Point (kinematics)
A point in kinematics is a point in
Cartesian geometry. It describes an
identifiable point in the real world, such as the center of a tennis ball, the
wrist joint center, or a marker placed on the forehead.
Cartesian coordinates
In kinematics, points are usually described in 2
dimensions or in 3 dimensions.
Given a view from a camera, one may think
that 2d measurements (such as distances, angles, velocities) may be made on the
view directly. However, all measurements made on the view directly are in
screen coordinates (in pixels). These measurements are only meaningful if
they are converted to world coordinates first.
The APAS/Digitize and APAS/Transform modules may be used to do
this:
Dimension |
Input |
Transformation |
Output |
2 Dimensions |
View - 2d screen coordinates |
� 2d transformation � |
2d world coordinates |
3 Dimensions |
View 1 - 2d screen coordinates
View 2 - 2d screen coordinates
View n - 2d screen coordinates |
� 3d transformation � |
3d world coordinates |
Time
In kinematics, points can move (their position changes) as a function of
time. Consider the following example, a ball rolling on the floor at 1 meters
per second in the positive X-direction:
Time |
X |
Y |
Z |
Short |
0.0 seconds |
0.0 meters |
0 meters |
0 meters |
(0.0, 0, 0) |
0.1 seconds |
0.1 meters |
0 meters |
0 meters |
(0.1, 0, 0) |
0.2 seconds |
0.2 meters |
0 meters |
0 meters |
(0.2, 0, 0) |
0.3 seconds |
0.3 meters |
0 meters |
0 meters |
(0.3, 0, 0) |
0.4 seconds |
0.4 meters |
0 meters |
0 meters |
(0.4, 0, 0) |
0.5 seconds |
0.5 meters |
0 meters |
0 meters |
(0.5, 0, 0) |
See also