This document provides guidance on how to plan flight routes for best-collecting images of a tower for the purpose of making a 3D model of a tower.
There are a few standard systematic flight paths used to collect images: columns, circles, and planes. Each serves the purpose of ensuring that the pilot obtains pictures of the entire tower with plenty of overlap. If these standard methods are not suitable for a specific tower, a tower specific flight path can be flown, but the following guidelines should be adhered to.
Guidelines for Any Method:
- Fly 10-15 meters (30-45ft) from the tower. Consider FOV of camera used.
- Obtain 80% overlap between images. This can be accomplished by keeping more than ¾ of the previous picture in the frame.
- Attempt to keep the sky out of frame. It is much more difficult to create a 3D model when the sky is included. To minimize the amount of sky in the frame, keep the camera pointed down from horizontal when necessary. Images of the top of the tower may require the drone to be 50ft above the point of interest and the camera to be pointed down in excess of 60˚ from horizontal. Refer to Figure 1 (right) for a general idea of camera angles over the height of a tower.
- Multiple hundreds of pictures are necessary for a quality 3D model. Up to 500 images are common for towers up to 400ft tall.
Figure 1: Camera Angles Over Tower Height
Standard Systematic Methods
Illustrations of each of the three standard methods, column, plane, and circle, are shown below in Figures 2, 3, and 4, respectively. In the figures below, blue shading indicates the drone’s flight path area and dots indicate example photo capture locations. At each capture location, the camera should be angled such that more than three-quarters of the previous image is in the frame and with a minimal amount of sky. As the names indicate, each method involves flying in a variable number of either discrete, columns, planes, or circles in order to cover the entire tower. This number should vary based on the size of the tower, location of guy wires, and obstacles in the surrounding areas.
Note: Both the column and plane methods (Figures 2 & 3) will work for flying guyed towers, as the spacing of the columns or planes can be adjusted to avoid the guy wires. However, the circle method (Figure 4) does not encompass the same characteristics and therefore is not recommended for flying guyed towers.