Hemispherical photography has become a widely used tool for the estimation of forest structural attributes and seasonal change of crown. Photographs of canopy were taken looking upwards from the forest floor, using a digital camera with 180° fisheye lens. The sheye camera was mounted vertically on a tripod using the two dimensional level and the orientation of image was turned to North using the compass. However, camera calibration was necessary for the exact registration of seasonal images. In this study, we proposed the method for rotate calibration of fisheye camera by using a nonlinear optimization.%森林内で円周魚眼力メラを鉛直上向きに設置して，林冠の季節変化を撮影している.異なる時期に同一地点·方位で撮影した全天画像を重ね合わせるために，撮影時にコンパスと電子水準器で回転パラメータを手動で統ーしている.しかし，半径約1500画素の画像円周部で100画素以上のずれが生じた.本研究では、非線形最小二乗法を用いてカメラの回転パラメータの推定を行い，その結果，画像を1画素以下の精度で校正することが出来た.
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