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3D Model

In the world of computers (above all in computer graphics, but also in physics simulations, 3D printing etc.) 3D model is a representation of a three dimensional object, for example of a real life object such as a car, tree or a dog, but also possibly something more abstract like a fractal or function plot surface. 3D models can be displayed using various 3D rendering techniques and are used mostly to simulate real world on computers (e.g. games), as real world is, as we know, three dimensional. 3D models can be created in several ways, e.g. manually with 3D modeling software (such as Blender) by 3D artists, by 3D scanning real world objects, or automatically by procedural generation.

There is a plethora of different 3D model types, the topic is very large when viewed in its whole scope because 3D models can be used and represented in many ways (and everything is yet more complex by dealing with different methods of 3D rendering) -- the mainstream "game" 3D models that most people are used to seeing are polygonal (basically made of triangles) boundary-representation (recording only surface, not volume) textured (with "pictures" on their surface) 3D models, but be aware that many different ways of representation are possible and in common use by the industry, for example various volume representations, voxel models, point clouds, implicit surfaces, spline surfaces, constructive solid geometry, wireframe etc. Models may also bear additional extra information and features, e.g. material, bone rigs for animation, animation key frames, density information, LODs, even scripts and so on.

3D formats: situation here is not as simple as it is with images or audio, but there are a few formats that in practice will suffice for most of your models. Firstly the most KISS one is (Wavefront) obj -- this is supported by almost every 3D software, it's a text format that's easy to parse and it's even human readable and editable; obj supports most things you will ever need like UV maps and normals, and you can hack it even for a primitive keyframe animation. So if you can, use obj as your first choice. If you need something a little more advanced, use COLLADA (.dae extension) -- this is a bit more bloated than obj as it's an XML, but it's still human readable and has more features, for example skeletal animation, instancing, model hierarchy and so on. Another noteworthy format is let's say STL, seen a lot in 3D printing. For other than polygonal models you may have to search a bit or just represent your model in some sane way, for example heightmap is naturally saved as a grayscale image, voxel model may be saved in some dead simple text format and so on. Also be always sure to distribute your model in universal format, i.e. don't just share Blender's project file or anything like that, that's like sharing pictures in Photoshop format or sending someone a Word document, only retards do that -- yes, you should also share the project file if possible, but it's more important to release the model in a widely supported, future proof and non discriminating format.

Let's now take a closer look at a basic classification of 3D models (we only mention the important categories, this is not an exhaustive list):

Animation: the main approaches to animation are these (again, just the important ones, you may encounter other ways too):

Let us also briefly mention texturing, an important part of making traditional 3D models. In the common, narrower sense texture is a 2D images that is stretched onto the model surface to give the model more detail, just like we put wallpaper on a wall -- without textures our models have flat looking surfaces with just a constant color (at best we may assign each polygon a different color, but that won't make for a very realistic model). Putting texture on the model is called texture mapping -- you may also hear the term UV mapping because texturing is essential about making what we call a UV map. This just means we assign each model vertex 2D coordinates inside the texture; we traditionally call these two coordinates U and V, hence the term UV mapping. UV coordinates are just coordinates within the texture image; they are not in pixels but are typically normalized to a float in range <0,1> (i.e. 0.5 meaning middle of the image etc.) -- this is so as to stay independent of the texture resolution (you can later swap the texture for a different resolution one and it will still work). By assigning each vertex its UV texture coordinates we basically achieve the "stretching", i.e. we say which part of the texture will show on what's the character's face etc. (Advanced note: if you want to allow "tears" in the texture, you have to assign UV coordinates per triangle, not per vertex.) Now let's also mention a model can have multiple textures at once -- the most basic one (usually called diffuse) specifies the surface color, but additional textures may be used for things like transparency, normals (see normal mapping), displacement, material properties like metalicity and so on (see also PBR). The model may even have multiple UV maps, the UV coordinates may be animated and so on and so forth. Finally we'll also say that there exists 3D texturing that doesn't use images, 3D textures are mostly procedurally generated, but this is beyond our scope now.

