Three-dimensional digital model of a maize plant

Mechanistic modeling of crop interactions with the atmosphere requires knowledge of the canopy architecture. For example, studies of light and rainfall interception and microwave radiative transfer modeling have motivated the development of a number of virtual canopies by agronomists, computer scientists, and hydrologists. While a number of canopy measuring techniques are already available, recent improvements in digital photography and the availability of affordable commercial photogrammetry packages have created an opportunity to develop highly detailed three-dimensional digital models of maize canopies. Here, we present a non-destructive one-man methodology to digitize plants that uses an unmodified consumer grade digital single-lens reflex (SLR) camera and commercially available photogrammetry software. This methodology allows tracking of individual plant development, which was not possible in earlier techniques. The construction of the digital plant model is divided into three parts: plant preparation, where several artificial targets are placed on the plant and their relative distances are measured; leaf digitizing in which the targets are marked and referenced by the software, thereby allowing the photographs to be oriented; and the creation of three-dimensional models of individual leaves and the final model buildup when, through cross-referencing, the complete digital plant model is arranged. We demonstrate the applicability of the presented methodology by digitizing the same plant at two different stages of development (6 and 10 leaves) and subsequently assessing the models’ precision. In both cases, the objective is to define the edges and mid-rib of the leaves as well as their vertical and horizontal orientation; this allows the calculation of geometric descriptive parameters including plant area, leaf overlap, leaf area index, and gap fraction. The two presented models were built from 48 and 119 pictures, respectively, which correspond to 348 and 1553 three-dimensional points.