil(10.87) + 1 = 11 + 1 = 12 photos per strip.
Formula
N_photos_per_strip = ceil(Project_length / B) + 1
Variables
N = number of photos per strip; Project_length = length of project area along flight direction (m); B = air base (m); ceil = round up to next integer
Application
Estimates the number of photo exposures needed per flight line, including end clearance.
Example
Project width = 8 000 m, strip spacing = 1 610 m. N_strips = ceil(8 000/1 610) + 1 = ceil(4.97) + 1 = 5 + 1 = 6 strips.
Formula
N_strips = ceil(Project_width / Strip_spacing) + 1
Variables
N_strips = number of parallel flight lines; Project_width = width of project area (m); Strip_spacing = lateral spacing between strips (m)
Application
Determines the number of flight lines needed to cover the full project width.
Example
p = 0.60, d = 0.230 m, f = 0.152 m. B/H = 0.40 × (0.230/0.152) = 0.40 × 1.513 = 0.605.
Formula
B/H = (1 − p) × (d / f)
Variables
B/H = base-to-height ratio (dimensionless); p = forward overlap fraction; d = format size in flight direction (m); f = focal length (m)
Application
The base-to-height ratio affects depth discrimination in stereo viewing. A larger B/H gives better vertical accuracy.
Exam Tips
- Air base B = (1 − p) × L_ground. For 60% overlap: B = 0.40 × L_ground. This is the most tested formula in flight planning.
- Strip spacing = (1 − q) × L_ground. For 30% sidelap: spacing = 0.70 × L_ground.
- For a square format at scale 1:S with d = 0.230 m: L_ground = 230S mm = 0.230S m. Then B = 0.40 × 0.230S = 0.092S m.
- Board exams often combine: find scale first, then L_ground, then B — a three-step chain calculation.
- Always round the number of photos/strips UP (ceiling function) — you cannot have a fractional photo.
Key Points
- Forward overlap (endlap): The percentage of a photo that is also seen on the next photo in the same flight line. Standard value: 60%.
- Sidelap: The percentage of a photo that is also seen on the adjacent flight line. Standard value: 30%.
- These overlaps ensure complete stereoscopic coverage of the project area and eliminate gaps due to aircraft attitude variations.
- The air base (B) is the horizontal ground distance between two successive exposure stations (camera positions) along a flight line.
- Net forward advance per photo = (1 − p) × L_ground, where p = forward overlap fraction and L_ground = ground coverage per side in the flight direction.
- Strip spacing = (1 − q) × L_ground, where q = sidelap fraction and L_ground = ground coverage in the cross-track direction.
- Number of photos per strip = (project length / air base) + 1; add photos for clearance at ends.
- Number of strips = (project width / strip spacing) + 1.
- Total photos = photos per strip × number of strips.
- For full stereoscopic coverage, 60% forward overlap means the base-to-height ratio B/H = (1 − p) × d/f = 0.40 × d/f.
Definitions
Term
Forward Overlap (Endlap)
Definition
The proportion of a photo that overlaps with the succeeding photo in the same flight strip, measured along the flight direction. Standard value: 60% (minimum 55%).
Importance
Ensures stereo coverage of every ground point. At 60% overlap, every ground point appears in at least two consecutive photos.
Term
Sidelap
Definition
The proportion of a photo that overlaps with photos from adjacent parallel flight lines, measured across the flight direction. Standard value: 30% (minimum 25%).
Importance
Ensures no gaps between strips due to aircraft drift or crab angle.
Term
Air Base (B)
Definition
The horizontal ground distance between two consecutive camera exposure stations along a flight line.
Importance
Determines the stereo base length and the base-to-height ratio, which controls vertical accuracy of the stereo model.
Term
Base-to-Height Ratio (B/H)
Definition
The ratio of the air base B to the flying height H above the ground. Typically 0.4–0.8 for standard metric photography.
Importance
Controls the precision of height determination in stereophotogrammetry; larger B/H = better height accuracy but increased parallax.
Term
Flight Line (Strip)
Definition
A straight flight path along which the aircraft photographs a corridor of terrain with consistent overlap between consecutive exposures.
Importance
The fundamental unit of aerial survey planning; multiple parallel strips cover an entire project area.
Section Title
4. Flight Planning — Overlap, Sidelap, and Air Base
Common Mistakes
- Computing air base as p × L_ground instead of (1 − p) × L_ground — the base is the NON-overlapping advance.
- Forgetting to add 1 to the number of photos per strip (you need one extra photo at each end).
- Using the same L_ground for both forward overlap and sidelap computations without checking if the format is square.
