Unfortunately I don’t have now access to pc to draw on your picture (and too clumsy to do it on mobile device), but here is a link to same info I found earlier:
So in the instructions the horizontal plane is the street, for you maybe the floor downstairs.
And the example tells to use for example light poles for vertical measurements, you could use for example a chair or even side of a cardboard box. You would put the box on the ground, draw ruler to match the height of the box, move the box, draw ruler again and do it for third time.
For horizontal measurement the example suggests road sign, you could put for example a broom laying on the ground and use that for measurement. Or you could use the same box and just draw the “depth“ (or width) of the box, measured on the part that is against the floor.
It is a bit hard to explain the process, but hopefully this helps you. But it also seems that your field of view might be challenging for making the calibration.
For two of my front door cameras installed at approximately face height, set in corridor mode and people approaching almost directly towards (and away from) the camera I could not get the IVS working perfectly even with the calibration. Maybe still playing with image adjustments is needed.
However, cameras are addictive (lol), so I got additional overview camera that will be installed to also work as a spotter for these cameras. The overview camera will be used to observe/recognize and it will trigger via
Blue Iris the front door cameras used for identifying. Also, more viewing angles is better. Of course all this comes with added expense of getting the overview camera, but for security purposes I think it is worth it and buying cameras over time makes it financially doable.