The quality of images taken when using UgCS photogrammetry tool is highly dependent on capabilities of the camera used. Thus the photogrammetry route has to be planned around the capabilities of the camera and not the drone.
Cameras usually have five main settings/parameters:
Furthermore the amount of light is crucial for taking good photos. Most cameras are set to adapt to the amount of light.
Below is an illustration how shutter speed, aperture and ISO can affect the result:
For best results the camera matrix needs to get as much light as possible. For example:
Matrix size. The main rule is - the larger the size of the matrix, the more sensitive the camera. That’s why a DSLR camera with a full-frame matrix will give higher quality photos than a cheap camera with a small matrix.
Focal length. If the focal length is increased, then exposure time or drone speed should be decreased. Otherwise the photos will be blurry.
Knowing the camera settings, it is possible to anticipate how they affect the results of a UgCS photogrammetry mission, adding two main conditions for a drone flight: speed and altitude.
Let us analyze 3 common types of illumination during daytime:
Note - It is not recommended to fly in low-light conditions such as during twilight or early morning.
Sunny day with clear skies
On a bright sunny day when there is a lot of light, a test flight with DJI Phantom 4 (GSD = 2.5, True focal length = 3,6 mm, resolution – max (4000x3000 px.) was made with the following settings:
The route calculated by UgCS had the following parameters:
The camera was set up in the field with these parameters (in Manual mode):
The particular values have to be adjusted individually according to illumination. The result of the test flight was excellent: photos were clear and sharp. Only one battery had to be used for the flight with a small reserve left.
If the GSD would be decreased, flight altitude will also be decreased. The true focal length will remain constant; therefore, the drone’s flight speed has to be decreased or the speed of the shutter increased (exposure time decreased). The minimal trigger interval for DJI Phantom 4 is 3sec, therefore the flight speed has to be decreased. If GSD is decreased to 1.5 cm, then drone's speed has to be decreased to 2 m/s (DJI has this limitation on minimal flight speed for auto mode). Covering the same test area will require 4 batteries instead of 1 and the flight height at 20m AGL will be unsafe due to hazards such as trees.
Downside of good illumination - photos can have sharp shadows, affecting the productions of orthophoto and 3D models.
Sun mixed with clouds
The level of cloudiness has to be monitored and the settings have to be adjusted accordingly – the speed of drone and shutter speed has to be decreased, other settings can be left as previously described. The ISO value can be increased if necessary.
Second option is to use the action 'Set camera mode' with 'Shot' parameter and additional waypoints. If interval between waypoints is less then 70-90m, it is useless to increase drone's speed – the drone will not have enough distance to reach the speed set. Mostly it is recommended to use the default flight speed - 5 m/s.
The main thing to take into account when flying on a cloudy day is to fly with 'Set camera mode' action to 'Shot' parameter and additional waypoints. Shutter speed can be set to a longer time, but should not exceed 1/60. Furthermore the ISO value can be increased but shouldn’t exceed 400.
As you can see, the capabilities of the drone exceed those of the camera. But the effectiveness of entire drone system is determined by the least efficient part. Therefore, many professional surveyors use DSLR cameras with wider lens aperture on drones with several batteries to deliver optimal and efficient result.
Get UgCS here: www.ugcs.com