Box. If youve modeled as far as you can at level 1 and still need to add more detail, you can refine the display further by right-clicking the components of the region you wish to refine and choosing Refine from the marking menu. The components will be subdivided another level further.Probably one of the most useful features of modeling with hierarchical subdivision surfaces is the ability to harden or crease edges without having to add any geometry. By selecting edges or vertices of a subdivision model, you can create either a full crease (Subdiv Surfaces | Full Crease Edge/Vertex) or a partial crease (Subdiv Surfaces | Partial Crease Edge/Vertex). You can continue to partially crease the selected edge until you are happy with the result. Figure 7-5 demon- strates a sphere whose edges have been fully creased and partially creased twice.This may seem like the most optimal way of modeling. The ability to add localized detail only where it is needed can save a lot of time. However, it is not possible to change the structure of the surface at different levels of the subdivision hierarchy. Polygonal editing tools such as Extrude Face and Split Polygon cannot be used on subdivision surfaces while in standard mode. Modeling in standard mode is therefore best suited for adding extra details to a model whose structure has already been laid out. Adding wrinkles to skin or creating hard edges are two examples of where this geometry type can be useful. But, to be able to change the structure of a subdivision surface, you must switch to polygon mode.Polygon ModeYou can switch from standard mode to polygon proxy mode at any time by right-clicking the surface and choosing Polygon from the marking menu. This creates a polygonal object that matches the base mesh (level 0) of the subdivision surface. Here, you are free to use any of the modeling tools in the Edit Mesh menu.The one thing to be aware of here is that every time you switch back to standard mode, the polygon shape is deleted. This means that if you have connected any other nodes, such as a deformer, to the polygon, they will be lost.210Maya 8 The Complete ReferenceFIGURE 7-5A full crease and partial crease are added to the edges of a subdivision sphere.Full creasePartial creaseTutorial:Modeling with Subdivision SurfacesIn this tutorial, we will use subdivision surfaces to add detail to our car. Well be using the front panel piece that we converted to polygons earlier in this chapter.1.Open the mcr8_car_frontPoly.ma file on the DVD. 2.Select the poly_frontPanel object and then choose Modify | Convert | Polygons to Subdiv ? to open the Options window. The main setting to be aware of here is Maximum Base Mesh Faces. By default, this attribute is set to 1000. This means that Maya will not convert the mesh to a subdivision surface if it exceeds 1000 faces. In this case, the front panel is less than 1000 faces, so this setting will work fine, but as you convert some other pieces, you may need to increase this to suit your model. Click the Create button to convert the polygonal mesh to a subdivision surface. Press the 3 key to display the subdivision surface smoothly. Your model should look like this:NOTEIf the conversion fails, you need to troubleshoot the model. Start byreading the errors in the Script Editor (Window | General Editor | Script Editor).You can use Mesh | Cleanup to fix any problems with nonmanifold geometry.Usually, its best to manually inspect the model with the border edges visible.Most of the time, the case will be that normals are reversed or edges arenot merged.3.We will start adding to the existing geometry by extruding the bottom edge to model with missing geometry. To make this type of edit, we must be in polygon mode. RMB- click the mesh and choose Polygon. A wireframe overlay of the original polygonal mesh will appear.Chapter 7211Preparing Models for Animation212Maya 8 The Complete Reference4.Select the bottom row of edges and extrude. Move the extruded edges back a bit, then extrude again and move them down to create a nice edge. Extrude one more time so that the surface is aligned to the base of the car in the underlay, as shown here: 5.In the Front view, select some of the vertices on the bottom edge, as shown next, and use the Move Normal tool (Modify | Transform Tools | Move Normal Tool) to move the vertices over a bit so that the edges align to the panel details in the underlay. Using this tool moves the vertices along the surface and ensures that the integrity of the surface is not broken.TIPThe Move Normal tool is a subset of the Move tool. You can access thissetting in the Move Tools Settings window or by holding down theWkey andRMB-clicking.6.Use the Insert Edge Loop tool to insert two edge loops, each one aligning to the base of both intakes shown in the underlay. Now we have all of the necessary topology to extrude. 7.Select the faces that align to the details in the underlay and extrude them back. Delete the three faces along