Fig. 1

Example of leaf inclination angle measurements from leveled photography. The measure of leaf inclination angle requires the identification of a hypothetical leaf plane xy, from which the leaf surface normal \( \overline{N} \) is calculated with respect to the zenith (z). In a 3-D space, calculation of the leaf surface normal requires the knowledge of the azimuth rotation angle φ, which is calculated from the 3-D coordinates of the leaves (right side of the figure). In a 2-D space, such as a digital image, the only measurable leaf normal is that oriented perpendicular to the camera viewing direction, since the leaf inclination plane is parallel to the leaves (the red dashed line on the left side of the figure)