What is an Orthomosaic v4

What Is An Orthomosaic? Orthomosaic Maps & Orthophotos Explained

Drones have become incredible tools for helping to create orthomosaics. But what is an orthomosaic? How are they being used? And why would you want one? 

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Orthomosaic Definition

Put simply, an orthomosaic is like Google Earth, but way sharper. It is a large, map-quality image with high detail and resolution made by combining many smaller images called orthophotos.

orthomosaic map with section highlighted and enlarged to show detail

An orthophoto, sometimes referred to as an orthophotograph or an orthoimage, is an aerial photo that has been corrected for lens distortion, camera tilt, perspective, and topographic relief, which is changes in the elevation of the earth’s surface. These corrected orthophotos have no distortion whatsoever and a uniform scale across the image. 


What’s the Difference Between a Normal Photo and an Orthophoto?

The key difference between a normal aerial photo and an orthophoto is the perspective and accuracy. A normal aerial photo, as you can see below, has a perspective view. You can see the sides of buildings and other objects, and the perspective changes depending on where the photo was taken. 

top down aerial photo perspective view

An orthophoto, on the other hand, is what is called “orthorectified”. It is geometrically corrected for this perspective view, along with lens distortion and camera angle, to create a perfectly straight-down view of all objects in the frame as you would see on Google Earth.  

aerial drone photo orthorectified to be orthophoto

The precision and accuracy of orthophotos means both orthophotos and orthomosaics have the same quality as maps and can be used to measure true distances.

perspective vs orthographic

How Are Orthomosaics Being Used and Why Would You Want One?

Get Updated Views of Large Land Areas

One of the main use cases for an orthomosaic is simply to get an updated view of a large area of land. Google Earth is helpful, but often the imagery is outdated. Your new development project could be finished, new construction projects could be underway, or the landscape could have changed from natural disasters. Real estate agents may also want an updated view of property to see if it is a good fit for their needs. Whatever the reason is, orthomosaics are the best way to combine aerial images for an updated view of your land. 

orthomosaic 2 compressed

Use Orthomosaics for Accurate Measurements

Construction firms also find orthomosaics particularly useful. They can get updated views of their construction sites on a regular basis, and they can leverage the accuracy of the orthomosaics for precise measurements. Software programs such as DroneDeploy allow users to measure distance, area, and volume. Construction firms can use these tools to calculate the volume of stockpiles, estimate material costs, and collect other valuable data without actually having to be at the construction site. Software programs can also use the raw data from the aerial photos to construct 3D models, which is another powerful tool for construction firms.

266 Waverly St Framingham MA compressed

Monitor Crop Health

The agriculture industry is also seeing a huge benefits from orthomosaics. Specialized drones have multispectral cameras that gather data from specific bands of light, such as Red, Green, Blue, Red Edge, and Near-Infrared. The added data from multispectral camera systems along with the ability to generate orthomosaic maps allows farmers to get a detailed understanding of their vegetation health with an NDVI index. They can use this data and treat areas that need immediate attention and have a more successful crop season.

Perform Inspections

Along with inspecting crops, orthomosaics are great for performing aerial inspections of equipment and other facilities. They can be used for inspecting rooftops, solar installations, buildings that are falling apart, and more. 

orthophoto of four residential houses in Florida

Legal Proceedings and Court Cases

Orthomosaics are occasionally used in legal cases too. Certain cases require updated and accurate imagery of a property in question. Orthomosaics provide the necessary imagery needed for the legal proceedings. 

orthophoto of parking lot in Manassas, VA

Count Cattle, Monitor Supplies, Measure Roofs, & More

And this list goes on. You can use orthomosaics to count trees, monitor forest health, count cattle, determine the number of cars in a parking lot, see the supplies on a construction site, measure rooftops, make annotations, and so much more depending on app or program you’re using.

orthomosaic image of wooded area in Raymond, ME

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About the Author

Stetson Doggett

Stetson is an Ithaca College alum and a certified drone pilot. He has been flying the DJI Mavic Pro since it first came out and loves finding new ways to improve his aerial photo and video quality. Stetson is from Acton, Massachusetts, and when not in the air he enjoys playing board games, producing YouTube videos, and watching Stranger Things.