Modélisation de la structure géométrique du maïs

A model of maize plant morphology has been presented. The different plant parts are described with simple parametric equations: second order polynomials and conicals. The plant is represented by its number of leaves and by the vertical distance between 2 adjacent leaves which is related to its insertion height (fig 5; table I). The leaf is represented by a model of a fully-developed leaf (figs 2, 3) and by a shape model of the central vein (figs 1, 4). The developed-leaf model involves leaf length which is related to its insertion height (fig 7; table III), a parameter relating its maximum width to its length (fig 6; table II) and a shape parameter, related to its sheathing (figs 3, 8, 9). The ascendant and descendant parts of the central vein are modeled as an arc of a parabola for the former and as an arc of an ellipse for the latter (fig 4). This model can be summarized by 6 shape parameters: the insertion angle of the leaf and parabola curvature, the curvilinear abscissa of the 2-arc junction and the angle formed by the 2 arcs, the elongation and the angular curvature of the ellipse. Discontinuity of the first derivative at the junction is allowed. In order to test the model, a data set of 56 maize plants is used. Leaf sizes were measured and the central vein shapes were digitalized (fig 1). The model is adjusted according to these experimental data, using a non-linear regression algorithm. The central vein model exhibits a very good ability to represent the various shapes observed (fig 10). Statistical distributions of the different model parameters are presented and discussed (fig 11). The developed-leaf model allows an estimation of leaf area (fig 12) and the whole model is used to estimate the leaf inclination distribution function of the canopy. Comparison with the results of the classical leaf profile method is satisfactory (fig 13). Dans cette étude, on présente et teste un modèle permettant une description détaillée de la structure géométrique du maïs. Chaque élément de la plante est décrit à l’aide de relations paramétriques simples. Le pied est représenté par son nombre de feuilles et par les distances entre les points d’insertion de 2 feuilles successives. La feuille est décrite par un modèle de feuille développée et par un modèle de nervure centrale. La feuille développée est représentée par sa longueur, un paramètre reliant sa plus grande largeur à sa longueur et un paramètre de forme, lié à son degré d’engainement. La nervure centrale est