5. Two-Dimensions vs Three-Dimensions

While the discussion here is limited to horizontal (two dimensional) coordinate systems, it is relatively easy to extend this into the third dimension by incorporating elevations or Z coordinates. An additional translation parameter would be needed for the elevation component, TElev.

The rotation angle, ρ, for a two dimensional transformation is a horizontal angle rotated about the vertical, or Z, axis. In a three dimensional transformation there would three rotation angles, one about each axis (X-Y-Z, or E-N-Elev). Figure H-23 Three Dimensional Transformation

Scale could again be Unitary, Uniform, or Differential. In the latter case, there would be three scale factors.

The total number of parameters in a three dimensional transformation could be:

• Six: Three translations, three rotations, 1:1 scale
• Seven: Three translations, three rotations, uniform scale
• Eight: Three translations, three rotations, one scale for horizontal, one scale for vertical
• Nine: Three translations, three rotations, three scales

The eight-parameter transformation would be used where there is a quality difference between horizontal and vertical positions in one system or the other.