Modeling with polygons (part 1)

Theory

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Introduction

The objects we create in Maya, like real objects, have certain properties which define their possible use. It can be compared with the different use of cardboard , MDF or clay in making a physical model. Each material has its own properties , ways how to modify it and the forms you can create with it. You would not use a saw on clay and you would not use MDF for making a model with a double curved surfaces. If we want to design in the computer we will have to know the properties of the geometry we use in the design process. It will define what kind of form can be generated, the possibilities of altering the form and the accuracy of the form ( interesting if you want to digitally manufacture the object) We will use polygons for the first two workshops.

The polygon is a very simple description of geometry. Its form is defined by a set of coordinate points (vertices). A set of coordinate points are maybe interesting for the computer to work with, we only see a lot of dots. To make the form visible they added between each three points a triangular surface, which is called a face. These faces together between all the coordinate points are what we are seeing. This structure has a substantial influence on what you can do with the geometry.

Polygon is a straight forward description of geometry in 3D.

The shape is defined by its coordinate point or vertices. The vertices will define the shape of the geometry
The surface of the geometry is defined by the planar triangular faces. The faces will define the surface of the geometry
The edges of the geometry are the edges of the faces. The edge is always a straight line

Advantages:

Possibility of describing volumes
Less memory intensive
Straight forward mathematical description
Commonly used geometry type

Disadvantage:

The curvature is only approximated by the face between the vertices
High poly count necessary for curved shapes approximation

Applications:

Modelling Cartesian architecture
Architectural visualisation
Architectural interactive virtual visualisation
Geometry for analysis
Geometry for Rapid Prototyping

The straight forward description of the polygon as a set of coordinate points makes it especially suitable for analysis and rapid prototyping. Distances, areas, volumes and angles can be calculated based on the position of the coordinate points. The low memory requirement for display makes polygons the favourite geometry for virtual reality environments like web based interactive virtual environment and games. The possibility of generating volumes makes polygons faster in modeling of straight angled surfaces

The disadvantage of not being able to describe curved surface accurately is a major drawback in designing with polygons. Because there is always a straight edge between two coordinate points (vertices) the curvature will always be a crude approximation. This one of the reasons polygons are not used in more complex designs with curved ore double curved surfaces.

The geometry

If you want to design in the computer you will have to know the properties of your design environment, its possibilities and its limitation. Not only the geometry type is of influence on the design process. Polygons for example have the problem of not being able to accurately describe curved surfaces. The form you start to design with is also of influence on the possibilities of generating a formal description of your design. There are 3 different kind of geometry forms you can start from.

The first one is the volume or predefined volumes ( primitives). If we start using volumes as a basis for modeling our design we have the advantage that the geometry is already defined in 3 dimensions. We can alter our 3D geometry by deforming it ( make a cube into a rectangular box) or making a combination of different kind of 3D objects ( subtracting one box from the other to create a hole) This starting form however has its limitations because the 3 dimensions are already defined from the start. The topology , organization of the surfaces, of the form predefined. Although complex objects can be made with this kind of geometry it can be quite difficult.

The second more flexible geometry to start with is the surface. If we can generate a surface, we can define its form in two dimensions. By extruding the form in the third dimension we can generate a 3 dimensional object. This extrusion process however is often limited to a simple straight extrusion. So the influence on the 3rd dimension is limited. The maximum freedom in this case is primarily limited to two dimensions. This makes this form especially suitable for geometry with a complex section and a simple extrusion, like a facade or a steel beam.

The third option is the most flexible and is widely used in digital design. In this case the basic form is a line or a combination of lines. The strength of the use of lines as a start for geometry is the fact that the line not only can define a surface in two dimensions ( a complex surface ) but by using a combination of lines the third dimension can also be defined by a line. This method of constructing complex geometry with the help of lines is called curved based modeling and is widely used in other industries like product design, car design and in the aero-space industry.

In this course we will use all the three techniques. We will start with the creation of volumes and the techniques how to modify them.

