An Introduction to SubD (Subdivision Surface Modelling) in Rhino3d v7

this is Phil it's simply rhino and today I'd like to take a look at sub D modeling which is new in Rhino version 7 here I'm using a work-in-progress version of the software and so some features may be further developed by the time the product ships so first of all what is sub D sub D or subdivision surfaces are a new object type inside of Rhino if we step back to version 6 we have NURBS objects and meshes in very simple terms NURBS surfaces can be regarded as being a continuous description of in this case a curved volume depending on the degree and the control point layout NURBS curves and surfaces can hold constant radii or can be used to describe curvature continuous freeform shapes meshes on the other hand can only approximate curved geometry if we look at the example of the mesh sphere then only the mesh vertices are touching the notional sphere the mesh edges our extrapolated from these vertices by tracing a straight path between pairs of points and flat mesh faces are then created between 3 or 4 mesh edges if you've been a Rhino user for some time then you may be familiar with plugins such as T splines and clay o these bought a sub D workflow - Rhino but crucially these were meshed based so the underlying geometry was a mesh which was smooth to approximate a curvature continuous surface or poly surface the new sub D objects in Rhino our spline based so just as with Rhino NURBS objects they provide a continuous description of curved geometry this means that sub D geometry can be created accurately in Rhino and this gets over one of the major criticisms of mesh based sub D workflows that are often regarded as being approximate rhinos new sub D objects can be created in a number of ways surface commands such as loft revolve sweep one sweep two and extrude all have the option of creating sub D output curved commands have sub D friendly options and of course there's a number of primitives there are also workflows where meshes can be converted into sub D objects finally Rhino sub D objects can be losslessly converted to NURBS objects so what makes a sub D different to NURBS and why do we need them let's look at the first part of that question and compare both an open and closed NURBS surface with an open and closed sub D surface on the Left I have a degree three deformable sphere and a degree three planar surface and on the right there sub D equivalence now we don't need to concern ourselves with the concept of degree with sub D objects but broadly speaking they are analogous to degree three curvature continuous surfaces with the closed NURBS surface I can turn on the control points pick some of those control points and smoothly adjust the shape I can do the same with the sub D object but I can also use sub-object selection which in Windows is shift ctrl and left click and I can pick either one or more phases or one or more edges to adjust the form smoothly while sub D surfaces are essentially smooth I can add creases to them and this is done by picking edges and here I can sub object select and double-click to pick an edge boundary and then once I've selected those edges I can add a crease to them creases can also be removed using the remove crease command perhaps the biggest difference though between NURBS and sub D is how we add local control into a surface if I just look at the NURBS surface to start off with if I want to add some local control into this area then I'll need to add rows and columns of control points so I'll do this for example by going to edit control points and insert not and I'll insert some knots in the U direction and then I'll hit toggle and I'll insert some knots in the V direction so this will give me a denser area of control points here but because the control points need to be added across the domain of the surface in other words from edge to edge in either the U or the V direction then I'm adding complexity to this part of the surface and this part of the surface it does however give me the ability to add local detail into the surface like this if we were to look at the sub D then with the sub D I can subdivide this surface so I can pick a face and then I can use the subdivide command to subdivide that face and I can keep going adding more subdivisions as I go along and then I can pick one of these faces and move this upwards to get my local control if I want to put in edges in a more controlled way rather than just subdividing a whole region I can use the insert edge command and copy an edge and insert it and if I want to move an edge I can use the slide edge command the insert edge command has a proportional mode of both sides mode and an absolute mode and you can see here the difference between the absolute and proportional mode likewise when I move edges with slide edge I can pick two edges and move them in and out at the same time and I have a proportional and an absolute mode for this to a major difference between the way in which NURBS and sub D works is that with NURBS you have the concept of either having a single surface or a poly surface which is more than one surface joined together by part or all of a coincident edge so using that metaphor I can take six surfaces that share coincident edges and join them into a solid closed poly surface there's no concept of a poly surface with sub D and so to replicate a shape like this in sub D we need to have a single sub D surface with creased edges there is however a workflow that allows us to simulate a NURBS poly surface in sub D and this comes with a proviso and that is that each of the individual constituent surfaces of the poly surface need to be untrimmed surfaces if this is the case then we can explode our poly surface and we can use the convert to sub D tool it's important that we want the corner option here to say yes so that we can maintain these sharp corners of the individual services will now have six individual sub D surfaces and then we can join these together using the join tool again we'll have an option here with as to what to do with the edges we can either have smooth edges or creased edges here I've chosen to have creased edges and now if we look at object properties you'll see I have a closed sub D and if I want to remove the creases from these three edges here