Memory AnchorsGELE · Photogrammetry & CartographyReal content

GELE Photogrammetry & Cartography — Stereoscopy, DEM and OrthophotoMemory Anchors

Summary Concepts Notes Revision Deep Dive Slides Flashcards Mistakes Cheat Mnemonics Templates

Mnemonics for Stereoscopy, DEM and Orthophoto in the GELE 2026. Every one of these anchors has been designed to help you recall the concept under the pressure of Professional Regulation Commission (PRC) — Board of Geodetic Engineering's GELE Photogrammetry & Cartography exam conditions.

Exam context

Professional Regulation Commission (PRC) — Board of Geodetic Engineering runs the Geodetic Engineer Licensure Examination on September 2026. Its Photogrammetry & Cartography section sits under a "Core" weighting, and Stereoscopy, DEM and Orthophoto is the 3rd chapter in the 6-chapter GELE Photogrammetry & Cartography rotation. The GELE passing mark is 70% weighted average, no sub-test below 50%, and the most recent 2026 paper drew about a meaningful share of questions from Photogrammetry & Cartography.

Stereoscopy, DEM and Orthophoto - Memory Anchors

Memory techniques can increase long-term recall by up to 70% compared to passive re-reading. For the PRC Geodetic Engineer Board Exam, where you must retrieve precise formulas, definitions, and procedures under pressure, these anchors act as mental 'hooks' — giving your brain a shortcut path to stored knowledge. Each anchor below links a vivid image, story, or sound-alike to an exact engineering concept. When exam anxiety strikes, your memory trigger fires first, pulling the concept along with it. Use these anchors during review drills, and rehearse each recall_trigger until it becomes automatic. Think of it as building a GPS route in your brain: the trigger is the starting point, the anchor is the road, and the concept is your destination.

Anchors

Topic

Stereoscopy

Concept

Stereoscopy — two overlapping photos fuse into a 3-D model

Anchor Id

Difficulty

easy

Memory Aid

Think of your two eyes. Your left eye and right eye each see a slightly different view of your finger when you hold it up. Your brain FUSES these two views into one 3-D image — you can judge depth. A stereoscopic pair of aerial photos works EXACTLY the same way: left photo = left eye, right photo = right eye, brain (or stereoscope) = fusion. Two views → one 3-D model.

Anchor Type

analogy

Why It Works

The eyes analogy is deeply embodied — every student has experienced this. It makes an abstract photogrammetric concept instantly tangible and self-referential.

Example Usage

Exam question: 'What is the principle of stereoscopy?' Answer: Two photos taken from slightly different positions (like your two eyes) are viewed together to create a 3-D model from which heights can be measured via parallax.

Recall Trigger

Hold up one finger and wink each eye alternately — that alternating shift IS parallax, and fusing them IS stereoscopy.

Topic

Stereoscopy

Concept

60% forward overlap is standard for stereo photogrammetry

Anchor Id

Difficulty

easy

Memory Aid

Remember '6-0 for Stereo Go!' — 60% overlap is the GO signal for a valid stereo model. Less than 60% and you may have gaps; exactly 60% means the air-base covers 40% of the ground strip. '60 = Stereo GO, 30 = Sidelap SO-SO.' Side note: sidelap between adjacent flight lines is ~30%.

Anchor Type

mnemonic

Why It Works

The rhyming phrase '6-0 for Stereo Go' creates a sound-pattern hook. Pairing 60% with 30% as a contrast solidifies both values simultaneously.

Example Usage

Exam question: 'What is the standard forward overlap for stereoscopic coverage?' Trigger: Green light GO → 60% forward overlap; sidelap = 30%.

Recall Trigger

Think of a traffic light: GREEN = GO = 60% forward overlap. YELLOW = sidelap warning = 30%.

Topic

Base-Height Ratio

Concept

Base-height ratio B/H = air-base ÷ flying height

Anchor Id

Difficulty

easy

Memory Aid

Visualize a BASKETBALL HOOP. The 'B' is the horizontal distance between two players (air-base = B), and the 'H' is how high the hoop is (flying height = H). The ratio B/H tells you how well you can judge depth from that position. Closer players spread apart (bigger B), same hoop height → better depth judgment (bigger B/H → stronger height determination). Picture the two aircraft exposure stations as two basketball players passing the ball vertically up to the camera.

Anchor Type

visual_association

Why It Works

Basketball is a culturally familiar sport in the Philippines. The spatial metaphor (horizontal spread vs. vertical height) mirrors the geometric meaning of B/H perfectly.

Example Usage

Given: air-base B = 900 m, flying height H = 1500 m. Recall the two players: B/H = 900/1500 = 0.60. A typical value near 0.6 indicates good height strength.

Recall Trigger

Imagine two basketball players on a court looking up at a hoop — B = their separation, H = hoop height. B/H is your 'depth power.'

Topic

Base-Height Ratio

Concept

Larger B/H → stronger height determination and greater vertical exaggeration

Anchor Id

Difficulty

medium

Memory Aid

Think of binoculars versus a cyclops. A cyclops has ONE eye at center — zero B, zero stereo depth. Binoculars spread the two lenses far apart (large B). The wider the lens spread relative to the distance to the object (larger B/H), the better you can judge depth. Sniper scopes have very wide lens spacing precisely for this reason. A LARGE B/H = sharp depth perception = strong height measurement. It also makes mountains look MORE exaggerated (vertical exaggeration increases).

Anchor Type

analogy

Why It Works

The binoculars-vs-cyclops contrast creates a memorable extreme comparison that encodes both the direction of the relationship and the physical intuition.

Example Usage

Exam question: 'What effect does increasing the air-base have on the stereo model?' Answer: Larger B increases B/H → stronger height determination and greater vertical exaggeration.

Recall Trigger

Cyclops = B/H = 0 (no depth). Binoculars = large B/H (strong depth). Which do you want for surveying? BINOCULARS.

Topic

Base-Height Ratio

Concept

Air-base = (1 − overlap fraction) × ground coverage of photo

Anchor Id

Difficulty

medium

Memory Aid

Remember: 'What's NOT overlapped IS the base.' The air-base equals the non-overlapping strip. If overlap is 60%, then 40% is non-overlapping → air-base = 0.40 × ground width. Formula memory hook: 'ONE MINUS overlap = your BASE fraction.' Write it as: B = (1 − p) × L, where p = overlap as a decimal and L = ground side length.

Anchor Type

mnemonic

Why It Works

The phrase 'what's NOT overlapped IS the base' turns a subtraction into a logical statement, making the formula derivable rather than just memorizable.

Example Usage

Exam: 60% overlap, photo scale 1:10 000, format 230 mm. Ground side L = 230 × 10 000 / 1000 = 2300 m. Air-base = (1 − 0.60) × 2300 = 920 m.

Recall Trigger

Think of two overlapping sheets of paper: the part sticking out from under = the air-base. The exposed part = (1 − overlap).

Topic

Digital Elevation Models

Concept

DEM = Digital Elevation Model — a grid/TIN of bare-earth elevations

Anchor Id

Difficulty

easy

Memory Aid

DEM = 'Dirt and Earth's Map.' It models the bare DIRT (ground surface without trees, buildings). Remember: DEM/DTM = bare earth. DSM = 'Don't Subtract the Malls' — it includes buildings and trees on top. The key contrast: DEM strips away everything sitting on the ground; DSM keeps it all.

Anchor Type

acronym

Why It Works

The playful expansion 'Dirt and Earth's Map' for DEM and 'Don't Subtract the Malls' for DSM creates a contrast pair that encodes both concepts and their difference simultaneously.

Example Usage

Exam: 'What is the difference between a DEM and a DSM?' DEM = bare-earth elevations (no buildings/vegetation); DSM = surface model including all objects above ground.

Recall Trigger

DEM = bare dirt. DSM = dirt + stuff on top (buildings, trees). Think: 'Did Every Mall disappear? Yes → DEM. No → DSM.'

Topic

Digital Elevation Models

Concept

Three methods of DEM production: photogrammetry (image matching), LiDAR, InSAR (radar)

Anchor Id

Difficulty

medium

Memory Aid

Remember 'PLI' — like a PLI-ers grip on the terrain: P = Photogrammetry (image matching from stereo photos), L = LiDAR (laser pulses), I = InSAR (radar interferometry). 'PLI grips the terrain from above.' You can also say: 'Photos, Lasers, and Interferometry — the three terrain-grabbers.'

Anchor Type

mnemonic

Why It Works

The acronym PLI is short, pronounceable, and the 'pliers' metaphor of gripping terrain reinforces the idea of extracting elevation data. Three-item lists are easy once anchored to a single word.

Example Usage

Exam: 'List three methods of producing a DEM.' Recall PLI: Photogrammetry (stereo image matching), LiDAR (airborne laser scanning), InSAR (satellite radar interferometry).

Recall Trigger

Visualize a plier gripping a mountain model from the sky. PLI = Photogrammetry, LiDAR, InSAR.

Topic

Digital Elevation Models

Concept

DEM applications: contour generation, volume computation, viewshed, drainage, orthorectification

Anchor Id

Difficulty

medium

Memory Aid

Remember 'C-V-V-D-O' → 'Contours Vanish, Volumes, Drainage, Ortho' or use the sentence: 'Clever Volumes Visit Drainage Ortho.' C = Contours, V = Volume/earthworks, V = Viewshed, D = Drainage analysis, O = Orthorectification. Think of a DEM as the 'master key' that unlocks all five doors.

Anchor Type

acronym

Why It Works

Listing five applications is hard without a hook. The CVVDO acronym compresses all five into a sequence, and 'master key' metaphor reminds the student that the DEM drives multiple downstream products.

Example Usage

Exam: 'What are the uses of a DEM in photogrammetric production?' Answer: Contour generation, volume/earthwork computation, viewshed analysis, drainage/watershed modeling, and orthorectification of imagery.

Recall Trigger

Master key = DEM. Five doors: C-V-V-D-O (Contours, Volumes, Viewshed, Drainage, Ortho).

Topic

Orthophoto

Concept

Orthophoto — relief displacement and tilt removed using a DEM → uniform scale

Anchor Id

Difficulty

easy

Memory Aid

Story: Engineer Ortho Foto was a perfectionist. She hated that in raw aerial photos, tall buildings leaned outward, mountains appeared shifted, and the scale kept changing from center to edge. One day, she picked up a DEM (a digital map of all elevations) and used it as a 'correction lens.' She pressed it onto every raw photo, pixel by pixel, pushing each point back to its TRUE planimetric position. The result: a photo where a ruler gives REAL distances — just like a map, but with the beautiful detail of a photograph. 'Now it's an ORTHO-FOTO,' she said proudly. 'Every pixel is where it belongs.'

Anchor Type

micro_story

Why It Works

The personification of 'Engineer Ortho Foto' makes the concept emotionally engaging. The story encodes: raw photo has variable scale → DEM is used to correct it → result is a uniform-scale image.

Example Usage

Exam: 'Why is an orthophoto preferred over a raw aerial photograph for distance measurement?' Because raw photos have variable scale due to relief displacement and tilt. Orthophotos are rectified using a DEM to achieve uniform scale, allowing metric measurements like a map.

Recall Trigger

Think of 'Engineer Ortho Foto with her DEM correction lens, pressing pixels back into place.'

Topic

Orthophoto

Concept

Raw photo has varying scale — it is NOT a map

Anchor Id

A10

Difficulty

easy

Memory Aid

Imagine a rubber sheet map pinned at the center but bulging up wherever there's a hill. The center might be 1:10 000 but the hilltop area is 1:9 000 and the valley is 1:11 000 — you can't measure reliably. A raw aerial photo is that rubber sheet — relief and tilt warp the scale everywhere. An orthophoto is that same rubber sheet flattened perfectly on a table: uniform scale everywhere. NEVER measure distances directly on a raw photo.

Anchor Type

analogy

Why It Works

The rubber sheet is a powerful physical metaphor that explains why scale varies with terrain — students can physically imagine pulling and warping the sheet.

Example Usage

Exam: 'Can a raw aerial photograph be used as a base map for land measurement?' No — it has variable scale due to relief displacement and tilt. Only an orthophoto has uniform, map-measurable scale.

Recall Trigger

Raw photo = warped rubber sheet. Orthophoto = same sheet pressed flat. Measure only on the flat one.

Topic

Orthophoto

Concept

Orthomosaic — multiple orthophotos tiled into a seamless base map

Anchor Id

A11

Difficulty

easy

Memory Aid

Picture a PAROL (Philippine Christmas star lantern) made of many triangular pieces of colored paper — each piece is an individual orthophoto, and together they form one beautiful seamless star (the orthomosaic). Each piece is individually corrected (orthorectified), then they are joined at their edges with radiometric balancing so the colors match — just like matching the colors of parol panels.

Anchor Type

visual_association

Why It Works

The parol is a deeply familiar Filipino cultural symbol. The multi-piece assembly directly mirrors the concept of mosaicking, and 'matching colors' parallels radiometric balancing.

Example Usage

Exam: 'What is an orthomosaic?' An orthomosaic is a seamless composite image created by tiling and radiometrically balancing multiple individual orthophotos into a single uniform-scale base map.

Recall Trigger

Parol = orthomosaic. Individual lantern panels = individual orthophotos. The whole star = seamless base map.

Topic

Orthophoto

Concept

Orthorectification requires a DEM — without it, relief displacement remains

Anchor Id

A12

Difficulty

medium

Memory Aid

Remember: 'No DEM, No ORTHO.' It's like saying 'No map, no navigation.' Without the DEM, you don't know how high each pixel's terrain is, so you can't compute where the light ray truly hit the ground. The DEM is the BACKBONE of orthorectification. Without a backbone, the body (photo) slumps and warps.

Anchor Type

mnemonic

Why It Works

The 'No DEM, No ORTHO' phrase is a direct conditional pair — easy to recall as a two-part rule. The backbone metaphor adds a physical sense of support/correction.

Example Usage

Exam: 'What data is required to produce an orthophoto from a raw aerial image?' A DEM is required. Without the DEM, relief displacement cannot be removed and the product will not have uniform scale.

Recall Trigger

'No DEM, No ORTHO' — say it like a rule. DEM = backbone of the orthophoto.

Topic

Orthophoto

Concept

Relief displacement: tall objects lean outward from the photo nadir in a raw photo

Anchor Id

A13

Difficulty

medium

Memory Aid

Story: Imagine you're above Rizal Park in Manila, looking straight down (nadir). The Rizal Monument appears directly below you. But the TALL buildings around the park seem to LEAN AWAY from you — their tops are displaced outward from the center of the photo. This is relief displacement. The taller the building, the farther it leans. If you're taking a photo of the Makati CBD from above, all those skyscrapers lean outward like a circle of people bowing away from you. This is why raw photos can't be measured.

Anchor Type

micro_story

Why It Works

Using Rizal Park and Makati CBD — familiar Philippine landmarks — makes the geometric concept of relief displacement immediate and local. The 'bowing people' metaphor captures the radial outward direction.

Example Usage

Exam: 'In what direction does relief displacement act?' Radially outward from the principal point (nadir) of the photograph. Tall objects appear displaced away from the center.

Recall Trigger

Makati skyscrapers bowing OUTWARD from the photo center = relief displacement. Fix it with an orthophoto.

Topic

Digital Elevation Models

Concept

DEM vs DTM — DTM may include breaklines and mass points; DEM is often used generically

Anchor Id

A14

Difficulty

hard

Memory Aid

DEM = 'D is for Dull grid' (just a regular elevation grid, generic term). DTM = 'T is for Terrain with Topology' — it adds breaklines (ridges, streams, roads) and mass points to better represent terrain shape. Think: DTM has MORE information than a plain DEM grid. Exam boards often use DEM and DTM interchangeably, but technically DTM is the richer dataset.

Anchor Type

mnemonic

Why It Works

Assigning personality to each acronym (DEM = 'dull grid', DTM = 'terrain with topology') creates a contrast that is easier to remember than a technical definition alone.

Example Usage

Exam: 'Differentiate DEM from DTM.' DEM is a generic term for a grid of terrain elevations. DTM includes additional topographic features such as breaklines and mass points for more accurate terrain representation.

Recall Trigger

DEM = dull grid. DTM = topology included. DSM = surfaces with stuff on top.

Topic

Stereoscopy

Concept

Parallax is the basis for height measurement in a stereo model

Anchor Id

A15

Difficulty

medium

Memory Aid

Hold a pen at arm's length. Close your right eye — note where the pen appears against the background. Now close your left eye — the pen SHIFTS against the background. That SHIFT is parallax. In stereo photogrammetry, the shift of a point between the left and right photos IS the parallax, and this shift is PROPORTIONAL to the height of the object. Taller object = bigger parallax shift. Use the parallax formula to compute height.

Anchor Type

analogy

Why It Works

The pen demonstration is a hands-on kinesthetic experience students can do right now. Connecting pen-shift to height measurement makes parallax physically intuitive.

Example Usage

Exam: 'How are elevations extracted from a stereo photo pair?' By measuring parallax — the difference in image position of a point between the left and right photos. Height is computed from the parallax formula: h = H × Δp / (p + Δp), where Δp = parallax difference, p = base parallax, H = flying height.