Polygons menuset interface

When you are modeling with polygons, it's recommended to switch to the polygons menu set. The File, Edit, Create, Display and Select menus are the same for all menu sets, but the others change depending on the selected menu set. When you select the Polygons menu set, the Mesh, Edit Mesh and a few other polygon-specific menus are available.

Creating geometry

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Creating objects using primitives

create

You can create polygon primitives by using the create > polygon primitives command. It can be convenient to turn on Interactive Creation in the bottom of the polygon primitives menu.

When you now double click somewhere in your view port a primitive with the standard dimensions will be created. You can also create the dimensions of the primitive now interactively by clicking the required dimensions. This can work really well in combination with the snapping tools. If you don't want to use the interactive creation and you want every new primitive to appear at the (0,0,0) point in your view port with the standard dimensions, you can turn it off (and on) by clicking create > polygon primitives > interactive creation.

Toolbox

Selection tools

There are a couple of ways of selecting objects in Maya. If you are still in another tool, make sure that the selection tool in the toolbox is selected or press Q on your keyboard. Select an object by clicking on it. By holding the Shift key it’s possible to select multiple objects. Clicking and dragging a window around the objects is a faster way of selecting multiple objects. With the lasso tool in the toolbox you can drag a non-rectangular selection around the objects. To remove objects from the selection hold the Control' key while clicking the objects.

Transforming Objects

When an object is selected, it can be transformed. To move, rotate or scale, select the particular tool in the toolbox. Click and drag the manipulator on the colored axis of choice to perform the desired transformation. When selecting one axis, the transformation is only performed on that particular axis. For transforming in all directions click the yellow icon in the center of the manipulator

For example, if we want our object to scale in the z-axis, we select the object, we then select the scale tool in the toolbox, the manipulator is shown and we click and drag the blue cube to scale the object.

The transformations are numerically shown in the ‘Channel Box’ on the right. You can input the transformation values manually here. So the use of exact measures is possible this way instead of dragging the manipulator a random amount. For mirroring objects it is possible to input a negative scale value in the channel box.

Note that all the transformations you do to objects will be done with the pivotpoint as base. If your pivotpoint is placed in the center of an object it will be scaled, rotated and moved from that point, if you want to transform your object from another point (for instance from one of the corners), you can move your pivotpoint (see under the section editing geometry below)

Channelbox

The Channelbox is on the right side of the screen. In this menu you will find all the properties of the selected object, and you can change those properties. If you apply a certain operation on an object, Maya will remember this. This is called the construction history of an object and that is also shown here.

If you create an object in Maya it will automatically get a unique name. When you are building a large building or model it can be useful to change the standard name of an object to something that makes a little more sense to humans. This can help you finding and selecting objects in larger scenes. You can change a name by clicking on the standard name in the channelbox. When you have already used a name, e.g: door and you name another object door, Maya will automatically suffix a number, making the name unique. So your new door will be named door1 and so on.

In the Outliner you can select objects by name, so giving them a logical name can be very useful.

Relative transform

You can transform your object relative to it's current place, scale or rotation with an exact number of units. To do this, go to the little triangle next to the input field at the right top of your screen. when this field is not visible it could be hidden (click the small bars to open it). Click on the triangle and choose relative transform:

Now select the tool corresponding to the transformation you want to do (eg. if you want to move the object from it's current location select the move tool) because that's the kind of transformation Maya will do and select the object you want to use it on. Now you can enter the amount of units you want to move, rotate or scale your object in the X, Y and Z fields shown above. You can either do it in only one direction or 2 or 3 directions at the same time. Press enter to execute the transformation.

Note that Maya always uses points as a decimal separator, not a comma.

You can use the relative transform for objects, but also for components or groups.

Snapping

Distance tool

Sometimes you need to know the exact distance or size of something, it can be convenient to use the distance tool for that. The distance tool can be found under Create > Measure tools > Distance tool. The distance tool measures the distance between the two points you specify by clicking in your view port. Using point snap can be really useful when doing this. If you move one of the pointers afterward with the move tool the distance is updated automatically.

Creating objects by duplicating

In Maya the way to duplicate objects is by using the menu Edit » Duplicate Special. By default it makes an exact copy of the selected objects on the exact same position. Use the move tool to change the position of the copy to make it visible.

