Length of the linear element, intended to support and simplify algorithms that use length and distance calculations. Note that the length typically is the distance along the 3D-alignment. Caution; this indicates that this length can be derived from the associated geometry. The user should clarify how this quantity was established and associate it with the observation circumstances; see this package for <a href="$package://{B2A724A9-ABD7-42d7-94E9-AFB9BDC703D4}"><font color="#0000ff"><u>observation and measures</u></font></a>.