Revit Links - Overlay vs Attachment

[Bluefairy]

is overlay vs attachment a similar concept to autocad xrefs? If you attach a revit link, any changes to the link file will not update?

[Steve_Stafford]

Exactly the same concepts

[dkoch]

is overlay vs attachment a similar concept to autocad xrefs? If you attach a revit link, any changes to the link file will not update?

As Steve said, the concepts are identical, but not as you described. Attached or overlaid, either will update to the current version when the host file is reopened (or, for a work-shared file, when synchronized). The difference is that an attached Revit link will come along for the ride if the host file is linked, while an overlaid file will not.

[Bluefairy]

In an attached xref drawing, the attachment does not update if you alter the attached xref file. It acts like a block. Yet it revit, an attachment will updated?

[Steve_Stafford]

Choosing between attached or overlay is to determine how Revit should regard it when the host file is linked into another file. For example, if File 1 is linked into File A and set to "attached", when File A is linked into File B, File 1 will also also be loaded into File B. If File 1 is changed, when its host File A is reloaded in their host File B, File 1 changes will also be seen, if its own changes have been saved before Reload is used. Both files are read independently during a Reload. You will only find the host File A listed in File B's Manage Links dialog however. Written another way, when a link is reloaded, it's attached nested links will also be reloaded.

When Overlay is chosen instead File 1 does not get loaded into File B. No circumstance will cause it to appear nor will we be aware of changes within the link.

We should use the "Attached" setting when we link a file into another file AND expect its own linked files to show up as if they are native elements in the file too. Changes in either the parent or child will appear when the parent file is reloaded into its host or if the host file is opened after changes have occurred in either.

If we create an architectural model that uses linked files for repeating units they will need to be set to Attached if we want the units to appear when linked into a structural model. When we pass along our model to the structural engineer we will need to send both the "parent" architectural model and the "child" repeating units. When we link in their structural model we should use "Overlay" so Revit does not try to load their structural model when the structural engineer links our architectural model into their model.

[dkoch]

In an attached xref drawing, the attachment does not update if you alter the attached xref file. It acts like a block. Yet it revit, an attachment will updated?

The updating is not "live" in either AutoCAD or Revit. After the the external file is updeated, you have to reload the external reference in AutoCAD or reload the link in Revit (as Steve described in more detail).

In AutoCAD, an external reference is similar to a block, but the definition remains external and even if you do not reload the external file after a change has been saved to it, if you close the host file and reopen it later, the updated definition will appear (whether it is placed as ATTACH or OVERLAY). An block definition (internally defined), created by INSERTing another file, will not update, unless the file is reINSERTed.

[patricks]

In our workflow, we, and all our consultants, link in each other's files always using Overlay. That's because I have the RST and RMEP files linked into my file, so I don't need to see the RMEP file that is linked into the RST file. Nor do I want to see the FTP version of my file that that consultants always use to link into their files, because I'm already in my file live.

[trongdong]

clearly, thanks