The duplicate menu is a little more advanced than you might think at first sight. By choosing Edit » Duplicate Special the duplicate options dialog is shown. These options enable you to create multiple copies and, if desirable, translate, scale or rotate these separate copies. To reset these settings, you can choose Edit » Reset Settings.

Maya will duplicate using the pivot point as base point. So if you want to use the rotate options, the duplicate will be rotated around the pivot point. Keep this in mind e.g. when you want to make a winding stair around a specific point.

Editing geometry

Pivot point

Every object in Maya has a pivot point, which can be seen as the center of gravity of that particular object. All transformations of the object, like moving, scaling and rotating, act around the pivot point. When one of the transformation tools in the toolbox is selected, the pivot point is visible as the red, green and blue axis. By default the pivot point is in the center of the object, but it can be moved to every other position. To change it's position press the ‘insert’ key on you’re keyboard to ‘unlock’ the pivot. Then click and drag the pivot to the position you want. Press the ‘insert’ key again to ‘lock’ the pivot. Now all transformation act around the new position of the pivot point.

In some cases you want the pivot point back in the center of the object. Via Modify » Center Pivot the pivot point is placed in the center of the object.

Booleans

Boolean operations can be performed on 2 overlapping polygon objects. Select both objects and go to Mesh > Booleans >

There are 3 options:

union: you keep the part of the objects that is part of one or both of the objects
difference: you keep the part of the object first selected that doesn't overlap with the object that has been selected second
intersection: you keep the part of both objects that overlaps

When you're using the union or the intersect option it doesn't matter in which order you select the objects. For the difference option, the second object you select will be subtracted from the first object you select.

When you're using the difference option it's possible you want to make a lot of holes in the object, like in the example below. It will be rather time-consuming to do them all one at a time and sometimes the geometry does odd things when doing it that way. So if you want to subtract these shapes all in once, you have to combine them first (select all the objects you want to subtract, then go to: mesh > combine). Now select the object you want to subtract from, then select the combined objects you want to subtract, then go to Mesh > Booleans > difference:

Component mode

Vertex

When the square icon is selected, the vertices become visible as purple dots. The vertices can be selected and the position can be altered by using the transform, rotate or scale tool. A single vertex can not be rotated or scaled, but when multiple vertices are selected, they can be rotated or scaled relative to each other.

Edge

When the icon with the blue line on a surface is selected, edges of polygonal objects can be selected and transformed. Edges can be moved, rotated and scaled. By transforming an edge, in fact the adjacent vertices are transformed.

Face

When the icon with the four squares is selected, faces can be selected and transformed. Faces become visible as blue dots on the faces of the object. Faces can be moved, rotated and scaled. By transforming a face, in fact the adjacent vertices are transformed.

The task

We now know how to create primitives and how to adjust them . To practice this technique we will make a sketch design of the construction of our observation post. One of the advantages of designing in the computer is that it is possible, like in this case, to directly design in 3d in a realistic representation of your building location. For this workshop we provided this location however if you use these techniques in other projects you can start with the construction of your building site in 3D. This gives you not only a better idea about the scale of the surrounding buildings, location of roads etc but also , if the facades are correctly materialized, a good reference of the surrounding architecture and material use. The act of building the location photo realistically in 3D in itself is an effective tool to get a better insight in the building site. The modeling techniques we be discussed in this semester, the materialization and rendering techniques ( image creation ) will be discussed in semester 3.

creation of a realistic virtual design environment

We will sketch the construction in 3D with the use of primitives. Because we are sketching ,accuracy is in this case not the main goal. This method resembles the making of physical sketch models from card board. We use the primitives as cardboard surfaces and combine them together in a rough design.

We will discuss the design in the first workshop, the focus will be on how you used the computer in the design of the structure and what the difference is with making a cardboard model. The architecture and structural design will discussed but not judged, the design process is the main topic.

Please don't use this structure as an example to be copied, the structure is not that good.

Troubleshooting

The page Modeling with polygons: Troubleshooting covers troubleshooting polygon modeling.