A novel method to model trees for building daylighting simulation using hemispherical photography

Abstract

The ability to simulate the effect of trees on natural light performance in buildings is contingent upon accurate simulation of light passing through the canopy. Accurate simulations require some assumption of leaf angle distribution (LAD) to compute canopy gap fractions. The ellipsoidal LAD can very closely approximate real plant canopies. The method requires calculation of leaf area density from observed distribution of gap fraction as a function of zenith angle. Two sets of Neem trees were studied (small and large). Hemispherical image acquisition and analysis for both groups was carried out to measure gap fractions. The results helped to develop a 3D tree model that was used to simulate the effect of tree interception of daylight. The illuminance levels were simulated under the tree model and the output results were validated against actual measurements using MBE and RMSE techniques (small trees: MBE = 0.33, RMSE = 0.20; large trees: MBE = 9.68, RMSE = 2.02).