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# Procedural Mesh Generation: Creating a spherical sector

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[i] = GameObject.CreatePrimitive(PrimitiveType.Sphere);
points[i].name = names[i];
points[i].transform.parent = transform;
points[i].transform.localScale = new Vector3(size, size, size);
points[i].transform.position = vertices[i];
}
}
}
```

Well, as a point of reference, if you simplify the mesh to a sure thing, does it still work?

For example, you could try something like:

```
vertices = new Vector3[]
{
new Vector3(-1f, -1f, 0f), // 0: bottom left
new Vector3(1f, -1f, 0f), // 1: bottom right
new Vector3(1f, 1f, 0f), // 2: top right
new Vector3(-1f, 1f, 0f) // 3: top left
};
triangles = new int[]
{
0, 1, 2,
0, 2, 3
};
```

If that's visible, then it's a flaw in your vertex/triangle generation.

However, if it's not visible, then it's a flaw in creating/applying the mesh.

^{Edit: Fixed a dumb error}

I added the DrawSphere function to visualize the vertices that are created. The Attached figure are the vertices that are resulting from given angles of 10 to 60 in theta and 0 to 60 in phi. The Vertices are verified to be correct because of it. The issue must be in the triangles then. As for the simpler meshes, they are working.

**Answer** by LionWare
·
Nov 26, 2020 at 08:03 AM

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[i] = GameObject.CreatePrimitive(PrimitiveType.Sphere);
points[i].name = names[i];
points[i].transform.parent = transform;
points[i].transform.localScale = new Vector3(size, size, size);
points[i].transform.position = vertices[i];
}
}
}
```

I removed the DrawSphere because I dont need it now.

**Answer** by Llama_w_2Ls
·
Nov 26, 2020 at 07:15 AM

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

I am almost sure that the problem I am getting is with triangles as my vertices are in correct position, (validated by the DrawSphere function) but I cant get the problem with the triangles. The Code that you have given is for a complete sphere I dont need to generate a complete sphere.

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