Creating mesh tiles from the terrain

This class lets you easily create a mesh from a specified terrain. Based on this class you can create what ever you want.

For larger terrains you have to split it to multiple meshes because a mesh can only hold 65000 vertices.

 using System.Collections.Generic;
 using UnityEngine;
 
     public class TerrainMesher
     {
         /// <summary>
         /// Converts a terrain to a mesh.
         /// </summary>
         /// <param name="terrain">The terrain to convert.</param>
         /// <returns>The mesh</returns>
         public static Mesh MeshFromTerrain(Terrain terrain)
         {
             // Create new mesh object
             Mesh mesh = new Mesh();
     
             TerrainData terrainData = terrain.terrainData;
     
             // Create all lists needed
             List<int> indices = new List<int>();
             List<Vector3> vertices = new List<Vector3>();
             List<Vector3> normals = new List<Vector3>();
     
             Vector3 heightmapScale = terrainData.heightmapScale;
     
             // Compute fractions in x and z direction
             float dx = 1f / (terrainData.heightmapWidth - 1);
             float dz = 1f / (terrainData.heightmapHeight - 1);
     
             for (int ix = 0; ix < terrainData.heightmapWidth; ix++)
             {
                 float x = ix * heightmapScale.x;
                 float ddx = ix * dx;
     
                 for (int iz = 0; iz < terrainData.heightmapHeight; iz++)
                 {
                     float z = iz * heightmapScale.z;
                     float ddz = iz * dz;
     
                     // Sample height and normal at dx, dz
                     Vector3 point = new Vector3(x, terrainData.GetInterpolatedHeight(ddx, ddz), z);
                     Vector3 normal = terrainData.GetInterpolatedNormal(ddx, ddz);
     
                     // Add vertex and normal to the lists
                     vertices.Add(point);
                     normals.Add(normal);
                 }
             }
     
             int w = terrainData.heightmapWidth;
             int h = terrainData.heightmapHeight;
     
             // Add triangle pairs (quad)
             for (int xx = 0; xx < w-1; xx++)
             {
                 for (int zz = 0; zz < h-1; zz++)
                 {
                     int a = zz + xx * w;
                     int b = a + w + 1;
                     int c = a + w;
                     int d = a + 1;
     
                     // Add indices in clockwise order (winding order)
                     indices.Add(a);
                     indices.Add(b);
                     indices.Add(c);
     
                     indices.Add(a);
                     indices.Add(d);
                     indices.Add(b);
                 }
             }
     
             mesh.vertices = vertices.ToArray();
             mesh.normals = normals.ToArray();
             mesh.triangles = indices.ToArray();
     
             // Recalculate mesh bounds
             mesh.RecalculateBounds();
             
             return mesh;
         }
     }

The triangles are constructed as shown on the image below.