An orthomosaic is a map made from photographs. Individual aerial frames are stitched, geometrically corrected, and placed in a real-world coordinate system so distances and areas can be measured. It looks like a photograph. It behaves like a map.
That distinction matters. A pretty aerial is not an ortho. A screenshot from Google is not your survey product. An orthomosaic is a controlled image of this site, at this time, in a known CRS.
How an ortho is made
The usual drone-mapping path:
- Fly a grid (or corridor) with enough overlap.
- Recover camera positions, often with GNSS/RTK or ground control.
- Build a dense reconstruction and a digital surface or terrain model.
- Orthorectify the imagery so relief and tilt are removed as far as the model allows.
- Mosaic the corrected frames into one raster, typically a GeoTIFF.
Accuracy depends on the control network, GSD, processing settings, and how well the surface model represents the ground. An ortho of a flat pad is a different problem from an ortho of a pit or a dense canopy.
Orthomosaic vs. aerial photo vs. basemap
| Product | Georeferenced | Measurable | Represents your flight |
|---|---|---|---|
| Handheld or drone still | Usually not | No | Yes, locally |
| Consumer map imagery | Yes, coarsely | Not for your job | No |
| Orthomosaic | Yes, by design | Yes, within project accuracy | Yes |
Clients sometimes treat all three as “the aerial.” If the deliverable is supposed to support quantities, overlays, or as-built context, only the ortho is doing that job.
Files you will actually export
Most photogrammetry tools write a GeoTIFF. For web delivery, a Cloud Optimized GeoTIFF (COG) is the practical upgrade: the same raster, structured so a browser can request the tiles it needs instead of downloading the whole file.
You may also export:
- A world file plus JPEG/TIFF for simpler GIS packages
- Tilesets for web maps
- A PDF sheet for people who need a plotted view
The GeoTIFF is the source of truth. The PDF is a view. Do not let the view replace the dataset.
How to share an ortho with a client
Sending a 2 GB TIF as an email attachment is not a delivery. Most clients cannot open it, and those who can will not thank you for the wait.
A client-ready ortho is:
- Openable in a browser, at the project CRS
- Paired with the report, photos, and any 3D that belong to the same job
- Labeled so it is obvious which capture it is
That is a mapping deliverable. A file in a folder is only the export.