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Digital Prototyping: Go beyond 3D

Subassembly Order Matters


Its come up a couple of times over the course of the last couple of weeks.  The manner in which you build you corridor assemblies does matter.  First of all, the side that you attach the first subassembly to sets the assembly to see everything that goes on that side first.  This can come in handy when you are targeting your subassemblies to alignments or profiles.  If I need the right side pavement to target a given alignment I know that the right side was first, so the first pavement in my list is going to the right.


Let me show you an example.  Here is a fairly straightforward assembly.  It is symmetrical with the crown at the center.  I first put in the right hand pavement.  Then it doesn’t matter what other parts I put in, or what order.  Anything attached to that first pavement is considered to  the right, and after the pavement in the list.  The entire left side is also after everything that is on the right side. 

Here is the corridor page where I target alignments and profiles.  When I target an alignment to identify the right edge of travelled way I know the first of the two pavements is to the right.


On a simple design that is really all I need.  On a more complicated design I might want to go in and change the names of the subassemblies so there is no doubt as to which is which.  But it never hurts to have a standard method for assembly creation, just in case.

Another place where this is of utmost importance is if you are using a Marked Point. 


 Some subassemblies allow the design to cross over to a specifically identified point to fill in gaps.  A perfect example is a median that is filling the gap between two sections of pavement.  The subassembly called Marked Point has to exist before the median subassembly is told to look for it.  Now, time order isn’t as important as is the list of items.  Since I always design to the right first my marked point goes on the right of my design, and the median goes on the left of my design and targets the marked point from there.


By the way, you will notice the median appears to be falling well short of its intended target.  This is just a function of the layout, and not how the assembly will work in the field.  It takes a little getting used to, but don’t judge a corridor by its layout assembly!

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