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    Senior Member Siberian's Avatar
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    Default What's the difference between layer keys and layers?

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    I'm having trouble understanding the difference between layer keys and layers. Supposedly the layer key is what "tells" an object which layer it should be placed on. I see it like this:

    Placed object → Layer key → Layer

    To me the middle part seems like an unnecessary step. In an object's system definition one selects a layer key. Why can't you just select the layer in the system definition? What is the point of the layer key?
    If at first you don't succeed - remove all evidence you ever tried.

  2. #2
    Luminous Being tzframpton's Avatar
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    Quote Originally Posted by Siberian View Post
    To me the middle part seems like an unnecessary step.
    Actually, it's the contrary. Think about it. Would you rather the unnecessary step come when mapping Layer Keys, or when you're designing? Using Layer Keys means that anytime you initiate an MEP Object Tool, it automatically is placed on the correct layer, with all the correct layer properties - period. You never have to pause, think what Layer you're on, then place the correct Layer current, then start the command. Or you'll never have to go back, select the MEP Object(s) and place them on the correct layer because you missed it to begin with. You're simply "free" to design away without interruptions. This comes in particularly handy when you have multiple systems, such as supply, return and exhaust duct. They can all be mapped to their own Layer and Layer Properties via Layer Keys and all you have to do is select the System of choice before, during or after you initiate the Duct tool.

    Layer Keys are simply a way to "map" AEC Objects to predefined Layers with certain Layer Properties. I've just explained one reason why this is useful above. But there are other reasons too. First, it provides a great way to pre-define Company or Design Standards. All one has to do is place the Pipe or Duct or Conduit on the right "System" and all the proper Layer and Layer Properties are set. No more "What layer does CHWS Pipe go on? And what color is the Layer?" This is not tied to a DWG Template file or anything - you open any DWG file, initiate an MEP Object Tool and it falls on the correct Layer with the correct Layer Properties no matter what. Also, AEC Objects act differently than normal AutoCAD entities. You might have numerous different types or sized objects in a single command (placing a long run of duct, for instance). Well, AutoCAD MEP sees these AEC Obects, but knows it's tied to Systems, which changes the game. So say I place a long run of Supply Duct when it should have been Return Duct. I want to select a piece of Duct in the run, and change the System, not the Layer. The System is what drives the Layer, etc. If I were to simply change the Layer, the System stays the same and can really monkey things up.

    What it truly boils down to is AutoCAD MEP is trying to recreate what Revit has created. But, AutoCAD at its core is married to Layers so this is why Layer Keys exist (my assumption anyways). Revit works the complete opposite. Duct is duct. Pipe is pipe. Conduit is conduit. Walls are walls. There's no Layers in Revit at all. Everything is categorized in a manner that relates exactly like the real world. AutoCAD can't recreate this completely so this is why I assume Layer Keys were put in place to merge the two types of approaches together.

    Have you ever used the Tool Palettes for standard AutoCAD blocks and entities? If so, have you ever used the right-click > Properties option to preset the Layer, Linetype, Rotate on insert, etc? It's basically the same thing just a lot more advanced, and only with AEC Objects.

    Hope this helps clear it up a bit.
    Tannar Z. Frampton | Hill & Wilkinson

  3. #3
    Senior Member Siberian's Avatar
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    Quote Originally Posted by StykFacE View Post
    Have you ever used the Tool Palettes for standard AutoCAD blocks and entities? If so, have you ever used the right-click > Properties option to preset the Layer, Linetype, Rotate on insert, etc? It's basically the same thing just a lot more advanced, and only with AEC Objects.
    Yes, I've done this many a time, and that was my reason for asking my qyestion. As you say - with blocks you preset the layer etc. directly. I'm still having some trouble seeing why it can't be the same with AEC objects.

    Another thing - I noticed different layer keys that lead to the same layer. Then why not just use a single layer key for these objects?
    If at first you don't succeed - remove all evidence you ever tried.

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    Luminous Being tzframpton's Avatar
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    Quote Originally Posted by Siberian View Post
    Yes, I've done this many a time, and that was my reason for asking my qyestion. As you say - with blocks you preset the layer etc. directly. I'm still having some trouble seeing why it can't be the same with AEC objects.
    Because AutoCAD MEP Objects sees the object first, and the layer second. I've explained this with Systems. Changing a duct object from one layer to another doesn't change the system. However, changing the same duct object's system changes the layer. Also, like I mentioned before, this behavior doesn't need Layers, but since it's AutoCAD there must be Layer's in place. The Layer's only confuse things but it's the way it has to be.

    Quote Originally Posted by Siberian View Post
    Another thing - I noticed different layer keys that lead to the same layer. Then why not just use a single layer key for these objects?
    You have a valid point, however this may not be the case for most people. For instance, CHW Supply & Return might be on the same layer. But some engineering firms might want them separated on different layers. Or there might be different types of equipment that all go to the same layer but you need different Layer Key's because they are different types of equipment. There are numerous reasons why this is true.
    Tannar Z. Frampton | Hill & Wilkinson

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