Precision 3-Dimensional Mapping

Topography Map, May 2020

Topography Map Draped Over the 2-D Map

Precision 3-Dimensional Mapping

Aerial drones are the ideal method for collecting precision aerial mapping information for your land development projects. This is exciting technology and the map products that we deliver are truly breathtaking.

Each project begins with a client-provided map that outlines the site that needs to be surveyed. We enter this information into our drone’s autopilot (a mapping application), which flies the drone and collects the photos. Our typical settings are 90% overlap and 3 cm/pixel, which are further explained in our Orthomosaic Mapping and Photomapping blogs (parts 1 and 2).

We’re very good at photographing and delivering precision map products. As described below, several of these deliverables require specialized software to take full advantage of 3-D mapping. We do not offer professional cartography services, but instead provide these files to professionals who have the specialized software for these types of projects. The free software applications described below are suggested for viewing our products, but are not endorsed by FAD-Photo as suitable for professional-level mapping. We do believe, however, that many users will find them quite useful.

3-D Map Processing

Using our typical settings, the drone takes 18 photos per acre of land. For large sites, where we collect hundreds of photos, each pixel of the surface is examined at 13 or more different angles. Map processing aligns the pixels and assembles them into a 3-D composite model that includes latitude, longitude, and elevation.

Accuracy? Each photo is tagged with its position and altitude, so the composite model’s position is as accurate as the Global Positioning System. Typically, 3-4 meters.

Altitude information is based on the drone’s barometer, which has an accuracy of 3-4 meters. (We covered this specification in our April 23, 2020 blog.) Map deliverables are normalized to sea level.

Image processing is highly complex, so we use a professional mapping service provider. These are the deliverable products you will receive:

Full Color 2-Dimensional Map

This JPG file is a composite map of the photos, which are combined into a single panoramic map. Instead of a traditional scale, such as 10 meters per centimeter (or 100 feet per inch), the map service provides scale in terms of centimeters per pixel (or inches per pixel).

The JPG map doesn’t include position information, but its TIF counterpart (also a deliverable) has position information for each pixel. Use an application, such as the free QGIS software to view.

3-Dimensional Maps

DEM – Although monochrome, the Digital Elevation Model map (a TIF file) includes position and elevation information for each pixel. Special software, such as QGIS, must be used to view. The mapping service also provides a JPG of the DEM map, but this product doesn’t include position information.

Point Cloud – This is a LAS file, developed for LIDAR applications. At first glance, this full-color type of 3-D map appears fuzzy and not very useful. However, with a good viewer, such as the free Fugro Viewer, you can zoom in on the left panel image and view its corresponding 3-D model on the right panel. This is useful for looking at pixels under trees which would otherwise be masked. Of note, the 3-D model can be rotated in any direction with the mouse.

3-D Object Map – This is also a full-color map that can be rotated in any direction with the mouse. It offers a much sharper appearance than the point cloud, but it doesn’t get under the trees. Three files are required: the main 3D.OBJ file, a 3D.JPG file, and a 3D.MTL file. (You can rename the OBJ file, but don’t rename the other two.) You can open this type of map with the Windows 10 Object Viewer, but the free MeshLab viewer allows full 3-D rotation and zoom with the mouse.

Other Deliverable Map Products from FAD-Photo

The map processing report provides details on your map products, including map location, output size in pixels, scale in inches per pixel, overlap report, etc.

Topographical map (traditional contour map), where the user can specify the color scheme and contour intervals. (A postprocessing fee applies.)

Topographical map draped over the panoramic map. Here, the contour intervals are overlaid onto the full-color 2D map. An example is provided above and a larger example appears on our portfolio page. (A postprocessing fee applies.)

Do you have a special application?

Contact us for the solution. We’re experts in drone photography, mapping, and postprocessing services.

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 our licensed 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 megapixels (rounded to 20 MP). 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 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 MP 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 3.6 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 1.5 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’ll display 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!

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 3.6 megapixels per acre. For example, an 80-acre map will have around 300 MP and a JPG image file of around 120 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. Tract size can range from less than one acre to thousands of acres.

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.

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.