Autodesk Inventor: View representations vs. levels of detail

by Kendred Cooper
Solutions Engineer
(Part 3 of 3)
 Levels of Detail: Capabilities and features
 Derived Component
There are many tools that we all use to help complete our design. Some of those tools help increase the speed at which we work on the design by reducing the complexity of the model. Derived Component is such a tool and best of all; it can utilize LOD’s. For example, say you have a very large, very complex “sub-assembly”. Well, sometimes loading such a file into your top-level assembly can reduce Inventor’s response time and eat more system memory. While LOD’s by themselves could help alleviate these issues, using Derived Component takes LOD’s power to another level. Deriving assemblies into IPT’s is nothing new to an Inventor user that has been through a release or two. Derive your sub-assembly into a single part; load that single part into the top-level assembly and memory management only needs enough for one part and not 30-40 plus for that sub-assembly. What if your sub-assembly still needs to be simplified by suppressing some components? Use those custom LOD’s and derive your sub-assembly into a part. Once done however, the IPT cannot be modified to look at a different LOD.

Copying VRs as LODs and vice versa
Copying VRs as LODs may bring another wrench into the works. Simply put, any VR that you have setup can quickly and easily be copied into the LODs with full memory salvaging capability. Now, how about the other way around? Absolutely! The key thing to remember is that while copying a VR to an LOD, you benefit from the memory salvaging, whereas it’s different with copying an LOD to a VR. In that scenario, you lose the memory salvaging in the VR and the components are loaded in memory, just not visible. So, be careful when back-tracking this way.

Bill of Material (BOM)
As with any tool and feature in Inventor, if it doesn’t play well with the BOM, it’s not much use. That’s no different with LOD’s. BOM support is provided for LOD’s, regardless of the components suppression or visibility. However, when working with a sub-assembly that has been Derived into a single part and placed into the top-level assembly, the BOM doesn’t recognize the individual components that were used to create the derived part.

Interference Checker & Contact Solver
Naturally for both Interference Checker and the Contact Solver, if a component doesn’t “physically” exist, then neither tool will be able to calculate any information from said component. The issue is that by means of suppression using LOD’s, the component is present in the assembly as an item (hence BOM support), however, there is no physical feature that is being loaded for Inventor to calculate against. This same limitation applies to View Representations as well. With VR’s, the objects, for lack of a better explanation, are seen as air by Inventor, therefore, no interference and no contact with other components.

Dimensions and Annotations
Before we get into the IDW utilization of LODs, it needs to be pointed out that if any existing dimensions or annotations refer to a component in an LOD view, and that component becomes suppressed, those dimensions and annotations will be orphaned. The reason is again, because the component no longer exists – physically. This can be changed under Document Settings of the IDW if desired, but it is not advised as this will affect all dimensions and annotations.

Levels of Detail Utilization in IDW’s
What LOD’s deliver to the IDW environment
When working in the IDW environment, LOD’s can also be used for Base View creation. Specifying the LOD to be used can be done either prior to placing the view or editing the view after placement. Taking a look at the Base View placement dialog below, all LODs are available to choose from. Like with VRs, if many LODs are used in the assembly, the selection window allows scrolling through the listing for quick and easy access.

LODs in the IDW environment give increased IDW updating performance when modifications are made to the assembly. Using an LOD, users will notice quicker response from the IDW upon opening and updating of any assembly modifications.

Once a Base View, using an LOD, is placed in the IDW, the LOD used can be changed by editing the view. Any Projected Views created from this Base View will “always” reflect the LOD used by that Base View. Unlike VR’s, the Projected Views cannot be a different LOD than the Base View that it is being projected from.
View Representations versus Levels of Detail
The differences . . . .
Well, at the basic level, we’re talking about memory management. With VR’s, no memory management exists other than minimal amounts of graphics memory. Again, it’s not substantial enough to yield any noticeable performance gains. With LODs, memory management is the heart and soul of LOD’s function. Visually hidden components (VR’s) as opposed to virtually suppressed components (LODs) is the best analogy of the two.

Which to use? Deciding factors and future unknown needs
When deciding on VRs or LODs for your assembly, look at your key needs now and any possible unforeseen future needs. For example . . .
1. Is the assembly large enough to cause Inventor to lag behind
2. What components are not currently needed to convey design intent
3. Are any components “not going” to be needed in the future
4. Are any “going” to be needed in the future
5. Can the assembly be broken down into lumps that might be revised
6. Will any certain view orientation help clear any design confusion
7. Do I want purchased parts shown or just listed in the Parts List and BOM

Deciding on these items (as well as any that you already question) will help to improve your efficiency and improve documentation of the design.

Summary
Inventor R11 brought many new tools to the Inventor user. Some tools are extremely powerful in design analysis and calculation, some to simplify the use of existing tools. But, the two major tools that influence program speed and stability when handling large assemblies are View Representations and Levels of Detail. Although VRs were already there, their functionality was enhanced by how well they work with LODs. Both give users the flexibility and power needed for everyday engineering design and everyday schedule rushes. Many of us have had an assembly that takes enough time to load that we can go and have a cup of coffee and maybe a donut before it's finished loading. The bad news with LOD’s is that we will no longer have time to get that cup of coffee. For VRs, well, all of the VRs that you now have, copy them to LODs and reap the benefits of increased productivity and memory stability.