Mesher (.NET)

This example loads a .implicit file, samples the body’s field function (ImplicitBody.Value, backed by ntop_core_query_field) over a regular 3D grid sized from the body’s bounding box (ntop_core_query_bounding_box), and reconstructs the surface using a from-scratch implementation of the “Marching Cubes” algorithm. The resulting triangle soup is written out as an STL file.

MainProgram.cs

using System;
using System.IO;

using nTop.Core.Examples.Utils;
using nTop.Core.Wrapper;

namespace nTop.Core.Examples.Mesher
{
    public partial class Program
    {
        static void Main()
        {
            // Get .implicit file path from user
            string path = CLI.LoadPrompt();

            // Create an ImplicitBody object
            var body = new ImplicitBody(path);

            // Invent some reasonable grid counts (number of voxels)
            int n = 200;
            int[] gridCounts = Mesher.GetGridCounts(body, n);

            // Make a box that's 10% larger than body's bounding box
            var boundingBox = body.Box;
            var paddedBox = boundingBox.Enlarge(1.1);

            // Do the meshing
            var triList = Mesher.CreateMesh(body, paddedBox, gridCounts);

            // Free the memory used by the implicit in the library
            body.Release();

            // Write out an STL file and display it in default viewer
            string meshFilePath = $"{Directory.GetCurrentDirectory()}{Path.DirectorySeparatorChar}mesher.stl";
            WriteSTL(triList, meshFilePath);
            System.Console.WriteLine($"Mesh data written to {meshFilePath}");
        }
    }
}

Mesher.cs

using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

using nTop.Core.Wrapper;

/// <summary>A simple implementation of the "Marching Cubes" algorithm</summary>
/// <remarks> Based on code from here: http://paulbourke.net/geometry/polygonise/ </remarks>

namespace nTop.Core.Examples.Mesher
{
    public class Mesher
    {
        /// <summary>Creates an array of triangles representing a given implicit body</summary>
        /// <param name="body">The implicit body to be meshed</param>
        /// <param name="box">The box inside which we want to construct the triangles</param>
        /// <param name="gridCounts">Counts of how many cells to use in the x,y,z directions</param>
        /// <returns>List of triangles, in no particular order (i.e. triangle soup)</returns>
        public static List<Triangle> CreateMesh(ImplicitBody body, Box3d box, int[] gridCounts)
        {
            int nx = gridCounts[0];
            int ny = gridCounts[1];
            int nz = gridCounts[2];

            double dx = (box.MaxX - box.MinX) / (nx - 1);
            double dy = (box.MaxY - box.MinY) / (ny - 1);
            double dz = (box.MaxZ - box.MinZ) / (nz - 1);

            // Calculate F(x,y,z) at points of a regular 3D array
            double[,,] valueArray = CalculateValues(body, box.MinPoint, dx, dy, dz, nx, ny, nz);

            Cell cell;
            List<Triangle> triList = new List<Triangle>();

            // Loop over cells, triangulating the surface within each of them
            for (int i = 0; i < nx - 1; i++)
            {
                for (int j = 0; j < ny - 1; j++)
                {
                    for (int k = 0; k < nz - 1; k++)
                    {
                        //Triangulate within the cell, and add resulting triangles to triList
                        cell = CreateCell(valueArray, box.MinPoint, dx, dy, dz, i, j, k);
                        Triangle[] cellTris = TriangulateCell(cell);
                        triList.AddRange(cellTris);
                    }
                }
            }

            return triList;
        }

        /// <summary>Calculate values of body's implicit function at cell corners</summary>
        /// <param name="body">The body</param>
        /// <param name="pt">The minXYZ corner of the box</param>
        /// <param name="dx">Step in x-direction</param>
        /// <param name="dy">Step in y-direction</param>
        /// <param name="dz">Step in z-direction</param>
        /// <param name="nx">Number of steps in x-direction</param>
        /// <param name="ny">Number of steps in y-direction</param>
        /// <param name="nz">Number of steps in z-direction</param>
        /// <returns>3D array of values of F(x,y,z)</returns>
        private static double[,,] CalculateValues(ImplicitBody body, Vector pt, double dx, double dy, double dz, int nx, int ny, int nz)
        {
            double x0 = pt.X;
            double y0 = pt.Y;
            double z0 = pt.Z;

            // Parallel version. About 3x faster than sequential one.
            double[,,] vals2 = new double[nx, ny, nz];
            Parallel.For
            (0, nx, i =>
                {
                    for (int j = 0; j < ny; j++)
                    {
                        for (int k = 0; k < nz; k++)
                        {
                            double x2 = x0 + i * dx;
                            double y2 = y0 + j * dy;
                            double z2 = z0 + k * dz;
                            vals2[i, j, k] = body.Value(x2, y2, z2);
                        }
                    }
                }      // End of lambda function
            );        // End of Parallel.For

            return vals2;
        }

        private static Cell CreateCell(double[,,] values, Vector pt, double dx, double dy, double dz, int i, int j, int k)
        {
            double x0 = pt.X + i * dx; double x1 = x0 + dx;
            double y0 = pt.Y + j * dy; double y1 = y0 + dy;
            double z0 = pt.Z + k * dz; double z1 = z0 + dz;

