Manual/PartII/Advanced Mesh Modelling
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Advanced Mesh Modelling
Symmetrical Modelling
对称建模
You often need to model objects which exhibit some sort of symmetry.
For radial, rotational or multiple symmetry the best approach is to
carefully model one base structure and then, as a last step,
duplicate the base cell via SpinDup or whichever command is most
appropriate.
你可能经常需要制作一些具有对称特性的模型。对于辐射状、旋转状或复等位对称模型，它们都有很好的弧度，这时只需要制作模型的基本结构；然后通过SpinDup或任何一个最为恰当的命令来复制基本结构的模型单元。
For objects with bilateral symmetry, those with one plane
of symmetry, such as most animals (humans included) and many machines,
the above method implies modelling one half of the object,
and then mirroring a duplicate of the first half to get the whole
object.
至于那些镜象对称的模型，他们都有一个对称面，例如大部分的动物（包括人类）和许多机器；以上所述现象，则暗示了只需要制作模型的一半模型，然后镜象复制制作好的一半以得到整个对象。
Since it is usually difficult to attain correct proportions by
only modelling a half, it is possible to duplicate the
half before it is completely modelled, and act on one half and
automatically update the other.
有时候即使镜像一半模型，也难以获得完美的模型；因为我们复制一半以后，还需要在原始模型上进行修改；而镜像的副本则需要自动更新。
In Front View add a plane or whatever
(A plane.). Consider it as a starting point
for one half of the object. Let's say the object's right half, which for
us in frontal view is on the left of the screen. The plane of
symmetry is the yz plane. Move the mesh, in EditMode,
so that it is completely on the left of center. Delete
some nodes, and add some others, to give it its general shape, as in
Right half..
在前视图添加一个平面或诸如此类的物体（A plane..)；假设把它作为一个物体其中一半的基点。在这里我们把它设想为物体右半部，而对于我们在前视图里，它位于屏幕的左边；那么该对称面是YZ平面。在编辑模式里，移动该网格物体，以使它完全定位在中心的左边。这时对它进行一些调整，来完成它的右半部外型。
Now switch to ObjectMode and, with the half selected, make a
linked duplicate with ALT-D.
Press ESC to exit from Grab Mode and
press NKEY. In the Numeric input panel
which appears, set SizeX to -1
(Mirroring the linked duplicate.). This effectively mirrors
the linked duplicate with respect to the Object's center, hence
the importance of keeping the center on the plane of symmetry.
现在切换到物体模式并且选择这一半，用ALT-Dlinked复制。请按ESC 从抓取模式退出，并按NKEY。在出现的数值输入面板里调整SizeX 为- 1（Mirroring the linked duplicate..)。这实际上是相对于该对象的中心镜象连接复制，从而维持以对称面为中心的重要性。
Having duplicated the Object as a linked duplicate implies that the two
objects share the same mesh data, which is
implicitly mirrored by the unitary negative scaling along the x
axis, which is normal to the symmetry plane.
Now you can edit either of the two halves. Since they share
mesh data any change, be it an extrude, delete, face loop cut etc.
immediately reflects on the other side (Editing one half.).
连接复制对象其隐含着这两个对象共享相同的网格数据的意思，它是沿着 X轴正负的定标镜象，它是垂直于该对称面的。现在你可以编辑这两个半的任何一部分；即使他们共享网格数据发生任何改变（例如挤压、删除，面环切等等）。这在另一半也立即反应出来（Editing one half.）。
By carefully editing one half, and possibly by using a blueprint
as a background to provide guidelines, very interesting results
can be achieved (A head. Left: EditMode; Center: ObjectMode; Right: Joined., left).
现在你可以仔细的编辑一半，或许你可以使用设计图作为背景来作参考，这样就可以很快速的完成模型的制作。(人头左：编辑模式按；中：物体模式；右：结合完成)
As a final step, when symmetrical modelling is complete, the two halves must
be selected and joined into a single Object (CTRL-J).
