Equirectangular Projection of Sphere onto Texture

Okay so I have a script that generates planets and that all works fine but I want to essentially create a "heightmap" of the surface of the sphere based on the vertex distance from the center minus the planet's radius (sea level). So I managed to get the latitude and longitude of every vertex but for whatever reason when I process these values in the xCord = ... and yCord = ... lines they always end up both equaling zero - no matter what, which I don't understand. Essentially with those two lines all I am doing is converting the latitude and longitude coordinates into x and y pixel coordinates. Part of my code is available below.

EDIT: By the way 72 and 36 are the dimensions of the texture.

EDIT 2: So I tried changing all of the constants in the xCord = ... and yCord = ... lines and now they aren't returning zero, so that was one of the problems and now I'm getting... something. The screenshot below shows the output. What I don't get is why 0,0 is the position of the bottom, left pixel and 72,36 is not the top, right pixel as I thought this was the case.

EDIT 3: I think I resolved a bunch of problems with calculating latitude and longitude and everything seems to be working but I'm still getting undesirable results, without any color changing yet I should get a completely black map, a full map... help? Screens below.

     void MakeMap () {
     
     texture = new Texture2D(72, 36);
     
     vertices = planetVars.vertices;
     
     float xCord = 0;
     float yCord = 0;
     
     for(int i = 0; i < vertices.Length; i++){
         
         Vector3 globalVertPos = planet.transform.TransformPoint(vertices[i]);
         
         Vector3 vectorA;
         vectorA = (globalVertPos - planet.transform.position);
         vectorA.y = 0;
         
         float lng = 0;
         Vector3 refRight= Vector3.Cross(Vector3.up, planet.transform.forward);
         float ang = Vector3.Angle (vectorA, planet.transform.forward);
         float sign = (Vector3.Dot(vectorA, refRight) > 0.0f) ? -1.0f: 1.0f;
         lng = sign * ang;
     
         //print(lng);
         
         float lat = 0;
         lat = Vector3.Angle (vectorA, (globalVertPos - planet.transform.position));
         if(globalVertPos.y < planet.transform.position.y){
             
             lat *= -1;
             
         }
     
         //print(lat);
         
         xCord = (lng + 180f) * (texture.width/360f);
         yCord = ((lat - 90f) * (texture.height/180f));
         
         float dist = Vector3.Distance(globalVertPos, planet.transform.position);
         color = Color.Lerp (white, black, dist);
         
         texture.SetPixel ((int)xCord, (int)yCord, color);
         
     }
     
     texture.Apply();
     
 }

EDIT 2:

EDIT 3: