Project Setup: The XREF command

I thought it’d be worth the time to dig into the XREF command options a little more.  Two in particular can have a big impact on model portability, the reference type, and the path type options.

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Path Type

The options available for path type are Full path, Relative path or No Path. However, if you are in a temporary drawing, the relative path option is not available to you.  So, before you attach xref’s you should save the current drawing where you will need to store it.

The full path type is most suitable for reference files that are specific to your company or location.  The full path contains the entire file name in the reference to locate the drawing file.  The path will include the drive letter and the entire folder structure down to the file (P:\Projects\Project subfolder\Drawing.dwg). For example, a reference to a different project or go-by drawing file that you won’t pass on to other people may use a full path.  Because the entire file path is included, in order to properly view the files without editing the location, the structure must be duplicated.  Personally, I have spent a lot of time going through drawings fixing the external reference path.  So far, I haven’t run across a good way to change the path in a bunch of drawings at one time, so if you know one, please let me know.

The No path and relative path options are to be used with drawings that you will end up sharing.  The No path option is the simplest as it requires that the drawing be stored in the same folder as the current drawing. 

The relative path option is probably the most used.  AutoCAD has a mechanism used to calculate a relative folder path which allows us to link files pretty easily.  If you’re path is really complicated, AutoCAD may not be able to calculate the path which will force you to use a Full path.

My personal favorite is to use the etransmit command, and specify that all the included files have relative links.  The etransmit command also has an option to bind and save the files to previous version making this the easiest way to send information to clients.  Of course, when you’re working with 3D models, the command may take a long time due to large file sizes, so make sure you leave enough time to process your files.

Reference Type

The reference type option is confusing at first for people who aren’t used to thinking about it.  Most of the time we work with other drawing files like they are blocks…they just come in every time we want them.  The Attach reference type acts most like a block.  It’s going to pull the file specified every time it can (even if you already have it in a different drawing that is already referenced).  Because it always brings the drawing in, the Attach option can cause circular references.  In general, you nearly always want to use the Overlay option.  However, just because there can be bad side effects doesn’t mean the attach option shouldn’t be used.

Let’s assume we have 3 drawings, 1 steel model (steel.dwg), a piping model (piping.dwg), and an equipment model (equip.dwg). 

As a piper, every time I open up the piping.dwg, I need to see the equipment.  In addition, I want anyone who uses my piping model as an xref, to see the equipment.  Otherwise, my steel guy will have to figure out what pieces of equipment need to be inserted into my piping model.  In this situation, the reference type should be set to attachment so that everyone will always see my equipment with the steel.

Let’s look at this from the other side, as a steel designer I need to see the piping and equipment.  However, I don’t want anyone who references my model to see the piping and the equipment (especially the pipers!).  In this situation (and most others) the reference type should be set to overlay, since I’m not concerned that my reference to piping/equipment get passed on downstream.

Hopefully, that explanation is clear.  Like I said, this concept can take a while to wrap your head around, but once you do, it can solve a lot of problems.

On the troubleshooting side, often times when creating piping layouts, designers may wonder where a piece of equipment is.  If you can see it in the piping model, but not in the layout drawing chances are it got referenced as an overlay instead of an attachment.