This makes the seam (very visible in A head. Left: EditMode; Center: ObjectMode; Right: Joined.,
center) disappear. Once you have a single object
(A head. Left: EditMode; Center: ObjectMode; Right: Joined., right), you can start modelling
the subtle asymmetries which every being has.
当对称的模型完全时，作为最后一步，我们必须选择这两个物体然后使用(CTRL-J)
结合成单个物体。这时接缝（人头 左：编辑模式按；中：物体模式；右：结合完成）会消失。一旦你得到单个对象（人头 左：编辑模式按；中：物体模式；右：结合完成），你可以针对模型进行细微调整，使的模型稍微有点不对称。
| Note：
In Blender 2.33 and earlier versions the OpenGL implementation causes mirrored linked duplicates to have wrong normals, so that one of the two halves is black. This is fixed in Blender 2.34, but older versions can use this technique anyway by setting the mesh to single sided while symmetrical modelling is used.
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| 注意：
在Blender 2.33以及早期版本，它的OpenGL执行会引起镜象连接复制有着错误的法线，以使两半之一是显示为黑色。这在Blender 2.34中修复，老的版本可以先调整单边网格然后复制完成对称模型的制作。
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Proportional Editing Tool
When working with dense meshes, it can become difficult to make subtle adjustments to the vertices without causing nasty lumps and creases in the model's surface. When you face situations like these, use the proportional editing tool. It acts like a magnet to smoothly deform the surface of the model, without creating lumps and creases. In a top-down view, add a plane mesh to the scene with SPACE>>Add>>Mesh>>Plane. Subdivide it a few times with WKEY>>Subdivide (or by clicking on the Subdivide button in the Editing Context Mesh Tools Panel) to get a relatively dense mesh (A planar dense mesh.). Or, add a grid directly via SPACE>>Add>>Mesh>>Grid, specifying the number of vertices in each direction. When you are finished, deselect all vertices with AKEY.
Select a single vertex in the mesh by clicking it with RMB (A planar dense mesh with just one selected vertex.).
While still in EditMode, activate the proportional editing tool by pressing OKEY or by using the toolbar icon and select either On or Connected. (Proportional Editing icon). When proportional editing is active the icon will have an orange color.
- Connected - Only vertices that are connected to each other in a mesh, can be affected.
- On - All vertices can be affected.
- Off - Proportional Editing is Off!
Change the curve profile used by either using the Mesh>>Proportional Falloff submenu, using the toolbar icon Falloff Menu. or by pressing SHIFT-O to toggle between the options Constant, Linear, Sharp, Root, Sphere and Smooth. (Constant - No Falloff. Linear Falloff. Sharp Falloff. Root Falloff. Sphere Falloff. Smooth Falloff.)
Switch to a front view (NUM 1) and activate the grab tool with GKEY. As you drag the point upwards, notice how nearby vertices are dragged along with it. When you are satisfied with the placement, press LMB to fix the position. If you are not satisfied, nullify the operation and revert your mesh to the way it looked before with RMB or ESC key. While you are editing you can increase or decrease the radius of influence (shown by the dark grey circle in Influence circle.) by pressing PAGEUP and PAGEDOWN respectively. As you change the radius, the points surrounding your selection will adjust their positions accordingly. You can also use MW to enlarge or shrink the influence radius.
You can use the proportional editing tool to produce great effects with the scaling (SKEY) and rotation (RKEY) tools, as A landscape obtained via Proportional Editing shows.
Combine these techniques with vertex painting to create fantastic landscapes. Final rendered landscape shows the results of proportional editing after the application of textures and lighting.
Noise
The Noise function allows you to displace vertices in meshes based on the grey-values of a texture applied to it. That way you can generate great landscapes or carve text into meshes.
