Layers – Freeze/Thaw vs. On/Off

I have been asked numerous times about the differences between freezing/thawing and turning on/off layers in Autocad. There are quite a few differences but I’ll just briefly touch on the high points…

At first, the differences may not be apparent because the results of freezing or turning off a layer appear to be the same….stuff disappears from your screen. The main difference between the two is how Autocad “sees” the objects that are frozen vs. turned off. Turning a layer on/off does not force Autocad to do a regen because it retains the object information of the layer when it is off. When a layer is frozen, Autocad releases any information about that layers objects from memory resulting in better performance. The objects are “forgotten” until they are thawed again. Objects that are on a layer that is turned off can still be selected if you use the select/all or select/similar commands. This could become a problem when you inadvertently erase the entire contents of layers that are turned off.

The on/off button was originally built for speed. Those of us old enough to remember what a 386 or 486 computer is are probably chuckling at the memory of running to the store for coffee and donuts while your computer performs a regen….and then having time to eat donuts and drink coffee when you returned and it still wasn’t finished. Back then, you could use on/off to hide layers and continue working without forcing Autocad to regen. With the computers we have currently, there is VIRTUALLY NO REASON to use the on/off button in layer manager.

Another difference between the two is how layers within a block are handled…which brings us to probably THE ONLY REASON TO EVER TURN OFF A LAYER. In the following example, I’ve frozen the B-WIPEOUT layer to better see window W-1. The window block is on layer A-WIND-INT but there is a sill within the block on A-WSILL-INT…

Layer FreezeThaw01

If you were setting this drawing up for a ceiling plan sheet, you would want to see the window sill lines but not the window itself. This can be done by turning off A-WIND-INT which does not affect the A-WSILL-INT layer….see the screenshot below. Freezing A-WIND-INT would make the entire window block go away, including the sill.

Layer FreezeThaw02

With the B-WIPEOUT layer now thawed, look what happens to the window tag when layer T-WIND is turned off

Layer FreezeThaw03

The window tag disappears and will not print, but the wipeout hatch remains on the screen because the B-WIPEOUT layer is not affected by turning off T-WIND. In this scenario, the wipeout hatch will remain on and carry thru to any drawings that this one is xreffed into….and it will be effective in hiding anything that it is on top of. The T-WIND layer should have been frozen in lieu of turned off. I frequently get calls about random objects (usually leader ticks) and/or wipeouts appearing on screen and in printed sets. The answer is most always that a layer that should be frozen is turned off somewhere. With the amount of xreffing in modern drawings, tracking down the culprit can sometimes be quite a task.

Until next time…

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