Effects of Wind on Virtual Plants in Animation

This paper presents the Growth-Flow method for animating the effect of wind on the motion and growth of virtual plant branches and leaves. The method incorporates changes to the growth rate when a plant is exposed to winds with speeds higher than a threshold. In particular, growth rate is reduced in branch elongation, increased in the branch radius, reduced in leaf length, and increased in leaf thickness. In addition, when a plant is exposed to wind for long time periods, the branch growth angle is changed to align more closely with the wind vector. The Growth-Flow method incorporates all these effects on growth and motion due to wind in one algorithm. 1. Introduction To enhance the realism of virtual plants, the effects of wind on the motion and growth of plants should be modeled. The effects of wind blowing through trees and especially its effects on branches have been extensively studied in computer animation. To date, only a few computer animation researchers have studied the effect of wind on leaf motion, with no consideration of the effects of wind on the growth of virtual plants. Plants are affected by wind immediately through physical motion and over time through changes in growth. Wind contact with a plant immediately causes physical motion by bending, swaying, or twisting the stem or leaves. Studies on branch movement in trees have approached the issue using physically based methods [1–4], procedurally based methods [5–8], motion capture [9], simulation [10], and shell dynamics [11]. Studies have examined leaf motion with respect to flow [12], biomechanics [13], spring and rotational movement [14], wilting [15], response to wind by broadleaf types [16], response to wind by both broadleaf and needle leaves [14], as a component of overall plant motion [10], and as part of shell space [11]. In addition, animation with leaf growth effects has been performed using a physically based approach without any consideration of wind [17]. Over time, plant growth is affected by wind, according to its strength and duration. Plants respond in three major ways: the girth of the stem is increased, the length of the stem is decreased, and the direction of growth is changed. The leaves of the plant also change in two ways: their thickness is increased and their shape becomes closer to round and stunted [18, 19]. This paper proposes the Growth-Flow method for animating the effect of wind on the motion and growth of stems and leaves of virtual plants. Incorporating the effects of wind on growth into a virtual plant that supports motion is an original contribution