Find the pixel position corresponding to a vertex


I am rendering a 3D model using THREEjs. My project requires me to find the pixel position of the final rendered vertex.

I found the following answer on stackoverflow: javascript - How Does a camera convert from clip space into screen space? - Stack Overflow

but the pixel position that I am getting are not exact to what they should have been? Could you tell me how we can get the final of pixels?

Thank You