Orthomosaic Mapping and Photomapping, Part 2

This 40-acre cornfield is a composite of 326 images

This 40-acre cornfield is a composite of 326 photos

Part 1 focused on orthomosaic photogrammetry maps – our high-tech mapping service that delivers image files with embedded position and altitude information for each pixel. Another service that we provide – photomapping – uses a more familiar image processing technique known as photo stitched panorama.

Although the photo collecting technique is similar to orthomosaic mapping, position and altitude information are tossed in favor of the less complicated panorama image processing. We use professional software to align features in the overlap areas, stitch the images together, and shade the transition zones.

Panorama Software is Common, but How Does it Work?

Panorama software works best when the camera is fixed and all images are taken from the same point in space. However, when using a moving camera the altitude must be high and a large overlap used. Therefore, we use the same flight control software and settings for photomapping that we use for orthomosaic mapping.

Our photomaps have the same high resolution as orthomosaic maps, but avoid the expense of the mapping service for generating 3D map sets. If position and altitude information aren’t required, then this is a less expensive way to get ultra-high-resolution maps of large properties.

Map Image Resolution (Geek Alert!)

Our Phantom 4 Professional V2 drone takes images that are 5,742 pixels across and 3,648 pixels high, which yield an image size of 19.98 megabytes (rounded to 20 MB). At an altitude of 400 feet, that image represents a ground view that’s 600 by 400 feet. Dividing pixels by distance yields the spatial resolution, which in this case is 9.6 pixels per foot. (In metric units, that’s 3.2 cm/pixel.)

For example, take an acre of land, which is 43,560 square feet. When photographed at an altitude of 400 feet, one acre takes up 18% of the camera’s image. The area-to-image ratio is scalable, so an orthomosaic map or photomap of 40 acres can be covered with 8 images. The composite image size is then 145 megapixels (MP), with a resolution of 3.2 cm/pixel. The key word here is “composite,” since a large number of photos (e.g. 326 photos at 20 MB each) contribute to this composite image.

Since a map’s image size is proportional to the number of acres, we can estimate your finished map’s image file at 6 MP per acre. This number can grow 20% or more because we’ll always be photographing a larger tract than required. In terms of file size, the finished JPG image file will end up at about 3 MB per acre.

Want to Proceed? Here’s What We Need to Know:

When specifying a mapping job, clients just need to provide their tract boundaries and we’ll take care of the rest. We’ll determine the appropriate parameters, such as 85% overlap frame to frame, 85% overlap track to track, and flying altitude. Overlap is partly determined by the height of objects on the ground (such as trees) and seasonal variations (such as leaves).

Our flight control software will use this information to generate the photo-taking commands to be used by the drone’s autopilot, which ensures the photo-taking process is accurate and repeatable. This is especially useful if the map needs to be updated for project progress or for seasonal variations.

Viewing Large Image Files on Your Computer

For our example above, a 145 MP image is too large to display on common photo viewers such as the MS Office Picture manager. However, it can be viewed with more advanced software such as Adobe’s Photoshop. Of note, we can resize large images so they’re viewable on your photo viewer, but the resolution will have to be decreased.

How Much Will Map Services Cost?

Every job has its own unique requirements, so we don’t publish our prices. However, our prices are very competitive and we deliver an excellent value. We’re happy to take your map requirements and give you an estimate within 24 hours. We guarantee our work will meet or exceed your requirements.

Call or e-mail. We’d love to hear from you!