Read it again. ;-) (and again…)
From the pdf by Marc Autret:
The linear component — a,b,c,d — typically allows to apply scaling, flipping, rotation, or skew, around the origin of the input coordinate system, while the translation component — e,f — allows to reposition the result within the destination space.
e for x direction
f for y direction
Thanks Uwe ;-)
Anyway poortip87's question definititely makes sense (and will be answered in Chapter 2).
In short: even when you know that (e,f) represent some (tx,ty) translation components which actually regulate the positioning within the parent space, the problem remains of determining where is the origin of a PageItem inner space. One might intuitively expect a simple rule based on some bounding box center point. However, this is not the case. The implicit origin of a PageItem inner space is absolutely determined as the origin of the pasteboard coordinate space, whatever the actual location of that graphic object in the document. Therefore the (e,f) values are somewhat frustrating: they give you the location of the PageItem inner space origin relative to the parent space, but you still don't know where the object "in itself"—that is, its visible bounding box—is located. Chapter 2 will explore InDesign's specific coordinate spaces and these related issues…
@Marc – yes, but one can resolve() the pageItem and check its position according to the Pasteboard Coordinate Space (and that is describing the Coordinate Space of the whole document). So, if you know on what spread the pageItem is positioned you can use the position of one of its path points in Pasteboard Coordinate Space and compare that to any parameter the user has chosen for meassurement units in horizontal or vertical direction and the current zero point.
At least I think so… ;-)
Of course might be, that a script has fooled around with Pasteboard Coordinate Space…
(Will think that through again when I have more time for it)
My point was about deciphering the translation parameters of the PageItem matrix relative to its parent space—as asked by poortip87. I did not mean that it is inherently difficult to check the position of an object. Indeed the PageItem.resolve(…) method provides all we need to get directly the location of some specific point—e.g., the center point of the bounding box—relative to any coordinate space.
I just was pointing out that the origin of the inner space is particularly counter-intuitive and does not help in understanding the translation values.
Where can I go through the chapter 2? Or where can I get more information on this?
Thanks a lot for the link. I am going thorugh it now..