Layer Freeze/Thaw vs On/Off
There are two ways to change the visibility of layers - turning it off using the little light-bulb, and freezing it using the little snowflake. Many times I've been asked, "What's the difference between freezing a layer and turning it off?". For years I had no idea what the difference was, or if in fact there was a difference at all! I simply got in the habit of just using the ON/OFF setting, but having found out what the subtle difference between them is, I've changed over to mainly freezing layers because it usually more accurately fits my intent.
Turning a layer off using the ON/OFF setting makes the objects on that layer hidden, but these object will still be considered part of the drawing. For example, you may have noticed that objects that have been turned off are still selectable in the drawing. Selecting it directly on screen of course still isn't possible, as you've nothing to click on. But other ways of selecting objects will still pick it up - try a SELECTALL for example, and your objects that are turned off will be selected.
Frozen layers on the other hand are completely off. They are not considered part of the drawing at all, and are therefore not selectable.
Due to the different ways that AutoCAD® handles these layer properties, each carries a different overhead. Objects on an off layer are basically just as usable in a drawing as if that layer was on, and therefore AutoCAD® has to still prepare the objects in the same way as if they were on. For example, when AutoCAD® regens, these objects will be regenerated too. Frozen layers are meant to be completely ignored, and therefore carry no such overhead.
There are some other interesting consequences of these two layer visibility toggles. ZOOM EXTENTS for example will zoom to the extent of objects in the drawing. As layers that are turned off are still considered part of the drawing, they will affect zoom extents. Frozen layers on the other hand will not.
Finally, there are some differences to how visibility is affected within blocks. Lets say I have a block with objects on layer BLUE and GREEN, and the block itself is inserted on layer RED. Toggling the visibility of BLUE and GREEN works as expected for both methods. However, there is a difference when toggling the insertion layer of the block. If the layer RED is turned off using the ON/OFF toggle, the objects on BLUE and GREEN will still be visible. However, if RED is frozen, all of the objects in the block will be hidden, regardless of their layer.
But why have these two different methods? It is less of an issue now, but historically these were added when regenerating a drawing took a lot longer. Therefore it was helpful to have the option to turn things off without the drawing requiring regeneration every time. Thus, the ON/OFF toggle was helpful for showing what you want, but keeping them available to be displayed quickly.
Hopefully you found this post both interesting and useful. However, I'm a realist - if it was only one of those adjectives, that still aint bad! But if you have your own adjective for describing this post that you'd like to add, please feel free to submit a comment below! :-)
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Thats all for today,
Excellent explanation of OFF vs. Freeze. This was a much needed explanation. I think a lot of us have been fuzzy, at best, about the differences. I am forwarding this to everyone who uses AutoCAD® in my office. Thanks!
Very good subject! I myself took awhile to understand the difference between those two. It is one the confusing commands in Autocad.
Thank you for your post. It was really helpful.
Something for lisp users to be aware of which I just discovered playing with on/off freeze/thaw properties is that: (command ".move" (ssget "x" '((0 . "line"))) "") moves objects on Off and Frozen layers. Not locked ones though.
With your explanation now I know the difference :) thx
Excellent explanation! I have also forwarded this article to our dev team that works on Cad functionality. Thanks for posting this.
WHAT IS THE COMMAND TO TURN ON THE FROZEN LAYER..
Use the LAYER command to open up the layer dialog box, then click the little snowflake symbol to freeze or unfreeze layers.
Thank you. A very easy to understand explanation. I haven't been able to really sort that one out completely myself and I've been using ACAD for many moons. Thanks again and can't wait for more tips.
No problems - more tips is the flavour of the month... expect more to roll in soon!
really ur posting make me to know the differences very welll.... i have a dielemma with this ... now i got clear idea... thanks alot
Very good advices! One more thing, you cannot freeze your current layer, but you can turn it off.
Thank Emi - good advice!
Thank you very much. I really needed that on my present project and it will allow me to complete it quicker than not knowing this.
I am a learner and this was really helpful....I am still confused what "Thaw" does actually......