Visualizing the hull surfaces to check for errors
Here's a good time to stop and check out the lines of the hull. Here are a few tips for checking them out and tuning them up.
Sometimes the lines of blueprints that you are handed are just not right. The power of 3d really shines when checking the lines of a 2D drafting. With blueprints it is difficult to imagine how the shape would look from any view, but with Rhino you can simply loft the curves and right click, drag in the Perspective view to see the object from any angle. You may take this for granted now but it wasn't that long ago I had to spend many hours at a drafting board to draft a object to project it as a Perspective view, and to see it from any view well forget about it...it would take way to much time and work. Anyway the point is that sometimes the yacht designer will give a blueprint to the customer that is a first draft, because the designer doesn't want his hard work falling into the wrong hands
Option: To better follow along Open the file Opt_1.3dm which is in the directory boats on the CD-ROM.
Select the curves and "divide" them with three points, turn on 'Point' osnap and connect the points with InterpCrv as shown below.
Select the curves for easier viewing and tumble in the perspective view (right click and drag in the perspective view). The top line looks okay but the lower lines need work. If the curves flow along smoothly, that's okay, but if they change direction and kind of stagger around that's something that would be good to deal with.
Turn on 'annotate curve numbers' layer.
Conclusion: Actually what I see (shown above) is that if I eliminated the #5, and maybe the #3 sections from a normal loft the hull would look pretty fair but it wouldn't hold very true with the plans. But rather than spend a lot of time trying to perfect the curves, the faster way to average out the hull is to use all the curves the way they are and use a normal loft and then RebuildSrf the hull surface when done. For this particular hull design RebuildSrf will give better results than using the "rebuild with _ points" or "looseloft" option, or spending hours trying to fiddle with the curves. And using normal loft and then RebuildSrf does a nice job of keeping true to the plans for this particular hull design, but for other hull designs RebuildSrf may not be the best solution.
Another method that Rhinoceros provides you to reverse engineer the original hull lines (although I don't find this method very practical for our purposes) is to use InsertKnot Direction = V on the resulting RebuildSrf at the stations, and RemoveKnotSrf the knots that are not on the stations.
Hit ExtractWireframe which will give you curves that are faired in at the stations, and delete the horizontal lines created by ExtractWireframe. It's a good idea to move the surface to another layer with a different color before using the ExtractWireframe command to keep things organized. So the payoff here is that you can hide the hull and have two sets of curves with two different colors (different layers) with one set faired and the other set being the original curves and you can compare the two sets using the PointDeviation command (shown below).
You can also select the original curves SelLayer(s) and hit Divide and give the curves say 10 points evenly divided along the curve. Then hit SelPt to select the Points and then hit PointDeviation then select the hull surface to get a graphical interface of how far the points deviate from the surface shown above. Like I say, it's academic, but I suppose you could edit the original curves to find some kind of compromise and find a hull that is as close to the original lines as possible yet still fair.
For other methods for reverse engineering a hull and visualization see the Alternative Hull Modeling Approaches section.