We may do many, many more things with 3D models, for example subdivide them (automatically break polygons down into more polygons to smooth them out), apply boolean operations to them (see above), sculpt them (make them from virtual clay), optimize them (reduce their polygon count, make better topology, ...), apply various modifiers, 3D print them, make them out of paper (see origami) etcetc.

{ Holy crab, there is a lot to say about 3D models. ~drummyfish }

Example

Let's take a look at a simple polygonal 3D model. The following is a primitive, very low poly model of a house, basically just a cube with roof:

               I
             .:..
           .' :':::..
        _-' H.' '.   ''-.
      .'    .:...'.......''..G
    .' ...'' :    '.    ..' :
  .::''......:.....'.-''    :
 E:          :      :F      :
  :          :      :       :
  :          :      :       :
  :          :......:.......:
  :        .' D     :     .' C
  :     .''         :   -'
  :  .''            : .'
  ::'...............:'
 A                   B

In a computer it would firstly be represented by an array of vertices, e.g.:

-2 -2 -2  (A)
 2 -2 -2  (B)
 2 -2  2  (C)
 2 -2 -2  (D)
-2  2 -2  (E)
 2  2 -2  (F)
 2  2  2  (G)
 2  2 -2  (H)
 0  3  0  (I)

Along with triangles (specified as indices into the vertex array, here with letters):

ABC ACD          (bottom)
AFB AEF          (front wall)
BGC BFG          (right wall)
CGH CHD          (back wall)
DHE DEA          (left wall)
EIF FIG GIH HIE  (roof)

We see the model consists of 9 vertices and 14 triangles. Notice that the order in which we specify triangles follows the rule that looking at the front side of the triangle its vertices are specified clockwise (or counterclockwise, depending on chosen convention) -- sometimes this may not matter, but many 3D engines perform so called backface culling, i.e. they only draw the front faces and there some faces would be invisible from the outside if their winding was incorrect, so it's better to stick to the rule if possible.

The following is our house model in obj format -- notice how simple it is (you can copy paste this into a file called house.obj and open it in Blender):

# simple house model
v 2.000000 -2.000000 -2.000000
v 2.000000 -2.000000 2.000000
v -2.000000 -2.000000 2.000000
v -1.999999 -2.000000 -2.000000
v 2.000001 2.000000 -2.000000
v 1.999999 2.000000 2.000000
v -2.000001 2.000000 2.000000
v -2.000000 2.000000 -2.000000
v -2.000001 2.000000 2.000000
v 0.000000 3.000000 0.000000
vn 1.0000 0.0000 0.0000
vn -0.0000 0.0000 1.0000
vn 0.0000 -1.0000 0.0000
vn 0.0000 0.0000 -1.0000
vn -1.0000 -0.0000 -0.0000
vn -0.0000 0.8944 0.4472
vn 0.4472 0.8944 0.0000
vn 0.0000 0.8944 -0.4472
vn -0.4472 0.8944 -0.0000
s off
f 6 2 5
f 2 1 5
f 6 9 3
f 3 2 6
f 4 1 3
f 2 3 1
f 5 1 8
f 4 8 1
f 8 4 9
f 4 3 9
f 9 6 10
f 6 5 10
f 8 10 5
f 8 9 10

And here is the same model again, now in collada format (it is an XML so it's much more verbose, again you can copy paste this to a file house.dae and open it in Blender):

