Procedural Mesh Generation: Creating a spherical sector

Questions & Answers
1

So, I am creating a spherical sector with the given theta and phi angles (Latitude and Longitude) and I know my vertices positioning is correct but no mesh is visible. Does any one have any idea about what is wrong with this code. Why isn’t it showing any mesh.

using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using UnityEngine;
using UnityEngine.UI;
using UnityEditor.UIElements;

public class Please : MonoBehaviour
{
    public int ThetaUpper = 30;
    public int ThetaLower = 40;
    public int PhiUpper = 30;
    public int PhiLower = 10;
    public bool edit = true;
    private int ThetaU;
    private int ThetaL;
    private int PhiU;
    private int PhiL;
    public float size = 0.001f;
    private readonly int res = 2;
    private Mesh mesh;
    private MeshFilter meshFilter;
    public float radius = 5.0f;
    private GameObject[] points;
    private Vector3[] vertices;
    private string[] names;

    // Start is called before the first frame update
    void Start()
    {
        this.gameObject.AddComponent<MeshFilter>();
        this.gameObject.AddComponent<MeshRenderer>();
        meshFilter = this.gameObject.GetComponent<MeshFilter>();
        meshFilter.sharedMesh = new Mesh();
        mesh = meshFilter.sharedMesh;
        Create();
        Assign();
    }

    // Update is called once per frame
    void Update()
    {
    }

    bool check()
    {
        if (ThetaLower == ThetaL && ThetaUpper == ThetaU && PhiLower == PhiL && PhiUpper == PhiU)
            return true;
        else return false;
    }
    void Assign()
    {
        ThetaU = ThetaUpper;
        ThetaL = ThetaLower;
        PhiL = PhiLower;
        PhiU = PhiUpper;
    }

    void Create()
    {
        int index1 = (ThetaLower - ThetaUpper) * 2;
        int index2 = (PhiUpper - PhiLower) * 2;
        vertices = new Vector3[index1 * index2];
        names = new string[vertices.Length];
        int[,] temp = new int[index1, index2];
        int no = 0;
        for (int i = 0; i < index1; i++)
        {
            float theta = ((0.5f * i) + ThetaUpper) * Mathf.Deg2Rad;
            for (int j = 0; j < index2; j++, no++)
            {               
                float phi = ((0.5f * j) + PhiLower) * Mathf.Deg2Rad;
                float x = radius * Mathf.Sin(theta) * Mathf.Cos(phi);
                float z = radius * Mathf.Sin(theta) * Mathf.Sin(phi);
                float y = radius * Mathf.Cos(theta);
                vertices[no] = new Vector3(x, y, z);
                names[no] = "Vertex No. " + no.ToString() + " Theta " + i.ToString() + " phi " + j.ToString();
                temp[i, j] = no;
            }
        }
        int[] triangles = new int[(index1 - 1) * (index2 - 1) * 6];
        int triIndex = 0;
        for (int i = 0; i < index1-1; i++)
        {
            for (int j = 0; j < index2-1; j++, triIndex += 6)
            {
                triangles[triIndex] = temp[i, j];
                triangles[triIndex] = temp[i , j + 1];
                triangles[triIndex] = temp[i + 1, j + 1];

                triangles[triIndex] = temp[i, j];
                triangles[triIndex] = temp[i + 1, j + 1];
                triangles[triIndex] = temp[i + 1, j];
            }
        }

        mesh.Clear();
        mesh.vertices = vertices;
        mesh.triangles = triangles;
        mesh.RecalculateNormals();
        DrawSphere();

    }


    void DrawSphere()
    {
        points = new GameObject[mesh.vertexCount];
        for (int i = 0; i < mesh.vertexCount; i++)
        {
            points *= GameObject.CreatePrimitive(PrimitiveType.Sphere);*

points_.name = names*;_
_points.transform.parent = transform;_
_points.transform.localScale = new Vector3(size, size, size);
points.transform.position = vertices;
}
}
}*_

3

Got it.
It was a silly silly mistake.
I was setting all the triangles on the same index. (Yeah I know. I should probably shoot myself)
Anyways thanks.
Here is the working code for those who need it.
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using UnityEngine;
using UnityEngine.UI;
using UnityEditor.UIElements;

public class Please : MonoBehaviour
{
    public int ThetaUpper = 30;
    public int ThetaLower = 40;
    public int PhiUpper = 30;
    public int PhiLower = 10;
    public bool edit = true;
    private int ThetaU;
    private int ThetaL;
    private int PhiU;
    private int PhiL;
    public float size = 0.001f;
    private readonly int res = 2;
    private Mesh mesh;
    private MeshFilter meshFilter;
    public float radius = 5.0f;
    private GameObject[] points;
    private Vector3[] vertices;
    private string[] names;

    // Start is called before the first frame update
    void Start()
    {
        this.gameObject.AddComponent<MeshFilter>();
        this.gameObject.AddComponent<MeshRenderer>();
        meshFilter = this.gameObject.GetComponent<MeshFilter>();
        meshFilter.sharedMesh = new Mesh();
        mesh = meshFilter.sharedMesh;
        Create();
        Assign();
    }

