6 Replies Latest reply on Mar 18, 2011 4:29 PM by Charles Culp

    Problem with creating boundary surface between splines

    jennifer stopford

      Hello,

       

      I am using Solidworks to model surfaces, which I create from splines. I have been successful so far with creating a boundary surface between 5 splines. Since increasing the resolution to use 10 splines I am getting an error "the feature could not be created as it would produce self intersecting geometry". As the splines themselves are not self intersecting I can only assume they are too complex for Solidworks - or I am doing something wrong!

       

      Any ideas would be appreciated. I can get around this problem by creating two adjoining boundary surfaces, however its not ideal as the surface is not continuous at the join. I've attached the file for reference.

       

      Best Regards,

       

      Jen

        • Re: Problem with creating boundary surface between splines
          Charles Culp

          SolidWorks really isn't the correct tool for this. Can you give us a little bit of detail on the project you are working on?

           

          You really need software that can take point clouds, and import it as a surface model. Boundary Surface is really designed to create transition surfaces between two (or in the opposite direction) four known constraints. It works best when those constraints are exisiting surfaces, because then you can control the tangency (direction). With just splines, all you can control is position.

           

          So the underlying problem is that when SolidWorks tries to connect each of the splines, you will find plenty of areas where it extends far "above" the underlying sketches. If you look at the preview, you will see these areas. I assume that is not part of the underlying data, and it just an artifact of using Boundary Surface.

           

          You can control this buy turning each sketch into a straight extrude. Then, you can make the boundary surface tangent to each of those extrudes. There are two problems with this method though. First, is that the surface you are trying to create will then be stair-stepped, which is probably not what you were looking for. The other problem, is that this is so complex that SolidWorks can't handle it. So, you could make it into 9 individual boundary surfaces. The end result will actually be almost the same. You still run into the first problem I discussed, however, which is that the surface will still be stair-stepped, and that isn't what you want.

           

          So, what can you do with one full boundary surface, without stair-stepping? You can adjust the connectors. Right click on either of the end splines, and select "add connector". This will allow you to control the flow of the surface. Right now, SolidWorks is doing whatever it thinks is best, and it often approximates incorrectly. What you really want to do is add enough connectors to make sure that the surface doesn't fold onto itself anywhere.

           

          The error you are seeing is because the surface is folding onto itself somewhere, because the automatic flow isn't tight enough. Adding and adjusting connectors will help you get there.

          WrinkleBad.png

          In the above image you can see where I highlighted a wrinkle, and also that I added one connector down the centerline.

           

          Connectors are great, but if you want even more control, add splines going in the direction of the connectors. Then you can use those for direction 2 of the boundary surface.

           

          This is all quite a bit of work, and we are still running into the problem that this is still probably the wrong tool. What you really need is a tool to import 3D point cloud data. Yes? This includes the SolidWorks add-in called "ScanTo3D", or another software package that can do this. Are you limited to only SolidWorks? Do you have ScanTo3D?

            • Re: Problem with creating boundary surface between splines
              Charles Culp

              Also note that you need to do a little hand clean-up to the ends of all your splines. For this surface, you will probably want to let the splines automatically control internal handles, but you need to set the end point handles.

               

              Take, for example, your sketch 9.

              Sketch9-Original.png

              Notice how it actually loops outward, before it continues towards your other points? I assume this is not what you want. You can fix this by controlling the handle, which is hidden by default. Normally you can just click on a spline to get gray shadows of any handles to appear. This complex spline won't do that, but you can right click on it and choose "Add tangency control" to get it to appear, then just move it around. You will want to make them fairly short, and just point them in the general direction of the next point, keeping the curve smooth. Here is an example for Sketch 9:

              Sketch9-WithHandle.png

              • Re: Problem with creating boundary surface between splines
                jennifer stopford

                Hi Charles,

                 

                Thank you very much for your excellent and comprehensive answer.  I am not limited to Solidworks, but am using it as I am (somewhat) familiar with it. I will look into ScanTo3D as suggested.

                 

                Jen