Umm, about all those little fiddly bits …
Which ones matter?
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Concept Illustrated: Pressure Against the Track Wall (Canine toe pad)
The idea: Show pressure against the wall while the track is forming
While every track is being made, some sort of outer wall is created by many parts of the foot. This portion of the track preserves and expresses significant information about how the being reacted to its world before, as, and even after the track was made. The ways it used the foot as it created the track left this information in the track wall. This in turn is a reflection of that beings’ reactions, choices, and emotions.
The illustration above is an effort to begin the process of illustrating the many variations (limitless?) of this tracking concept in 3D motion to allow trackers and students to watch the formation of this aspect of the track.
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Concept Illustrated: The Wave … how simple?
The Idea: Illustrate the movements of the substrate (in this case dry-ish sand) as waves are generated by a foot moving at a slow walking pace.
The wave can be an obvious or subtle track feature. Two waves made by the same foot with the same energy and intent, can look quite different, for example if one is made on damp sand , and the other in dry sand.
A wave has a least two phases …
The first-phase wave begins at the point where the heel contacts the ground, as the substrate begins responding to the movement of the incoming foot. This phase surges forwards as the initial contact between the sole of the foot and the ground progresses until the ball lands and the toes reach the ground. At this point all weight is on the foot and the first-phase wave is complete.
The second-phase wave begins as the heel starts to lift and weight begins concentrating on the reducing surface area where the bottom of the foot contacts the substrate. This continues as the foot rolls up onto the ball, and while the foot continues rotating to maintain forward motion.
After the foot leaves and everything settles down, the final form of the wave remains. This final form is an indicator of how much energy was exerted to keep the body moving and where that push aimed the body.
Following is a link to a clip illustrating measurements of the timing and amounts of pressure created by a human foot during a walking step. This is graphical representation of data, not a simulation. If you watch it, the heel lands first on the right, then the foot rolls towards the left. Notice there is an overall increase in pressure from heel towards toe, with the highest pressure generated at the toes (the darker the color, the greater the pressure).
(Link to an illustration of pressure applied to ground by foot during a step. From the University of Essen, Essen, Germany. Prof. Ewald M. Hennig, Ph.D.)
Expectations: For a walking pace the wave can be a subtle aspect of a track … depends on substrate type.
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Concept Illustrated: The Ridge Between Canine Front Toes
The idea: As a canine foot is making a simple forward walking step, some of the earth under the two front toes is compressed and moved inwards and upwards into a sharp-edged ridge between them.
This essential track feature must be correctly reproduced in the simulations if they are to be accurate.
The goal here is to create a way to test for, by observing the result, the physics settings in Blender to that will best create this ridge. Eventually the most realistic settings found by this test will be used to configure sand objects so they create realistic tracks for other track simulations.
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Concept Illustrated: The Layer of Sand in Contact With The Foot
The idea: Is mostly to stir curiosity. As a beginning tracker the author skipped this fundamental perspective. Just to be able to identify a species from its track seemed like big progress.
No one gets to watch the foot surface interact with the soil as the track is made, and this interaction really is one of the fundamentals of track formation. What actually goes on? Is it worth learning about?
Maybe the usefulness of this perspective is just to help define the boundaries of what one needs to know?
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Stacking Sand 