PiP format of FLIR cam

[RémyClaverie]

Hello,
I'm trying to understand how Flir can make Pip with some of its thermal cameras. I've read the threads on the exiftool forum (https://exiftool.org/forum/index.php?topic=4898.msg24156#msg24156), where I've found some valuable information. I have applied the various command lines with exiftool and imagemagick to the files in this thread. But I do not understand the principle of matching the IR image to the visible image from the metadata. For example, in the last convert command, where do the 270x270x and 240x values come from?

Is there a document explaining this principle ? If not, could one of you explain it to me?

Thank you so much!

Rémy