            Vector p0 = new Vector(x0, y0, z0); double v0 = values[i, j, k];
            Vector p1 = new Vector(x0, y1, z0); double v1 = values[i, j + 1, k];
            Vector p2 = new Vector(x1, y1, z0); double v2 = values[i + 1, j + 1, k];
            Vector p3 = new Vector(x1, y0, z0); double v3 = values[i + 1, j, k];
            Vector p4 = new Vector(x0, y0, z1); double v4 = values[i, j, k + 1];
            Vector p5 = new Vector(x0, y1, z1); double v5 = values[i, j + 1, k + 1];
            Vector p6 = new Vector(x1, y1, z1); double v6 = values[i + 1, j + 1, k + 1];
            Vector p7 = new Vector(x1, y0, z1); double v7 = values[i + 1, j, k + 1];

            Vector[] pts = { p0, p1, p2, p3, p4, p5, p6, p7 };
            double[] vals = { v0, v1, v2, v3, v4, v5, v6, v7 };

            Cell cell = new Cell(pts, vals);
            return cell;
        }

        #region edgeTable
        private static int[] edgeTable =
            {
                0x0  , 0x109, 0x203, 0x30a, 0x406, 0x50f, 0x605, 0x70c,
                0x80c, 0x905, 0xa0f, 0xb06, 0xc0a, 0xd03, 0xe09, 0xf00,
                0x190, 0x99 , 0x393, 0x29a, 0x596, 0x49f, 0x795, 0x69c,
                0x99c, 0x895, 0xb9f, 0xa96, 0xd9a, 0xc93, 0xf99, 0xe90,
                0x230, 0x339, 0x33 , 0x13a, 0x636, 0x73f, 0x435, 0x53c,
                0xa3c, 0xb35, 0x83f, 0x936, 0xe3a, 0xf33, 0xc39, 0xd30,
                0x3a0, 0x2a9, 0x1a3, 0xaa , 0x7a6, 0x6af, 0x5a5, 0x4ac,
                0xbac, 0xaa5, 0x9af, 0x8a6, 0xfaa, 0xea3, 0xda9, 0xca0,
                0x460, 0x569, 0x663, 0x76a, 0x66 , 0x16f, 0x265, 0x36c,
                0xc6c, 0xd65, 0xe6f, 0xf66, 0x86a, 0x963, 0xa69, 0xb60,
                0x5f0, 0x4f9, 0x7f3, 0x6fa, 0x1f6, 0xff , 0x3f5, 0x2fc,
                0xdfc, 0xcf5, 0xfff, 0xef6, 0x9fa, 0x8f3, 0xbf9, 0xaf0,
                0x650, 0x759, 0x453, 0x55a, 0x256, 0x35f, 0x55 , 0x15c,
                0xe5c, 0xf55, 0xc5f, 0xd56, 0xa5a, 0xb53, 0x859, 0x950,
                0x7c0, 0x6c9, 0x5c3, 0x4ca, 0x3c6, 0x2cf, 0x1c5, 0xcc ,
                0xfcc, 0xec5, 0xdcf, 0xcc6, 0xbca, 0xac3, 0x9c9, 0x8c0,
                0x8c0, 0x9c9, 0xac3, 0xbca, 0xcc6, 0xdcf, 0xec5, 0xfcc,
                0xcc , 0x1c5, 0x2cf, 0x3c6, 0x4ca, 0x5c3, 0x6c9, 0x7c0,
                0x950, 0x859, 0xb53, 0xa5a, 0xd56, 0xc5f, 0xf55, 0xe5c,
                0x15c, 0x55 , 0x35f, 0x256, 0x55a, 0x453, 0x759, 0x650,
                0xaf0, 0xbf9, 0x8f3, 0x9fa, 0xef6, 0xfff, 0xcf5, 0xdfc,
                0x2fc, 0x3f5, 0xff , 0x1f6, 0x6fa, 0x7f3, 0x4f9, 0x5f0,
                0xb60, 0xa69, 0x963, 0x86a, 0xf66, 0xe6f, 0xd65, 0xc6c,
                0x36c, 0x265, 0x16f, 0x66 , 0x76a, 0x663, 0x569, 0x460,
                0xca0, 0xda9, 0xea3, 0xfaa, 0x8a6, 0x9af, 0xaa5, 0xbac,
                0x4ac, 0x5a5, 0x6af, 0x7a6, 0xaa , 0x1a3, 0x2a9, 0x3a0,
                0xd30, 0xc39, 0xf33, 0xe3a, 0x936, 0x83f, 0xb35, 0xa3c,
                0x53c, 0x435, 0x73f, 0x636, 0x13a, 0x33 , 0x339, 0x230,
                0xe90, 0xf99, 0xc93, 0xd9a, 0xa96, 0xb9f, 0x895, 0x99c,
                0x69c, 0x795, 0x49f, 0x596, 0x29a, 0x393, 0x99 , 0x190,
                0xf00, 0xe09, 0xd03, 0xc0a, 0xb06, 0xa0f, 0x905, 0x80c,
                0x70c, 0x605, 0x50f, 0x406, 0x30a, 0x203, 0x109, 0x0
        };
        #endregion

