What is the definition of "scene center"?

Certain view angles are described as being defined from "the scene center point". However, a definition of that point is not given - what was in mind when it was written? Is there a standard industry definition?

I can think of a few different interpretations:

• The projected location of the central pixel in the camera array for frame imagers, or the "central" pixel in a scan. I'm unsure if this concept makes sense for all possible datasets the extension covers (SAR in particular).
• The centroid of all pixels containing data (is the centroid derived in sensor space and projected, or from the pixels after projection?)
• The centroid of the bounding box or bounding polygon
• Something else!

Admittedly, if one cares enough to ask, then per-pixel metadata is probably needed, but it'd be good to pin down the definition.

Review the view extension text that uses “scene center point” and the alternatives listed in this issue, including whether the concept applies across datasets such as SAR. Done means the intended definition or standard reference is agreed and the extension wording clearly documents it.