  We study the motions of G band bright points (GBPs) in the quiet Sun to
obtain the characteristics of different motion types. A high resolution image
sequence taken with the Hinode/Solar Optical Telescope (SOT) is used, and GBPs
are automatically tracked by segmenting 3D evolutional structures in a space
time cube. After putting the GBPs that do not move during their lifetimes
aside, the non stationary GBPs are categorized into three types based on an
index of motion type. Most GBPs that move in straight or nearly straight lines
are categorized into a straight motion type, a few moving in rotary paths into
a rotary motion, and the others fall into a motion type we called erratic. The
mean horizontal velocity is 2.18 km/s, 1.63 km/s and 1.33 km/s for straight,
erratic and rotary motion type, respectively. We find that a GBP drifts at a
higher and constant velocity during its whole life if it moves in a straight
line. However, it has a lower and variational velocity if it moves in a rotary
path. The diffusive process is ballistic, super and sub diffusion for straight,
erratic and rotary motion type, respectively. The corresponding diffusion index
and coefficients are 2.13 and 850 km2/s, 1.82 and 331 km2/s, 0.73 and 13 km2/s.
In terms of direction of motion, it is homogeneous and isotropical, and usually
persists between neighbouring frames, no matter what motion type a GBP belongs
to.
