Beskydy 2012, 5, 111-120
Spline representation of irregular and malformed stem profiles of broadleaved tree species in White Carpathian Mountains
The paper deals with representation of individual stem profiles of beech and oak in White Carpathian Mountains, Czech Republic. Due to complicacy and irregularity of stem profiles of most trees common taper functions are not applicable for individual stem profile description. Selected spline functions were used to model the irregular stem profiles. To fit complicated stem profiles with a spline more input points are needed than for regular stems. The splines were computed using four fixed input points representing diameters in four conventional heights (base diameter, stump diameter, DBH and the height) and another two input points interactively added to describe the location of the most significant malformation. More input points were added in respect of the malformation position. To evaluate the accuracy of each spline a number of stems have been measured. For each stem diameters with interspaces of 0.2 m have been measured from the base to the top. At each measurement position predicted diameters with the real value were compared. Five different statistical indicators were used to evaluate the accuracy of the spline models. The profiles were the best represented by Catmull-Rom spline with tangent vector length corrections. Previously frequently used natural cubic spline is not suitable for irregular stems. When interpolating complicated stem profiles it suffers from oscillation considerably more than for regular stems of coniferous species.
