I had a couple of questions on Curvy Stuff 101, slide 29. Was the point of that slide to show that is easier to put limited loft sections at the points on the spline versus many more sections at regular intervals? Also, in the model, a sketch is named "predicts total sections required for smooth loft". What predicted the 12 sections needed for the smooth loft. Thanks Pedro
Many thanks to Ed Eaton for making this information available. Great job!
Pedro, The point of the slide is to show that lofts are spline based, and that you can use sketch splines to help you decide where to put your loft sections.
I wanted to show that if, like a lot of folks, you really insist on using evenly spaced sections, you can use a sketch spline with evenly spaced nodes (achieved in sketch mode by using a lot of centerlines with equal relationships) to see just how many nodes/profiles are required to meet your design intent. In the case I show, the loft would require 12 evenly spaced sections. Its a lot easier to use a quick sketch spline to predict how many sections are required than to try the loft with 8 or so sections, see that it doesn't work, edit all 8 planes and profiles to add a ninth, see that THAT doesn't work, then do it again and again until you get to the twelve sections that will work.
I also use this technique when trying to follow two intent curves, like the top and bottom curves in an elevation layout sketch. I will draw a sketch spline on the top curve with as few spline nodes as possible, then draw another with the same number of nodes and see if I can use that spline to match the bottom curve (the line between corresponding spline nodes indicating my loft profile planes). Of course, it never works the first time - I have to add nodes and move them around until I get the right fit, but at least I quickly end up knowing exactly where to put my loft profiles. Also, I have to take into account the effects of angled profiles. Still, it is tons faster to take a little time in a sketch to get things right than to take a lot of time blindly editing, adding, subtracting, and repositioning loft profiles.
But, of course, the real revelation of the slide is to point out that relying exclusively on evenly spaced sections like we are taught is kind of dumb (with the exception of simple models or industries where other factors pop up, like bulkhead spacing or whatnot). Even the inventor of NURBS surfaces told me that the concept of using evenly spaced loft sections is inherently silly when applied to NURBS - the whole point is that these surfaces are NON UNIFORM rational b-splines, not 'uniform' (URBS?) which is what you would get with evenly spaced profiles.
By using non uniform profile spacing, we can take advantage of the math used behind the scenes to meet the design intent in the sample with only five profiles - thats a LOT less set up, and a lot less to modify for design changes or tweak when fine tuning a model. Less work and better results? I thought that was a revelation that was worth passing on.
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