- Confusing sidelap (between strips) with forward overlap (within a strip).
- Not rounding up (ceiling) when computing number of photos or strips — always round up to ensure full coverage.
Formulas
Example
PROBLEM: f = 152 mm, H = 1 520 m above ground, format = 230 mm × 230 mm, forward overlap p = 60%, sidelap q = 30%, project = 6 km × 4 km. Find: (a) photo scale, (b) ground coverage per photo, (c) air base, (d) strip spacing, (e) total number of photos. SOLUTION: (a) Scale = f/H = 0.152/1520 = 1/10 000 (b) L_ground = 0.230 × 10 000 = 2 300 m; Area = 2 300² = 5 290 000 m² = 529 ha (c) B = (1 − 0.60) × 2 300 = 920 m (d) Strip spacing = (1 − 0.30) × 2 300 = 1 610 m (e) Photos/strip = ceil(6 000/920) + 1 = ceil(6.52) + 1 = 7 + 1 = 8; Strips = ceil(4 000/1 610) + 1 = ceil(2.48) + 1 = 3 + 1 = 4; Total photos = 8 × 4 = 32 photos.
Formula
Complete Solution Chain: Scale → L_ground → B → N_photos
Variables
Input: f, H, d, p, q, project dimensions. Output: scale, coverage, air base, number of photos/strips.
Application
Standard end-to-end flight planning computation combining all formulas from this chapter.
Exam Tips
- Exercise solutions (from reference): (1) f=210 mm, H=3150 m → Scale = 0.210/3150 = 1:15 000. (2) 1:8000, d=230 mm → L=0.230×8000=1840 m, Area=1840²=3386 ha (338.6 ha). (3) Road 62 mm on 1:12 000 → D=0.062×12000=744 m. (4) 60% overlap at 1:10000, d=230mm → L=2300m, B=0.40×2300=920 m.
- Memorize the 'magic numbers': standard format 230 mm, standard focal lengths 88/152/210 mm, overlap 60%/30%.
- If given both f and scale, solve for H: H = f × S — useful for back-computing flying height.
Key Points
- Problem-solving strategy: (1) Identify known quantities and units, (2) Convert all units to meters, (3) Apply Scale = f/H, (4) Compute L_ground = d × S, (5) Apply overlap formulas as needed.
- Always show unit analysis alongside computation.
- State the final answer with correct units and appropriate significant figures.
- Board exam problems are typically 3–5 steps; never skip a step in the solution chain.
Definitions
Term
Representative Fraction (RF)
Definition
The ratio of a distance on the photo (or map) to the corresponding horizontal ground distance, expressed as a dimensionless fraction (e.g., 1/10 000 or 1:10 000).
Importance
Standard way to express photo or map scale; must be dimensionless — both numerator and denominator in the same units.
Section Title
5. Worked Board-Style Problems
Common Mistakes
- Solving for S algebraically: if Scale = f/H, then S = H/f — make sure to compute this correctly. Example: H = 3 150 m, f = 0.210 m → S = 3 150/0.210 = 15 000 → Scale = 1:15 000.
- Not setting up the problem systematically — skipping the scale step before computing coverage leads to errors.
- Rounding intermediate results too aggressively — keep 4–5 significant figures through the computation chain, round only the final answer.
Connections
- Photo scale (Scale = f/H) is the gateway formula linking camera geometry to all other photogrammetric computations — master this first.
- Ground coverage formulas directly feed into flight planning (number of photos, strips, total flight distance) — these topics are inseparable in board exams.
- The interior orientation parameters (f, PP coordinates) established in this chapter are prerequisite to understanding exterior orientation, collinearity equations, and bundle adjustment in advanced photogrammetry.
- Relief displacement (studied in the next chapter) is built on the same similar-triangle geometry — a ground point at height h above the base plane is displaced radially on the photo by r = h × r_image / H.
- Stereophotogrammetry and parallax equations use the air base B derived in this chapter as a fundamental input — the base-to-height ratio B/H determines the precision of elevation determination.
- In Philippine practice, aerial photography for cadastral surveys (PD 1529, CA 141) and geodetic control (RA 8560) must achieve specified accuracy standards that directly dictate the required photo scale and flying height.
- PPCS/UTM coordinates — used for all Philippine geodetic control and mapping — serve as the ground coordinate system into which photogrammetric measurements are ultimately transformed.
- WGS84/PRS92 ellipsoid heights and geoid models are needed when converting aircraft barometric altimeter readings (MSL) to the accurate H-above-terrain values used in Scale = f/H.
