GTA IV C# Draw inside world

//copy these functions to your script
private Vector2 CoordToScreen(Vector3 vect)
    {
        int Screen = 0;
        GTA.Native.Pointer x = new GTA.Native.Pointer(typeof(float));
        GTA.Native.Pointer y = new GTA.Native.Pointer(typeof(float));
        Vector3 xpos = vect;
        GTA.Native.Pointer ViewportId = new GTA.Native.Pointer(typeof(int));
        GTA.Native.Function.Call("GET_GAME_VIEWPORT_ID", ViewportId);
        Screen = ViewportId;
        GTA.Native.Function.Call("GET_VIEWPORT_POSITION_OF_COORD", xpos.X, xpos.Y, xpos.Z, Screen, x, y);

        return new Vector2(x,y);
    }

    private bool isCoordVisibleStopsAfterLoad(Vector3 WorldCoord, float AreaSize = 1f) //stops working after you load a save game
    {
        if(Game.Exists(Game.CurrentCamera))
        {
            return GTA.Native.Function.Call<bool>("CAM_IS_SPHERE_VISIBLE", Game.CurrentCamera, WorldCoord.X, WorldCoord.Y, WorldCoord.Z, AreaSize);
        }
        else{return false;}
    }

private bool isCoordVisible(Vector3 WorldCoord)
{
    if (Vector3.Subtract(Vector3.Normalize(Vector3.Subtract(myPed, Game.CurrentCamera.Position)),Game.CurrentCamera.Direction).Length() > 0.6f) return false;
    return true;
}

//put this in PerFrameDrawing
Vector3 WorldPosition = //insert Vector3 you want shown here (eg: Game.LocalPlayer.Character.Position)
if(isCoordVisible(WorldPosition))
{
    Vector2 ScreenPosition = CoordToScreen(WorldPosition);
    e.Graphics.DrawRect(ScreenPosition.X, ScreenPosition.Y, 32, 32, System.Drawing.Color.White);
    //or e.Graphics.DrawSprite
    //or e.Graphics.DrawText
}