External Files: Hotlinks and XREFs
The previous chapter introduced Teamwork, the primary collaboration method in ARCHICAD. Now let’s evaluate the other basic project-sharing solution/internal collaboration method: the concept of linked external files.
This approach, typical for almost all CAD applications, allows you to develop and store parts of the main project file - also called the host - in a separate external file - also called the source file. The project file (host) includes only a reference (hotlink or Xref) to the content of the source file. Modifications to the source file can be updated and represented in the host file.
The project file can contain several instances of the same linked content, making this method ideal for managing repetitive elements in a project. According to the type of the linked file, we can distinguish two solutions in ARCHICAD:
•Hotlinks of ARCHICAD files and IFC files
•Xrefs for 2D drawings saved in DWG and DXF format
Hotlinks are external ARCHICAD files, such as modules (.mod), plan files (.pln), and Teamwork projects, or IFC files inserted into the currently open project (host). Hotlinked elements inserted into the host reflect all modifications made to the source files (as soon as you update the hotlinks). Hotlinked elements are included in the Project, which means that even if the hotlinked source file is not currently available, the placed hotlinks are still present and visible, although they cannot be updated as long as the referred source file is absent.
ARCHICAD also supports nested hotlinking: that is, hotlinking a file which itself contains a hotlink. These are called nested modules.
One workflow is to split an ARCHICAD model into multiple PLN files, then hotlink them to each other as modules. For example, you can save the building facade as a separate file from the rest of the building, or save two wings of the building in separate files. You can hotlink the two files of the “split” model into each other automatically.
ARCHICAD’s Hotlink Module Manager dialog provides an overview of the hierarchy of even very complex hotlink file structures, plus feedback on the status of the individual source files (e.g. missing, modified). Updating the entire hotlink structure, or just individual source files, requires just a mouse-click.
For example, hotlinks can be used to manage the repetitive structures of buildings, such as hotels or offices, which have a large number of identical rooms: you can modify all instances in a single step. Moreover, the same structures can be used in multiple projects.
If a building contains several identical stories, you can hotlink the typical story of the host file into the other stories.
Hotlinking in ARCHICAD
The hotlink solution has advantages and disadvantages compared to the Teamwork method. The concept itself is easy to understand and can be used with any kind of project. It can be very effective when multiple instances of the same elements are used in a project (e.g. the rooms in a hotel). However, the hotlinked file method cannot solve the project coordination problems of an architectural firm, since the project owner doesn’t get any feedback about the kinds of changes made in the source files. The location and name of the source files are critical to project consistency, so this method requires active file management from the project team leader. Furthermore, if the project is complex, changing the hotlink file structure can be very difficult at a later stage of the design.
•Hotlinks can be updated whenever their source files are modified.
•Updating hotlinks is fast and easy.
•The host project file size can be greatly reduced by placing repetitive elements as hotlinks.
•Hotlinks enable larger models to be divided into smaller, easier-to-handle logical parts.
•Teamwork projects can also be hotlinked to each other. This way, the size of the Teamwork project files and the regeneration time of the 3D models and the documentation can be reduced significantly.
•Comprehensive user interface provides a clear overview of hotlinked file instances and hierarchy.
•Owner of the host file doesn’t have automatic control over the content of the hotlinked source files.
•Changes to the hotlinked source file can cause conflicts in the host project.
•Moving or deleting the hotlinked source file will break the hotlink to the host file.
•A detailed module organization chart has to be created by the project coordinator before the project is started. Changing the hotlink structure can be difficult in later stages of the project.
•Matching of attributes needed between the host file and hotlinks.
Tip: To avoid creating unnecessary and unwanted layers, pens, line types, fills, etc. (also known as “attribute pollution”), you can hotlink a story inside the host project itself.
Although hotlinking can be used as an alternative to the Teamwork technology (e.g. different floors of a multi-story building can be managed as separate hotlinks), they can’t provide the same flexibility and security as Teamwork. The main purpose of using hotlinks should be to manage repetitive elements and to divide very large projects into easy-to-handle smaller parts.
External References (Xref’s), like hotlinks, are linked external files. However, they can only be used to reference 2D drawings. Xrefs provide an easy way to manage and merge the consultants’ DWG/DXF drawings into the ARCHICAD project. External DWG/DXF drawings will be updated in the ARCHICAD project if they are referenced as an Xref.
The Xref Concept
Xrefs Listed in the Xref Manager Dialog
•DWG and DXF drawings from consultants can be easily integrated into the BIM as Xrefs.
•Repetitive DWG/DXF files (such as detail drawings) can be controlled and modified easily.
•Modifications made by consultants are automatically updated in the ARCHICAD project. Collisions and design conflicts can be easily located by using the Virtual Trace feature.
•The content of the Xref drawing is saved with the ARCHICAD project. If the link to the DWG/DXF file is broken, the drawing content is still visible.
•Xrefs cannot be used to hotlink 3D data into the ARCHICAD project.
•DWG Translator Settings must be set manually prior to attaching the DWG/DXF files.
•The location and the name of the Xrefs shouldn’t be changed; otherwise the link will be broken.
•Matching of attributes needed between the host file and the linked file.
Xrefs should be used almost exclusively for merging consultants’ drawings, legacy AutoCAD projects or standard manufacturer details into the ARCHICAD project. We recommend placing the Xrefs onto independent ARCHICAD worksheets, rather than onto the floor plan, to keep the BIM model intact.
Tip: Unused Xrefs should always be “Unloaded” in order to remove all Xref related layers and other attributes from the master project.