  Recurrence Quantification Analysis (RQA) defines a number of quantifiers,
which base upon diagonal line structures in the recurrence plot (RP). Due to
the finite size of an RP, these lines can be cut by the borders of the RP and,
thus, bias the length distribution of diagonal lines and, consequently, the
line based RQA measures. In this letter we investigate the impact of the
mentioned border effects and of the thickening of diagonal lines in an RP
(caused by tangential motion) on the estimation of the diagonal line length
distribution, quantified by its entropy. Although a relation to the Lyapunov
spectrum is theoretically expected, the mentioned entropy yields contradictory
results in many studies. Here we summarize correction schemes for both, the
border effects and the tangential motion and systematically compare them to
methods from the literature. We show that these corrections lead to the
expected behavior of the diagonal line length entropy, in particular meaning
zero values in case of a regular motion and positive values for chaotic motion.
Moreover, we test these methods under noisy conditions, in order to supply
practical tools for applied statistical research.
