SolidWorks Featured Author Blog: Getting the most out of the Boundary Feature

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SolidWorks Featured Author Blog - August 2012

Featured Author:


Mark Biasotti


The Boundary feature is perhaps the most versatile and often used surfacing feature when it comes to creating complex shapes. It is a general purpose one or two directional surfacing patch that operates as both a solid and surface body feature.


For Old’ timers to SolidWorks, there is some confusion understanding the difference between Boundary and Loft. First a little background. Around 2004, when I first joined SolidWorks, the modeling group had started some initial work on the boundary surface feature based on customer feedback that were complaining that SolidWorks did not have the needed surfacing tools to accomplish their shapes – especially when trying to create curve-continuous matching to adjacent surfaces. It was clear that we had to do something that went beyond Loft. You see, with loft, there is a bias between the profile (1st direction) and the guide curves (2nd direction) that would does not allow C2 (curve continuous) in both the first and second direction.  (See figure 1)



Figure 1 – illustrating the influence of Profiles over guide curves


In non-technical terms, it is somewhat like sweep in that the profile(s) are exact and the guide curves are approximations. This would present a problem in some cases, when knitting the guide-curve edge of the Loft with adjacent surfaces. The desire was to have a general purpose surface that would have equal influence (non-bias) in both 1st and 2nd (see figure 2) direction.



Figure 2 – influence is equal between 1st and 2nd direction curves in Boundary


Also, we wanted to build a new mechanism for selecting partial curves for the feature and as a result, the SelectionManager debuted when Boundary was introduced. Unfortunately (or fortunately) we had high expectations for Boundary based on 8 years of feedback from our users and originally, Boundary was to be introduced in SolidWorks 2006. We had to make the hard decision as to whether we would introduce it short of all that we wanted it to be, or hold it back for another development period and future release. With much angst, we decided to hold it back for SW2006. That short-term pain paid off; with the debut of Boundary in SW2007 we were able to close many issues and add a handful of useful productivity innovations. SW2008 and SW2009 filled out the list with a feature that was on par and more importantly surpasses the capabilities of the long-time loft feature (see figure 3.) Not well known also is that Boundary out performs (creation and rebuild) Loft when 10 or more curves are involved. Because Boundary is more precise than loft, care does have to be taken with the sketch curves and model edges that are used to drive it. In many ways loft was much more forgiving and sometimes this is an advantage while many times it is not.  So let me briefly go thru the matrix and point out some less-known capabilities for Boundary. Additionally, Loft still stays in the system, of course, for Legacy reasons.




C2 in both Directions – is one of the main advantages of Boundary over Loft and the primary reason it was created. As explained previously, it was necessary to create a general purpose surface in order to introduce this capability – i.e. the algorithms for Loft did not allow this.


Accuracy – because Boundaries’ curves are not approximations like Loft’s guide curves, boundary surfaces can be more accurately fitted to existing sketch curves and existing model edges.


Curve X Curve – one of my favorite features of Boundary, is to ability to create a Boundary surface with just one curve in the 1st direction and one curve in the 2nd direction. I use this capability many times when creating reference surfaces for the Fill feature by drawing a simple 3D sketch of 2 lines that are tangent to the bounding curve, and then use those two as the 1st direction while using the cross curve (curve that connects the two 3D sketch lines.) (See figure 4)


boundary ref surface.png

Figure 4  using curve x curve capability in Boundary to create a simple reference surface


Curve Network – is the ability to use a serious of curves that cross each other (like tick-tack-toe) and then “de-limited” your resultant surface to just a portion of where the curves cross each other using either the moveable black dot in the selection manager or using the “Trim by direction 1 or 2” (see figure 5)

network curves.png

Figure 5 – with a network of curves, boundary can give the user many alternate possibilities


Curve to Point – can be performed by both Loft and Boundary but it’s even cooler when you create a single sketch point on a plane perpendicular to the 1st direction and then assign tangency. It is a great way to get a dome-like feature. (See figure 6)


curve to point.png


Figure 6 creating a boundary surface between 1st direction curve 1 (actually a point – Sketch5)

and 1st direction curve 2 (elliptical sketch – Sketch4)


Close Loop – Simply the ability to make a continuous surface loop between the first profile (or 1st direction) and the last profile (3rd in 1st direction.)

