Orthomosaic
An orthomosaic is a geometrically corrected, stitched aerial image made from many overlapping drone photos. Unlike a regular aerial photo, every pixel in an orthomosaic represents an accurate, true-scale position — so distances, areas, and feature locations can be measured directly off the image.
Why "ortho" + "mosaic"
"Ortho" refers to orthorectification — a process that removes perspective distortion. A raw aerial photo shows tall objects leaning outward from the camera's nadir point, the way buildings appear to fan out in a downtown skyline. Orthorectification flattens that to a top-down view at uniform scale.
"Mosaic" refers to the stitching of hundreds (sometimes thousands) of those orthorectified images into one seamless map covering the full survey area.
How an orthomosaic differs from a regular aerial photo
| Property | Aerial photo | Orthomosaic |
|---|---|---|
| Scale across image | Varies (perspective distortion) | Uniform |
| Measurable | No | Yes — distance, area, position |
| Coverage | Single frame | Hundreds of frames stitched |
| Geo-referenced | No (unless tagged) | Yes — overlays in GIS, AutoCAD |
| Typical resolution | 12-50 MP per frame | 2 cm/pixel GSD or finer |
How an orthomosaic is built
- Drone flies a grid pattern over the area with 80% forward + 70% side overlap.
- Photogrammetry software estimates the position and orientation of every photo.
- A dense point cloud and digital surface model are generated.
- Each photo is reprojected from camera-perspective to a uniform top-down view using the DSM.
- The reprojected images are colour-balanced and blended along seam lines into one continuous map.
What you can do with an orthomosaic
- Measure distance + area: direct measurements right on the image, accurate to centimetres
- Overlay on GIS: drop into ArcGIS, QGIS, AutoCAD Civil 3D as a georeferenced raster
- Progress comparison: overlay weekly orthos from a construction site to see exactly what moved
- Stockpile boundary digitization: trace pile outlines on the ortho to feed volume calculations
- As-built records: capture site condition at a known date
- Reporting: embed in PDF reports for clients, regulators, and stakeholders
Typical UAV Imaging orthomosaic specs
- Ground sample distance: 2 cm per pixel (the default; finer available on request)
- Horizontal accuracy: 2-5 cm with RTK / PPK and ground control points
- Coverage per flight: 50-100 hectares per battery cycle on the DJI Matrice 300 RTK
- Output formats: GeoTIFF (full-resolution), JPEG (compressed), KML/KMZ (Google Earth overlay)
Frequently Asked Questions
What's the difference between an orthomosaic and a regular drone photo?
A regular photo has perspective distortion — objects lean and scale varies across the image. An orthomosaic is corrected so every pixel is true-scale and the image can be measured on directly.
What file format does an orthomosaic ship in?
Standard delivery is GeoTIFF for full-resolution mapping work, with a compressed JPEG copy for reports and a KMZ for Google Earth viewing. All include the geographic coordinate system metadata.
How big are orthomosaic files?
A 50-hectare ortho at 2 cm GSD is typically 500 MB to 3 GB as a GeoTIFF. UAV Imaging delivers via WeTransfer, Google Drive, or directly to client cloud storage.
Can the orthomosaic be loaded into AutoCAD?
Yes — AutoCAD Civil 3D and Map 3D import GeoTIFF orthomosaics natively. The image georeferences itself to the project's coordinate system if the .prj file is included.
How current is the data?
The orthomosaic is a snapshot of the site at the flight date. For active sites, weekly or monthly captures are typical so progress can be tracked.
Need a quote? Call 587-532-9000 or
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