Hi, i hope is the right section.

I need to know how to compute sphere tangents. For the normals i saw i can approximate them with vertices coordinates.

But for tangents i don’t find nothing. I did this:

```
Vec3s triangle = shape.triangle.at(k);
Vec3f vertex1 = shape.vertex.at(triangle[0]);
Vec3f vertex2 = shape.vertex.at(triangle[1]);
Vec3f vertex3 = shape.vertex.at(triangle[2]);
Vec3f v1 = vertex3-vertex1;
Vec3f v2 = vertex2-vertex1;
Vec2f tex1 = shape.texture.at(triangle[0]);
Vec2f tex2 = shape.texture.at(triangle[1]);
Vec2f tex3 = shape.texture.at(triangle[2]);
Vec2f st1 = tex3-tex1;
Vec2f st2 = tex2-tex1;
float coef = 1/ (st1[0] * st2[1] - st2[0] * st1[1]);
Vec3f tangent;
tangent[0] = coef * ((v1[0] * st2[1]) + (v2[0] * -st1[1]));
tangent[1] = coef * ((v1[1] * st2[1]) + (v2[1] * -st1[1]));
tangent[2] = coef * ((v1[2] * st2[1]) + (v2[2] * -st1[1]));
```

It works for 3d models but not for a sphere…