Recall Trigger

Close one eye, open the other, watch your pen shift — that's parallax. Bigger shift in a stereo pair = taller feature.

Topic

Base-Height Ratio

Concept

Typical B/H ≈ 0.6 for 60% overlap; values of 0.3–1.0 are practical range

Anchor Id

A16

Difficulty

hard

Memory Aid

Chunk the B/H scale into three zones: LOW (B/H < 0.3) = weak depth, risky; GOLDILOCKS ZONE (B/H = 0.5–0.8) = just right for most projects; HIGH (B/H > 1.0) = strong depth but more shadow and occlusion problems. Remember: '60% overlap → 40% exposed → B/H ≈ 0.4–0.6 typical.' The Goldilocks Zone is your target.

Anchor Type

chunking

Why It Works

Chunking the range into three labeled zones (weak / Goldilocks / strong) reduces cognitive load and helps students quickly classify a given B/H value as acceptable or problematic.

Example Usage

Exam: 'Is a B/H ratio of 0.25 acceptable for stereo height measurement?' No — it falls in the weak zone, below the practical minimum. Height determination will be unreliable.

Recall Trigger

Three zones: Weak → Goldilocks → Strong. 60% overlap lands you in Goldilocks (B/H ≈ 0.6).

Topic

Stereoscopy

Concept

Vertical exaggeration in a stereo model increases with larger B/H

Anchor Id

A17

Difficulty

medium

Memory Aid

Rhyme: 'The wider the base, the taller the hills appear in space. B/H goes high, mountains touch the sky. B/H goes low, flat terrain — although it's so.' Vertical exaggeration is a perceptual effect: large B/H makes terrain look more exaggerated in 3-D, which can help detect subtle features but must be understood to avoid misinterpretation.

Anchor Type

rhyme

Why It Works

The rhyme encodes both the direction of the relationship (larger B/H → more exaggeration) and a caution (it's a perception, not reality). Rhymes create phonological memory loops.

Example Usage

Exam: 'What is vertical exaggeration in a stereo model and what controls it?' Vertical exaggeration is the apparent amplification of terrain relief in a stereo view. It increases with larger B/H ratios.

Recall Trigger

Recall the rhyme: 'Wider base, taller hills in space.' Large B/H = large vertical exaggeration.

Topic

Orthophoto

Concept

Orthophoto can be measured like a map — it has uniform scale

Anchor Id

A18

Difficulty

easy

Memory Aid

Visualize a Philippine TOPOGRAPHIC MAP (1:50 000 NAMRIA topo sheet) lying flat. Now imagine a beautiful, full-color aerial photograph lying right next to it — same area, same scale, same measurability. THAT is an orthophoto. It is the marriage of photographic detail and map geometry. You can put a ruler on it and get real ground distances. Remember: Orthophoto = Photo + Map. It has the FACE of a photo and the SOUL of a map.

Anchor Type

visual_association

Why It Works

Referencing NAMRIA topo maps (familiar to all Philippine geodetic engineering students) grounds the concept locally. The 'face of a photo, soul of a map' phrase is memorable and concise.

Example Usage

Exam: 'What makes an orthophoto different from a photograph for mapping purposes?' An orthophoto has uniform scale (like a map) because relief displacement and tilt have been removed using a DEM. Distances and areas can be measured directly from it.

Recall Trigger

NAMRIA topo map + aerial photo combined = orthophoto. Same geometric accuracy as a map, same visual richness as a photo.

Topic

Digital Elevation Models

Concept

Image matching (autocorrelation) is the photogrammetric method for automated DEM extraction

Anchor Id

A19

Difficulty

hard

Memory Aid

Image matching is like FACIAL RECOGNITION on your phone. Your phone's algorithm scans both your stored face and the live camera image, finds matching features (eyes, nose, lips), and from the slight differences in their positions (parallax), it can even estimate 3-D face structure (Face ID depth sensing). Photogrammetric image matching does the same: find matching pixels/patches in the left and right images → compute parallax → compute elevation. Stereo matching = aerial photo's 'Face ID.'

Anchor Type

analogy

Why It Works

Smartphone Face ID is a universally familiar technology. The direct analogy (match features → compute 3-D from disparity) maps perfectly onto photogrammetric dense matching.

Example Usage

Exam: 'Describe image matching in the context of DEM generation.' Image matching (or stereo correlation) automatically identifies corresponding points in stereo image pairs, computes parallax, and calculates terrain elevations to generate a DEM.

