Model-based conifer-crown surface reconstruction from high-resolution aerial images

Abstract

Knowledge of tree-crown parameters such as height, shape, and crown closure is desirable in forest and ecological studies, but those parameters are difficult to measure on the ground. The stereoscopic capability of high-resolution aerial images provides a method for crown-surface reconstruction. However, existing digital photogrammetry packages, designed to map terrain surfaces, cannot accurately extract tree-crown surfaces, particularly for conifer-crowns with steep vertical profiles. In this paper, we integrate crown features derived from images with stereo matching, and develop a model-based approach for reconstructing conifer-crown surfaces. The model is based on the fact that most conifer crowns are a form of solid geometry. We model a conifer crown as a generalized hemi-ellipsoid, establish the optimal tree model using a geometric equation, and apply the optimal tree model to guide a conventional pyramidal image matching in crown-surface reconstruction. The effectiveness of the approach is illustrated using an example of a redwood tree on 1:2,400-scale aerial photographs.