三角函数干形方程与广义Brink干形方程的比较

利用来自澳大利亚新南威尔士州不同生长条件下的辐射松人工林样木干形数据，比较三角函数干形方程与广义Brink干形方程对估计树干任意高度处对应去皮直径的效果;利用非线性回归拟合干形方程中的参数，将拟合残差、预测均方误差、绝对偏差、决定系数等作为评判准则。结果表明:通过样本数据回归拟合得到方程中的参数后，用三角函数干形方程预测新的干形数据集中给定树干上任意高度对应的去皮直径时，估计结果更准确；三角函数干形方程对树干底部直径的估计结果要优于广义Brink干形方程，且三角函数干形方程对树干整体拟合结果更稳定。另外，依据三角函数干形方程参数估计结果将其化简并检验化简后的拟合效果，从而证明三角函数干形方程的易变形性及灵活性。 

Comparing trigonometric variable-form taper function with generalized Brink stem profile function

Using sample taper data collected from Pinus radiata plantations at different sites of New South Wales State,Australia,this paper compares trigonometric variable-form taper function ( Bi function) with generalized Brink stem profile function ( GB function) when estimating diameter under bark at any height of stem. Nonlinear least square regression was used to estimate parameters of both functions. The residual errors, mean square error of prediction, mean absolute difference of prediction and determination coefficient were chosen as the criteria for evaluation of the fitting effective. Results showed that after the parameters in the two taper functions were obtained by regression,Bi function performed more accurately than GB function in predicting diameter under bark at any height of stems; the Bi function was superior to GB function on bottom stem fitting effect,and the Bi function was overall stabler than GB function. In addition,based on parameter estimating results,the Bi function is simplified and the fitting effect of the simplified taper function has been validated,which verifies the deformation and flexibility of Bi function.