9 Replies Latest reply on Jun 27, 2012 10:04 AM by Ditmars Veinbachs

    fully defined line

    Brad S

      Can I just ask a really basic, possibly irrelevant and pedantic question, please?

       

      Why is the horizontal line in this sketch fully defined? The glossary defines fully defined as "cannot be moved. Fully defined sketch entities are shown in black."

      But grab any of the 3 vertices and drag them and the 'fully defined' line will move. Ok the end point of the line is blue, so you can easily figure out that only the length of the line can change. (You can make it flip direction.) But at the end of the day that line has 1DoF just like the dimensioned line.

      Is anything in the underlying SW behaviour here useful to understand?

        • Re: fully defined line
          Raghvendra Bhargava

          Hi Brad,

           

          Line which u r saying is fully defined is not fully defined actually ..see in 2D sketch the entity like line point or anything will be fully defined or constarint DOF(degree of freedom) for x direction and y direction will be arrested.....in ur picture line is defined lke u have arrested X direction DOF but in y direction it can move...i think u got ur answer...:)

          • Re: fully defined line
            Glenn Schroeder

            Brad S wrote:

             

            But grab any of the 3 vertices and drag them and the 'fully defined' line will move.

            The way I look at is that this line doesn't move if you drag any of the 3 vertices.  It just gets longer or shorter.

            • Re: fully defined line
              Chris Michalski

              Brad -

               

              the LINE is fully defined, but the endpoints are not.  A line is a vector with direction that goes on forever in both directions, the endpoints are not yet defined, hence they are in blue.

               

              I get your point though, it would be nice to be able to change settings so that it won't call a line fully defined unless both endpoints are defined.

              • Re: fully defined line
                Warren Isaacs

                Expanding a little on

                 

                Chris's reply:

                 

                • The line's left-hand end is coincident with the origin, so is fully defined and, thus, shown black.
                • The line is constrained to be horizontal, so it is black.

                 

                • The line's right-hand end point is not fully defined and it is blue.

                 

                The only problem I find is that the colour of the end points can be tricky to discern.

                  • Re: fully defined line
                    Chris Michalski

                    yeah, I didn't look close enough to see the coincident to origin (plus sketch relations clutter the page so I never show them so my mind just ignored them)

                     

                    I know they reserve red for overdefined, but under-defined endpoints would be better suited in red in my mind, I'd rather have 2 problems in red than what could be a problem left unrecognized because it was in blue

                  • Re: fully defined line
                    Scott McFadden

                    It is basically defind horizontally only because it is constrained to the csys.

                    • Re: fully defined line
                      Ditmars Veinbachs

                      This is a good example of degrees of freedom in geometry. In the most reduced form, this line segment is really three pieces of geometry in a 2D space. There is an infinite line and two end points which must remain coincident to the line.

                      The line (y=mx+b):

                      - A horizontal relation defines the orientation of the line (m=0).

                      - Coincident to the origin (b=0).

                      The line is fully defined. For any X value Y is always zero. It should appear in black on the screen.

                       

                      The Points (x,y) coincident to the line:

                      - One point is coincident to the origin (x=0,y=0). The point is black and should report its state as fully defined.

                      - The other point is coincident to the line (y=0). The x value of the point is variable.  It should report that it is under defined and remain blue. The user may drag the point anywhere as long as Y=0.

                       

                      Best Regards,

                      Ditmars VEINBACHS

                      R&D SolidWorks, Modeling, Development Senior Manager