Data set for article: Developing a Model for Curve-Fitting a Tree Stem’s Cross-Sectional Shape and Sapwood–Heartwood Transition in a Polar Diagram System Using Nonlinear Regression

This data set contains the raw observed measurement of the circumference of a tree stem’s cross-section and its heartwood–sapwood transition, the transformation of rectangular coordinates (x, y) of the observed data points’ positions into polar coordinates (r, theta), and the nonlinear regression to curve-fit it. The curve-fit models are circle, ellipse, rotated ellipse, and superellipse.