Photogrammetry

Photogrammetry is the science of taking measurements from photographs—especially to create maps, models, or 3D images of objects, land, or buildings.

Imagine you take two pictures of a mountain from slightly different angles. Photogrammetry uses those photos to figure out the shape, size, and position of the mountain—just like our eyes do when we see in 3D!

Concepts and Terminologies

1. Photograph

A picture captured by a camera, either from the ground (terrestrial) or from above (aerial or drone).

2. Stereo Pair

Two overlapping photos taken from different angles. When seen together, they help create a 3D effect—just like how two human eyes work.

3. Overlap

To get a 3D model, photos must overlap each other:

Forward overlap: Between two photos in a flight line (usually 60–70%)
Side overlap: Between adjacent flight lines (usually 30–40%)

4. Scale

The ratio of the photo size to real-world size. Example: A 1:10,000 scale photo means 1 cm on the photo = 10,000 cm (100 m) on the ground.

5. Ground Control Points (GCPs)

Known points on the ground used to correct and align the image accurately.

6. Digital Elevation Model (DEM)

A 3D map of land elevations, often created using photogrammetry.

7. Orthophoto

A photo that has been corrected for tilt, scale, and relief—so it can be used like a map.

How Does Photogrammetry Work?

Capture:
- Take multiple photos from different angles (usually using drones, planes, or satellites).
Process:
- Use software to find matching points between images.
- Generate 3D points (point cloud) from photo overlaps.
- Create a 3D surface or model of the area.
Output:
- 2D maps
- 3D models
- Elevation data
- Orthophotos

Types of Photogrammetry

Type	Description	Used For
Aerial	Taken from planes/drones	Mapping large areas, topography
Terrestrial	Taken from the ground	Architecture, archaeology
Close-range	Small objects with handheld cameras	Engineering, medical imaging

Applications of Photogrammetry

Urban planning and mapping
Forestry and agriculture
Disaster management (flood/landslide mapping)
Construction and 3D modeling
Heritage preservation (3D models of monuments)

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