Mesure de la superficie et de l'orientation foliaire par vision stéréoscopique | Leaf area and leaf orientation measurement by using stereo-vision
2013
Leemans, Vincent | Dumont, Benjamin | Destain, Marie-France
This paper presents a 3D stereo-vision system aiming at the measurement of plantcharacteristics. The method is intended to be used in an Ecotron where the availability ofplant material is limited and where crop should be characterised non destructively. The plantswere not considered as individuals, it was the crop as a whole that was characterised. Theleaf area index (LAI) was measured. It is an important property of vegetation, since itdetermines the photosynthetic primary production, the plant evaporation and characterises theplant growth. The average leaf angle (ALA) was also measured. For the computation, leafpixels were differentiated from soil pixels by using linear discriminant analysis. The stereovision system computed the distance to the camera of each pixel in the image in the regionwhere the pixels are present in both images. The observed area was computed on the basis ofthe average distance of the leaf pixels in the region. The leaf area was evaluated for eachtriplet of adjacent pixels by computing the cross product of the vectors defined by those threepoints. The sum gave the leaf area for the same region. The area of these triangles wassummed for all the pixels in the region and the ratio to the observed area gave the LAI. TheALA was the mean orientation of the pixel triplets. After calibration, the method was foundto present a coefficient of correlation of 0.93 with destructive reference measurements and aprecision of 0.12 for the LAI. It was possible to measure the LAI and the ALA from thegermination up to the ripening stage with a minimum of work load.
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