Using reference files in MicroStation is nothing new. It has been a powerful tool since its Intergraph days. Using references for large models was essential before the file format was changed. This was due to a file size limit of 32 Mb for the DGN file. Yes, you read that correctly: 32 megabytes. How did we ever cope with that? I remember using many reference files while processing mapping data and compiling 1:10,000 scale contour maps over the Herbert River area.
What a Reference File Is
A reference file is a DGN attached to the model you have open and displayed alongside your own graphics, without being copied into it. The attachment stores a path to the other file and the position, scale, and rotation it displays at, so the referenced design stays in one place and every model that needs it points at that single copy. Save a change to the referenced file and every attachment picks it up on reload. Elements in a reference cannot be edited from the active model, so to change one you exchange into the reference file and work on it directly.
While there is no longer a file size limit, the use of reference files remains a highly effective method of managing CAD data. It allows for the segregation of different design disciplines, such as Civil, Plumbing, Electrical, and HVAC, into separate models. This not only facilitates simultaneous work by different team members but also enhances the overall efficiency of the design process.
MicroStation attaches a model rather than a whole file, so one DGN can hold several models and you attach the one you want. AutoCAD does the same job with external references, and if your organisation runs both formats, missing AutoCAD Xrefs covers the same ground on the DWG side.
The References Manager
The list of what is attached lives in the References dialogue, which Bentley documentation also calls the Reference Manager and which people commonly search for as RefManager. It is the one place that answers what the model you have open is actually made of.
For each attachment it shows the file, the model being attached, the logical name and description, and the full path the file was found at, along with the toggles that control display, snap, and locate. Working from that list you attach and detach, reload after somebody else has saved, move or clip an attachment to a boundary, and reorder attachments so the right one draws on top.
Two settings on that dialogue are worth agreeing across a project before the drawings multiply:
- Relative or absolute paths. A saved relative path lets a whole project folder move, or be copied to another machine, with the attachments intact. An absolute path survives the master file moving on its own and breaks the moment the folder tree changes around it.
- Logical names. A logical name labels what an attachment is for rather than what it happens to be called on disk. It is the difference between a list a drafter can decode and a list a reviewer can read.
Assigning a Level to a Reference
In the early days, MicroStation's referencing features were not as capable as AutoCAD's Xref feature set. However, with the advent of MicroStation V8i, the software introduced the ability to assign a Level to a reference, a significant enhancement. This feature is accessible from the Reference Attachment Settings window, and it changed how a combined model gets managed.
Let's say we are modelling a water treatment plant. We have a separate model for each discipline, such as Electrical, Structural, and Plumbing. Each model has many levels to represent the different items in each discipline.
After attaching all models into a combined design model and then into a sheet model, there would be so much detail about each discipline. Turning off disciplines becomes cumbersome as you must turn off each discipline reference level. Assigning a level to the reference makes it easier to manage the final model. So, instead of managing multiple levels per reference, we only work one level per reference.
When a Reference Breaks
Attachments break when the file they point at is moved, renamed, or sent on to somebody without its dependencies. The master file still lists the attachment and still records the path it expects, and nothing displays.
To find them, open the References dialogue and read the path. An attachment that cannot be resolved shows the saved path with nothing found at the end of it, the same failure AutoCAD reports as a missing Xref. Nested attachments are the ones that hide, because a reference two levels down can be missing while the model still looks broadly right on screen.
There are three fixes, in ascending order of how long they hold:
- Repoint the attachment. Detach and reattach against the file's new home. This fixes one model, and only until the folder moves again.
- Set the search path. MicroStation resolves reference file names against the directories listed in the
MS_RFDIRconfiguration variable, so adding the new location there fixes every model that looks for that file, without opening any of them. - Stop depending on the folder tree. Reference paths break because a directory structure is the only thing recording the relationship. A system that reads the attachments out of the DGN and holds them as a recorded relationship no longer cares where the file sits on disk.
Handover is where this bites hardest. A package of DGNs arrives with attachments pointing at a consultant's folder structure that you have never seen and never will, and the gaps go unnoticed until somebody needs the drawings for maintenance years later.
Tracking References Outside MicroStation
Reference files are a great way to manage your CAD data within the MicroStation system; however, if you are storing your CAD files on a network drive or a system like SharePoint, there is no easy way to know what files are referenced to each other. Many current Engineering Data and Drawing Management Systems, such as Lunr, can read and manage the reference information within your DGN files. This allows you to easily search and find all related models without the need to open each of the models. They also enable non-CAD users to view the models with all references without requiring a MicroStation installation.
Lunr reads DGN through the same CAD connector it uses for DWG and Revit, so the attachments arrive as part of the record rather than as something a drafter has to remember. See drawing management software for how the rest of the drawing record fits around them.