I am a building codes plan reviewer for the City of Tempe Arizona. The City of Tempe’s Building Safety Department has made a commitment to have electronic plan review in operation by July 2010. We have looked a number of software products. Adobe, Bluebeam, Avolve and E-Gov and some others.
Bottom line we must have the ability to have scanned cad drawings or scanned hand drawings electronically reviewable – must have the ability to overlay transparently these scanned files. We also need the ability to slide these drawings around over each other for comparison purposes. I believe I have seen a demonstration of Adobe 9's ability to do this but do not remember how it was done. Any help would be appreciated. There will only 6 of us doing the reviews initially. There are only 2 of us that have any CAD experience. I have gotten the Compare function to work will with pure CAD files but not with scanned drawings. Gerald the azhirise gerald_koziol [at] tempe [dot] gov
If a new layer is created from an image or another PDF which has transparency, it will be preserved in the resulting stack. Acrobat 9 does not have the ability to blend layers in the way Photoshop does (lighten, screen, multiply, etc), so it cannot create transparency where it doesn't already exist. Scanned drawings are almost always non-transparent as they come from the scanning application, so would need to be processed to turn the white pixels into transparent ones, then the image saved in a format that includes that channel (such as PNG or TIFF) before Acrobat will recognize them. It won't therefore be a trivial workflow, and you may find assembling and aligning the layers in another application (Illustrator, etc) would be better before saving to a PDF for electronic review.
One caveat - in Photoshop there's an option to save as PDF with a "preserve layers" checkbox, but this does [i]not[/i] create layers that Acrobat can see - it only allows them to re-appear if the PDF is opened in Photoshop again. Documents assembled in Illustrator or InDesign and saved to PDF with layers preserved do indeed keep them in Acrobat, but only the top level of the tree. Although the PDF specification supports multi-layered layers, it won't let you create them individually.