I. Concept of external reference
You can select the interpretation of the external reference from the CAD help:
You can attach an entire drawing to the current drawing as a reference drawing (external reference). With external reference, changes made in the referenced drawing will be reflected in the current drawing. Attached xrefs are linked to another drawing instead of being actually inserted. Therefore, using external references can generate drawings without significantly increasing the size of the drawing file.
By using reference drawings, users can coordinate their work by referring to other users' drawings in the drawings, so as to keep pace with the changes made by other designers. Users can also use component diagrams to assemble a master diagram, which will be modified with the development of the project.
Make sure that the latest version of the reference drawing is displayed. When you open a drawing, each reference drawing is automatically reloaded to reflect the latest status of the reference drawing file. Do not use layer names, dimension styles, text styles and other named elements that already exist in the drawing.
When the project is completed and ready for archiving, the attached reference drawing and the current drawing will be permanently merged (bound).
The above statement is very abstract. Briefly explain: Suppose A is the current drawing and B is the drawing for external reference. When B is inserted into A as an external reference, the contents in B can be completely displayed in a drawing, but the size of a drawing will not change obviously when it is saved, only the path of B drawing is saved. When Figure B is modified, the part of Figure B in Figure A will be updated automatically. If Chart B is deleted or removed, the contents of Chart B will not be displayed when Chart A is opened again. Therefore, when Figure A is transmitted to others, Figure B must be transmitted to the other party together. When Figure A is opened, Figure B is modified and saved. Figure A will prompt that the external reference has been updated and can be directly overloaded. Besides inserting B in Figure A, other diagrams can also be inserted as external references. Besides a diagram, you can also insert a diagram as an external reference into other diagrams.
Second, the simple application of external reference
I don't know if the tongue twister-like text above makes the basic characteristics of the outer finger clear, which may be more clear in combination with practical application. At present, external reference has two main uses: standardization and collaborative design.
Design companies usually have their own drawing specifications, which stipulate that the parts that need to be unified in the drawings should either remain unchanged or need to be unified, such as drawing frames. Some companies use template files, some use blocks, and some use external references. The advantage of using external reference is that as long as the original drawing of the drawing frame is modified, all drawings that reference this drawing frame will be automatically updated.
Simple collaborative design can be carried out by using external reference. Taking architectural design as an example, architectural design includes not only architectural drawings, but also HVAC, water supply and drainage, and electrical design. The majors of plumbing and electricity can use the architectural base map as an external reference, and then draw their own design content on this basis. When architectural designers update the architectural base map, the base map of the downstream specialty can be updated automatically, and they only need to adjust their own drawing parts according to the architectural drawings.
Third, the difference and connection between external reference and block
A block is a graph combination defined in a graph, which can be copied, inserted and deleted as a whole. After defining a block, the block definition will be saved in a CAD drawing file, and then it can be referenced repeatedly. Blocks referenced on a drawing are also called block references. Even if all the block references on the drawing are deleted, the definition of the block still exists (unless it is cleared) and can be inserted again at any time.
When inserting blocks, you can also browse other DWG/DXF files directly and insert external files as blocks, so people will have questions: What is the difference between blocks and external references? Although all external files are inserted into the current drawing, after being inserted as a block, the inserted drawing has nothing to do with the original file, and all drawings have been saved in the current drawing. Even if the external file is deleted, it will not have any impact on the current drawing. Of course, the inserted file will not change with any changes in the current drawing, which is obviously different from our previous description of external references.
Block is more widely used in drawing. After all kinds of equipment and parts are made into blocks, the drawing efficiency will be greatly improved. Many professional softwares, such as Chen Hao Architecture and Chen Hao Machinery, provide a large number of galleries, which can be directly called. The use of external reference usually depends on the requirements of the design unit, and individuals rarely use external reference. Block now has many extended applications, such as attribute block and dynamic block.
Fourthly, about the editing of references.
Both blocks and xrefs can be edited by reference. The operation forms are basically the same, but the results are different. Reference editing of a block is equivalent to directly editing the block definition saved in the drawing. After modification, all block references with the same name will be updated automatically. Reference editing of an external reference is equivalent to editing the referenced original drawing. After editing, not only the external reference in the drawing will be modified, but also the referenced original drawing will be modified.
After editing the reference, you need to close or save the reference in the reference editing toolbar to exit the reference editing status, otherwise many subsequent operations such as saving cannot be performed. And prompt "XXXX is not allowed by reference editing status". If you accidentally edit the reference toolbar, you can run the refclose command to exit the reference editing status.
In earlier versions of AutoCAD and Chen Hao CAD, double-click the common block to enter the reference editing state. If you double-click the attribute block, the enhanced attribute editor will pop up. If you double-click a block in AutoCAD 2007 or Chen Hao CAD 20 12, you will enter the state of block editing (dynamic block). If you can't directly enter the reference editing by double clicking, you can enter the refedit command, or open the reference editing toolbar and click the reference editing button in the toolbar.
Some blocks cannot be edited by reference, such as anonymous blocks with * names, multiple inserted blocks and blocks with unequal XYZ proportions.