GSD Calculator
Calculate Ground Sample Distance, Field of View, and focal length requirements for camera-based geotechnical monitoring, slope surveillance, and infrastructure inspection.
- Slope monitoring: Detecting rockfall, landslides, and surface deformation
- Infrastructure inspection: Identifying cracks, corrosion, and structural changes
- Drone surveys: Planning flight altitude for photogrammetry and mapping
- Environmental monitoring: Tracking coastal erosion, vegetation changes, and sediment movement
Sensor & Units
Quick Reference
GSD = Ground Sample Distance (pixel size on ground)
FOV = Field of View (angular coverage)
Focal Length = Lens magnification factor
Typical GSD values:
- 1–5 mm: crack detection, structural inspection
- 5–20 mm: slope monitoring, rockfall detection
- 20–50 mm: large-scale site surveys
Calculate the Ground Sample Distance and Field of View given your camera setup and distance to target.
Results
Determine the focal length needed to achieve a specific Field of View, and optionally compute the minimum resolution for a target GSD.
Results
Calculate the focal length needed to frame a target of known physical dimensions, with GSD based on the resolution set in the Sensor & Units panel. The target occupies the entire field of view if the maximum focal length allows it (sufficient zooming capabilities). Otherwise the target will occupy only a portion of the image plane with the background taking the rest. The resulting metric field of view can be read from "Resulting FOV (m)" label.
Results
GSD Requirements by Application
Selecting the right GSD depends on what you need to detect. Higher resolution (lower GSD) lets you see smaller details but requires more powerful optics or closer positioning.
| Application | Recommended GSD | Detectable Features |
|---|---|---|
| Crack Detection | 1–3 mm/pixel | Hairline cracks, surface defects, concrete spalling |
| Structural Inspection | 3–5 mm/pixel | Corrosion, joint separation, anchor bolt condition |
| Rockfall Detection | 5–15 mm/pixel | Individual rocks, debris accumulation, slope failures |
| Slope Deformation | 10–20 mm/pixel | Surface displacement, tension cracks, bulging |
| Coastal Erosion | 15–30 mm/pixel | Cliff recession, beach changes, vegetation loss |
| Site Surveys | 20–50 mm/pixel | Terrain features, stockpile volumes, general monitoring |
Worked Examples
Real-world camera setup scenarios to help you plan your monitoring system.
Rockfall Monitoring
Scenario: Monitoring an unstable slope for falling rocks
- Distance: 200 m
- Target GSD: 15 mm/pixel
- Sensor: Full Frame (36×24 mm), 61 MP
Dam Crack Inspection
Scenario: Detecting hairline cracks on a concrete dam face
- Distance: 100 m
- Target GSD: 3 mm/pixel
- Sensor: Full Frame (36×24 mm), 45 MP
Coastal Cliff Erosion
Scenario: Tracking cliff recession over time
- Distance: 1,000 m
- Target GSD: 25 mm/pixel
- Sensor: APS-C (23.5×15.6 mm), 26 MP
GSD Calculator – FAQ
Common questions about Ground Sample Distance, camera setup, and monitoring applications.
Ground Sample Distance (GSD) is the real-world size that each pixel in an image represents. For example, a GSD of 10 mm/pixel means each pixel covers a 10×10 mm area on the target surface.
Lower GSD values provide higher detail but cover a narrower field of view. GSD is critical for determining whether your camera system can detect the features you need to monitor, such as cracks, displacement, or erosion.
GSD is calculated using the formula:
GSD = (Sensor Width × Distance) / (Focal Length × Image Width in pixels)
You need to know your camera's sensor dimensions (width and height in mm), the focal length of your lens (in mm), the distance to your target (in meters), and your camera's resolution (in pixels).
Our calculator handles all the math automatically. Just enter your parameters in Calculator 1 above and get instant results.
The required GSD depends on what you're trying to detect:
- 1–5 mm GSD: For crack detection and structural inspection where small details matter
- 5–20 mm GSD: For rockfall detection and slope deformation monitoring
- 20–50 mm GSD: For large-scale site surveys and general terrain monitoring
The right GSD depends on the smallest feature you need to reliably detect. As a rule of thumb, your GSD should be at least 3–5 times smaller than the smallest feature of interest.
GSD (Ground Sample Distance) measures the size each pixel represents on the ground. It determines the image detail and resolution you can achieve.
FOV (Field of View) measures the total area or angle your camera can capture in a single image.
They have an inverse relationship: a narrower FOV (achieved with longer focal length lenses) gives you better GSD (more detail per pixel) but covers less area. Use GSD when planning for detail requirements, and FOV when planning coverage area.
Focal length and GSD have an inverse relationship:
- Longer focal lengths (more zoom) reduce GSD, giving you more detail per pixel but a narrower field of view
- Shorter focal lengths increase GSD, capturing more area but with less detail per pixel
For example, doubling your focal length from 50mm to 100mm will halve your GSD (improving detail) but also halve your field of view coverage. This is the fundamental trade-off in camera system design.
Yes, this calculator works for both drone-mounted cameras and fixed monitoring cameras. For drone surveys:
- The "distance to target" is your flight altitude above ground level (AGL)
- Use Calculator 2 to determine the required flight height for a target GSD
- Our sensor presets include common drone cameras like DJI Mavic and Phantom series
The same GSD principles apply whether your camera is on a drone, tripod, or permanently mounted for infrastructure monitoring. IRIS specializes in fixed camera monitoring for geotechnical applications, but the calculator is universal.