        #region triTable
        private static int[,] triTable =
                    {{-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 8, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 1, 9, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 8, 3, 9, 8, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 2, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 8, 3, 1, 2, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {9, 2, 10, 0, 2, 9, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {2, 8, 3, 2, 10, 8, 10, 9, 8, -1, -1, -1, -1, -1, -1, -1},
                {3, 11, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 11, 2, 8, 11, 0, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 9, 0, 2, 3, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 11, 2, 1, 9, 11, 9, 8, 11, -1, -1, -1, -1, -1, -1, -1},
                {3, 10, 1, 11, 10, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 10, 1, 0, 8, 10, 8, 11, 10, -1, -1, -1, -1, -1, -1, -1},
                {3, 9, 0, 3, 11, 9, 11, 10, 9, -1, -1, -1, -1, -1, -1, -1},
                {9, 8, 10, 10, 8, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {4, 7, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {4, 3, 0, 7, 3, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 1, 9, 8, 4, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {4, 1, 9, 4, 7, 1, 7, 3, 1, -1, -1, -1, -1, -1, -1, -1},
                {1, 2, 10, 8, 4, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {3, 4, 7, 3, 0, 4, 1, 2, 10, -1, -1, -1, -1, -1, -1, -1},
                {9, 2, 10, 9, 0, 2, 8, 4, 7, -1, -1, -1, -1, -1, -1, -1},
                {2, 10, 9, 2, 9, 7, 2, 7, 3, 7, 9, 4, -1, -1, -1, -1},
                {8, 4, 7, 3, 11, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {11, 4, 7, 11, 2, 4, 2, 0, 4, -1, -1, -1, -1, -1, -1, -1},
                {9, 0, 1, 8, 4, 7, 2, 3, 11, -1, -1, -1, -1, -1, -1, -1},
                {4, 7, 11, 9, 4, 11, 9, 11, 2, 9, 2, 1, -1, -1, -1, -1},
                {3, 10, 1, 3, 11, 10, 7, 8, 4, -1, -1, -1, -1, -1, -1, -1},
                {1, 11, 10, 1, 4, 11, 1, 0, 4, 7, 11, 4, -1, -1, -1, -1},
                {4, 7, 8, 9, 0, 11, 9, 11, 10, 11, 0, 3, -1, -1, -1, -1},
                {4, 7, 11, 4, 11, 9, 9, 11, 10, -1, -1, -1, -1, -1, -1, -1},
                {9, 5, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {9, 5, 4, 0, 8, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 5, 4, 1, 5, 0, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {8, 5, 4, 8, 3, 5, 3, 1, 5, -1, -1, -1, -1, -1, -1, -1},
                {1, 2, 10, 9, 5, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {3, 0, 8, 1, 2, 10, 4, 9, 5, -1, -1, -1, -1, -1, -1, -1},
                {5, 2, 10, 5, 4, 2, 4, 0, 2, -1, -1, -1, -1, -1, -1, -1},
                {2, 10, 5, 3, 2, 5, 3, 5, 4, 3, 4, 8, -1, -1, -1, -1},
                {9, 5, 4, 2, 3, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 11, 2, 0, 8, 11, 4, 9, 5, -1, -1, -1, -1, -1, -1, -1},
                {0, 5, 4, 0, 1, 5, 2, 3, 11, -1, -1, -1, -1, -1, -1, -1},
                {2, 1, 5, 2, 5, 8, 2, 8, 11, 4, 8, 5, -1, -1, -1, -1},
                {10, 3, 11, 10, 1, 3, 9, 5, 4, -1, -1, -1, -1, -1, -1, -1},
                {4, 9, 5, 0, 8, 1, 8, 10, 1, 8, 11, 10, -1, -1, -1, -1},
                {5, 4, 0, 5, 0, 11, 5, 11, 10, 11, 0, 3, -1, -1, -1, -1},
                {5, 4, 8, 5, 8, 10, 10, 8, 11, -1, -1, -1, -1, -1, -1, -1},
                {9, 7, 8, 5, 7, 9, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {9, 3, 0, 9, 5, 3, 5, 7, 3, -1, -1, -1, -1, -1, -1, -1},
                {0, 7, 8, 0, 1, 7, 1, 5, 7, -1, -1, -1, -1, -1, -1, -1},
                {1, 5, 3, 3, 5, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {9, 7, 8, 9, 5, 7, 10, 1, 2, -1, -1, -1, -1, -1, -1, -1},
                {10, 1, 2, 9, 5, 0, 5, 3, 0, 5, 7, 3, -1, -1, -1, -1},
                {8, 0, 2, 8, 2, 5, 8, 5, 7, 10, 5, 2, -1, -1, -1, -1},
                {2, 10, 5, 2, 5, 3, 3, 5, 7, -1, -1, -1, -1, -1, -1, -1},
                {7, 9, 5, 7, 8, 9, 3, 11, 2, -1, -1, -1, -1, -1, -1, -1},
                {9, 5, 7, 9, 7, 2, 9, 2, 0, 2, 7, 11, -1, -1, -1, -1},
                {2, 3, 11, 0, 1, 8, 1, 7, 8, 1, 5, 7, -1, -1, -1, -1},
                {11, 2, 1, 11, 1, 7, 7, 1, 5, -1, -1, -1, -1, -1, -1, -1},
                {9, 5, 8, 8, 5, 7, 10, 1, 3, 10, 3, 11, -1, -1, -1, -1},
                {5, 7, 0, 5, 0, 9, 7, 11, 0, 1, 0, 10, 11, 10, 0, -1},
                {11, 10, 0, 11, 0, 3, 10, 5, 0, 8, 0, 7, 5, 7, 0, -1},