Add a plane and subdivide it at least five times. To do that you can either use the Subdivide or Subdivide Multi entry in the Specials menu accessed via the WKEY;see (Subdivide tool). Using Subdivide Multi is faster and easier. Select Subdivide Multi and enter "5" for the number of cuts popup dialog.
Now add a material and assign a Clouds texture to it. Adjust the NoiseSize: to 0.500. Choose white as the color for the material and black as the texture color, to give us good contrast for the noise operation.
Ensure that you are in EditMode and that all vertices are selected, then switch to the Editing Context F9. Press the Noise button in the Mesh Tools Panel (Noise button in EditButtons) several times until the landscape looks nice. (Noise application process) is an example of applying the noise tool. From top left to bottom right: Plane with texture, sub-divided plane, "Noise" button hit 2, 4, 6 and 8 times. shows the original - textured - plane as well as what happens as you press Noise.
Remove the texture from the landscape now because it will disturb the look. Then add some lights, some water, set smooth and SubSurf the terrain, and so on. (Noise generated landscape).
| Note: The noise displacement always occurs along the mesh's z coordinate, which is along the direction of the z axis of the Object local reference. |
Decimator Tool
The Decimator tool is an often overlooked feature which allows you to reduce the vertex/face count of a mesh with minimal shape changes. This is not applicable to meshes which have been created by modelling carefully and economically, where all vertices and faces are necessary to correctly define the shape, but if the mesh is the result of complex modelling, with proportional editing, successive refinements, possibly some conversions from SubSurfed to non-SubSurfed meshes, you might very well end up with meshes where lots of vertices are not really necessary. A simple example is a plane, and a 4x4 undeformed Grid object. Both render exactly the same, but the plane has 1 face and 4 vertices, while the grid has 9 faces and 16 vertices, hence lots of unneeded vertices and faces. The Decimator Tool (Decimator buttons.) allows you to eliminate these unneeded faces. Its NumButton reports the number of faces of the selected mesh in ObjectMode. The decimator tool only handles triangles, so each quadrilateral face is implicitly split into two triangles for decimation.
Let's consider the example we used in the Bevel section. As you might notice there is a tiny triangular face on each cube vertex which might very well be unnecessary (Decimator at work., top left). The header says the cube has 98 faces and 96 vertices. The Decimator button says the cube has 188 triangular face, namely 90 quads (which are 180 tris) and 8 tris.
By changing the number in the decimator NumBut, by either clicking or typing it in, the mesh immediately changes to triangles only. As the number gets lower, faces disappear one after the other. Blender causes coplanar faces and vertices on aligned edges to disappear first. This tends to keep the shape of the mesh. As more and more faces are asked to be removed faces less and less coplanar and vertices less and less colinear are merged, hence sensible shape change might occur (Decimator at work., top center). In this particular case, if we just want the central tri face of each cube vertex to disappear we expect the final mesh to be 2x6=12 faces for each cube face, 2x3x12=72 faces for each bevelled edge, and 9x8=72 faces for each bevelled vert, totalling 156 faces. It is very uncommon to know beforehand how many faces the final mesh can have, usually you must look carefully at the mesh in a 3D window to check that the shape is still good. The two buttons below the Decimator finalize or cancel the decimation. Once it is finalized triangles are not shown any more (Decimator at work., top right) but the mesh is nevertheless made only of triangles (Decimator at work., bottom left). You can revert to quads if you so wish, by selecting all vertices and hitting ALT-J (Decimator at work., bottom center). This way we reduce the vertex count to 80 and face count to 82 without any noticeable shape loss. It might look a small gain, but if this cube is going to be dupliverted on a particle system with 1000 particles it might be worth it.
Decimated landscape, top: original; middle: lightly decimated; bottom: heavily decimated. shows a landscape generated via a careful application of the Noise technique described earlier, on a quite vast grid. On top, the result for the original mesh and below, two different levels of decimation. To the eye the difference is indeed almost unnoticeable, but as the vertex count goes down there is a huge gain.
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