Orthomosaic Mapping and Photomapping, Part 1

Aerial Drone Photography is the Ideal Technology for Orthomosaic Mapping and Photomapping!

Digital Elevation Model

Digital Elevation Model Topographical Map

Realm of Possibilities

In this article, the term orthomosaic mapping is used to describe the orthomosaic photogrammetry mapping technique, which is a computationally-intense method that yields position and altitude information for each pixel in the map. The term photomapping is used to describe the use of photostitching software to generate large panoramic maps.

Our orthomosaic map deliverables include: ultra-high resolution 2D maps, 3D Digital Elevation Model (DEM) topographical maps, 3D models, and 3D point clouds.

Our Photomap deliverable is a 2D map image similar to Earth-type maps but with ultra-high resolution.

As implied, “high-resolution” means these map image files can be very large – on the order of 3-4 megapixels per acre. For example, an 80-acre map will have around 300 MP and a JPG image file of around 160 MB. Large files for sure, but the terrain detail is amazing!

Who Can Use Orthomosaic Maps?

Surveyors, Architects, and Civil Engineers are several of the many professions that use orthomosaic maps for their land development and construction projects. They have the budget for high-end software, which can further process our orthomosaic map products.

Real Estate marketers and landowners may also need high resolution maps but don’t want to make the significant investment in photogrammetry software. For these users, we offer photomaps, which provide beautiful full-color map images. More on photomapping in Part 2.

Either way, these maps have high enough resolution to detect very small features. For example, a 1 foot by 1 foot object is represented with around 100 pixels. Tract size can range from less than one acre to thousands of acres.

What Makes Aerial Drone Orthomosaic Maps So Special?

Three dimensional computing is at the heart of calculating position and altitude information for each pixel. The numerically-intense software that does this, to my knowledge, hasn’t been made available for personal computers, so most users have to use online mapping services. For more detailed information on how this specialized software works, please refer to this article at ScienceDirect.com.

How Is It Done?

Orthomosaic mapping software requires many photographs of the landscape so each pixel gets multiple look angles. The software then assigns position and altitude information to each pixel. As you might reason, this is a very complicated process. To get good results, very high overlaps of the subject area are required – on the order of 75 to 90%. This requires that each ground point is photographed 16 to 100 times.

Aerial drones with precise GPS-based navigation are ideal for photographing landscape with this kind of precision. Hundreds or even thousands of high-resolution photographs are taken, typically looking straight down, and stored on the drone’s internal memory card. Back at the office, these photos are then uploaded to the mapping service and reconstructed by their orthomosaic software to create stunning, full-color maps, DEM maps, 3D models, and point clouds.

To achieve good results, the drone’s altitude must be around 4-5 times the altitude of the highest object, such as trees. The algorithms work best when there’s low wind and lots of leaves on the trees. Water can be a challenge due to its reflectivity. With less-than-ideal photography, the algorithms have difficulty assigning position and altitude information to the pixels. If done incorrectly, the resulting map either has strangely-shaped areas or areas that are blanked out.

Orthomosaic Map Deliverable Products:

  • 2D Map – full-color image of the landscape, including position and altitude information.
  • Digital Elevation Model – color-coded for elevation, any color scheme is possible as well as contour lines.
  • 3D model – full color three dimensional image. The model can be viewed on-screen from any perspective.
  • Point Cloud – typically viewed with high-end software. It’s a full color 3D model using points.

In part 2, we’ll examine photomapping, which will be of particular interest to real estate marketers and landowners.