When selecting a photogrammetry camera for your
drone, there are a number of factors to consider. There are
some physical constraints such as size and weight, but also
some technological considerations such as GPS tagging,
lens distortion, and sensor size. We’re going to quickly go
over some common concerns and a few cameras that seem
to be popular amongst the community.
First of all, we’ve got to talk about the action cameras.
The GoPro is the quintessential action camera with high
quality video, photos, and a rugged design.
These cameras survive kayaking, mountain biking, and
even falling out of an airplane. One video online shows a
GoPro that falls over 12,500 ft (3810 m) and still works fine
A genuine GoPro is several hundred dollars, but there
are a number of knock-off products (which I call Faux Pros)
that are available for less than $100. While durable and
affordable, these cameras have their disadvantages. For
starters, they have a very wide angle lens to capture a large
action scene. This lens introduces significant distortion,
making straight lines appear to be curved (Figure 1). As
you can imagine, when trying to reconstruct a
dimensionally accurate representation of the world, this
warping causes problems!
There are ways to correct for the distortion, but it is
certainly not ideal. Another problem is the lack of geo-tagging in all but the most expensive action cameras. As
we’ll see, having no GPS data in the photos causes the
processing to become more difficult and time-consuming.
Finally, there is the problem of the camera image sensor size.
The size of the sensor determines what
size of details can be resolved in the image,
as well as other image performance factors.
One thing to always keep in mind is that
two small objects viewed from far away may
appear as one combined object; this
minimum object separation can be described
by the Rayleigh criterion, but is a bit beyond
the scope of what we’re trying to do here.
Next, “point-and-shoot” cameras have
become a popular option. These cameras
have larger sensors than a GoPro and lenses
that provide much less distortion. These
simple cameras run from a hundred dollars
to several hundred depending on the
capabilities, resolution, age, and features.
The Ricoh GR and a number of Sony and
Canon cameras have been used for aerial
OpenDroneMap — Part 2
By John Leeman
12 SERVO 05.2017
Last month, we got up and running with OpenDroneMap (ODM) and its new web interface,
WebODM. This month, we’re going to learn about referencing our photos to real life coordinates
with ground control points (GCPs) and collect some real data of our own to experiment with. Grab
your cameras, drones, and laptops; it’s time to make some meshes and orthophotos!
Figure 1: The wide angle lens on most action cameras causes significant distortion of
the image. The gravel road and fence line cutting diagonally across the photo are
straight lines. Notice how they bow significantly — especially towards the edges.
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