<?xml version="1.0" encoding="utf-8"?>
<COLLADA xmlns="http://www.collada.org/2005/11/COLLADASchema" version="1.4.1"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <!-- simple house model -->
  <asset>
    <contributor> <author>drummyfish</author> </contributor>
    <unit name="meter" meter="1"/>
    <up_axis>Z_UP</up_axis>
  </asset>
  <library_geometries>
    <geometry id="house-mesh" name="house">
      <mesh>
        <source id="house-mesh-positions">
          <float_array id="house-mesh-positions-array" count="30">
             2  2 -2      2 -2 -2      -2 -2 -2      -2  2 -2
             2  2  2      2 -2  2      -2 -2  2      -2  2  2
            -2 -2  2      0  0  3
          </float_array>
          <technique_common>
            <accessor source="#house-mesh-positions-array" count="10" stride="3">
              <param name="X" type="float"/>
              <param name="Y" type="float"/>
              <param name="Z" type="float"/>
            </accessor>
          </technique_common>
        </source>
        <vertices id="house-mesh-vertices">
          <input semantic="POSITION" source="#house-mesh-positions"/>
        </vertices>
        <triangles material="Material-material" count="14">
          <input semantic="VERTEX" source="#house-mesh-vertices" offset="0"/>
          <p>
            5 1 4   1 0 4    5 8 2    2 1 5    3 0 2    1 2 0    4 0 7
            3 7 0   7 3 8    3 2 8    8 5 9    5 4 9    7 9 4    7 8 9
          </p>
        </triangles>
      </mesh>
    </geometry>
  </library_geometries>
  <library_visual_scenes>
    <visual_scene id="Scene" name="Scene">
      <node id="house" name="house" type="NODE">
        <translate sid="location">0 0 0</translate>
        <rotate sid="rotationZ">0 0 1 0</rotate>
        <rotate sid="rotationY">0 1 0 0</rotate>
        <rotate sid="rotationX">1 0 0 0</rotate>
        <scale sid="scale">1 1 1</scale>
        <instance_geometry url="#house-mesh" name="house"/>
      </node>
    </visual_scene>
  </library_visual_scenes>
  <scene> <instance_visual_scene url="#Scene"/> </scene>
</COLLADA>

TODO: other types of models, texturing etcetc.

3D Modeling: Learning It And Doing It Right

WORK IN PROGRESS

Do you want to start 3D modeling? Or do you already know a bit about it and just want some advice to get better? Then let us share a few words of advice here.

Let us preface with mentioning the hacker chad way of making 3D models, i.e. the LRS way 3D models should ideally be made. Remeber, you don't need any program to create 3D models, you don't have to be a Blender whore, you can make 3D models perfectly fine without Blender or any similar program, and even without computers. Sure, a certain kind of highly artistic, animated, very high poly models will be very hard or impossible to make without an interactive tool like Blender, but you can still make very complex 3D models, such as that of a whole city, without any fancy tools. Of course people were making statues and similar kinds of "physical 3D models" for thousands of years -- sometimes it's actually simpler to make the model by hand out of clay and later scan it into the computer, you can just make a physical wireframe model, measure the positions of vertices, hand type them into a file and you have a perfectly valid 3d model -- you may also easily make a polygonal model out of paper, BUT even virtual 3D models can simply be made with pen and paper, it's just numbers, vertices and triangles, very manageable if you keep it simple and well organized. You can directly write the models in text formats like obj or collada. First computer 3D models were actually made by hand, just with pen and paper, because there were simply no computers fast enough to even allow real time manipulation of 3D models; back then the modelers simply measured positions of someone object's "key points" (vertices) in 3D space which can simply be done with tools like rulers and strings, no need for complex 3D scanners (but if you have a digital camera, you have a quite advanced 3D scanner already). They then fed the manually made models to the computer to visualize them, but again, you don't even need a computer to draw a 3D model, in fact there is a whole area called descriptive geometry that's all about drawing 3D models on paper and which was used by engineers before computers came. Anyway, you don't have to go as far as avoiding computers of course -- if you have a programmable computer, you already have the luxury which the first 3D artists didn't have, a whole new world opens up to you, you can now make very complex 3D models just with your programming language of choice. Imagine you want to make the said 3D model of a city just using the C programming language. You can first define the terrain as heightmap simply as a 2D array of numbers, then you write a simple code that will iterate over this array and converts it to the obj format (a very simple plain text 3D format, it will be like 20 lines of code) -- now you have the basic terrain, you can render it with any tool that can load 3D models in obj format (basically every 3D tool), AND you may of course write your own 3D visualizer, there is nothing difficult about it, you don't even have to use perspective, just draw it in orthographic projection (again, that will be probably like 20 lines of code). Now you may start adding houses to your terrain -- make a C array of vertices and another array of triangle indices, manually make a simple 3D model of a house (a basic shape will have fewer than 20 vertices, you can cut it out of paper to see what it will look like). That's your house geometry, now just keep making instances of this house and placing them on the terrain, i.e. you make some kind of struct that will keep the house transformation (its position, rotation and scale) and each such struct will represent one house having the geometry you created (if you later improve the house model, all houses will be updates like this). You don't have to worry about placing the houses vertically, their height will be computed automatically so they sit right on the terrain. Now you can update your model exporter to take into account the houses, it will output the obj model along with them and again, you can view this whole model in any 3D software or with your own tools. You can continue by adding trees, roads, simple materials (maybe just something like per triangle colors) and so on. This approach may actually even be superior for some projects just as scripting is superior to many GUI programs, you can collaborate on this model just like you can collaborate on any other text program, you can automatize things greatly, you'll be independent of proprietary formats and platforms etcetc. This is how 3D models would ideally be made.