                {11, 10, 5, 7, 11, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {10, 6, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 8, 3, 5, 10, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {9, 0, 1, 5, 10, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 8, 3, 1, 9, 8, 5, 10, 6, -1, -1, -1, -1, -1, -1, -1},
                {1, 6, 5, 2, 6, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 6, 5, 1, 2, 6, 3, 0, 8, -1, -1, -1, -1, -1, -1, -1},
                {9, 6, 5, 9, 0, 6, 0, 2, 6, -1, -1, -1, -1, -1, -1, -1},
                {5, 9, 8, 5, 8, 2, 5, 2, 6, 3, 2, 8, -1, -1, -1, -1},
                {2, 3, 11, 10, 6, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {11, 0, 8, 11, 2, 0, 10, 6, 5, -1, -1, -1, -1, -1, -1, -1},
                {0, 1, 9, 2, 3, 11, 5, 10, 6, -1, -1, -1, -1, -1, -1, -1},
                {5, 10, 6, 1, 9, 2, 9, 11, 2, 9, 8, 11, -1, -1, -1, -1},
                {6, 3, 11, 6, 5, 3, 5, 1, 3, -1, -1, -1, -1, -1, -1, -1},
                {0, 8, 11, 0, 11, 5, 0, 5, 1, 5, 11, 6, -1, -1, -1, -1},
                {3, 11, 6, 0, 3, 6, 0, 6, 5, 0, 5, 9, -1, -1, -1, -1},
                {6, 5, 9, 6, 9, 11, 11, 9, 8, -1, -1, -1, -1, -1, -1, -1},
                {5, 10, 6, 4, 7, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {4, 3, 0, 4, 7, 3, 6, 5, 10, -1, -1, -1, -1, -1, -1, -1},
                {1, 9, 0, 5, 10, 6, 8, 4, 7, -1, -1, -1, -1, -1, -1, -1},
                {10, 6, 5, 1, 9, 7, 1, 7, 3, 7, 9, 4, -1, -1, -1, -1},
                {6, 1, 2, 6, 5, 1, 4, 7, 8, -1, -1, -1, -1, -1, -1, -1},
                {1, 2, 5, 5, 2, 6, 3, 0, 4, 3, 4, 7, -1, -1, -1, -1},
                {8, 4, 7, 9, 0, 5, 0, 6, 5, 0, 2, 6, -1, -1, -1, -1},
                {7, 3, 9, 7, 9, 4, 3, 2, 9, 5, 9, 6, 2, 6, 9, -1},
                {3, 11, 2, 7, 8, 4, 10, 6, 5, -1, -1, -1, -1, -1, -1, -1},
                {5, 10, 6, 4, 7, 2, 4, 2, 0, 2, 7, 11, -1, -1, -1, -1},
                {0, 1, 9, 4, 7, 8, 2, 3, 11, 5, 10, 6, -1, -1, -1, -1},
                {9, 2, 1, 9, 11, 2, 9, 4, 11, 7, 11, 4, 5, 10, 6, -1},
                {8, 4, 7, 3, 11, 5, 3, 5, 1, 5, 11, 6, -1, -1, -1, -1},
                {5, 1, 11, 5, 11, 6, 1, 0, 11, 7, 11, 4, 0, 4, 11, -1},
                {0, 5, 9, 0, 6, 5, 0, 3, 6, 11, 6, 3, 8, 4, 7, -1},
                {6, 5, 9, 6, 9, 11, 4, 7, 9, 7, 11, 9, -1, -1, -1, -1},
                {10, 4, 9, 6, 4, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {4, 10, 6, 4, 9, 10, 0, 8, 3, -1, -1, -1, -1, -1, -1, -1},
                {10, 0, 1, 10, 6, 0, 6, 4, 0, -1, -1, -1, -1, -1, -1, -1},
                {8, 3, 1, 8, 1, 6, 8, 6, 4, 6, 1, 10, -1, -1, -1, -1},
                {1, 4, 9, 1, 2, 4, 2, 6, 4, -1, -1, -1, -1, -1, -1, -1},
                {3, 0, 8, 1, 2, 9, 2, 4, 9, 2, 6, 4, -1, -1, -1, -1},
                {0, 2, 4, 4, 2, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {8, 3, 2, 8, 2, 4, 4, 2, 6, -1, -1, -1, -1, -1, -1, -1},
                {10, 4, 9, 10, 6, 4, 11, 2, 3, -1, -1, -1, -1, -1, -1, -1},
                {0, 8, 2, 2, 8, 11, 4, 9, 10, 4, 10, 6, -1, -1, -1, -1},
                {3, 11, 2, 0, 1, 6, 0, 6, 4, 6, 1, 10, -1, -1, -1, -1},
                {6, 4, 1, 6, 1, 10, 4, 8, 1, 2, 1, 11, 8, 11, 1, -1},
                {9, 6, 4, 9, 3, 6, 9, 1, 3, 11, 6, 3, -1, -1, -1, -1},
                {8, 11, 1, 8, 1, 0, 11, 6, 1, 9, 1, 4, 6, 4, 1, -1},
                {3, 11, 6, 3, 6, 0, 0, 6, 4, -1, -1, -1, -1, -1, -1, -1},
                {6, 4, 8, 11, 6, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {7, 10, 6, 7, 8, 10, 8, 9, 10, -1, -1, -1, -1, -1, -1, -1},
                {0, 7, 3, 0, 10, 7, 0, 9, 10, 6, 7, 10, -1, -1, -1, -1},
                {10, 6, 7, 1, 10, 7, 1, 7, 8, 1, 8, 0, -1, -1, -1, -1},
                {10, 6, 7, 10, 7, 1, 1, 7, 3, -1, -1, -1, -1, -1, -1, -1},
                {1, 2, 6, 1, 6, 8, 1, 8, 9, 8, 6, 7, -1, -1, -1, -1},
                {2, 6, 9, 2, 9, 1, 6, 7, 9, 0, 9, 3, 7, 3, 9, -1},
                {7, 8, 0, 7, 0, 6, 6, 0, 2, -1, -1, -1, -1, -1, -1, -1},
                {7, 3, 2, 6, 7, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {2, 3, 11, 10, 6, 8, 10, 8, 9, 8, 6, 7, -1, -1, -1, -1},
                {2, 0, 7, 2, 7, 11, 0, 9, 7, 6, 7, 10, 9, 10, 7, -1},
                {1, 8, 0, 1, 7, 8, 1, 10, 7, 6, 7, 10, 2, 3, 11, -1},
                {11, 2, 1, 11, 1, 7, 10, 6, 1, 6, 7, 1, -1, -1, -1, -1},
                {8, 9, 6, 8, 6, 7, 9, 1, 6, 11, 6, 3, 1, 3, 6, -1},
                {0, 9, 1, 11, 6, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {7, 8, 0, 7, 0, 6, 3, 11, 0, 11, 6, 0, -1, -1, -1, -1},
