CompuServe Messages

Hi David, Wow. Thanks a lot for the detailed answer. << This is all on the screen at the same time. Instant feedback. >> So is there *only* a 1-viewport interface, or can you set-up a traditional 4-viewport scheme ? How fast are screen redraws with a lot of geometry present ? << An interesting feature is you can work in two modes, NURBS or Polygon mode but many of the tools allow you to act on the polygons like NURBS >> Are you referring to the *Control Polygon* for the B-Spline Curve/Surface, or to either Spline or Polygonal modeling ? << like one pluck tool allows you to pull on a vertix and the others follow gradually, It's like you are pulling on a bed sheet in the middle. >> Yes, that would be a Non-Linear Transformation/Deformation. Are there other Deformations such as various types of bend operations which work in different ways ? << Don't quite know what you mean by Trimmed Surface but it includes a Contour feature that allows you to define four profiles for a surface and the intermediate surface is generated. >> One of the compelling reasons to use NURBS is to use Trimmed Surfaces. With TS, you can trim away portions of a surface using an open/closed curve or another surface as the "knife". The Contour feature you describe is just a standard boundary Patch. << It exports to DXF >> Have you tested the output to 3DS via DXF ? Can *any* model, no matter how it was created, be accurately exported without problems to 3DS ? << Yes, you can use both polygons and NURBS in booleans, though once you boolean a NURB it obviously becomes a polygon since it now has holes or additions pieces added. >> Well no, it doesn't have to become a polygon (except on export), as that is what Trimmed Surfaces are….you can trim away portions of the surface (similar to a Boolean Subtract), yet the spline surface retains it's spline characteristics. However, a *surface* is implicity hollow by definition. Some systems let you treat the surfaces as *solids*, and let you perform standard Boolean operations **instead of using Trimmed Surfaces**. The difference being that the interior surface or faces are created as necessary for the *Boolean-operated* geometry, as dictated by considering it a *solid*. So, are you saying that by *whatever method used*, the spline surface loses it's spline characteristics inside Amapi when cut/drilled (becomes a polygonal mesh) ? If not, when a cut/drilled surface is exported via DXF to 3DS, are cuts/holes still present and accurately represented without problems once inside *3DS* ? << You can select explicitly the points you want to move or add and subtract points interactively using the + and – on the keypad. >> No, I mean can you adjust the "weight" of a Control Point ? … which is another compelling reason to use NURBS, but not always supported in some systems I've seen. Usually, a good NURBS implementation will include the ability to specify *Multiplicity* for a CV (multiple CV's at the same point) as possible with "normal" B-Splines, as well as "Weight" which is not possible with "normal" "non-rational" B-Splines. Both Multiplicity and Weight draw the spline closer to the CV in the Control Lattice (Polygon), thus allowing more control over the shape in addition to merely *defining* and *moving* control points. << It does filleting and chamfering interactively as well as entering a precise value. >> It does filleting on *surfaces* interactively (or not), in addition to *curves* ? << This depends on the export format, but the resulting filleted polygon is a single polygon>> Again, with a *surface* (spline mesh), does the fillet operation create the fillet between the 2 surfaces as a *seperate object*, or does it create a single seamless mesh composed of Surface1, Surface 2, and the Fillet ? And if so, does this export properly ? << You can solder to two polygons and then smooth them over at the join. >> Yes, but can you blend (solder as you called it) both *curves* AND *surfaces* together, and with control over the tangency and continuity at the blend point ? This is another compelling reason to use NURBS. << Yep, they are really good. You can perform twists and complex deforms by specifying a spline that will be the centre of the resulting deformation. >> Are you saying that a seperate spline curve can be used as a Deformation Axis which the surface conforms to ? <<Can IsoParms be easily extracted and dropped into the mesh under construction ?>> <<< I don't understand the question. >>> Well, for instance when you Skin a series of open curves into a surface….the curves are constructed in the "U" direction, then the program creates "V" lines which are orthogonal (perpendicular) to the defined "U" lines when it creates the surface from the curves. This U&V matrix is the lines you see in wireframe representing the surface. With a good system, you can freely extract or add "Isoparms", which are the actual curves making up the U&V lines of the mesh. Thanks SO MUCH for your time. I'm always interested in new PC modeling systems such as this. Regards, BILL