- Digital photogrammetry and UAV surveys use the same fundamental geometry (Scale = f/H, coverage, overlap) — only the platform and sensor change, not the underlying mathematics.
Exam Strategy
For the PRC Geodetic Engineer board exam on Aerial Photography and Camera Geometry, follow this systematic approach: (1) IDENTIFY — read the problem completely and list all given values with units before writing any formula. (2) CONVERT UNITS — convert f to meters and ensure H is in meters above ground (subtract terrain elevation from aircraft MSL altitude if needed). (3) COMPUTE SCALE — apply Scale = f/H; write the answer as 1:S where S is the scale denominator. (4) COMPUTE COVERAGE — if needed, L_ground = 0.230 × S (for standard format); Area = L_ground² in m², then divide by 10 000 for hectares. (5) APPLY OVERLAP FORMULAS — B = (1 − p) × L_ground for 60% forward overlap; strip spacing = (1 − q) × L_ground for 30% sidelap. (6) COUNT PHOTOS/STRIPS — always use ceiling function and add 1 for end clearance. (7) VERIFY — check that your scale is reasonable (most aerial surveys are 1:5 000 to 1:50 000) and that your air base is less than L_ground. Memorize: standard format = 230 mm, standard overlaps = 60%/30%, Scale = f/H is the master formula. Time allocation: these problems are typically solvable in 3–5 minutes if you have the formula chain memorized. Practice the 4 chapter exercises until you can solve each in under 3 minutes.
Quick Review Questions
A vertical aerial photo is taken with a camera having f = 210 mm from an altitude of 4 200 m above mean sea level. The mean ground elevation of the area is 600 m MSL. What is the photo scale?
H above ground = 4 200 − 600 = 3 600 m. Scale = f/H = 0.210/3 600 = 1/17 143... Wait — re-checking: 0.210/3600 = 1/17 143. Using exact values: f = 0.210 m, H = 3600 m, Scale = 0.210/3600 = 1:17 143. (Note: the exercise answer 1:15 000 corresponds to H = 3 150 m with no terrain correction.)
A camera with f = 152 mm and format 230 mm × 230 mm takes photos at 1:10 000 scale. What is the ground area covered by one photo, in hectares?
Ground side = 0.230 m × 10 000 = 2 300 m. Area = 2 300² = 5 290 000 m². Converting: 5 290 000 / 10 000 = 529 ha.
Two control points are measured 87 mm apart on a vertical photo at scale 1:15 000. What is the horizontal ground distance between them?
D_ground = d_photo × S = 0.087 m × 15 000 = 1 305 m. Always convert mm to m first.
At 60% forward overlap and photo scale 1:10 000 with a 230 mm format, what is the air base (ground distance between consecutive exposures)?
L_ground = 0.230 × 10 000 = 2 300 m. B = (1 − 0.60) × 2 300 = 0.40 × 2 300 = 920 m.
For the same 1:10 000 photo with 30% sidelap, what is the spacing between adjacent flight lines?
Strip spacing = (1 − 0.30) × L_ground = 0.70 × 2 300 m = 1 610 m.
On a truly vertical photo, which two geometric points coincide?
The principal point is where the optical axis meets the image plane. The nadir is the image of the ground point directly below the camera. When the camera axis is vertical, these two points are the same.
A road appears 62 mm long on a 1:12 000 photo. What is the actual ground length of the road?
D_ground = 62 mm × 12 000 = 744 000 mm = 744 m. Alternatively: 0.062 m × 12 000 = 744 m.
What flying height above the ground is required to achieve a photo scale of 1:8 000 with a camera having f = 152 mm?
From Scale = f/H → H = f × S = 0.152 × 8 000 = 1 216 m above the ground.
At a hilltop with elevation 400 m MSL, the aircraft flies at 2 700 m MSL. In the valley at elevation 100 m MSL, the aircraft altitude is still 2 700 m MSL. If f = 0.152 m, which location has the LARGER photo scale — hilltop or valley?
Hilltop: H = 2 700 − 400 = 2 300 m → Scale = 0.152/2 300 = 1:15 132. Valley: H = 2 700 − 100 = 2 600 m → Scale = 0.152/2 600 = 1:17 105. Smaller denominator = larger scale. Hilltop is closer to camera, so it appears at larger scale.
How many photos are needed per flight strip to cover a 5 000 m project length with an air base of 920 m (include end-clearance photo)?
N = ceil(5 000 / 920) + 1 = ceil(5.43) + 1 = 6 + 1 = 7 photos. Always add 1 for the final clearance photo.
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