What is Photogrammetry?
Photogrammetry is the science of making measurements from photographs. It's used to create accurate 3D models, maps, and measurements from overlapping images taken from different positions.
Key Concepts
Ground Sampling Distance (GSD)
The Ground Sampling Distance represents how much area on the ground each pixel in your image covers. This is crucial for determining the accuracy and detail level of your photogrammetry project.
Image Overlap
For successful photogrammetry reconstruction, images must overlap significantly. Typical overlap requirements are:
- Forward overlap: 80-90% (between consecutive images in the same flight line)
- Side overlap: 60-80% (between adjacent flight lines)
Camera Parameters
Understanding your camera and lens specifications is essential for accurate calculations:
- Sensor size: Determined by the crop factor relative to full-frame (36mm)
- Focal length: The lens focal length in millimeters
- Resolution: Image dimensions in pixels
How Photogrammetry Works
Photogrammetry works by analyzing the geometric relationships between multiple overlapping photographs of the same subject taken from different positions. The process involves several key steps:
- Image Capture: Taking multiple overlapping photographs of the subject from different angles and positions
- Feature Detection: Software identifies common features (tie points) across multiple images
- Camera Calibration: Determining the internal geometry and lens distortion characteristics of the camera
- Triangulation: Using the known camera positions and orientations to calculate 3D coordinates of features
- Dense Point Cloud Generation: Creating millions of 3D points to represent the surface detail
- Mesh Generation: Connecting the points to create a continuous 3D surface
- Texture Mapping: Applying the original photograph colors and textures to the 3D model
Applications of Photogrammetry
Photogrammetry has a wide range of applications across various industries:
Surveying and Mapping
- Topographic mapping
- Land surveying
- Cadastral mapping
- Change detection over time
Architecture and Construction
- Building documentation
- Progress monitoring
- As-built surveys
- Historic preservation
Archaeology
- Site documentation
- Artifact recording
- Virtual museum exhibits
- Cultural heritage preservation
Agriculture
- Crop monitoring
- Yield estimation
- Precision agriculture
- Irrigation planning
Environmental Monitoring
- Erosion assessment
- Vegetation analysis
- Disaster response
- Wildlife habitat mapping
Advantages of Photogrammetry
- Cost-effective: Relatively inexpensive compared to traditional surveying methods
- Non-contact: Can measure objects without physical access
- High accuracy: Can achieve millimeter-level precision with proper planning
- Versatile: Works at any scale from small objects to large landscapes
- Rich data: Provides both geometric and visual information
- Rapid data collection: Can capture large areas quickly
Types of Photogrammetry
Aerial Photogrammetry
- Uses aircraft or drones to capture images from above
- Ideal for mapping large areas
- Common for topographic mapping and surveying
Close-Range Photogrammetry
- Images taken from ground level or handheld cameras
- Used for detailed object documentation
- Common in archaeology, architecture, and industrial applications
Satellite Photogrammetry
- Uses satellite imagery for very large-scale mapping
- Lower resolution but covers vast areas
- Used for global mapping and monitoring
Next Steps
To learn more about the challenges involved in planning photogrammetry projects, see our guide on Photogrammetry Planning Challenges.
For hands-on planning tools, check out our interactive Photogrammetry Distance Calculator in the Labs section.