                {7, 11, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {7, 6, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {3, 0, 8, 11, 7, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 1, 9, 11, 7, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {8, 1, 9, 8, 3, 1, 11, 7, 6, -1, -1, -1, -1, -1, -1, -1},
                {10, 1, 2, 6, 11, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 2, 10, 3, 0, 8, 6, 11, 7, -1, -1, -1, -1, -1, -1, -1},
                {2, 9, 0, 2, 10, 9, 6, 11, 7, -1, -1, -1, -1, -1, -1, -1},
                {6, 11, 7, 2, 10, 3, 10, 8, 3, 10, 9, 8, -1, -1, -1, -1},
                {7, 2, 3, 6, 2, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {7, 0, 8, 7, 6, 0, 6, 2, 0, -1, -1, -1, -1, -1, -1, -1},
                {2, 7, 6, 2, 3, 7, 0, 1, 9, -1, -1, -1, -1, -1, -1, -1},
                {1, 6, 2, 1, 8, 6, 1, 9, 8, 8, 7, 6, -1, -1, -1, -1},
                {10, 7, 6, 10, 1, 7, 1, 3, 7, -1, -1, -1, -1, -1, -1, -1},
                {10, 7, 6, 1, 7, 10, 1, 8, 7, 1, 0, 8, -1, -1, -1, -1},
                {0, 3, 7, 0, 7, 10, 0, 10, 9, 6, 10, 7, -1, -1, -1, -1},
                {7, 6, 10, 7, 10, 8, 8, 10, 9, -1, -1, -1, -1, -1, -1, -1},
                {6, 8, 4, 11, 8, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {3, 6, 11, 3, 0, 6, 0, 4, 6, -1, -1, -1, -1, -1, -1, -1},
                {8, 6, 11, 8, 4, 6, 9, 0, 1, -1, -1, -1, -1, -1, -1, -1},
                {9, 4, 6, 9, 6, 3, 9, 3, 1, 11, 3, 6, -1, -1, -1, -1},
                {6, 8, 4, 6, 11, 8, 2, 10, 1, -1, -1, -1, -1, -1, -1, -1},
                {1, 2, 10, 3, 0, 11, 0, 6, 11, 0, 4, 6, -1, -1, -1, -1},
                {4, 11, 8, 4, 6, 11, 0, 2, 9, 2, 10, 9, -1, -1, -1, -1},
                {10, 9, 3, 10, 3, 2, 9, 4, 3, 11, 3, 6, 4, 6, 3, -1},
                {8, 2, 3, 8, 4, 2, 4, 6, 2, -1, -1, -1, -1, -1, -1, -1},
                {0, 4, 2, 4, 6, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 9, 0, 2, 3, 4, 2, 4, 6, 4, 3, 8, -1, -1, -1, -1},
                {1, 9, 4, 1, 4, 2, 2, 4, 6, -1, -1, -1, -1, -1, -1, -1},
                {8, 1, 3, 8, 6, 1, 8, 4, 6, 6, 10, 1, -1, -1, -1, -1},
                {10, 1, 0, 10, 0, 6, 6, 0, 4, -1, -1, -1, -1, -1, -1, -1},
                {4, 6, 3, 4, 3, 8, 6, 10, 3, 0, 3, 9, 10, 9, 3, -1},
                {10, 9, 4, 6, 10, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {4, 9, 5, 7, 6, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 8, 3, 4, 9, 5, 11, 7, 6, -1, -1, -1, -1, -1, -1, -1},
                {5, 0, 1, 5, 4, 0, 7, 6, 11, -1, -1, -1, -1, -1, -1, -1},
                {11, 7, 6, 8, 3, 4, 3, 5, 4, 3, 1, 5, -1, -1, -1, -1},
                {9, 5, 4, 10, 1, 2, 7, 6, 11, -1, -1, -1, -1, -1, -1, -1},
                {6, 11, 7, 1, 2, 10, 0, 8, 3, 4, 9, 5, -1, -1, -1, -1},
                {7, 6, 11, 5, 4, 10, 4, 2, 10, 4, 0, 2, -1, -1, -1, -1},
                {3, 4, 8, 3, 5, 4, 3, 2, 5, 10, 5, 2, 11, 7, 6, -1},
                {7, 2, 3, 7, 6, 2, 5, 4, 9, -1, -1, -1, -1, -1, -1, -1},
                {9, 5, 4, 0, 8, 6, 0, 6, 2, 6, 8, 7, -1, -1, -1, -1},
                {3, 6, 2, 3, 7, 6, 1, 5, 0, 5, 4, 0, -1, -1, -1, -1},
                {6, 2, 8, 6, 8, 7, 2, 1, 8, 4, 8, 5, 1, 5, 8, -1},
                {9, 5, 4, 10, 1, 6, 1, 7, 6, 1, 3, 7, -1, -1, -1, -1},
                {1, 6, 10, 1, 7, 6, 1, 0, 7, 8, 7, 0, 9, 5, 4, -1},
                {4, 0, 10, 4, 10, 5, 0, 3, 10, 6, 10, 7, 3, 7, 10, -1},
                {7, 6, 10, 7, 10, 8, 5, 4, 10, 4, 8, 10, -1, -1, -1, -1},
                {6, 9, 5, 6, 11, 9, 11, 8, 9, -1, -1, -1, -1, -1, -1, -1},
                {3, 6, 11, 0, 6, 3, 0, 5, 6, 0, 9, 5, -1, -1, -1, -1},
                {0, 11, 8, 0, 5, 11, 0, 1, 5, 5, 6, 11, -1, -1, -1, -1},
                {6, 11, 3, 6, 3, 5, 5, 3, 1, -1, -1, -1, -1, -1, -1, -1},
                {1, 2, 10, 9, 5, 11, 9, 11, 8, 11, 5, 6, -1, -1, -1, -1},
                {0, 11, 3, 0, 6, 11, 0, 9, 6, 5, 6, 9, 1, 2, 10, -1},
                {11, 8, 5, 11, 5, 6, 8, 0, 5, 10, 5, 2, 0, 2, 5, -1},
                {6, 11, 3, 6, 3, 5, 2, 10, 3, 10, 5, 3, -1, -1, -1, -1},
                {5, 8, 9, 5, 2, 8, 5, 6, 2, 3, 8, 2, -1, -1, -1, -1},
                {9, 5, 6, 9, 6, 0, 0, 6, 2, -1, -1, -1, -1, -1, -1, -1},
                {1, 5, 8, 1, 8, 0, 5, 6, 8, 3, 8, 2, 6, 2, 8, -1},
                {1, 5, 6, 2, 1, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 3, 6, 1, 6, 10, 3, 8, 6, 5, 6, 9, 8, 9, 6, -1},
                {10, 1, 0, 10, 0, 6, 9, 5, 0, 5, 6, 0, -1, -1, -1, -1},
                {0, 3, 8, 5, 6, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {10, 5, 6, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {11, 5, 10, 7, 5, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {11, 5, 10, 11, 7, 5, 8, 3, 0, -1, -1, -1, -1, -1, -1, -1},
