What is Orthomosaic Imaging?

January 1, 2023

Orthomosaic images are like ultra-high resolution, near real-time satellite imagery. Just as Google Earth provides a top-down view of the world, orthomosaic imaging creates accurate, ortho-rectified images of areas of interest. Before diving deeper, it’s essential to understand that orthomosaic maps can have different grades of accuracy: Absolute and Relative, which we’ll explore shortly.

The Process of Capturing Orthomosaic Images

  1. Image Capture:
    The process begins with capturing hundreds—or even thousands—of high-resolution photographs. These are taken at various angles and heights above the ground using either manned aircraft (e.g., helicopters) or drones equipped with advanced cameras.

    • Drones and aircraft cover vast areas quickly and efficiently.
    • This method saves time and money compared to traditional ground-based methods like LiDAR scanning, which requires expensive equipment and manual data collection.
    • While LiDAR can also be used aerially, this discussion focuses on RGB imagery, which is more cost-effective for applications like construction progression monitoring.

     

  2. Stitching and Orthorectification:
    Once the photos are captured, they are processed using specialized software designed for creating orthorectified mosaic images. This process involves:

    • Stitching the images together to form one cohesive, seamless image.
    • Eliminating distortions caused by terrain variations, camera lenses, or sensor angles to ensure the image maintains accurate scaling.

Traditional Photo vs Orthomosaic Image

Here's a real-world example of a traditional photo vs an orthomosaic image. Use the slider on the image to shift between both images. A traditional photo (left) compared to an orthomosaic image (right).

Standard PhotoOrthomosaic

Take a look at:

  • The north side of the building at the bottom of the image
  • The yellow and red sign at the top-right of the bottom building
  • The HVAC units of the main building
  • The bottom-right corner of the roof on the main building overlap in relation to the sidewalk
You'll notice that you can no longer see the sides of these objects and in the case of the sidewalk overlap that the corner is now hidden under the building. This is because the ortho-rectification removes the perspective from the image to give it a true* top-down view. You'll also notice that the cars are gone. That's because the software will take away moving objects from the scene if it doesn't notice them in more than one or two photos.

Absolute vs Relative Accuracy

Orthomosaic images can provide two types of accuracy: absolute and relative.

Absolute Accuracy: Refers to the exact geographic location of an object on Earth. This level of accuracy is crucial for applications like determining whether a building corner is encroaching on a lot line.

Relative Accuracy: Focuses on the spatial relationship between objects, such as measuring the distance between a dig site and a building corner or calculating stockpile volumes. This is often sufficient for many project needs and does not require precise geo-location data.

Advantages of Orthomosaic Imaging

Orthomosaic imaging provides unique benefits, especially when analyzing changes over time. Key advantages include:

    • Comparing Changes Over Time: Since all datasets are registered spatially, you can easily compare current conditions against previous ones without manual alignment.
      • Ideal for monitoring progress on construction projects.
      • Useful for tracking erosion patterns after natural disasters.

 

  • Efficiency and Versatility:
    • Saves time and costs compared to traditional methods.
    • Offers precision, scalability, and adaptability for various industries.

The Bottom Line

Orthomosaic imaging is a game-changing solution for capturing high-resolution aerial visuals with speed, precision, and scalability. Whether you're monitoring construction progress, analyzing erosion patterns, or planning land use, its ability to provide detailed, accurate, and spatially aligned data makes it an invaluable tool.

*An orthomosaic image or map may not be accurate enough for scale measurements. If you require total accuracy make sure to hire a professional surveyor to do this task as they are the only ones with the right credentials to ensure total, legal accuracy.

Ready to kick off your next project? Let’s connect to see if orthomosaic imaging can help your project!