Best Practices for Drone Photography
Overview
This article describes best practices of taking images using
drones for the purpose of being processed by Datumate’s software, such as
DatuBIM and DatuSurvey.
Most commercial drones, including the popular DJI drones, are
supported by Datumate’s automatic drone flight planning application, DatuFly Professional, available
for iOS tablets. The following guidelines may be used when handling a drone that
is not supported by DatuFly or when DatuFly is not available to you.
General Guidelines
Guidelines below
are true for any flight type.
- Use a high-resolution
camera - It is recommended to
use a camera with resolution between 18-megapixel and 36-megapixels. Typically,
an 18-megapixel camera provides a 1 to 2 centimetre (3 to 6 hundredth of a
foot) measurement accuracy at a distance of about 100 to 150 meters (110 to 160
yards, 330 to 480 feet). Make sure your
camera is set to the maximum resolution available.
- Use
a camera with a large sensor - It is recommended to use a camera with a
CCD/CMOS sensor size larger than 100 mm2.
- Use a camera with a
manual mechanical shutter - If you are using a camera with a rolling
shutter, make sure the drone is set to stand still on each image taking
location.
- Set the drone speed
properly - When you use a camera with a mechanical shutter it is possible
to take images while the drone is moving without having to stop and take each
image, which is the case when cameras with rolling shutter are used. The speed of the drone should be set to a
speed suitable for taking crisp images. This may be a trial and error
process. Taking images while the
drone is moving is a big battery power saver, yet going too fast may still
cause images to be blurry. For DJI
drones using 20-megapixel cameras with mechanical shutter, the optimum speed is
6m/sec.
- Set Focus and
Shutter speed to automatic - It is strongly recommended to at least set the
camera to auto-focus.
- Save Geo-Tagging
information - Make sure your camera is set to save the geo-location of the
images. In general, it is not possible
to process images that do not have geo-tagging information, especially images
that are taken vertically. If your
camera does not allow this, you may want to consider changing the camera, or
finding a way to add the geo-tagging information in offline.
- Use a lens with a
fixed focal length – Datumate solutions require that the camera’s focal
length will not change after the calibration of the camera and during the
photographing of the survey area. Thus, it is strongly recommended to use a
fixed focal length lens, i.e., a lens without an optical zoom. If the camera does have zoom, make sure that
the zoom is on the same setting throughout the whole photography session.
- Make sure GCP’s are clear and covered properly - If you are photographing an
area where Ground Control Points are marked, make sure that most of the control
points are covered and appear clearly in several images each. It is strongly recommended to scan the area
in person to make sure that GCP’s are clearly marked. This is specifically important when you
photograph construction areas over and over for progress reporting as GCP’s may
be erased, covered by dirt or dust, or totally removed in such sites.
- Take your images in
good and consistent lighting conditions - Take all images in similar
lighting conditions, preferably at the same time of the day and preferably
close to noon. Avoid photographing the survey area during different times of
the day. This will minimize changes in shadings and lighting conditions that
may degrade the performance of the automatic image processing algorithms
employed by Datumate. Do not take or use images of dark areas.
- Set Cloudy/Sunny
properly – If the application you are using to fly the drone has a
Cloudy/Sunny setting option, make sure it is set to the proper option based on
what you see in the area you are about to photograph.
- Take images only in
landscape format - Datumate solutions do not support images in portrait
format. If your camera is equipped with Auto Rotate functionality, set
it on “Off” so that all images remain in landscape format.
- Make sure you have
enough batteries - As mentioned above, it is recommended to take a-images
as much as possible in the same lighting conditions. So, make sure you have enough batteries to
cover the whole area as quickly as possible so you will not need to wait for
battery recharge.
- Consider drone flying regulations – Local drone flying regulations may limit the height, distance of drone from controller, distance of drone from urban area, and possibly other limitations. To avoid issues, review your local drone flying regulations regularly and make sure you follow them.
Guidelines for Vertical Image Taking
In
addition to the general guidelines above, the guidelines below are true for
taking images in vertical mode. Vertical
or Nadir image taking means that the camera is pointing straight down to the
ground and the drone flies over an area scanning it back and forth in straight lines
taking images at set intervals. There
should be a good overlap percentage between images in the same row, as well as
overlap between rows.
Vertical flight
mode is used to generate precise orthophotos of large areas as well as
elevation color maps. This is used more in infrastructure construction sites
for tracking progress of work.
- Maintain proper and constant overlap - It is recommended
to maintain at least 75% front overlap and 60% side overlap. (80% front overlap
and 70% side overlap is recommended).
- Set the height of the drone properly - The height of the
drone sets the pixel resolution. For
example, if you are looking to get a sub 2cm sample resolution (GSD) using a
20-megapixel camera (5472x3648) that has an 84-degree Field of View (FOV), then
you should set the height at about 60 meters.
- Maintain a uniform distance from the ground as much as
possible - If you are flying a hilly area that has large differences in
elevation you may want to consider splitting the area into several flights
where each flight covers an area that has a smaller variance in elevation. So,
if you are flying at 60-meter elevation from take-off point, then make sure the
area covered had elevations of +/- 10 meters. This will give you a consistent
GSD.
- Watch for areas with traffic or moving objects - If you
are photographing an elongated area, such as a road, it is normally recommended
to define your flying pattern with the rows of flying running down the long
side of the area. This is usually more
efficient as far as battery usage. Yet,
if you are flying a road with traffic in it, it may be better to photograph it
going back and forth across the road.
This will assure cars will not appear in images over and over because
you are flying in the same direction as the traffic.
- Split the flying mission - If you are flying an area
with narrow legs, such as a T shaped area, or an H shaped area,
sometimes you may want to consider defining multiple flight missions where each
one covers one leg. This may be more
efficient as far as battery usage, and also it makes sure you photograph only
areas of interest.
- Keep drone nose pointing in flight direction - When planning missions allow the drone to turn 180 degrees between the flight lines keeping the drone nose pointing in flight direction. See figure below.
- Keep camera stabilization feature turned off - Turning off camera stabilization feature allows variability of pitch and roll angles during image capture.
Guidelines for Oblique Image Taking
Below guidelines
are true for taking images in oblique mode.
Oblique image taking is when the drone flies in a circle and the camera
is pointing to the center of the circle while the camera is angled in a way
that the center point of the circle on the ground stays in the center of the
image.
Oblique flight
mode is used to generate precise 3D models with more accurate elevations. It is not possible to cover huge area in
oblique mode.
- Maintain proper overlap - It is recommended take
enough images at a constant distance on the circle between them to maintain a
good overlap. For example, for a 40-meter
radius circle at a height of 40 meters, take about 45 images.
- Set the height of the drone and the radius of the
circle properly - The height of the drone and the circle radius set the
pixel resolution at the center of the image.
For example, if you are looking to get a sub 2cm sample resolution (GSD)
using a 20-megapixel camera (5472x3648) that has an 84-degree Field of View
(FOV), then you should set the height at about 42 meters and the radius at
about 42 meters.
- Maintain a uniform division of image taking on the circle as much as possible - This will give you a consistent overlap and a more accurate model.
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