                {5, 11, 7, 5, 10, 11, 1, 9, 0, -1, -1, -1, -1, -1, -1, -1},
                {10, 7, 5, 10, 11, 7, 9, 8, 1, 8, 3, 1, -1, -1, -1, -1},
                {11, 1, 2, 11, 7, 1, 7, 5, 1, -1, -1, -1, -1, -1, -1, -1},
                {0, 8, 3, 1, 2, 7, 1, 7, 5, 7, 2, 11, -1, -1, -1, -1},
                {9, 7, 5, 9, 2, 7, 9, 0, 2, 2, 11, 7, -1, -1, -1, -1},
                {7, 5, 2, 7, 2, 11, 5, 9, 2, 3, 2, 8, 9, 8, 2, -1},
                {2, 5, 10, 2, 3, 5, 3, 7, 5, -1, -1, -1, -1, -1, -1, -1},
                {8, 2, 0, 8, 5, 2, 8, 7, 5, 10, 2, 5, -1, -1, -1, -1},
                {9, 0, 1, 5, 10, 3, 5, 3, 7, 3, 10, 2, -1, -1, -1, -1},
                {9, 8, 2, 9, 2, 1, 8, 7, 2, 10, 2, 5, 7, 5, 2, -1},
                {1, 3, 5, 3, 7, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 8, 7, 0, 7, 1, 1, 7, 5, -1, -1, -1, -1, -1, -1, -1},
                {9, 0, 3, 9, 3, 5, 5, 3, 7, -1, -1, -1, -1, -1, -1, -1},
                {9, 8, 7, 5, 9, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {5, 8, 4, 5, 10, 8, 10, 11, 8, -1, -1, -1, -1, -1, -1, -1},
                {5, 0, 4, 5, 11, 0, 5, 10, 11, 11, 3, 0, -1, -1, -1, -1},
                {0, 1, 9, 8, 4, 10, 8, 10, 11, 10, 4, 5, -1, -1, -1, -1},
                {10, 11, 4, 10, 4, 5, 11, 3, 4, 9, 4, 1, 3, 1, 4, -1},
                {2, 5, 1, 2, 8, 5, 2, 11, 8, 4, 5, 8, -1, -1, -1, -1},
                {0, 4, 11, 0, 11, 3, 4, 5, 11, 2, 11, 1, 5, 1, 11, -1},
                {0, 2, 5, 0, 5, 9, 2, 11, 5, 4, 5, 8, 11, 8, 5, -1},
                {9, 4, 5, 2, 11, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {2, 5, 10, 3, 5, 2, 3, 4, 5, 3, 8, 4, -1, -1, -1, -1},
                {5, 10, 2, 5, 2, 4, 4, 2, 0, -1, -1, -1, -1, -1, -1, -1},
                {3, 10, 2, 3, 5, 10, 3, 8, 5, 4, 5, 8, 0, 1, 9, -1},
                {5, 10, 2, 5, 2, 4, 1, 9, 2, 9, 4, 2, -1, -1, -1, -1},
                {8, 4, 5, 8, 5, 3, 3, 5, 1, -1, -1, -1, -1, -1, -1, -1},
                {0, 4, 5, 1, 0, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {8, 4, 5, 8, 5, 3, 9, 0, 5, 0, 3, 5, -1, -1, -1, -1},
                {9, 4, 5, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {4, 11, 7, 4, 9, 11, 9, 10, 11, -1, -1, -1, -1, -1, -1, -1},
                {0, 8, 3, 4, 9, 7, 9, 11, 7, 9, 10, 11, -1, -1, -1, -1},
                {1, 10, 11, 1, 11, 4, 1, 4, 0, 7, 4, 11, -1, -1, -1, -1},
                {3, 1, 4, 3, 4, 8, 1, 10, 4, 7, 4, 11, 10, 11, 4, -1},
                {4, 11, 7, 9, 11, 4, 9, 2, 11, 9, 1, 2, -1, -1, -1, -1},
                {9, 7, 4, 9, 11, 7, 9, 1, 11, 2, 11, 1, 0, 8, 3, -1},
                {11, 7, 4, 11, 4, 2, 2, 4, 0, -1, -1, -1, -1, -1, -1, -1},
                {11, 7, 4, 11, 4, 2, 8, 3, 4, 3, 2, 4, -1, -1, -1, -1},
                {2, 9, 10, 2, 7, 9, 2, 3, 7, 7, 4, 9, -1, -1, -1, -1},
                {9, 10, 7, 9, 7, 4, 10, 2, 7, 8, 7, 0, 2, 0, 7, -1},
                {3, 7, 10, 3, 10, 2, 7, 4, 10, 1, 10, 0, 4, 0, 10, -1},
                {1, 10, 2, 8, 7, 4, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {4, 9, 1, 4, 1, 7, 7, 1, 3, -1, -1, -1, -1, -1, -1, -1},
                {4, 9, 1, 4, 1, 7, 0, 8, 1, 8, 7, 1, -1, -1, -1, -1},
                {4, 0, 3, 7, 4, 3, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {4, 8, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {9, 10, 8, 10, 11, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {3, 0, 9, 3, 9, 11, 11, 9, 10, -1, -1, -1, -1, -1, -1, -1},
                {0, 1, 10, 0, 10, 8, 8, 10, 11, -1, -1, -1, -1, -1, -1, -1},
                {3, 1, 10, 11, 3, 10, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 2, 11, 1, 11, 9, 9, 11, 8, -1, -1, -1, -1, -1, -1, -1},
                {3, 0, 9, 3, 9, 11, 1, 2, 9, 2, 11, 9, -1, -1, -1, -1},
                {0, 2, 11, 8, 0, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {3, 2, 11, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {2, 3, 8, 2, 8, 10, 10, 8, 9, -1, -1, -1, -1, -1, -1, -1},
                {9, 10, 2, 0, 9, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {2, 3, 8, 2, 8, 10, 0, 1, 8, 1, 10, 8, -1, -1, -1, -1},
                {1, 10, 2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {1, 3, 8, 9, 1, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 9, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {0, 3, 8, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},
                {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1}};
        #endregion

