Encountering BIG Files

File size is one of those parameters that we tend to take for granted. Every file has a ‘size’ and, with the advent of cheap memory and hard-drives, we’ve pushed this and other associated parameters to the back of our minds. After all, we’re being paid to put lines on paper – not to worry about the size of a file. Being recently and rudely reminded that even the "boundless" Internet sometimes imposes limits on us – usually when we are not paying attention and/or facing a looming deadline – it’s worthwhile to take look for BIG file causes and solutions. On that reminder occasion, a floor plan file and a half-dozen XREF’s, totaling about 9 Mb, was zipped up and emailed to a client. An hour or so later a message from the email demon (pun intended) told me in computerese that my message was too big. In other similar cases the attachment was simply dropped and the text message sent on to the recipient. But, NO! Not in this case. My 9 Mb un-compressed file set had turned into a giant 20.5 Mb ZIP file and my client was waiting.

We’ll spare you the details of everyone denying responsibility for the "refusal to transmit" and move on to develop a procedure for early discovery and workarounds to fix or avoid the problem in the future.

Some of the known causes for enlarged files are:

	Corrupted files
	Image files
	AEC Objects
	3D Objects, views
	Exporting to AutoCAD® by Autodesk’s vertical applications
	Save to DWG by other CAD programs
	Scan & Convert
	Round Trips – up and down the AutoCAD revision list

Corrupted files fall into two categories: 1) Those that crash AutoCAD and, 2) those that don’t. In the first case, options are few: a) Find a backup file, b) Run Recovery. If neither of those works you may be out of luck. On one occasion a file would crash AutoCAD when using certain edit commands. Workaround: With the file open, copy the visible contents to the clipboard and paste into a new drawing. This, and the Wblock operation, is also a convenient way to capture just the stuff you want and discard anything extraneous or not useful.

Image files are not "embedded" when inserted into AutoCAD. They remain an external reference file. Large image files can impact Load, Save, Zoom, Pan and Regen operations. DWG files compress about 50% with a commonly used ZIP program. Image files, on the contrary, compress little or not at all. Workaround: Delete or Freeze layers with image files when no longer in use or needed. Convert logo and similar image files to AutoCAD entities.

AEC Objects are generally 3D, Multi-view, and sometimes known as "intelligent," objects. Like an iceberg, however, an AEC object – usually containing multiple views and parametric data - may have 90% of its content hidden from view. AEC Objects are generally created and used in vertical applications (MEP, ARCH, Revit, etc.) AutoCAD will display AEC entities by substituting a "proxy" object with limited editable features as an accommodation. AutoCAD can move, erase and copy certain AEC objects but cannot purge or remove the hidden views and data features. Workaround: Use the original CAD application to generate an "Export to AutoCAD" file. Edit the file with the originating CAD program. Use AutoCAD’s Flatten command to set all Z coordinate values to Zero. (Takes a long time for large files and creates an even larger DWG file). Try the Explode command (sometimes yields unexpected results).

Exporting to AutoCAD is a program feature of Autodesk’s vertical CAD applications, i.e. MEP, ARCH, Revit, etc. In my experience, exporting to AutoCAD always generates a large DWG file, because all objects, blocks, etc. are exploded into basic line, arc & circle objects. For a large floor plan, for example, this explodes all doors, windows, furniture and other blocks into lines – generating a huge file. Workaround: Not many options here. Re-blocking repetitive items is labor intensive but may facilitate easier editing and re-use in other drawings. This feature does preserve text in the original font and style.

Save as DWG is a feature of many CAD programs (other than AutoCAD) and produces a "DWG" file that is their programmer’s idea of what a DWG file should look like. (Some work well, some work poorly, most are not supported by the authors.) Most of these operations take a sophisticated 3D file and export a flat file of lines, arcs and circles. Some export text as text and others export text as line entities which cannot be edited by AutoCAD. Some also export long lines as a quantity of smaller lines – often to the point of absurdity. Such was the case in the 9 Mb example in the opening paragraph. In another example, a 15 Mb floor plan contained no blocks and Audit reported 465,000 entities, an unwieldy file and a pain to edit. Workaround: Using the Wblock-to-a-new file operation cited in the Corrupted topic above, this file was reduced to a manageable 7.5 Mb.

Scan & Convert has been around for many years and there have been some notable improvements in conversion routines. Shop around & test and chances are good you will find something useful. The limitations, however, are often similar to what you get with Exporting to AutoCAD and Save as DWG operations: Broken lines, lines that look like text, no blocks and lots of basic line entities.

Round-Trips are the repeating cycles of creating and editing a file in one version of AutoCAD, saving down to an earlier version, than opening again in a later version. This may cause some file integrity problems but it’s difficult to know because the history of these "open up" and "save down" operations is non-existent. (For more on Drawing Integrity see our Cadtales article on the subject). Some users, for economic and limited use reasons, have not upgraded to the current version of AutoCAD. Workaround: For almost all 2D applications AutoCAD LT is an economical substitute with most of the features of AutoCAD and complete file cross-version support. Avoid round trips internally by hosting your entire drawing library on your current version of AutoCAD and using Etransmit to save-down to earlier versions.

In general a process to test and validate incoming files will discover file problems and offer an early opportunity to find a solution:

Virus-scan all incoming files.
Run File Recovery on all incoming root and XREF files.
Repair errors before starting the design/edit process.
Open project/sheet files in their native application.
Export to AutoCAD if necessary (larger file size).

Do you see a benefit in educating your operators, designing and integrating a drawing quality & validation process into your CAD operation? Contact your Hagerman sales representative for training, custom programming and software upgrades.