Database Reference
In-Depth Information
2. Starting position: among these are the initial, starting position of the limbs, i.e., the
geometrical relationship between limb positions prior to the start of active move-
ments.
3. Unit scales: among these are the unit of change in the angle of every joint's fi rst and
second degrees of freedom (measured in partial degree units), the value of the unit
of change in the motion velocity of each joint (measured in percentage units), and
velocity measurement units (km/hr, cm/min., etc.).
4. Sampling frequency: the number of samplings per second.
5. Motion constants: i.e., constants, constraints and relationships that remain consistent
throughout motion performed by a number of limbs, as for example in the synergistic
movements of the fi nger joints of the hands. These are in addition to various parameters
contained in the “creature's anatomy” category, which relate separately to each of the
creature's individual limbs.
As in any process where analog signals are converted into digital signals (the Nyquist
Law (Casavant & Mukesh, 1994; Stallings, 1988) for sampling for the purpose of A/D
conversion), the accuracy and sensitivity of the represented motion depend on the rate of
sampling used for producing data. Thus, a high sampling rate makes it possible to use very
small units of change, and at the same time produce quick movements. For example, a sam-
pling frequency of 5 Khz (5000 samplings per second, as is common in motion simulating
systems), allows us to defi ne an angular unit of change with a magnitude of 1.08 degree-
minutes, at a rate of 90 degrees per second. It also supports using a unit of velocity change
at a rate of 0.1% to facilitate an acceleration value, for which the velocity increases by a
factor of 150 in the span of one second.
Motion Patterns
In the representation and storage of motion, our model make use of partitas and mea-
sures (borrowed from the “language” of music), which employ the binary building blocks
to defi ne motion patterns, i.e., a beginning of a motion text.
Partitas and Measures
A partita is a special structure of motion data with one of the following four formats,
each of which comprises the coordination aspect and one space dimension or time dimen-
sion (see Figure 5):
1. The space component's fi rst dimension partita - composed of bits 1+2+3
2. The space component's second dimension partita - composed of bits 1+4+5
3. The space component's third dimension partita - composed of bits 1+6+7
4. The time component partita - composed of bits 1+8+9
Despite its redundancy, it is still worthwhile storing the time component. The gener-
ality of each partita structure is achieved by using the 9-bit structure of the motion byte,
even though not all the binary combinations are fully used. As mentioned previously, the
coordination component represents the precise moment at which a given limb goes from
rest to motion, and vice versa. It delineates starting and ending points of every movement
(“enter”-”exit”). This piece of information is necessary in each and every partita.
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