I just select them and use the remove crease tool now we'll come back to an object similar to this shortly and look at an alternative to a NURBS workflow in sub D so now we know a little about what sub D objects are let's get to the second part of the question which was why do we need them one answer to this is that subdivision surface modeling is really useful in situations where modeling in NURBS is difficult or problematic a simple example of this is the y branch this is something that is pretty easy to model in NURBS but becomes more difficult if the branches are as in this example different in diameter or the branch arrangement is in any way unequal there's a number of techniques we can use in NURBS but the distinct disadvantage of most of them is that if we want to produce iterations or refinements of the shape then this can be time-consuming as we have to concern ourselves not only with controlling the shape but also matching the continuity across the different surfaces subdivision surface modeling gives us an easier alternative here I've converted the three tubes to sub D objects so let's take a look at a quick approach in the NURBS example our used split edge and then blend surf to create the transitions at the sides of the Y shape in sub D I can use the bridge command to similar effect now I don't need to split these edges because I can pick the individual edge segments so I'm going to go into my bridge command and I'm going to pick the one half of the large tube and there are four separate sections to that and then the matching four segment of the smaller tube and then enter will get me into the options for the command I can choose the number of segments and I'm going to say I want four segments here and I have a slider to control how straight that geometry is and I'll accept that value I can control this shape later on if I want to adjust it next I'll repeat the process on the other side of the y branch so again I go to the bridge command pick the four segments pick the same four segments here okay and leave the options as previous in the NURBS example I built this top surface before building the front surface but I can do this the other way around in the sub D example and again I can use the bridge command to create the the top of the why exactly the same processes previous and I'll accept that result okay so now we have the sides of the Y shape and all I need to do now is to close off this hole now I want to do this in a way which is structured and preserves some regularity to the topology so once again I'm going to use the bridge command but I'm just now going to bridge between pairs of edges and now I want to reduce the number of segments to just one and I can straighten these out okay so I went to bridge here and here okay so you see I'm now left with four holes I'll repeat the process on the bottom and then all I need to do now is to fill these holes and there's a command called fill sub D hole that I can use for this again if I double click on the boundary here it will just select all of the hole I can pick all of these at once enter and that's the result and you can see how it gives me a really nice topology here mr. hole here so let's just fill that up there we go so let's take a look at this now with the environment map so we can see this is smooth all over but you can see that we've got a little bit of a high point here just there so let's have a look at how we might reduce that so what I'm going to look at doing is taking this edge here and deleting it and I think that will just give me a much smoother transition from this point to that edge I'll repeat the process on the underside and let's take a look at this with the environment map so we can see that that High Point looks better now now the big advantage now is that if I want to start playing with the shape of this so for example if I want to look at maybe pushing in the shape of the Y here this now is where we get the big advantage of sub D so I'm gonna turn on the gumball and it's gonna push this face inwards I'm gonna disable the object snaps just so I don't inadvertently snap to anything and you can see now that when I push this face in or this pair of edge is in now how the adjacent edges and faces are moving with it so the whole idea behind this sub D surface is that it intrinsically it's smooth so it's analogous in some ways to a degree 3 surface so it's intrinsically smooth for curvature continuity unless of course we specify any creases so all I need to concern myself with here is the shape of these objects I don't need to concern myself with the smoothness on Julie and again if we're seeing high points here we can use the same process as we did before and removing those little edges here to improve the shape so that's looking nice and smooth now another way in which we can use the bridge command in a similar way to blend surface is to create a transition between these two open edges so I'll use the bridge command double-click to pick the whole loop here double click to pick the whole loop here enter to get into the preview I'll add some segmentation and just play slightly with that straightness value okay so we have a nice smooth transition between those two surfaces and again the big advantage here of sub D is this whole object here is treated as one curvature continuous surface so if I want to adjust the shape locally for example to make this asymmetric let's say I want to push this area upwards here is I can do this okay and I don't have to worry at all about the smoothness here you know I might need to look at what happens down here and insert and remove some edges or put in another constraint here so to avoid the shape changing too much here I could maybe insert an edge here double click for a whole edge loop and just put some more control in here and this will mean that this change in shape drops down a little more quickly and doesn't affect this area okay so you can see that in this example that sub D gives us a means to an end to create a smooth set of transitions between these various branches that would be difficult to model and certainly difficult to adjust if we looked at this purely as NURBS geometry the subti workflow can be very useful for developing styling surfaces not just fast approximations but good quality weld topology