Whether And When To Purge Drawings

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Cleaning out the clutter cuts file size and processor time. April 11, 2005

When emailing a drawing, we purge it to reduce its size. We sometimes also zip it. Someone has suggested to us that we should be purging the drawings all the time to improve the computer performance. How do other people feel about this?

Forum Responses
(CAD Forum)
From contributor A:
I guess it depends on how much junk you have in the drawing. When I start a drawing from scratch using my template and Iím not inserting anything from an architectís drawing I donít purge until Iím finished. If you constantly purge you have to pick and choose which items to keep or purge. For me, this becomes too time consuming and I always accidentally purge out something Iím going to use later. If I have a drawing where I am harvesting items out of an architects drawing, I will purge if I bring over some unwanted stuff.

When working on a large project I will break the drawing down into reasonable files to keep my system from becoming sluggish. I also have a blank drawing saved that has my template setup, so if I need to repopulate my dim styles or layers I just insert it and everything is back at the click of the mouse. I imagine everyone has a different system for achieving this, but this one has served me well. I am always looking for the fastest way to get down the road so any ideas posted are always worth looking into.

From the original questioner:
To contributor A: Thanks, it is always useful to see how what you are doing compares to another person's approach. We seem to operate the same way I'm glad to hear. I imported an architect's floor plan into my drawing last week to arrange the furniture and the file size went up to 7.7MB - a good time to purge.

From contributor B:
Here's something that I found, I think on this forum - sorry I can't give credit to whomever posted it, but I won't take credit either. I find this useful...mainly since it's pretty much what I've always done. This is paraphrased from the original to keep it simple.

Working with Architects files:

1. Make a copy of their file. Always keep a clean copy of their file to refer back to if needed.

2. Use layer manager to make sure all their layers are unlocked, thawed, etc. so you can see everything.

3. In model space, Zoom extents. Look for any stray stuff that may cause a layer to not purge. Look for "blank" text entities, or points that may be floating around somewhere.

4. Delete all layout tabs to get rid of any titleblocks or trash hanging around in paperspace. One little note floating way off in PS will prevent that layer from purging.

5. Set layer to 0, and purge all. This gets rid of a lot of stuff, but not everything.

6. Type xref to see if there are any attached. If so, bind them if you want to keep them. Otherwise, detach them.

7. Purge again. This will clean up more garbage. Some entities may not purge out if they are nested in blocks. If a block contains entities drawn on layers A, B, & C, but the block is inserted on layer D, you may have to explode the block (perhaps multiple times) or delete it, to get rid of those layers. I find that is usually the reason why entities don't purge...they are blocks within blocks (within blocks!) This takes some sleuthing to decide whether you want to keep a block and use it or totally delete it. I experiment by copying a block and doing multiple explodes to see how nested it is.

8. Use layiso command to isolate layers and see what's on them and whatís not. Layon and Layoff work nicely too.

9. Take what you want, like an Archies floor plan (IMO, it should all be on one layer, and pedited), and cut/paste into your drawing file. Put it on the layer of your standards, and then delete the Archies layer so as not to pollute your file with other peopleís layer standards.

10. Save a copy of the clean and purged drawing - you may want to snatch something else from it. I routinely scour other peopleís drawings for blocks and stuff that I can use. I've gotten some nice looking faucets, and plumbing fixtures that way.

One thing that I still have trouble with is when someone screws around with rendering - it creates an "ashade" layer that I always have trouble getting rid of. If anyone knows how to delete these layers I'd appreciate a heads up. It probably is something relatively simple.

We have a standard shut down procedure to purge out unused blocks, layers and other poo once a job is completed (i.e. plotted for submittal) and before the CAD file is archived. This helps keep our standards consistent. We've got legacy data that is just full of bad drawing practices from the past, and it's a pain when we've got to go back into one of them for something. When I get around to it, it'll be automated with a lisp routine to make the process easier for all our users to be assimilated.

From contributor C:
Here's a little lisp routine I used in ACAD2002 (doesn't work in ACAD2004 yet). It will purge the drawing 3 times then do an audit. It's called Clean-N-Audit, load it then type CNA to run.

(defun C:CNA ()
(princ "\nAutomatic Purge for AutoCAD 2002\n")

(command ".purge" "all" "*" "n")

(command ".purge" "all" "*" "n")

(command ".purge" "all" "*" "n")
(command "audit" "y")

From the original questioner:
Would I be right in thinking that compared to us furniture folk, architects have super computers with incredible graphics cards to produce these drawings? In AutoCAD samples there is a drawing of the Sydney Opera House in 3D with shading and the Harbour Bridge in the background. This has been stored at less than 1MB and does not cause our computers any grief. However some of our attempts at 3D produce drawings of single tables which slow the whole computer right down even at 2MB file size.