  In this paper, as the third part of the third step of our study on developing
data analysis procedures for using 3-dimensional information offered by
directional direct Dark Matter detection experiments in the future, we
introduce a 3-dimensional effective velocity distribution of halo Weakly
Interacting Massive Particles (WIMPs), which, instead of the theoretically
prediction of the entire Galactic Dark Matter particles, describes the actual
velocity distribution of WIMPs scattering off (specified) target nuclei in an
underground detector. Its target and WIMP-mass dependences as well as ("annual"
modulations of) its "anisotropy" in the Equatorial/laboratory and even the
Galactic coordinate systems will be demonstrated and discussed in detail. For
readers' reference, all simulation plots presented in this paper (and more) can
be found "in animation" on our online (interactive) demonstration webpage
(http://www.tir.tw/phys/hep/dm/amidas-2d/).