        /// <summary>Computes triangles for the portion of the surface within a given cell</summary>
        /// <param name="cell">The cell</param>
        /// <returns>Triangles representing intersection of surface with cell</returns>
        private static Triangle[] TriangulateCell(Cell cell)
        {
            Vector[] vertlist = new Vector[12];

            // Determine the index into the edge table, which tells us which vertices are inside the surface
            int cubeindex = 0;
            if (cell.val[0] < 0) cubeindex |= 1;
            if (cell.val[1] < 0) cubeindex |= 2;
            if (cell.val[2] < 0) cubeindex |= 4;
            if (cell.val[3] < 0) cubeindex |= 8;
            if (cell.val[4] < 0) cubeindex |= 16;
            if (cell.val[5] < 0) cubeindex |= 32;
            if (cell.val[6] < 0) cubeindex |= 64;
            if (cell.val[7] < 0) cubeindex |= 128;

            // Cell is entirely in/out of the surface, so return an empty array of triangles
            if (edgeTable[cubeindex] == 0) return System.Array.Empty<Triangle>();

            // Find the vertices where the surface intersects the 12 edges of the cell
            if ((edgeTable[cubeindex] & 1) != 0) vertlist[0] = VertexInterp(cell.p[0], cell.p[1], cell.val[0], cell.val[1]);
            if ((edgeTable[cubeindex] & 2) != 0) vertlist[1] = VertexInterp(cell.p[1], cell.p[2], cell.val[1], cell.val[2]);
            if ((edgeTable[cubeindex] & 4) != 0) vertlist[2] = VertexInterp(cell.p[2], cell.p[3], cell.val[2], cell.val[3]);
            if ((edgeTable[cubeindex] & 8) != 0) vertlist[3] = VertexInterp(cell.p[3], cell.p[0], cell.val[3], cell.val[0]);
            if ((edgeTable[cubeindex] & 16) != 0) vertlist[4] = VertexInterp(cell.p[4], cell.p[5], cell.val[4], cell.val[5]);
            if ((edgeTable[cubeindex] & 32) != 0) vertlist[5] = VertexInterp(cell.p[5], cell.p[6], cell.val[5], cell.val[6]);
            if ((edgeTable[cubeindex] & 64) != 0) vertlist[6] = VertexInterp(cell.p[6], cell.p[7], cell.val[6], cell.val[7]);
            if ((edgeTable[cubeindex] & 128) != 0) vertlist[7] = VertexInterp(cell.p[7], cell.p[4], cell.val[7], cell.val[4]);
            if ((edgeTable[cubeindex] & 256) != 0) vertlist[8] = VertexInterp(cell.p[0], cell.p[4], cell.val[0], cell.val[4]);
            if ((edgeTable[cubeindex] & 512) != 0) vertlist[9] = VertexInterp(cell.p[1], cell.p[5], cell.val[1], cell.val[5]);
            if ((edgeTable[cubeindex] & 1024) != 0) vertlist[10] = VertexInterp(cell.p[2], cell.p[6], cell.val[2], cell.val[6]);
            if ((edgeTable[cubeindex] & 2048) != 0) vertlist[11] = VertexInterp(cell.p[3], cell.p[7], cell.val[3], cell.val[7]);

