Date: Sun, 4 Jan 1998 14:23:25 +0000 From: George Cole Subject: [IML] QUEST: definitions and sweeps I'm trying to do a simple cabinet top using the method of a sweep with only 4 sections to create a squeare with my desired edge. When I do this though I end up with an object with 3756 edges, and this is jsut for the top piece. Is there a way to decrease this number? Also what is the difference between a sweep and a spin, and a merge and a join? Thanks, ---------------------------------- Date: Sun, 4 Jan 1998 12:01:29 +0400 From: Charles Blaquiere First of all, both spin and sweep are sensitive to the ordering of the points making up your profile. If you use Add Lines to create the profile, from one end to another, you'll be OK, but if you begin with a primitive (e.g. an 8-sided disk from which you've deleted all but the rightmost 3 points, in the Front view), the points may not be ordered the way you think. Again, following my example, enter Pick Points mode, Highlight First (Ctrl-H), and press Ctrl-N twice. The points will not highlight from top to bottom, but starting at the 3 o'clock position and going counterclockwise. This is how disks are created. You would need to pick the top point, then Shift-pick the middle and bottom point, and Sort them to achieve correct results. With that warning out of the way, let's move on to the difference between Spin and Sweep. Sweep is the familiar lathing tool: it stitches together several copies of your profile, created by rotating around the object Y axis. The top and bottom of the object will be left open. Spin closes the top and bottom of the object. The first and last points in the outline are not duplicated, but serve as anchoring points. Faces will be stitched between the first point and each copy of the second point, creating a "roof". (Remember, the 2nd, 3rd... (n-1)th outline points will be copied as the outline is Spun around Y; the first and nth point remain unique) Similarly, faces will be added at the bottom, between the last point and all the copies of the next-to-last point, creating a "floor". In all instances, because rotation occurs around the object axis, its placement is crucial. Leave a disk's axis in place, and Spinning or Sweeping it will create a sphere. (An unnecessarily complex one, BTW) Move the axis along local X until it's outside the disk, and Sweeping will create a torus, or donut shape. (Spinning will create a mess) Now, regarding your first question ("Why is my cabinet top so complex?"), I assume your profile must've contained a large number of points, for nicely-defined curves. - If the profile contains n points, after sweeping it will obviously contain n*4 points. - The profile is made up of (n-1) edges; after sweeping, each of these edges is extruded into a rectangular polygon, made up of 2 triangular faces. If you look at the cabinet top from one end, you'll see this: BEFORE SWEEPING: n edges * | | * | | * | | * AFTER SWEEPING: (3*n)+1 edges *--* | /I |/ I *--* | /I |/ I *--* | /I |/ I *--* (The edges marked with "I"s actually belong to the next side of your cabinet top, so I didn't count them.) Each of the 3 original edges was tripled: * *--* | --> | / | |/ * * And a lonely horizontal edge was added at the bottom. Thus, (3*n)+1. Because your final object has 4 sides and 3756 edges, one side would have 949 edges. If (3*n)+1 is 949, then 3*n is 948, and n is 316. May I assume your profile had 316 edges? ---------------------------------- Date: Sun, 4 Jan 1998 21:41:24 +0000 From: George Cole Thanks Charles, a very useful message. I actually had an object with 3576 edges (I wrote the message a short time after leaving Imagine). The original profile was made in the spline editor and extruded a short depth when I added points. This meant that it actually had two profiles joined by edges (but I did not fill front or back faces). The object had 600 edges but also had lines going back from the edge to the axis as I didn't realize that spin would create a top and bottom for me. It looked a little like this: *---------------* | \ | *---\ | \ *----------------------* /\ / \ | | and the axis was here Thanks to your message I understand what I'm doing better. I've got the profile down to 48 edges by deleting the extra profile and the points going to the axis. The total object now has 564 edges which is much better. Before was practically a black blob in the editors as it had so many lines. I thought that it couldn't be right to have so many lines covering the very top as it was just a perfect square. Now it is just 2 triangles.