Recall Trigger

Smartphone Face ID = photogrammetric image matching. Both compute 3-D from matched features in two slightly different views.

Topic

Digital Elevation Models

Concept

LiDAR produces the most accurate DEM, especially under forest canopy

Anchor Id

A20

Difficulty

medium

Memory Aid

Story: The photogrammetry team was flying over the Sierra Madre rainforest in Luzon. The image-matching algorithm kept trying to find the ground — but the thick canopy fooled it, matching tree tops instead of ground. Enter the LiDAR team. Their laser pulses fired at thousands of points per second. Most pulses hit the canopy — but a few sneaked through gaps and hit the actual forest floor. The computer filtered out the canopy returns and revealed the true terrain underneath. The photogrammetrist said, 'LiDAR sees through the forest. We can't.' And that is why LiDAR DEMs are gold standard under dense vegetation.

Anchor Type

micro_story

Why It Works

The Sierra Madre setting is Philippine-specific and ecologically significant. The story encodes LiDAR's key advantage (penetrating canopy via last-return filtering) in a narrative that is easy to retell.

Example Usage

Exam: 'Which DEM production method is most effective in densely forested terrain and why?' LiDAR, because laser pulses can penetrate gaps in the canopy. Last returns provide bare-earth elevations that image matching cannot reliably achieve under forest cover.

Recall Trigger

Sierra Madre + laser pulses sneaking through canopy gaps = LiDAR seeing the real ground. Best DEM under forests.

Revision Game

Orthophoto

Clue

I am a photo where every pixel is in its correct planimetric position. You can put a ruler on me and get real ground distances. What am I?

Memory Link

A9 (Engineer Ortho Foto micro-story) and A18 (NAMRIA map + photo = orthophoto)

Base-height ratio (B/H)

Clue

I am the ratio of air-base to flying height. A value of 0.6 means you have good stereo strength. What am I?

Memory Link

A3 (basketball hoop visual association)

DEM (Digital Elevation Model)

Clue

I model bare earth elevations as a grid or TIN. I am required for orthorectification. Without me, relief displacement stays. What am I?

Memory Link

A6 (Dirt and Earth's Map acronym) and A12 (No DEM, No ORTHO)

60% forward overlap

Clue

I am the standard forward overlap for conventional aerial stereo photography. I ensure every point on the ground appears in at least two photos. What number am I?

Memory Link

A2 (6-0 for Stereo GO mnemonic)

DSM (Digital Surface Model)

Clue

I include buildings, trees, and all objects above the ground surface in my elevation values. My cousin DEM strips me of everything except bare earth. What am I?

Memory Link

A6 (Don't Subtract the Malls) and A14 (DEM=dull grid, DTM=topology, DSM=stuff on top)

Image matching (stereo correlation / dense image matching)

Clue

I am the photogrammetric method that automatically finds matching pixels in a stereo pair and computes parallax to extract terrain heights. I am like a phone's Face ID for aerial photos. What am I?

Memory Link

A19 (Face ID analogy)

LiDAR (Light Detection and Ranging)

Clue

I am the three-letter acronym for the DEM production method that uses laser pulses fired from an aircraft. I can see through forest canopy gaps to the bare ground. What technology am I?

Memory Link

A7 (PLI mnemonic) and A20 (Sierra Madre forest micro-story)

Relief displacement

Clue

I am the phenomenon in a raw aerial photo where tall buildings appear to lean outward from the center of the photo. I am caused by the perspective projection of objects with height above the reference plane. What am I?

Memory Link

A13 (Makati skyscrapers bowing outward micro-story)

Use when measuring building heights, tree heights, or terrain relief from a stereo pair using a parallax bar or stereoplotter readout.

What Each Part Means

h = height of object above datum (m); H = flying height above datum (m); Δp = parallax difference between top and base of object (mm, same units); p_b = base parallax of the object's base point (mm).

Two overlapping photos taken from different positions
Viewed stereoscopically → fused 3-D model
Parallax measured between left and right images
Parallax used to compute heights
B/H ratio controls height measurement strength
Larger B/H → greater vertical exaggeration

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Scale, Relief Displacement and Parallax

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Map Projections

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GELE Photogrammetry & Cartography — Stereoscopy, DEM and OrthophotoMemory Anchors

Exam context

Stereoscopy, DEM and Orthophoto - Memory Anchors

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