Understanding Layers in Pro/ENGINEER

July 24, 2012

We had a great time at the Northern Ohio PTC User’s (NOPUG) meeting last Thursday.  The weather wreaked havoc on the golf outing and generally scrambled the schedule, but it was a good meeting and Doug’s presentation, although abbreviated, was well received.

For a full copy of the presentation, download it here: Pro/ENGINEER, Understanding Layers.

Enjoy, and please post any questions you have at the end.

Understanding Layers in Pro/ENGINEER

Layers in Pro/E are a powerful tool that allow you to control the visibility of different parts of the model.  Although solid geometry can be placed on a layer (in a single ‘blob’), typically layers are used to control the visibility of non-solid geometry items.  What layers let you do that other built in controls can’t is control individual items, control groups of unlike items together and control items that don’t have built in display toggles.

I’m going to assume here that you know the basics about layers and focus on two specific things that will help you get the most out of your layers on Pro/E.

Understand Visibility Hierarchy

Lots of different types of things can be placed on a layer.  Not only different geometry types (plane, curve, axis, point, etc.) but different object types as well.  Anything from assemblies down to geometric entities can be placed on a layer and, as illustrated above, that gives you various levels of control over visibility.

The hierarchy is easy to see at the assembly or part level. Assemblies contain parts (and other assemblies) and parts contain features.  Hiding an assembly hides all the parts and assemblies inside it and hiding a part hides all the features inside it.  What’s not as easy to understand is that features contain geometric entities.  An obvious example is that a sketch feature contains several sketch entities (lines, arcs, spines, etc.)  within it.   Less obvious is that a datum plane feature contains a plane entity, a datum axis feature contains an axis entity and so on.

The important thing to understand is that once an item is hidden, all of the sub-items below it will also be hidden and they cannot be made visible by any means.  For example, after placing a single datum point entity on a layer and isolating it, it will not appear if the parent datum point feature is on another layer that is hidden.

Understanding this principle will help you make better choices about what to put on layers and to diagnose what’s going on when you can’t get what you want to see to be visible.  I’ve found that only placing features on layers is a good practice that keeps this pretty simple.  Over time, you’ll find situations where placing an entity or even less frequently, a part,  on a layer makes sense, but most of the time sticking with features works best.

Understand Layer States

There are three possible states that any layer can have, Hidden, Unhidden and Isolated.  These are accessible under the layer button inside the layer tree (for some reason, only Hidden and Unhidden are available when you right click on a layer).  There are rules that govern the display of items on multiple layers with different display states:

• If all layers that the item belongs to are Unhidden, it will usually be visible.
• If any one layer is Hidden, the Hidden status trumps the Unhidden and the item is invisible.
• If any one layer is Isolated, the Isolated status trumps the Hidden status and the item is visible.

Furthermore, Isolating a layer, like its name implies, turns that layer and only that layer (and other isolated layers) on, making all other layers invisible.  Effectively, Isolated beats Hidden which beats Unhidden. Clear as mud?  How about some examples.

In all three we have three layers with 4 items on each.  Some of the items are on two different layers and one is on all three.  We also have one item not on any layers at all.  (Notice that the item that’s not on any layers is always visible, layer state changes have absolutely no effect on it.)

In the example on the left, all three layer states are used.  Because of the nature of the Isolated state, only items on that state will be visible.  Even the items on layers set to Unhidden will be invisible.

In the other two examples, only two states are used.  In the middle, Hidden trumps Unhidden so whatever you Hide goes away, regardless of if they are also on layers that are Unhidden.  On the right, Isolated trumps Hidden, so whatever you Isolate will be shown, regardless of if they are also on layers that are Hidden.  Notice that the end result of the image on the left is the same as the image on the right.

This leads to a few conclusions:

• Because of the special nature of the Isolate status, using all three states doesn’t make much sense as it makes all other layers behave as if they were set to Hidden, even if they are set to ‘Unhidden’.
• If you prefer to see everything and hide only the items that you want to not see, you should use Hidden and Unhidden.  Save your layers as Unhidden and Hide as needed.
• If you prefer to hide everything and show only the items that you want to see, you should use Hidden and Isolated.  Save your layers as Hidden and Isolate as needed.

Summary

These two concepts are the underpinnings of the Pro/E layers system.  By understanding them, you are better prepared to plan out your layer usage and therefore gain control over the clutter on screen.  You’ll also be able to better predict what changes in layer states will produce on screen and better able to diagnose why what you thought would happen didn’t.

Special thanks to Glenn Beer from Lawrence Livermore National Laboratory for his 2007 PTC/User conference presentation “Mastering Layers” which inspired this post and provided the images.

Download the full presentation here: Pro/ENGINEER, Understanding Layers.