Tips for CAD external reference and its applications in design
The following contains contents and concepts about external references that you can easily find on the Internet, I’ve also made some modifications to them and I would like to share with all of you.
The xref of CAD has made design more convenient and save more time — different designers can share design information and improve precision and collaborative efficiency. The following is how to use xref and its main functions, in order to better illustrate the tips and tricks about it, I take the architectural industry as an example.
Xref or External Reference is a method in CAD system to refer to other drawings in the current drawing.
There are two ways in CAD to import other graphics to the current drawing: Insert graphics as blocks; use xref to refer.
When inserting graphic files as blocks into drawings, the definition and related graphic information of the blocks will be saved in the current drawing data and there is no link between current drawing file and the inserted file. Using the Xref, however, will not save the related information of the referred file in the current drawing, it only records the location, name and layer states of the Xref, so when opening a file containing Xref, it will search for the Xref file according to the path. If the original Xref file is modified, graphic files containing this Xref will automatically update. In architectural and other industry where collaboration and cooperation are needed, the Xref can make sure the project team always get the latest updates and unnecessary copies and lagging information can be replaced by better design quality and team efficiency.
2. The advantages of xref
There are many advantages of xref, I would like to name few of them take architectural industry as an example.
- Ensure consistency and collaboration of different departments
Xref can make all groups and teams of the same project keep in step with each other in design and modifications. For example, if the construction conditions has changed, other groups just need to open the modified drawing or reload the current drawing to see the latest changes, and they can continue their work according to the latest construction conditions.
- Smaller file size
Files containing xref just record a path and the size of the file won’t change much. Using xref can greatly increase the speed of generating graphics by attaching xref files to smaller graphic files, which generating complex graphic files. In design process, we can easily handle graphic files that need cooperation from multiple project teams if we use xref in CAD system.
- Improve drawing speed
We have know that using xref will get us the latest updates of the drawing, and it’s easy to understand how much benefits we can get: speed improved and time and energy saved.
- Optimize the number of design files
One Xref file can be referred to by multiple files and one file can refer to the same Xref file multiple times, making the graphic files number to the fewest and therefore improve the efficiency in file management.
3. Related operations and concepts about xref
Enter XREF command to open the external reference manager, shown as the following picture.
Please note: different CAD software or different version has different interface but similar functions.
- Types of xref
There are two types of Xref: Attachment and Overlay, as shown in the following picture.
Normally, we don’t make any distinction between those two unless nested reference (Nested reference is to have Xref in the Xref graphics) happens. The former will have the nested reference lined to the current graphic file while the latter will not and this is to avoid circular reference (a situation where the current file refers to itself via another file).
- The Unload and Detach of xref
If the current drawing doesn’t need the xref anymore, we can click the Detach button to delete the xref and the detached file won’t have any connection with the current file any more. If we want to hide a certain xref but we don’t want to cut off the connection, we can click the unload button to do this. When we reload the xref, the information will be recovered, this is like layer freeze and thaw, which all improve the running speed and efficiency of the CAD system.
- Bind of xref
Having said a lot about the advantages of xref, but there also the disadvantages. For example, if the xref is deleted or moved to other places, or we forget to attach the xref files when sending files to other will all affect the normal display of the xref in the graphic files, in this case, it can only display the path and name of the xref. We can bind the external files to the current files when completing a project or sending a third party drawing files. Bind will convert the xref to standard internal block definition and be an inherent part of the graphics.
There are two ways to bind:
• Bind the xref to the current drawing to make the xref a part of the current drawing.
• Use XBIND to add settings and objects of the xref to the current drawing.
Bind and Insert are two types of Bind: Bind xref changes the name of the xref while Insert doesn’t. To bind a nested xref, we must select the upper level of xref.
Bind the selected xref to the current drawing. The x-ref-dependent naming properties or objects will change from reference name|definition name to reference name$n$definition name, those properties and objects include layers, text style, dimension style, blocks and line type. For example, if the xref named FLOOR1 contains layer named WALL, the layer manager displays the layer name as FLOOR1|WALL before binding, and the layer name will change into internal definition layer named FLOOR1$0$WALL. If the internal named objects have already existed, the number of $0$ will automatically increases. For example, FLOOR1$0$WALL has already existed in the drawing before binding the xref, then xref-dependent layer FLOOR1|WALL will be renamed as FLOOR1$1$WALL.
When inserting, the x-ref-dependent naming properties or objects don’t use the form of “block name$n$symbolic name, but directly remove the xref name from the name. For the inserted graphics, if the named objects in the current drawing have the same name as the bound xref-dependent named objects, new names won’t be added to the symbol table, the bound xref-dependent named objects will use the properties of the defined name objects in the current drawing. Using the same example, if the xref named FLOOR1 contains layer named WALL, xref-dependent layer FLOOR1|WALL will become WALL after using Insert option under the Bind. If there is WALL layer in the drawing, we can directly use the settings for WALL layer in the current drawing.
XBIND command can bind Xref settings or block definition to current drawing and add Xref-dependent named objects in the current drawing, such as block, text style, dimension style, layer, and line type. As shown in the following picture.
Those bound layers, settings or blocks will remain in the drawing even the Xref is detached.
For archive, to make sure the xref graphics don’t be modified, binding the xref to graphics can be really useful, it’s also a simple way to send files to proofreaders.
- CLIP, partial reference
Using XLIP command, designers can edit with a rectangle, polygon, or select boundaries with closed polyline to refer to parts of the internal boundaries. We can switch on/off the XCLIP status. Similar operations apply to blocks and graphics.
Command and prompts are as followings:
Select object: 1 found/ select object: Enter clipping option
[ON/OFF/Clipdepth/Delete/generate Polyline/New boundary] <New>
4. Some tips for the xref in the architectural design
Xref is simple to use, but there will be some problems in the architectural design process, these problems could be a poor command of the Xref function so I’ve concluded some tips from my own experience, hope they’ll help you in some way or another.
- There are strict standards for Xref in the architectural industry. Industrial and civil projects have different standards and therefore respective rules are needed to follow. They all need to strictly control layers, irrelevant contents can’t be displayed in the xref files, or it will cause great inconvenience to aother project group.
- Using the same version of the drawing software is very important to perform perfect Xref function since the Xref functions differently in different version. Or else, the drawing speed will be affected and the whole efficiency of the project team will slow down.
- Project teams need to have a uniform naming rules for the Xref file and can’t have symbols in the file name in case of reference failure.
- The BASE of Xref file is the basics of collaborative design and all project groups should set (0, 0, 0) as base point by default, which is the intersection point of A axis and first architectural plane.
- There shouldn’t be any content at the 0 layer of the Xref since the 0 layer and attributes of 0 layer in the current drawing (color and line type) will overlap the 0 layer and attributes of 0 layer of Xref file when using Xref.
- Don’t directly delete the Xref file if you don’t need it anymore, instead, you should use the Detach button in the External Reference manager to remove the Xref.
- Xref files can modify the scale and rotation angle just like the blocks.
- The referred graphic file name can’t be the same as the block name of the current files, or else, it won’t be referred. And in this way, we can only refer after changing the block name.
- Don’t directly delete or bind nested Xref.
Xref is very effective in architectural design as well as many other designs that need collaboration and cooperation of different project groups and teams. It can minimize the size and number of graphic files to the fewest, reducing the time for repeated drawing and modifying drawings.
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