OK, back to the mainstream now. Nowadays as a FOSS user you will most likely do 3D modeling with Blender -- we recommended it to start learning 3D modeling as it is powerful, free, gratis, has many tutorials etc. Do NOT use anything proprietary no matter what anyone tells you! Once you know a bit about the art, you may play around with alternative programs or approaches (such as writing programs that generate 3D models etc.). However as a beginner just start with Blender, which is from now on in this article the software we'll suppose you're using.

Start extremely simple and learn bottom-up, i.e. learn about fundamentals and low level concepts and start with very simple models (e.g. simple untextured low-poly shape of a house, box with a roof), keep creating more complex models by small steps. Do NOT fall into the trap of "quick and easy magic 3D modeling" such as sculpting or some "smart apps" without knowing what's going on at the low level, you'll end up creating extremely ugly, inefficient models in bad formats, like someone wanting to create space rockets without learning anything about math or physics first. Remember to practice, practice, practice -- eventually you learn by doing, so try to make small projects and share your results on sites such as opengameart to get feedback and some mental satisfaction and reward for your effort. The following is an outline of possible steps you may take towards becoming an alright 3D artist:

  1. Learn what 3D model actually is, basic technical details about how a computer represents it and roughly how 3D rendering works. It is EXTREMELY important to have at least some idea about the fundamentals, i.e. you should learn at least the following:
  1. Manually create a few extremely simple low-poly untextured models, e.g. that of a simple house, laptop, hammer, bottle etc. Keep the vertex and triangle count very low (under 100), make the model by MANUALLY creating every vertex and triangle and focus only on learning this low level geometry manipulation well (how to create a vertex, how to split an edge, how to rotate a triangle, ...), making the model conform to good practice and get familiar with tools you're using, i.e. learn the key binds, locking movement direction to principal axes, learn manipulating your 3D view, setting up the free/side/front/top view with reference images etc. Make the model nice! I.e. make it have correctly facing triangles (turn backface culling on to check this), avoid intersecting triangles, unnecessary triangles and vertices, remove all duplicate vertices (don't have multiple vertices with the same position), connect all that should be connected, avoid badly shaped triangles (e.g. extremely acute/long ones) etc. Keep the triangle count as low as possible, remember, there always has to be a very good reason to add a triangle -- there must be no triangle at all whose purpose is not justified, i.e. which is not absolutely necessary to achieve something about the model's look. If you can take the triangle away and still make the model look more or less the same, the triangle must be taken away. Also learn about normals and make them nice! I.e. try automatic normal generation (fiddle e.g. with angle thresholds for sharp/smooth edges), see how they affect the model look, try manually marking some edges sharp, try out smoothing groups etc. Save your final models in OBJ format (one of the simplest and most common formats supporting all you need at this stage). All this will be a lot to learn, that's why you must not try to create a complex model at this stage. You can keep yourself "motivated" e.g. by aiming for creating a low-poly model collection you can share at opengameart or somewhere :)
