Java3d read each polygon of an 3d-object

问题

I'm using Java3d (VERSION 1.6) and am trying to read all polygons from any object.

I loaded one object using following code:

private BranchGroup loadObj(String p) {
        BranchGroup objRoot = new BranchGroup(); 
        TransformGroup tg = new TransformGroup();
        Transform3D t3d = new Transform3D();
        t3d.setScale(0.3);
        Matrix4d matrix = new Matrix4d();
        t3d.get(matrix);
        try
        {   
            Scene s = null;
            ObjectFile f = new ObjectFile ();
            String basepath = new File(p).getAbsolutePath();
            System.out.println(basepath);
            f.setBasePath(basepath);

            f.setFlags (0);

            s = f.load (s1);

            s.getSceneGroup().setBoundsAutoCompute(true);
            tg.addChild (s.getSceneGroup ());


            objRoot.addChild(tg);
            bounds.add(objRoot.getBounds());
            objRoot.compile();

        }

Now I like to read the computed polygons from that BranchGroup or Scene Object and put each in a class of mainly an array of Point3d's. With that class I build some algorithms to search for specific points and stuff. So how would I get these polygons?

The reason I need it is because I'm trying to "walk" over an uneven surface. I can't use BoundingBoxes or spheres, for that is not precise enough. I would appreciate a different solution as well!

EDIT: With the help of gouessej I got so far:

    try
    {   
        Scene s = null;
        ObjectFile f = new ObjectFile ();
        String basepath = new File(p).getAbsolutePath();
        System.out.println(basepath);
        f.setBasePath(basepath);

        f.setFlags (ObjectFile.TRIANGULATE);

        String s1 = p;
        s = f.load (s1);

        BranchGroup branch = s.getSceneGroup();
        branch.setBoundsAutoCompute(true);
        Shape3D shape = (Shape3D)branch.getChild(0);
        Geometry g = shape.getGeometry();
        TriangleArray ta = (TriangleArray)shape.getGeometry();
        System.out.println(ta.getVertexCount()); // Prints around 95.000, sounds about right
        System.out.println(ta.getVertexFormat()); // prints 387

        double[] coords = ta.getCoordRefDouble(); // line: 526; Here it throws the exception


        System.out.println(Arrays.toString(coords));  


        tg.addChild (branch);


        objRoot.addChild(tg);

        bounds.add(objRoot.getBounds());
        System.out.println();
        objRoot.compile();

    }

But on the line ta.getCoordRefDouble(), it throws me an Exception:

Exception in thread "main" java.lang.IllegalStateException: GeometryArray: cannot access individual array references in INTERLEAVED mode
    at javax.media.j3d.GeometryArray.getCoordRefDouble(GeometryArray.java:5755)
    at com.object.simpleTest.Test1.loadObj(Test1.java:526)
    at com.object.simpleTest.Test1.<init>(Test1.java:428)
    at com.object.simpleTest.Test1.main(Test1.java:686)

What does it mean and how to fix it?

回答1:

At first, Java 3D is NOT dead as you can see here (please edit your question).

Secondly, you can look at the Java documentation of the class ObjectFile. I advise you to use the flag "TRIANGULATE" to be sure to get a polygon array containing only convex polygons to ease your computations.

The branch group of your Scene object contains one Shape3D object. This Shape3D object contains a Geometry object, it stores your polygons. The source code of ObjectFile is here. Look at this line.

Edit.: You can get the BranchGroup of your scene by calling Scene.getSceneGroup(). You can see that the group is added into the scene here. Call Group.getAllChildren(), loop on all children, use instanceof to check whether a child is an instance of Shape3D. For each Shape3D, call getGeometry() or getAllGeometries(). The geometry should be a GeometryArray, maybe a TriangleArray. getCoordRefBuffer() might not work exactly in the same way in Java 3D 1.6 because we removed J3DBuffer, use getCoordRefDouble(), getCoordRefFloat() or any variant of getCoordinate() or getCoordinates(). Please ensure that you use Java 3D 1.6 so that we are talking about the same code and the same version. Older versions are obsolete and unmaintained.

Edit.2: Rather call getInterleavedVertices() as its name implies if the vertices are interleaved. Keep in mind that it might contain the normals too (in first position), not only the vertex coordinates (in second position): nx ny nz vx vy vz

来源：https://stackoverflow.com/questions/25714777/java3d-read-each-polygon-of-an-3d-object