What is an Orthophoto (Orthomosaic)?
An orthophoto looks like an ordinary aerial photo, but it has a special property: you can measure on it. This short guide explains what makes an orthophoto different, and how it pairs with a DEM.
Corrected, not just captured
A raw aerial photo has perspective distortion — objects lean, and scale changes across the frame. An orthophoto is geometrically corrected so that every point is shown as if viewed straight down, giving a uniform scale across the whole image.
Because the scale is uniform and the image is georeferenced, real distances and areas can be measured directly on it, like a map.
Orthophoto vs orthomosaic
The terms are often used interchangeably. An orthomosaic is simply an orthophoto stitched together from many corrected images to cover a large area, which is what a drone survey typically produces.
Why pair it with a DEM
An orthophoto gives visual context — what is actually on the ground — while a DEM gives the elevation. Together they let you interpret a site and measure it at the same time.
In practice you drape the orthophoto over the terrain and use it as a precise basemap to digitize vectors and read the site alongside slope, contours and volumes.
View and measure on large orthophotos in STREAM
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