The 3D Helmert transformation is a frequently used method in geodesy
to produce transformations between different Cartesian coordinate systems:

Xt=T+sRX (1)

where Xt = transformed coordinate vector
X = initial coordinate vector
T = translation vector
R = rotation matrix including rx, ry, rz
rx, ry, rz = rotations around the coordinate axes
s = scale factor
Seven parameters are required for this kind of transformation
and can be calculated from a set of at least three point correspondences.
helmparms3d (a free command-line tool) reads two ASCII point-files and
calculates all necessary papameters for Helmert transformation.
All parameters are written to an ASCII file for further computations.

$ helmparms3d src_points.txt dest_points.txt outfile_name.txt