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Incorporating Spectral and Directional Leaf Reflectance into Virtual Plant Models via Phong Shader Parameter Fitting.
Jens Balasus1, Felix Wirth1, Alexander Herzog1
1Laboratory of Adaptive Lighting Systems and Visual Processing, Technical University of Darmstadt, Hochschulstr. 4a, 64289 Darmstadt, Germany.
Accurate virtual plant light simulations now incorporate spectral bidirectional reflectance distribution function (BRDF) data. This improves canopy micro-light climate analysis by using Phong model parameters for cucumber leaves, enhancing realism in agricultural and remote sensing applications.
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Area of Science:
- Plant science
- Computer graphics
- Optics
Background:
- Accurate light simulations in virtual plant models are crucial for understanding canopy micro-light environments.
- Current models often simplify leaf optical properties, neglecting spectral and angular variability described by the bidirectional reflectance distribution function (BRDF).
Purpose of the Study:
- To experimentally measure the spectral BRDF of cucumber leaves.
- To determine Phong reflectance model parameters for use in the GroIMP simulation environment.
- To enhance the realism of light modeling in virtual plant canopies.
Main Methods:
- Experimental measurement of spectral BRDF for cucumber leaves.
- Determination and optimization of Phong reflectance model parameters.
- Evaluation of the Phong model against a diffuse reflectance model and per-wavelength error analysis.
Main Results:
- The Phong model successfully replicated key BRDF features, including spectral and angular reflectance patterns.
- Increased diffuseness in green and far-red spectral regions was captured, though deviations occurred at high incidence angles.
- The Phong BRDF reduced per-wavelength error compared to a diffuse model between 30-60° incidence angles.
Conclusions:
- Phong model parameters provide a practical method for integrating wavelength- and direction-dependent leaf reflectance into virtual plant simulations.
- These parameters can be adapted for other leaf types using hemispherical reflectance measurements.
- The study enables more realistic light modeling within virtual canopies, benefiting applications like remote sensing and greenhouse optimization.