            // Create the triangles */
            List<Triangle> triList = new List<Triangle>(5);

            for (int i = 0; triTable[cubeindex, i] != -1; i += 3)
            {
                Vector v0 = vertlist[triTable[cubeindex, i]];
                Vector v1 = vertlist[triTable[cubeindex, i + 1]];
                Vector v2 = vertlist[triTable[cubeindex, i + 2]];
                Triangle tri = new Triangle(v0, v1, v2);
                triList.Add(tri);
            }

            return triList.ToArray();
        }

        /// <summary>Linearly interpolate along an edge cut by the surface</summary>
        /// <param name="p1">Point at start of edge</param>
        /// <param name="p2">Point at end of edge</param>
        /// <param name="val1">Function value at start of edge</param>
        /// <param name="val2">Function value at end of edge</param>
        /// <returns>Point on edge where function value is zero</returns>
        private static Vector VertexInterp(Vector p1, Vector p2, double val1, double val2)
        {
            if (System.Math.Abs(val1) < 0.00001) return p1;
            if (System.Math.Abs(val2) < 0.00001) return p2;
            if (System.Math.Abs(val1 - val2) < 0.00001) return p1;
            double mu = val1 / (val1 - val2);
            Vector p = p1 + mu * (p2 - p1);
            return p;
        }

        public static int[] GetGridCounts(ImplicitBody body, int n)
        {
            var box = body.Box;
            double dx = box.MaxX - box.MinX;
            double dy = box.MaxY - box.MinY;
            double dz = box.MaxZ - box.MinZ;

            double[] dxyz = { dx, dy, dz };
            double dmax = dxyz.Max();

            int countX = (int)(dx / dmax * n);
            int countY = (int)(dy / dmax * n);
            int countZ = (int)(dz / dmax * n);

            return new int[] { countX, countY, countZ };
        }

        private class Cell
        {
            public Vector[] p;
            public double[] val;

            public Cell(Vector[] points, params double[] vals)
            {
                this.p = points;
                this.val = vals;
            }
        }
    }
}

Triangle.cs

namespace nTop.Core.Examples.Mesher
{
    public class Triangle
    {
        /// <summary>The three vertices of the triangle, v0, v1, v2</summary>
        public Vector[] Vertices;

        /// <summary>Unit normal vector, in the direction of (v1 - v0) x (v2 - v1)</summary>
        public Vector UnitNormal;

        /// <summary>Constructor</summary>
        /// <param name="vertices">Vertices, in CCW order when viewed from outside the body</param>
        public Triangle(params Vector[] vertices)
        {
            this.Vertices = vertices;
            Vector v0 = vertices[0];
            Vector v1 = vertices[1];
            Vector v2 = vertices[2];
            this.UnitNormal = Vector.Cross(v1 - v0, v2 - v1).Unit;
        }
    }
}

WriteSTL.cs

using System.Collections.Generic;
using System.IO;

namespace nTop.Core.Examples.Mesher
{
    public partial class Program
    {
        private static string VectorToSTL(Vector v)
        {
            string sx = v.X.ToString("F6");
            string sy = v.Y.ToString("F6");
            string sz = v.Z.ToString("F6");
            string space = "  ";
            return sx + space + sy + space + sz;
        }

        public static void WriteSTL(List<Triangle> triList, string filePath)
        {
            using (var writer = new StreamWriter(filePath))
            {
                writer.WriteLine("solid object");

                foreach (var triangle in triList)
                {
                    writer.WriteLine("  facet normal " + VectorToSTL(triangle.UnitNormal));
                    writer.WriteLine("    outer loop");

                    foreach (var vertex in triangle.Vertices)
                    {
                        writer.WriteLine("      vertex " + VectorToSTL(vertex));
                    }

                    writer.WriteLine("    endloop");
                    writer.WriteLine("  endfacet");
                }

                writer.WriteLine("endsolid object");
            }
        }
    }
}

nTop

nTop Automate

nTop Core

Mesher (.NET)

MainProgram.cs

Mesher.cs

Triangle.cs

WriteSTL.cs

​MainProgram.cs

​Mesher.cs

​Triangle.cs

​WriteSTL.cs

MainProgram.cs

Mesher.cs

Triangle.cs

WriteSTL.cs