使用类似GeoJson的数据生成物体(建筑等)的功能逻辑

来源：cnblogs　　作者：tiancaiKG　　时间：2019/6/21 12:39:23　　对本文有异议

　　GeoJson作为一种模型传输格式, 用的最多的就是地图里面的各种简单模型了, 比如下图中很贴切的俄罗斯方块楼:

　　它的格式大概就是下面这样:

{
    "type": "FeatureCollection",
    "crs": {
        "type": "name",
        "properties": {
            "name": "EPSG:3857"
        }
    },
    "features": [{
        "type": "Feature",
        "id": 0,
        "geometry": {
            "type": "Polygon",
            "coordinates": [
                [
                    [-2066.3279353108665, -7427.2858673485389],
                    [-2071.2341353108641, -7436.5054673485392],
                    [-2090.8278353108617, -7426.2554673485392],
                    [-2092.9139353108621, -7430.4644673485382],
                    [-2096.9763353108574, -7438.1128673485382],
                    [-2089.4294353108708, -7441.1304673485392],
                    [-2091.4216353108641, -7448.0708673485387],
                    [-2090.0935353108653, -7448.4624673485378],
                    [-2086.7887353108672, -7449.4635673485391],
                    [-2087.0934353108605, -7450.4654673485384],
                    [-2077.6715353108593, -7453.5912673485382],
                    [-2071.241835310866, -7455.724267348538],
                    [-2070.8513353108574, -7455.8531673485377],
                    [-2070.5388353108574, -7454.7720673485383],
                    [-2066.2340353108593, -7440.1365673485379],
                    [-2064.8513353108574, -7440.5699673485396],
                    [-2064.2340353108593, -7438.5963673485385],
                    [-2064.3123353108676, -7437.5268673485389],
                    [-2068.0935353108653, -7436.5689673485394],
                    [-2064.1636353108624, -7428.1470673485383],
                    [-2066.3279353108665, -7427.2858673485389]
                ]
            ]
        },
        "properties": {
            "FID": 0,
            "CZWCODE": "4403050050110200020",
            "ADDRESS": "湾厦路2号海鲜交易中心",
            "NAME": "海鲜交易中心",
            "LAYERS": 2,
            "floor": 2,
            "height": 6,
            "朝向": -61.9803735785,
            "面积": 540.39058542500004,
            "ID": "4403050050110200020",
            "分类": " ",
            "usage": "商服"
        }
    }]
}

　　一般的多边形, 它是给了一个底面的各个顶点, 然后给了一个高度让你去生成简单模型, 这个顶点列表是有序的, 所以这个可能是个凹多边形. 这就关联到前面写的这篇文章了 : 二维空间内的三角剖分 -- (给出边缘顶点的例子)

通过三角剖分我们就能正确生成底面的所有三角面了, 然后底面加上高度就是顶面的所有三角面了, 然后因为底边和顶边是对齐的, 我们就可以按照顺序每个相对应的边组成一个四边形进行三角形划分. 逻辑实在过于简单, 不解释了.

问题在于三角形面的朝向问题, 这里只计算了三角面, 并没有对朝向进行计算, 如果要进行朝向计算的话就要对每个三角面的朝向是否向外(相对于该多边形来说), 这样逻辑会很复杂, 这里为了简便直接把所有三角形添加一个朝向相反的三角形即可.

　　代码 :

        public static Mesh CreateGeoJsonMesh(List<Vector3> basePoints, float height)
        {
            Mesh mesh = new Mesh();
            mesh.name = "GeoJsonMesh";
            List<Vector3> vertices = new List<Vector3>();
            // bottom and top triangles
            var baseVerts = Triangulation.GenericTriangulate(basePoints);
            var topVerts = new List<Vector3>();
            for (int i = 0; i < baseVerts.Count; i++)
            {
                var p = baseVerts[i];
                p.y += height;
                topVerts.Add(p);
            }
            vertices.AddRange(baseVerts);
            vertices.AddRange(topVerts);
            // vertical triangles
            for(int i = 0; i < basePoints.Count; i++)
            {
                bool loop = i + 1 >= basePoints.Count;
                var p0 = basePoints[i];
                var p1 = basePoints[loop ? 0 : i + 1];
                var p2 = p1 + Vector3.up * height;
                var p3 = p0 + Vector3.up * height;
                vertices.Add(p0);
                vertices.Add(p1);
                vertices.Add(p2);
                vertices.Add(p0);
                vertices.Add(p2);
                vertices.Add(p3);
            }
            // add inverse triangles for clip
            for(int i = 0, imax = vertices.Count; i < imax; i += 3)
            {
                vertices.Add(vertices[i + 2]);
                vertices.Add(vertices[i + 1]);
                vertices.Add(vertices[i]);
            }
            // set vertices
            mesh.vertices = vertices.ToArray();
            // set triangles
            int[] triangles = new int[vertices.Count];
            for(int i = 0; i < vertices.Count; i++)
            {
                triangles[i] = i;
            }
            mesh.triangles = triangles;
            // set uvs
            Vector2[] uv = new Vector2[vertices.Count];
            for(int i = 0; i < vertices.Count; i++)
            {
                uv[i] = Vector2.zero;
            }
            mesh.uv = uv;
            mesh.RecalculateNormals();
            mesh.RecalculateBounds();
            mesh.RecalculateTangents();
            return mesh;
        }

　　测试代码, 还是那个凹字 :

        List<Vector3> points = new List<Vector3>();
        points.Add(new Vector3(0.5f, 1, 0.5f));
        points.Add(new Vector3(0.5f, 1, 1.5f));
        points.Add(new Vector3(1.5f, 1, 1.5f));
        points.Add(new Vector3(1.5f, 1f, -1f));
        points.Add(new Vector3(-1.5f, 1f, -1f));
        points.Add(new Vector3(-1.5f, 1f, 1.5f));
        points.Add(new Vector3(-0.5f, 1f, 1.5f));
        points.Add(new Vector3(-0.5f, 1f, 0.5f));
        var go = GameObject.CreatePrimitive(PrimitiveType.Quad);
        var mesh = WhiteHouseRuntimeMaker.CreateGeoJsonMesh(points, 5.0f);
        go.GetComponent<MeshFilter>().mesh = mesh;
        go.GetComponent<MeshCollider>().sharedMesh = mesh;