    // Update is called once per frame
    void Update()
    {
    }

    bool check()
    {
        if (ThetaLower == ThetaL && ThetaUpper == ThetaU && PhiLower == PhiL && PhiUpper == PhiU)
            return true;
        else return false;
    }
    void Assign()
    {
        ThetaU = ThetaUpper;
        ThetaL = ThetaLower;
        PhiL = PhiLower;
        PhiU = PhiUpper;
    }

    void Create()
    {
        int index1 = (ThetaLower - ThetaUpper) * 2;
        int index2 = (PhiUpper - PhiLower) * 2;
        vertices = new Vector3[index1 * index2];
        names = new string[vertices.Length];
        int[,] temp = new int[index1, index2];
        int no = 0;
        for (int i = 0; i < index1; i++)
        {
            float theta = ((0.5f * i) + ThetaUpper) * Mathf.Deg2Rad;
            for (int j = 0; j < index2; j++, no++)
            {               
                float phi = ((0.5f * j) + PhiLower) * Mathf.Deg2Rad;
                float x = radius * Mathf.Sin(theta) * Mathf.Cos(phi);
                float z = radius * Mathf.Sin(theta) * Mathf.Sin(phi);
                float y = radius * Mathf.Cos(theta);
                vertices[no] = new Vector3(x, y, z);
                names[no] = "Vertex No. " + no.ToString() + " Theta " + i.ToString() + " phi " + j.ToString();
                temp[i, j] = no;
            }
        }
        int[] triangles = new int[(index1 - 1) * (index2 - 1) * 6];
        int triIndex = 0;
        for (int i = 0; i < index1-1; i++)
        {
            for (int j = 0; j < index2-1; j++)
            {
                triangles[triIndex] = temp[i, j];
                triangles[triIndex + 1] = temp[i + 1, j + 1];
                triangles[triIndex + 2] = temp[i, j + 1];

                triangles[triIndex + 3] = temp[i, j];
                triangles[triIndex + 4] = temp[i + 1, j];
                triangles[triIndex + 5] = temp[i + 1, j + 1];

                triIndex += 6;
            }
        }

        mesh.Clear();
        mesh.vertices = vertices;
        mesh.triangles = triangles;
        mesh.RecalculateNormals();

    }


    void DrawSphere()
    {
        points = new GameObject[mesh.vertexCount];
        for (int i = 0; i < mesh.vertexCount; i++)
        {
            points *= GameObject.CreatePrimitive(PrimitiveType.Sphere);*

points_.name = names*;_
_points.transform.parent = transform;_
_points.transform.localScale = new Vector3(size, size, size);
points.transform.position = vertices;
}
}
}*_

I removed the DrawSphere because I dont need it now.

2

Maybe the triangles are being drawn on the inside? If not, here’s one example from the web:

        public static MeshGeometry3D Sphere(double radius, int TopBottomDetail, int SidesDetail)
        {
            MeshGeometry3D sphere_mesh = new MeshGeometry3D();

            double dphi = Math.PI / TopBottomDetail;
            double dtheta = 2 * Math.PI / SidesDetail;

            // Remember the first point.
            int pt0 = sphere_mesh.Positions.Count;

            // Make the points.
            double phi1 = Math.PI / 2;
            for (int p = 0; p <= TopBottomDetail; p++)
            {
                double r1 = radius * Math.Cos(phi1);
                double y1 = radius * Math.Sin(phi1);

                double theta = 0;
                for (int t = 0; t <= SidesDetail; t++)
                {
                    sphere_mesh.Positions.Add(new Point3D(r1 * Math.Cos(theta), y1, -r1 * Math.Sin(theta)));
                    sphere_mesh.TextureCoordinates.Add(new Point((double)t / SidesDetail, (double)p / TopBottomDetail));
                    theta += dtheta;
                }
                phi1 -= dphi;
            }

            // Make the triangles.
            int i1, i2, i3, i4;
            for (int p = 0; p <= TopBottomDetail - 1; p++)
            {
                i1 = p * (SidesDetail + 1);
                i2 = i1 + (SidesDetail + 1);
                for (int t = 0; t <= SidesDetail - 1; t++)
                {
                    i3 = i1 + 1;
                    i4 = i2 + 1;
                    sphere_mesh.TriangleIndices.Add(pt0 + i1);
                    sphere_mesh.TriangleIndices.Add(pt0 + i2);
                    sphere_mesh.TriangleIndices.Add(pt0 + i4);

                    sphere_mesh.TriangleIndices.Add(pt0 + i1);
                    sphere_mesh.TriangleIndices.Add(pt0 + i4);
                    sphere_mesh.TriangleIndices.Add(pt0 + i3);
                    i1 += 1;
                    i2 += 1;
                }
            }

            return sphere_mesh;
        }

Some classes such as MeshGeometry3D, are only found in WPF, however, you can just replace it with Unity’s mesh class instead. @LionWare