eyes surfaces that can be used for final data in this model of a mouse the majority of the shape was created as a sub D prior to being converted to NURBS where it was then split into sections before adding the smaller details just as with modeling a NURBS surface managing the topology and maintaining the simplicity is essential for creating good quality surfaces so let's start by taking a look at creating sub D friendly curves and building surfaces directly from them with rhino's surface commands if we look first at the control point curve then we can enable the sub D option this fixes the degree at three if I visualize the control points of an open sub D curve then I'll see two hidden constrained control points that sit between the first two and the last two live picked points if we look next at the interpolated curve there's a much more straightforward relationship with edit points in sub D friendly curves and if I create an interpolated curve through the edit points of my first curve will see that the two curves are identical so going back to the upper surface of the mouse the surface on the left is what I'd like the initial sub D surface to look like before I fill in the sides to achieve the surface on the right in the simply Rhino intermediate-advanced classes there's a lot of discussion about the importance of topology when creating NURBS surfaces to the effect that if the topology is correct then the shape will almost sort itself out and can be adjusted directly so here just as with nerves the curve layout is important I drew the large blue curve first as a sub D friendly control point curve and then the smaller blue curve is a scaled and adjusted version of this the red cross-section curves are then created with an interpolated sub D friendly curve that passes through the Edit points of the blue curves this gives me a curve layout that I can loft with either the blue or the red curves and achieve a sub D surface which is effectively the same as the curve layout at this stage the sides of the shape are still open and we have a number of ways of closing these off that takes full advantage of the fact that sub D surfaces are inherently smooth or curvature continuous first of all I can use the bridge command with an appropriate straightness and number of segments and I can then use a command called stitch to close up the two remaining edge pairs so let's take a quick look at this so I'm going to use bridge first of all to bridge between this edge and this edge but I'm using this in a way very similar to why I would use blend surf if I was building a NURBS shape so I'm going to set two segments and just play with the straightness a little bit here and then accept this and then to close up these two edges here and these two edges here I'm going to use stitch gonna pick the first two pairs of edges the second two pairs of edges this will close these up I can slide up either to the top or the bottom of these edges I can pick first or second here first would be here second would be here and average would be the midpoint of these so I'll just pull this up to the top and then this gives me a crease which I can then remove using remove crease and now I have a nice smooth sided shape which maintains the regular top that I initiated with my curved layout an alternative to this approach would be to close off the side of the shape with one or more sub D faces this is difficult to visualize with the sub D in its smooth form so I'm going to use a command called sub D display toggle which visualizes flat faces through the control points rather than the smooth form interpolated through the Edit points now there's no icon for this at the moment so this is my homemade icon here so if you're watching this video with a later release of version 7 beta or work-in-progress then you almost certainly won't see this icon okay so I'm now going to use a command called single sub D face and I'm going to snap to the vertex points here and then I can join the single face to the rest of the sub D there's a smooth or a creased option here I'm going to select smooth and then toggle the display back and we'll see the result so this gives me slightly different topology than I had previously and a kind of straighter section across here an advantage to working in this boxing mode is that the shape is expressed very simply as straight lines between vertex points so if I wanted to create two faces in the side of the shape here I can very simply draw a couple of lines here that give me if you like a target for where to place my sub D faces so again I can snap two vertex points here and now I can create two separate faces that I can join in to the rest of the sub D as before I'll use the smooth option for joining and then I can toggle the display back to smooth I'll remove these curves and then we can see the shape so just as with NURBS objects I can actually use the control points themselves to edit the shape and here I just want to pull out this bottom point slightly to add a little bit of curvature to this bottom edge so I'll do this constraining to the sea plane y-direction and I'll just pull this out very slightly just to give me a little bit of curvature on this bottom edge again just like NURBS it helps if this point this point and this point are aligned because it maintains the regularity of the shape so if we have a look at this shape now with our environment map particularly if we use the fluorescent tube you can see that we have a really nice progression of the shape here and this is really due to this simple topology or layout of the sub D faces now with sub D we're not limited to using four-sided faces and the limitation here is my choice because I know that the downstream workflow will involve a conversion to NURBS and nerves does of course have a four-sided topology I'm just going to modify the shape slightly by adjusting the sub and I'm going to use the gumball manipulator to do this now if I'm editing vases it's a good idea to set the gumball to align to object because then if I sub object select a face the blue Direction here is pointing in the normal direction of that surface and they fight pick a couple of surfaces then it will be the average normal direction of those surfaces if I'm going to edit edges sometimes I find it better to constrain the