Drone Harmony’s Top-Down Scans: An Introduction and an Advanced Use Case
May 23, 2017
From obtaining a bird’s eye view of a large park to performing centimeter-perfect inspection of several roofs in your neighborhood, Drone Harmony’s Top-Down scan is a powerful and flexible tool letting you achieve these tasks quickly and easily. In this post we first cover the basics of Top Down scans and then demonstrate some of the advanced features that are unique to the Drone Harmony mission planner by means of an example use case. If you are an advanced user, you might want to skip the next section and jump straight to the example.
In its simplest form, a Top Down scan is a flight plan in which the drone flies over an area or a structure in a grid-like pattern at a fixed relative altitude, taking images with the camera facing straight down.
It is possible to generate a Top-Down plan both for flat areas (representing farm fields, parks etc.), as well as structures (e.g. buildings, piles of material etc.). In both cases, the user is required to specify two simple parameters:
The altitude above the top facet of the scanned structure that is scanned.
Desired overlaps in the forward and sideways directions between captured images.
The altitude determines the ground resolution of the resulting images, or in other words, how many square centimeters (resp. inches) of the captured object one pixel in the resulting images represents. For example, a relative altitude of 23 meters (75 feet) will correspond to a ground resolution of 1 centimeter (0.4 inches) per pixel, for the Phantom 4 camera. When you choose an altitude for your top down plan in the Drone Harmony planner, the ground resolution is displayed underneath.
The overlap percentage determines the amount of overlap between successive images that will be captured. For example, a Forward overlap of 50% mean that two successive images in the direction of flight will share half of their content. It is important to choose an overlap that is suited for you needs. For example, if the goal is to inspect a rooftop by capturing images that cover it, one can choose a low overlap, such as 20%. If, on the other hand, the images are intended for creating a 2D map of an area (an Orthomosaic), a larger overlap such as 70% should be chosen to facilitate the image processing algorithms.
Note that the higher you fly, the fewer images the drone needs to make to cover a certain area with a given overlap. However, at the same time a higher flight altitude leads to worse ground resolution. It is hence important to choose a good compromise: fly low enough to obtain the resolution you need, but not much lower, as it will result in more images than you need.
Drone Harmony lets you control additional parameters to tune your Top Down flight. For example, you can let the app choose optimal scan directions, or specify a preferred scan direction. This can be useful, for example, in windy weather conditions, in which it is not desirable to let the drone fly against the wind, as this can drain the battery very quickly.
As we indicated before, Drone Harmony’s Top Down scan is a powerful tool that is able to deal with complex scanning tasks. We demonstrate this by means of the following advanced use case.
Use Case: Multiple Rooftop Inspection
Consider a rooftop inspection task, in which the rooftops of numerous buildings need to be inspected. The buildings, spread across a medium-sized region, might have different heights, they might be separated by obstacles, and might have complex roof shapes. Here is an example of such a complex scenario in which we want to scan the rooftops of all blue buildings. Recall that such a scene can be easily defined in the map view by outlining all structures that are relevant for the scan, as explained in the blog post Scene-centered planning: The powerful workflow of Drone Harmony’s flight planner app, and as demonstrated in the Youtube video scene-centered workflow.
With the Drone Harmony Mission Planner it is possible to automatically generate a flight plan to perform the latter task with just a few taps.
First, tap on the plus icon to start planning a new scan and select “Top Down”. Then, select all the structures you would like to inspect. Select your preferred takeoff and landing locations on the map and set the basic parameters for your scan: flight altitude above the rooftops and desired overlap between neighboring images. Adjust advanced parameters if you like, or let the planner select optimal parameters for the scene you defined. Tap “submit” and see Drone Harmony compute the plan for you. The computed plan is optimized for flight time, avoids obstacles and is ready to fly. But before you start your drone, take another look at the plan in the 3D view to make sure you will get the images you need. After all, if you got the altitude, or any other parameter wrong, you will likely see it in the 3D view, and that perfect plan with adjusted parameters is, again, just a few taps away.
There are numerous other use cases in which advanced Top Down planning can be utilized to great effect. These included scanning multiple farm fields, vineyards on sloped hillsides and more. In the near future, Top Down scan will be facilitated by a new powerful feature we will introduce: ground elevation that automatically incorporates the topography of the area in the planning process. Stay tuned.
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