About the invalid Home entry, I don't think it's worth trying something; first, if it's corrupted, the other entries (if present) are generally not accessible because it's the first entry in the file. Second, the other entries contain images or 3D models with no information about their role, place and size in the plan.

Well, you're right that if the first entry is not accessible probably neither would be the rest of entries. But in case they are, would depend on each case that it worth to extract or not.

If the user has other copies of the images/objects or he/she can access these elements any way then all is fine, but I just think of the possibility that the user has no access to the elements he/she used and doesn't have other copies. In such cases I guess it would be interesting to recover what can be recovered so it can be used in a new project, even if some information like the size is lost. Let's say it's just a way that user may think at least not everything is lost. [:)]