Maybe my issue is that I don’t understand the Earth-fixed coordinate system. I was thinking that there was a “world” coordinate system that related to the earth via ENU … so in world coordinates, the x-axis is east, y-north, z-up. And I’ve just been guessing that the origin is the center of the earth ellipsoid. To stay sane, I’m assuming that when we spin the earth, it’s actually the earth that spins, and not the camera, such that we don’t have to worry about which direction the camera is facing, etc.
So, then, I expected that an undefined orientation would put the model’s x-axis pointing east (because of ENU, like you mention), but that an identity orientation would do the same.
Are you suggesting that there are three coordinate systems here?
- The “world” coordinate system like I mentioned, which is ENU
- An earth-fixed coordinate system that stays locked with the earth as it spins such that a point on the globe is always the same (x,y,z) point in that frame
- A model coordinate system
And you’re saying that an undefined orientation places the unit at an identity transform in frame 1, but that an identity orientation places it at an identity transform in frame 2?
If I have that right, that will raise more questions in my head because I’m not quite sure why the earth-fixed coordinate system would have its x-axis pointing down and to the left with regard to the ENU system in that Sandcastle demo.