用JavaScript计算STL文件的边界框

Question

所以我正在使用这个 npm 包：node-stl

而且效果很好。然而，正则表达式语法、数学和几何计算让我有些困惑。尤其是同时。

基本上我想要实现的是扩展脚本来计算STL的边界框。

这是计算STL体积和重量的主要文件parsed/read。

var fs = require('fs');

// Vertex
function Vertex (v1,v2,v3) {
    this.v1 = Number(v1);
    this.v2 = Number(v2);
    this.v3 = Number(v3);
}

// Vertex Holder
function VertexHolder (vertex1,vertex2,vertex3) {
    this.vert1 = vertex1;
    this.vert2 = vertex2;
    this.vert3 = vertex3;
}

// transforming a Node.js Buffer into a V8 array buffer
function _toArrayBuffer (buffer) {
    var 
    ab = new ArrayBuffer(buffer.length),
    view = new Uint8Array(ab);

    for (var i = 0; i < buffer.length; ++i) {
        view[i] = buffer[i];
    }
    return ab;
}

// calculation of the triangle volume
// source: 
function _triangleVolume (vertexHolder) {
    var 
    v321 = Number(vertexHolder.vert3.v1 * vertexHolder.vert2.v2 * vertexHolder.vert1.v3),
    v231 = Number(vertexHolder.vert2.v1 * vertexHolder.vert3.v2 * vertexHolder.vert1.v3),
    v312 = Number(vertexHolder.vert3.v1 * vertexHolder.vert1.v2 * vertexHolder.vert2.v3),
    v132 = Number(vertexHolder.vert1.v1 * vertexHolder.vert3.v2 * vertexHolder.vert2.v3),
    v213 = Number(vertexHolder.vert2.v1 * vertexHolder.vert1.v2 * vertexHolder.vert3.v3),
    v123 = Number(vertexHolder.vert1.v1 * vertexHolder.vert2.v2 * vertexHolder.vert3.v3);
    return Number(1.0/6.0)*(-v321 + v231 + v312 - v132 - v213 + v123);
}

// parsing an STL ASCII string
function _parseSTLString (stl) {
    var totalVol = 0;
    // yes, this is the regular expression, matching the vertexes
    // it was kind of tricky but it is fast and does the job
    var vertexes = stl.match(/facet\s+normal\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+outer\s+loop\s+vertex\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+vertex\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+vertex\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+endloop\s+endfacet/g);

    vertexes.forEach(function (vert) {
        var preVertexHolder = new VertexHolder();
        vert.match(/vertex\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s+([-+]?\b(?:[0-9]*\.)?[0-9]+(?:[eE][-+]?[0-9]+)?\b)\s/g).forEach(function (vertex, i) {
            var tempVertex  = vertex.replace('vertex', '').match(/[-+]?[0-9]*\.?[0-9]+/g);
            var preVertex   = new Vertex(tempVertex[0],tempVertex[1],tempVertex[2]);
            preVertexHolder['vert'+(i+1)] = preVertex;
        });
        var partVolume = _triangleVolume(preVertexHolder);
        totalVol += Number(partVolume);
    })

    var volumeTotal = Math.abs(totalVol)/1000;
    return {
        volume: volumeTotal,        // cubic cm
        weight: volumeTotal * 1.04  // gm
    }
}

// parsing an STL Binary File
// (borrowed some code from here: https://github.com/mrdoob/three.js/blob/master/examples/js/loaders/STLLoader.js)
function _parseSTLBinary (buf) {
    buf = _toArrayBuffer(buf);

    var 
    headerLength    = 80,
    dataOffset      = 84,
    faceLength      = 12*4 + 2,
    le = true; // is little-endian

    var 
    dvTriangleCount = new DataView(buf, headerLength, 4),
    numTriangles    = dvTriangleCount.getUint32(0, le),
    totalVol        = 0;

    for (var i = 0; i < numTriangles; i++) {
        var 
        dv          = new DataView(buf, dataOffset + i*faceLength, faceLength),
        normal      = new Vertex(dv.getFloat32(0, le), dv.getFloat32(4, le), dv.getFloat32(8, le)),
        vertHolder  = new VertexHolder();
        for(var v = 3; v < 12; v+=3) {
            var vert = new Vertex(dv.getFloat32(v*4, le), dv.getFloat32((v+1)*4, le), dv.getFloat32( (v+2)*4, le ) );
            vertHolder['vert'+(v/3)] = vert;
        }
        totalVol += _triangleVolume(vertHolder);
    }

    var volumeTotal = Math.abs(totalVol)/1000;
    return {
        volume: volumeTotal,        // cubic cm
        weight: volumeTotal * 1.04  // gm
    }
}

// NodeStl
// =======
// > var stl = NodeStl(__dirname + '/myCool.stl');
// > console.log(stl.volume + 'cm^3');
// > console.log(stl.weight + 'gm');
function NodeStl (stlPath) {
    var 
    buf = fs.readFileSync(stlPath),
    isAscii = true;

    for (var i=0, len=buf.length; i<len; i++) {
        if (buf[i] > 127) { isAscii=false; break; }
    }

    if (isAscii)
        return _parseSTLString(buf.toString());
    else
        return _parseSTLBinary(buf);
}

module.exports = NodeStl;

如果有人能帮我解决这个问题那就太好了。我知道，而且感觉很简单。我只需要知道不同方向 (x,y,z) 的 max/min，然后就可以计算边界框。

但我不明白这里的 x、y 和 z 的 max/min 是什么。有想法请回答

Answer 1

我创建了一个新分支https://github.com/johannesboyne/node-stl/tree/boundingbox能否请您验证应用的算法是否有效？

最好，约翰内斯

编辑：如果分支稳定 -> 工作我会把它推到 v.0.1.0（不知道为什么它仍然是 0.0.1）

用JavaScript计算STL文件的边界框

Calculate the bounding box of STL file with JavaScript

node.js

npm

3d-model

stl-fileformat