【threejs】计算矩阵、网格等总面积

核心思路

将面分为无数个三角面 ，使用向量计算面积

/**
* data [
* [  [x,y,z],[x,y,z],[x,y,z],[x,y,z],  ],
*  [  [x,y,z],[x,y,z],[x,y,z],[x,y,z],  ],
* [  [x,y,z],[x,y,z],[x,y,z],[x,y,z],  ],
* .......
* ]
*/
// 计算表面积
const calculateFaceArea = (data) => {
    let area = 0
    let max_i = data.length
    let max_j = data[0].length
    for (let i = 1; i < max_i; i++) {
        for (let j = 1; j < max_j; j++) {
            let p = data[i][j]
            let p1 = data[i][j - 1]
            let p2 = data[i - 1][j - 1]
            let p3 = data[i - 1][j]
            if (p && p1 && p2) {
                let a1 = getTriangleArea(...p, ...p1, ...p2)
                area += a1
            }
            if (p && p2 && p3) {
                let a1 = getTriangleArea(...p, ...p2, ...p3)
                area += a1
            }
        }
    }

    return area
}
// 计算三角面面积
const getTriangleArea = (x1, y1, z1, x2, y2, z2, x3, y3, z3) => {
    var v1 = [x1 - x2, y1 - y2, z1 - z2];
    var v2 = [x1 - x3, y1 - y3, z1 - z3];

    var crossProduct = [
        v1[1] * v2[2] - v1[2] * v2[1],
        v1[2] * v2[0] - v1[0] * v2[2],
        v1[0] * v2[1] - v1[1] * v2[0]
    ];

    var area = 0.5 * Math.sqrt(
        crossProduct[0] * crossProduct[0] +
        crossProduct[1] * crossProduct[1] +
        crossProduct[2] * crossProduct[2]
    );

    return area;
}
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