© 2005 Heron Publishing—Victoria, Canada
A method for 3D reconstruction of tree crown volume from photographs: assessment with 3D-digitized plants
J. Phattaralerphong (1, 2, 3) and H. Sinoquet (1)
1. UMR PIAF INRA-UBP, Site de Crouelle, 234 Avenue du Brézet, 63039 Clermont-Ferrand Cedex 2, France / 2. Department of Botany, Faculty of Science, Kasetsart University, Bangkok, 10900, Thailand / 3. Corresponding author (agrjes@yahoo.com) / Received October 5, 2004; accepted February 18, 2005; published online August 1, 2005
Summary
We developed a method for reconstructing tree crown volume from a set of eight photographs taken from the N, S, E, W, NE,
NW, SE and SW. This photographic method of reconstruction includes three steps. First, canopy height and diameter are estimated
from each image from the location of the topmost, rightmost and leftmost vegetated pixel; second, a rectangular bounding box
around the tree is constructed from canopy dimensions derived in Step 1, and the bounding box is divided into an array of
voxels; and third, each tree image is divided into a set of picture zones. The gap fraction of each picture zone is calculated
from image processing. A vegetated picture zone corresponds to a gap fraction of less than 1. Each picture zone corresponds
to a beam direction from the camera to the target tree, the equation of which is computed from the zone location on the picture
and the camera parameters. For each vegetated picture zone, the ray-box intersection algorithm (Glassner 1989) is used to
compute the sequence of voxels intersected by the beam. After processing all vegetated zones, voxels that have not been intersected
by any beam are presumed to be empty and are removed from the bounding box. The estimation of crown volume can be refined
by combining several photographs from different view angles. The method has been implemented in a software package called
Tree Analyzer written in C++.
The photographic method was tested with three-dimensional (3D) digitized plants of walnut, peach, mango and olive. The 3D-digitized
plants were used to estimate crown volume directly and generate virtual perspective photographs with POV-Ray Version 3.5 (Persistence
of Vision Development Team). The locations and view angles of the camera were manually controlled by input parameters. Good
agreement between measured data and values inferred from the photographic method were found for canopy height, diameter and
volume. The effects of voxel size, size of picture zoning, location of camera and number of pictures were also examined.
Keywords:
crown dimension, gap fraction, image processing, perspective image, Tree Analyzer.
