If you need to do a compare ..
What has worked well for me, and requires little effort in finding unexpected changes, is to overlay a version of the new onto the old images; opening PDFs with Photoshop or Photoshop Elements. I make the new version image solid green with a 40% transparency***, the old version solid red with 60% transparency, and a background layer solid black. Every pixel that matches is yellow; non-matching new stuff is green; non-matching old is red****. A-size to J-size, takes the same time to overlay. Typical comparison is done at 200 dpi.
Anything that doesn't match needs an explanation.
It can be saved as a PDF; as many versions of the drawing can be added as you have memory for the layers, so that an entire drawing check history can be kept. And the results can be stored and reviewed using Adobe Reader, so those without special software can access the result.
We needed to go with .pdf for our output. We looked at overlay capabilities, with a thread here last year about comparing two .pdfs to see what the difference is.
Here's what I learned then:
1. You can compare two .pdfs by opening up two sessions of Acrobat (one for each drawing). Maximize each screen, and by selecting either the CTRL or ALT key (I forget which one), you can "cycle" the view back and forth between each drawing quickly, and you can easily see the differences in both drawings.
2. Or you purchase Bluebeam Software. www.bluebeam.com . They have a CAD extension. Bluebeam compares two .pdfs in two different ways: the first is that it "overlays" both .pdfs on top of each other (in different colors). You can easily see the differences by looking at the different colors. YOu can save out as .pdf for proof of checking.
Or, you can show the differences by "balloon", where the software will draw a balloon cloud around areas of the drawing that has changed.
The software compares pixels, and if it sees something has moved, it registers it. It doesn't cost more than Adobe Pro, but has far better functionality.
- Randy Mees
All views my own, and do not reflect views of Edwards Lifesciences.
I suppose lack of familiarity with it is the lack of seeing a need for it; lack of imagination rather than lack of intrinsic value. 99.9% of users would understand overlay as a way to compare drawings. Perhaps if PTC called it drawing UDF or live embed?
I can see a minor reason why Drawing Overlay isn't often used, in bold - from http://www.mcadcentral.com/creo-tips-tricks-drawing/7042-copy-drawing-into-another-drawing.html (apparently copied from PTC Help)
Using overlays, you can superimpose selected views or an entire sheet of one drawing over the current drawing sheet. This functionality is available for drawings, layouts, reports, and diagrams; each can reference objects of these four types, as well as formats.
When working with overlays, keep in mind the following:
?Overlays are read-only in the current drawing.
?The system updates overlays to changes in the source drawing.
?Overlaid views appear with all detail items.
?You cannot select overlays for any drawing procedure.
?If the size of the current drawing is different from the size of the source drawing, the overlays brought into the current drawing maintain the same screen size (that is, they occupy the same portion of the graphics window) as they had in the source drawing. <- this is the part that would slow people down. Why does PTC perform so many operations in drawings as based on a ratio to drawing or view size when users view drawing operations in absolute size?
It doesn't look like there's any insurmountable problem, though the same question in the Windchill section may turn up some differing opinion for data management. Is the Windchill TC any help? I guess it depends on whether the Windchill guys paid enough attention.
These are some results I found for "drawing overlay" here.
http://portal.ptcuser.org/p/fo/st/topic=3&post=27744#p27744 Detail splines wander about in Overlay
http://portal.ptcuser.org/p/fo/st/topic=24&post=19487#p19487 Weblink, JLink, Toolkit don't add Overlays
http://portal.ptcuser.org/p/fo/st/topic=3&post=56280#p56280 Font changes for no reason
http://portal.ptcuser.org/p/fo/st/topic=14&post=99936#p99936 RSD & Creo no longer overlay together
http://portal.ptcuser.org/p/fo/st/topic=24&post=18252#p18252 Drawing overlay scale problem
http://portal.ptcuser.org/p/fo/st/topic=3&post=29058#p29058 Drawing overlay scale problem
Sorry - didn't notice you'd posted the Overlay help; on the website the text of your help posting is spread over about 200 vertical lines; about 3 screens high, so I didn't recognize it until later.