[Tutorial] The Basics of Object Meshes


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Post [Tutorial] The Basics of Object Meshes

#1  Tormie 22 Jun 2007 22:57

Note by Tormie: I moved this tutorial here from the knowledge base in order to have all the tutorial in one place easy to find

The Basics of Object Meshes by Melamkish

Every object created in 3 dimensional space has to have some way to define it's geometry. Once you know how this is done, the concept of the geometry or more commonly referred to as the mesh, become easy to understand.

So let's jump into Poser and open Posette (P4 nw hi resolution) and build a working knowledge of her mesh.

You should now have Posette in your preview window. Look for the Document Display Style buttons. Slide your mouse over the buttons until you find the one named Wireframe and click on it. You should now see a series of interconnected lines. These lines are called the wireframe because they look like wires strung together. This wireframe is the mesh of the object. It's a little hard to see this way, so at your Document Display Style buttons find Flat Lined and select it. You should now see both the wireframe and preview texture together. Position Posette so you can zoom in and see her upper body and head.

You'll notice her mesh is composed of many triangles and polygons. Every place that a series of lines intersect is a point in space (vertex). As I mentioned, the placement of these points defines the object. Pretty simple, huh. Lines are drawn in by the program to play connect the dots because it is easier to visualize an object this way rather than by vertices alone.

To continue our discussion we will have to discuss some basic geometry. Don't despair, there are no calculations involved, only some basic concept review.

Recall the Cartesean Coordinate system. This is a way of mathematically defining a point's location in 3D space consisting of the x, y, and z axis. Imaginary lines intersect at the origin and represented as (0, 0, 0). So the location of each vertex is defined by 3 numbers relative to the origin. A table of these vertices would look like this:

(2, -2, 5)
(3.2, 3, 4)
(-8, -2, 4), and so on.

Just a couple more ideas and we are done.

Every object in 3D space has to be referenced to something and that is the absolute origin. When you open any character, you will notice that it always starts in the same location. open another object and it is also in the same location. That is because the object comes into your scene referenced to the absolute and unchanging origin that was defined when the program was written. That is, the center of the floor grid. What happens when we spin the x, y or zTran dials? Well, we have just changed her position relative to the absolute origin. Posette now has a relative coordinate for every vertex which is offset by the change in her position. Don't worry. Poser calculates and remembers these relative coordinates for you.

At this point, we are pretty much done. The geometry file is saved in a format that the program understands. Wavefront who developed the format Poser uses assigned the .obj (object) file extension. 3DS Studio Max uses .3DS, Lightwave uses .lwo and so on. Poser can convert some of these formats. There are other programs that also can convert various formats.

All the character, pose, prop, face etc. files are nothing more that text files with instructions for the program to use to access the geometry of the object and create the changes. You can even open these files with a text editor and edit them the old fashioned way. This is how 3D was done in the early days.

By now you are probably tired of looking at a flat lined Posette. Let's expand on a couple of things and call it quits. You may have looked at a 2D wireframe looking picture that is used for creating texture maps.

Unless you have some really expensive and sophisticated software, it is hard to draw a texture on a 3D object. So, there are programs that will take the verices of the mesh, unwrap them and create what is called a UV map in 2 dimensions. The texture is drawn over the UV map, usually on a different layer in a graphics program such as PSP) is a bitmap graphics editor for computers running the Microsoft Windows operating system that was originally published by Minneapolis-based Jasc Software. In October 2004, Corel Corporation bought out Jasc software">PSP) is a bitmap graphics editor for computers running the Microsoft Windows operating system that was originally published by Minneapolis-based Jasc Software. In October 2004, Corel Corporation bought out Jasc software">paint shop pro, and then the UV map is deleted and only the colored texture saved.

Some common terms you may hear.

Hi poly count - Usually an object with a very high number of polygons in the mesh, i.e. hi resolution.
lo poly count - the opposite.

That's about it. Mesh is the most common term used when discussing geometry, although wireframe is also appropriate. Modeling programs that can create objects in 3d space are required to build a wireframe that is then saved in the required format. UV mapping programs convert the geometry to a flat texture template. A texture is then painted and you have your figure complete.
 




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