Surface and Solid – anything you can do in surface, you can do in solid (when applicable) – i.e. create to close profiles in the 1st direction and Insert>Solid>Boundary.


Connectors – are probably the most under-used, and misunderstood feature of Boundary yet they are so powerful that without them, some boundary features cannot even be achieved.  By adding connectors, the user can adjust the flow (U/V) of the surface. This is especially useful when “turning corners” as is in some cases the profiles wrapping around the corner default to the UV’s being skewed, and adding connectors allows the user to adjust a more even spacing of the UV. Also, whenever you have very dissimilar profiles – i.e. circle to square, connectors allow for you to find the right solution. (See figure 7)



Figure 7 – using connectors to influence UV of surface to desired shape and flow


Curve Influence Type - Curve Influencing options in the Boundary Feature (and Loft too) are available to give the user selectable control over the different solutions that can result for bounding between curves. Global (default) the boundary will “average” the shape solution from first direction 1st curve to the 1st direction last curve. (See figure 8)


curve influence type.png

Figure 8 – Using the drop down selection for 1st and 2nd Direction Curve influence type allows for alternate solutions


Depending on the 1st Direction Profiles, there can be many different solutions. These options are available to let the user determine which solution is the correct design intent.  BTW - This feature was put into Loft and Boundary as a result of comments by Ed Eaton in 2003, who wanted a better control the way lofts work.


Curvature Explorer – is an “on-the-fly” dynamically curvature plot curve that you can drag over your Boundary Surface to inspect the overall quality of your Boundary feature while defining it. A magenta blob appears on the surface with a curvature comb attached and you simply drag it. This is available by clicking your right mouse button, while over surface, and choosing “Curvature Explorer.”


curvature explorer.png

Figure 9 – Curve Explorer, magenta blob at white arrow, can be dragged across surface to inspect curvature


SelectionManager consolidates 2006 functions formally known as Smart Select and Contour Select under one versatile selection mechanism. Although currently for 2007, we have not “rolled out” SelectionManager to all functions that can use it, it is best exemplified when using it in Sweep, Loft and Boundary features. For instance, you can build a single Boundary Surface from a single 3D sketch. Previous to Selection Manager, SolidWorks users often first build sketch features with predetermined lengths and combinations of geometry to represent profiles, guide curves, paths and curves. With SelectionManager this is no longer necessary. SelectionManager allows you to select and modify single or multiple sketch elements and/or model edges and change their length “on-the-fly” thereby eliminating pre-built features and reducing the amount of “over-head” needed to create surfaces and solid features.


Centerline Loft - is the one option not available to Boundary, but available in Loft to give the user the capability to loft thru multiple profiles using a single unifying path. It is better termed a “boundary blend” or “Swept Blend” in that it generally Lofts but is influenced greatly by a path. (See figure 10)


centerline loft.png

Figure 10 – Centerline Loft. The one feature that Boundary does not share with Loft


Opaque and Zebra View – are different ways to visualize your boundary surface as you define it. The toggle that is available by Right Mouse Button click on the previewed Boundary surface allows the user to turn off the transparency to see a more clearly the previewed surface. Likewise, there also exists a toggle on the RMB menu to Show/Hide Zebra stripes while interactively working on your Boundary Feature. (See figure 11 and 12)


opaque view.png

Figure 11 – Opaque view/Transparent View toggle on RMB menu


zebra stripes.png

Figure 12 – Zebra Stripes Preview on RMB Menu



A degreed Industrial Designer, Mark has worked in the product design industry for over 25 years for such companies as Atari, Hewlett Packard and IDEO. Joining SW in 2004 as a Product Manager, he currently is Senior Product Manager for Definition.


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