  2. Learn texturing -- just take the models you have and try to put a simple texture on them by drawing a simple image, then unwrapping the UV coordinates and MANUALLY editing the UV map to fit on the model. Again the goal is to get familiar with the tools and concepts now; experiment with helpers such as unwrapping by "projecting from 3D view", using "smart" UV unwrap etc. Make the UV map nice! Just as model geometry, UV maps also have good practice -- e.g. you should utilize as many texture pixels as possible (otherwise you're wasting space in the image), watch out for color bleeding, the mapping should have kind of "uniform pixel density" (or possibly increased density on triangles where more details is supposed to be), some pixels of the texture may be mapped to multiple triangles if possible (to efficiently utilize them) etc. Only make a simple diffuse texture (don't do PBR, material textures etc., that's too advanced now). Try out texture painting and manual texture creation in a 2D image program, get familiar with both.
  3. Learn modifiers and advanced tools. Modifiers help you e.g. with the creation of symmetric models: you only model one side and the other one gets mirrored. Subdivide modifier will automatically create a higher poly version of your model (but you need to help it by telling it which sides are sharp etc.). Boolean operations allow you to apply set operations like unification or subtraction of shapes (but usually create a messy geometry you have to repair!). There are many tools, experiment and learn about their pros and cons, try to incorporate them to your modeling.
  4. Learn retopology and possibly sculpting. Topology is an extremely important concept -- it says what the structure of triangles/polygons is, how they are distributed, how they are connected, which curves their edges follow etc. Good topology has certain rules (e.g. ideally only being composed of quads, being denser where the shape has more detail and sparser where it's flat, having edges so that animation won't deform the model badly etc.). Topology is important for efficiency (you utilize your polygon budget well), texturing and especially animation (nice deformation of the model). Creating more complex models is almost always done in the following two steps:
  1. Learn about materials and shaders. At this point you may learn about how to create custom shaders, how to create transparent materials, apply multiple textures, how to make realistic skin, PBR shaders etc. You should at least be aware of basic shading concepts and commonly encountered techniques such as Phong shading, subsurface scattering, screen space effects etc. because you'll encounter them in shader editors and you should e.g. know what performance penalties to expect.
  2. Learn animation. First learn about keyframes and interpolation and try to animate basic transformations of a model, e.g. animate a car driving through a city by keyframing its position and rotation. Then learn about animating the model's geometry -- first the simple, old way of morphing between different shapes (shape keys in Blender). Finally learn the hardest type of animation: skeletal animation. Learn about bones, armatures, rigging, inverse kinematics etc.
  3. Now you can go crazy and learn all the uber features such as hair, physics simulation, NURBS surfaces, boob physics etc.

Don't forget to stick to LRS principles! This is important so that your models are friendly to good technology. I.e. even if "modern" desktops don't really care about polygon count anymore, still take the effort to optimize your model so as to not use more polygons that necessary! Your models may potentially be used on small, non-consumerist computers with software renderers and low amount of RAM. Low-poly is better than high-poly (you can still prepare your model for automatic subdivision so that obtaining a higher poly model from it automatically is possible). Don't use complex stuff such as PBR or skeletal animation unless necessary -- you should mostly be able to get away with a simple diffuse texture and simple keyframe morphing animation, just like in old games! If you do use complex stuff, make it optional (e.g. make a normal map but don't rely on it being used in the end).

So finally let's recount some of the advice:

Good luck with your modeling!


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