manipulator in this case to a sea plane so I can be sure that I'm moving these edges in line in this case with the y-axis of the sea plane and I'm gonna use the scale icon here and just push these edges inward slightly and then push these two edges outwards just to give me the indent in the side of the mouth shape something like this and then I just want to make the back slightly more rounded when I see this from above so I should be able to do that by picking these two faces here sorry these two edges here and pulling these forwards so again I'll choose to move these in the sea plane x-axis so just pull these forward you can see how it's rounding that back off now this should maintain the topology and the shape but again it's a good idea just to check with the environment map to make sure that we've still got the nice delineation of the shape here so when I'm happy with the shape I can convert this to a NURBS poly surface using the convert to NURBS tool and when I do this I have the option of deleting the input object ie the sub D or not and in this case I'm going to select set no so I can compare the nerves and the poly surface with each other so I'll just use my filter here to filter out the poly surface so I can pick the sub D and move this out of the way and now we can see the poly surface on the left and the sub D on the right now at the moment when we use the NURBS conversion each face on the sub D becomes a surface patch on the poly surface but the continuity between them and the overall shape should be the same so here you can see that we have the same resolution of the shape on the nerves and the sub D so moving onwards I extruded the lower half of the mouse by duplicating the boundary of the poly surface then I joined the extrusion to the poly surface and created a blend edge between them and then a fill it along the bottom of the mouse at this stage I had a solid poly surface which I could then in the usual way start to split out until I got most of the major components that I could then apply the materials and textures to another strategy to develop a shape in sub D is to consider using the control point or vertex positions and start with the metaphor of the Boxee rather than the smooth sub D object this is a workflow that you may be familiar with if you've had experience of play U or T splines so here for example I could start by creating a series of lines that define the control point layout of my desired shape then I can go to my mesh tools and I can use a tool called mesh from lines here I can set that I want to consider only a maximum of four sides per face and I can select all of these lines in one go and press ENTER and I'll have a closed mesh object now this closed mesh object now will be the same as the boxy version of the sub D that I want to create so I can now pick the mesh and run this tool convert to sub D I'll just for now select delete' input yes it's important here that the interpolate points option says no because I don't want to interpolate the points I want to use a control point layout here and creases and corners are also going to say no this is my boxy display now of the sub D and if I smooth this off we'll see the shape earlier in the video I looked at building a sharp-edged poly surface equivalent as a single sub the object with creased edges very often in NURBS modeling starting with controlled sharp edges is the correct way of creating fill its blends or transitional surfaces and very often this geometry is better suited to a NURBS workflow however iterating through and adjusting the results can be time-consuming version 7 introduces an improvement in the blend edge command that allows for setback corners in difficult circumstances as for example if I wanted three different nominal radii on these blended edges so let's first of all look at the NURBS workflow so I'll go to solid fill each edge and blend edge and I'll choose my first radius which I want to be 20 millimeters then my next radius which is going to be 60 millimeters and then finally the vertical corner which I want to be 50 millimeters and you'll see in the preview now that the blend edge command now creates the set back corners which is a big improvement on the standard way in which corners are produced in version six the problem still arises however if we want to iterate through these corners and play with the radii because at the moment we would need to keep rerunning the command and undoing and redoing the previous result and so we can simulate this type of corner as a sub d so if we start with this same or similar topology then what I'm going to do here is just a mark with a point object where the blends start and stop and also a reference point for this corner and then I'm going to move these points and snap them onto the sub D then what I can do with my sub D here to simulate this corner which is going to give me something which is much easier to play with and adjust then I can remove the crease in this edge this edge and this edge and then I can use the slide edge command to slide these edges and snap to these points now when I'm you doing this and I'm snapping two points this is the control point layout that I'm actually moving here that I'm snapping to that edge so if you look at the boxy object you'll see that's where those edges are whereas this is the interpolation of the shape the smooth interpolation so I'll just keep sliding these edges and these are pretty close but I'll move them anyway okay and if I look at both of these with the environment map you'll see that the results are similar in fact the sub D equivalent here might be slightly better in the way it's controlling that edge so this is an example of where we can use sub D to create quick design iterations even though we may model the final result as NURBS surfaces so that's about all I wanted to cover in this video please feel free to leave any comments below and if you found this video useful please hit the like button to keep up with all the latest news on Rhino and Rhino related topics please subscribe to this channel thanks very much for watching and I hope to catch up with you soon in the next video

Channel: Simply Rhino 3D Tutorials & Events

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Length: 37min 32sec (2252 seconds)

Published: Tue Jan 28 2020