AutoCAD’s magic vanishing attachments

There are now quite a few file types that you can attach to an AutoCAD drawing as a reference, in the same way that you can attach other drawings as xrefs. We’ve been able to attach other drawings since Release 11 (1990) and images since Release 14 (1997), but every release since 2007 has introduced a new kind of attachment. In AutoCAD 2010, you can now also attach PDFs, MicroStation DGNs (v7 and v8), DWF and DWFx files.

But should you? Maybe not. It depends who is going to use those drawings after you. If you know for certain that every user of that drawing is going to be using 2010 and later, that’s no problem. But if there is the possibility of earlier releases being used, your fine-looking attachments could vanish silently in the night. Attach a PDF to your drawing in 2010, give it to a user of last year’s AutoCAD 2009 (you’ll need to save it as a 2007 DWG) and what will he see? Nothing. There is no text-screen warning, no bounding box, no piece of text indicating the file name, nothing. Just a blank space where there should be useful drawing content.

This problem isn’t new to 2010, because there are similar problems with the other recent attachment types. Let’s examine them one by one:

  • PDF – visible only in 2010 and later (except for the special case of 2009 with the Subscription-only Bonus Pack 2).
  • DWFx – visible only in 2009 and later.
  • DGN v7 – visible only in 2009 and later.
  • DGN v8 – visible only in 2008 and later.
  • DWF – visible only in 2007 and later.

It’s important to note that the attachments don’t actually disappear from the drawing. They are still stored there, even if you save to an earlier DWG format like 2000 or 2004. The attachments survive the round trip to an earlier DWG format intact; they will reappear just fine if reopened in 2010. (Round-tripping of new object types is something that Autodesk has done extremely well over the years).

In most cases, the objects are stored invisibly as proxy objects (object name ACAD_PROXY_ENTITY, known in the early days as zombies). In some cases, they are listed as special Underlay objects (e.g. DGNUnderlay, DWFUnderlay). In 2000 to 2006, they all list as proxies. How can you list these objects in earlier releases when you can’t see them? With a bit of LISP, or old tricks like LIST ALL Remove Crossing.

The moral of the story for drawing creators is to look before you leap whan attaching new object types. For drawing recipients, it’s something to carefully watch out for. If you’re the customer and you use an earlier release, you may even wish to include a don’t-use-this-attachment-type clause in your specifications.

1 comment to AutoCAD’s magic vanishing attachments

  • Chris Wade

    This is one good to reason to make sure that you always have the latest release. We love being able to attach PDFs to our drawings, it makes attaching our Title 24 Compliance forms (a California requirement) much easier.

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