During an earlier phase of annotation, we placed bounding boxes around
all elephant ears, while simultaneously marking them as either
Left
Ear or
Right Ear. The purpose of this was to train an algorithm to
find the ears. During the current phase, we go one step further by
tracing the outline of each ear.
This outline contains the identifying
information for that particular elephant, and is what will eventually be
used to train the identification algorithm. Given that it is
prohibitively time-consuming to trace the ear outline perfectly, we
compromise by tracing the outline at two levels of detail:
- a very narrow pencil-like line that follows the outline closely while accepting small imperfections as inevitable and
- a broader, paintbrush-like outline that traces a coarse approximation of the contour such that it is guaranteed that the true outline lies within the traced outline.
These are traced simultaneously. Finally, we indicate those contour
points where the contour cannot be traced reliably, such as when the ear
is hidden by the branches, leaves, or another elephant.
Each image shows the bounding box that was drawn around the ear, as well
as a small margin around it to provide context. The exact bounding box
around the ear may be displayed by checking the
Show
Guidelines checkbox. This is useful when there are multiple ears visible in an
image, in which case the bounding box may resolve ambiguity about which
ear to trace.
Tip: Use the hotkey G (for guidelines) to toggle showing the original annotation's bounding box without the added margin
Below we show two complete examples. Note how, in the second image,
the part of the contour behind the tusk has been marked to
indicate unreliable points.
Example 1
Example 2
Initiate a contour by using
left-click to place the start point, which
will appear as a green circle (
). The start point should be placed as
close as possible to the point where the outline of the ear meets the
top of the elephant's head. In some cases, it may be that this start
point is far from the actual ear/head meeting point, such as when
viewing a right ear from the elephant's left, but that is OK.
Next, use the mouse to trace the ear outline. The dark blue dots should follow
the outline as closely as possible, but are not required to lie exactly
on the outline at every point. Instead, the outline should be contained
entirely within the surrounding transparent blue region at all points.
Once the contour is complete, use
left-click to place the endpoint,
which will appear as a red circle (
). The endpoint should be placed as
close as possible to the point in the image where the outline of the ear
meets the side of the elephant's head.
If the traced outline is
satisfactory, simply click
Accept to continue. If
not, the contour may be corrected by following the procedure outlined in
the next section.
Tip: Use the hotkey Enter to accept the current contour and continue
Mistakes are inevitable given the difficulty of the task. It is always
possible to delete a contour and start over by pressing the
Delete key or
clicking
Clear. It is also possible, however, to fix mistakes without
starting from scratch. If a mistake is made, simply use left-click to
place an end point, and then move the cursor back to the last correct
point. The point to be used for restart will turn red, and may be
selected by hovering over the point such that the cursor turns to a "+"
sign. The restart is then initiated with a left-click. All contour
points traced after that point will be erased immediately and tracing
can continue from there.
When tracing very fast, it may happen that the browser loses track of
the cursor movement. In such a case, an endpoint will automatically be
placed at the last point that registered and a warning message will be
displayed. In this case, simply initiate the restart procedure
described above to continue from any previous point on the contour. If
you decide that the contour is actually completely drawn, you may simply
choose to accept it without change.
Given the real-world nature of the images, it may happen that a part of
the ear outline to be traced is obscured by branches, leaves, the
boundary of the image or another elephant. In these cases, simply trace
across the boundary of where you can see the ear until your tracing
rejoins the actual edge of the (unobscured) edge. In doing so, you may
specify that the points you are tracing are unreliable. This may be
done in two ways, namely:
- holding down the Shift key while tracing the
contour, or
- completing the contour and then holding the Shift key while
moving the cursor over the unreliable points.
Points that have been
marked as unreliable will be shown in orange rather than blue. If a
point is mistakenly marked as unreliable, it may be changed back to
reliable by holding down
Ctrl key (rather than
Shift) and moving the
cursor over the desired points, which will turn blue.
If you miss a spot on the boundary of the ear, it is quite tempting to
trace backward to cover it and then trace forward again. Please do not
do this because it creates artificial duplication of the actual recorded
contour and makes it confusing for the machine learning algorithms we
need to train. Instead, stop tracing with a left click of your mouse
and then treat this as something you need to fix by following the
procedure described under the Correcting Mistakes section.