About the "connection lines":
Here below an ANALOGY
You remember this picture showing foreshortening.
Below my own hand from one side % the reverse:
Very roughly, let's assume that, as a real measurement, the red distance is the same lenght as the the green one.
Because of the effect of perspective, they look different depending on the position of the camera; the "apparent length" is observer dependent.
Apparently, length 1 (red) and length 2 (green) are linked by "connection lines" in white color.
The situation is perfectly symmetric. The length of line 1 (red) in the first picture corresponds to line 2 (green) in the second, and the length of line 2 (green) in the first corresponds to line 1 (red)in the second.
If someone links lines 1 & 2 with a bold red line that "jumps" somehow vertically between lines 1 & 2, it is possible to calculate some result of the operation but the result will correspond to exactly nothing.
If you want to "jump" from line 1 to line 2, you must follow the white lines. Otherwise the result is wrong.