% 在这里编写计算光照强度的代码 % 输入参数： % - 太阳高度角 sun_altitude 和太阳方位角 sun_azimuth % - 树冠内的点坐标 x 和 y % - 树木的高度 tree_height

以下是一个简单的计算光照强度的 MATLAB 代码：

function illuminance = calculateIlluminance(sun_altitude, sun_azimuth, x, y, tree_height)
    % 太阳方位角转弧度
    sun_azimuth = deg2rad(sun_azimuth);
    
    % 太阳高度角转弧度
    sun_altitude = deg2rad(sun_altitude);
    
    % 树冠顶部坐标
    tree_top = [x, y, tree_height];
    
    % 树冠中心坐标
    tree_center = [x, y, tree_height/2];
    
    % 树冠直径
    tree_diameter = tree_height/2;
    
    % 计算太阳方向向量
    sun_dir = [cos(sun_azimuth)*sin(sun_altitude), sin(sun_azimuth)*sin(sun_altitude), cos(sun_altitude)];
    
    % 计算树冠顶部到太阳的向量
    tree_top_to_sun = sun_dir - tree_top;
    
    % 计算树冠中心到太阳的向量
    tree_center_to_sun = sun_dir - tree_center;
    
    % 计算太阳到树冠顶部的距离
    d_top = norm(tree_top_to_sun);
    
    % 计算太阳到树冠中心的距离
    d_center = norm(tree_center_to_sun);
    
    % 如果太阳在树冠上方，则无光照
    if dot(tree_top_to_sun, [0, 0, -1]) >= 0
        illuminance = 0;
        return;
    end
    
    % 如果太阳在树冠下方，则光照强度为直射光照强度
    if dot(tree_center_to_sun, [0, 0, -1]) <= 0
        illuminance = calculateDirectIlluminance(sun_altitude);
        return;
    end
    
    % 计算树冠底部的圆
    base_circle = [x, y, 0];
    r = tree_diameter/2;
    [xc, yc] = circleLineIntersect(base_circle(1), base_circle(2), r, sun_dir(1), sun_dir(2), tree_center(1), tree_center(2));
    if isempty(xc) || isempty(yc)
        illuminance = calculateDirectIlluminance(sun_altitude);
        return;
    end
    
    % 计算树冠底部的法向量
    normal_vector = [0, 0, -1];
    
    % 计算光照强度
    illuminance = calculateIlluminanceAtPoint(sun_dir, normal_vector, d_center, d_top, tree_diameter);
end

function [x, y] = circleLineIntersect(x0, y0, r, a, b, x1, y1)
    % 计算二次方程参数
    A = a^2 + b^2;
    B = 2*a*(x1-x0) + 2*b*(y1-y0);
    C = (x1-x0)^2 + (y1-y0)^2 - r^2;
    
    % 计算判别式
    delta = B^2 - 4*A*C;
    
    if delta < 0
        x = [];
        y = [];
        return;
    end
    
    % 计算交点坐标
    t1 = (-B + sqrt(delta)) / (2*A);
    t2 = (-B - sqrt(delta)) / (2*A);
    x = [x0 + a*t1, x0 + a*t2];
    y = [y0 + b*t1, y0 + b*t2];
end

function illuminance = calculateDirectIlluminance(sun_altitude)
    % 计算直射光照强度
    illuminance = 1361 * sin(sun_altitude);
end

function illuminance = calculateIlluminanceAtPoint(sun_dir, normal_vector, d_center, d_top, tree_diameter)
    % 计算树冠表面的法向量
    surface_normal = normal_vector ./ norm(normal_vector);
    
    % 计算太阳光线与树冠表面的夹角
    cos_theta = dot(surface_normal, sun_dir);
    
    % 计算树冠表面到太阳的距离
    d_surface = d_center * cos_theta + sqrt(d_top^2 - d_center^2 * (1-cos_theta^2));
    
    % 计算光照强度
    illuminance = calculateDirectIlluminance(acos(d_center/d_top)) * cos_theta^2 * exp(-0.5 * (d_surface/tree_diameter)^2);
end

其中，`circleLineIntersect` 函数用于计算直线和圆的交点坐标，`calculateDirectIlluminance` 函数用于计算直射光照强度，`calculateIlluminanceAtPoint` 函数用于计算某个点的光照强度。