to a Mesh
command has the same functionality as the Attach mode of the
Draw->Polygon command, and it can be used by itself to
either fill holes left in polygons or add new polygons that
share edges with the current mesh. Polygons can only be added
to open edges, so that no more than two polygons can ever
share an edge. You can show the open edges of a mesh with
the Show->Edge flags command (see Figure 7.14).
the Polygon->Polygon command, pick at least two vertices
to attach a polygon. If you are adding a new polygon, then
click somewhere off the mesh to place a new point in space,
and continue to place new points until you have defined the
polygon you want. To complete the polygon, click the middle
7.14 A polygonal mesh with holes showing the
If you are patching
a hole in a polygon, continue to select only existing vertices
until you have plugged the hole. Then use the middle mouse
button to complete the polygon.
Take a Shortcut:
Working from a Primitive
Now that you
know how to start from scratch, making your own objects out
of nothing but ambition and the Polygon menu cell, I should
tell you that it is almost always easier to start out with
a simple geometric polygon primitive and use the polygon duplication
and transform tools to create the object you need. From one
polygon, you can make many by duplicating the original and
transforming it in a number of interesting ways. Many types
of angular, precise looking objects can be easily created
this way, such as buildings, machines, ovens, and all manner
of other manufactured devices. But before we dive in, first
a word about the polygon transformations and the Polygon Local
and Local Coordinates
When you are
in the POL (polygon) mode, remember that only the selected
polygons are acted upon by the Transformation menuss
cells and a number of other commands, including Duplicate
and Delete. This means that the object stays as it is, and
only the pink polygons colored pink are translated, scaled,
rotated, and so on (see Figure 7.15). Don't forget to return
to OBJ mode when you want to work on the entire object and
not just the individual polygons.
7.15 A polygonal object with selected polys translating
on their own axes.
When you transform
a polygon, it needs to have its own local axis to which to
transform relative (unless you are in GBL mode). By default,
if you select a single polygon and show centers, you will
observe that the center is in the geographic middle of the
polygon, with the X and Z objects oriented towards the edges
of the polygon, and the Y axis pointed outwards along the
normal. This is very useful, because you can now use the Y
axis to move the polygon in and out along the normal, and
you can scale X and Z to make the polygon smaller or larger.
However, if you
select more than one polygon and they share an edge, the center
is located in the middle of the group, and the orientation
is the average of all the polygons in the group (see Figure
7.16). Although this does give the group a center for transformations,
it might not be a very meaningful one. (You could create your
own center with Cluster Centers.)
If none of the
selected polygons in the group shares an edge with another
selected polygon, each polygon has its very own center, aligned
with just that polygon. This factmakes it possible to transform
polygons in large groups instead of individually. Pay attention
to the centers on the groups of polygons you transform, or
their behavior will make very little sense to you.
7.16 A polygonal object with grouped polys translating
on a common axis.
When you are
in POL mode, the Trans menu cells operate only on the selected
group of polygons, causing the polygons to move in space relative
to the object to which they belong. If you want to animate
this change of transformation, use the SaveKey->Object->Shape
command, not the SaveKey->Object->Translation command,
because you are really adjusting the location of the points
that make up the surface. The Rot menu cells rotate the polygons
around their local axes (see Figure 7.17).
7.17 A polygonal object with polys rotated about
Y (the normal).
The Scale menu
cells make the polygons larger or smaller in X or Y (see Figure
7.18 A polygonal object with selected polygons
scaled in X and Z.
You can make
more elaborate transformations to a polygon by simply moving
the vertices around with the M supra key.
When you duplicate
a selected polygon by using the Duplicate->Selection command
while in POL mode, a bunch of special things happen. You might
expect that another polygon would be made on top of the last,
but that's not what happens. The original polygon is cut into
a number of new polygons, one for each edge, and connected
to the new polygon that takes over the shape and location
of the original (see Figure 7.19). In other words, a border
of new polygons is made, all connected by shared edges to
a new central polygon.
7.19 The selected polygon is duplicated and then
scaled slightly smaller. Note the bordering polygons.
If this new central
polygon is translated away from the object, the new border
polygons connect it to the other polygons in the object. If
the new center polygon is scaled, the border polygons create
a bevel. You should also remain in the Model module while
using polygon duplication.
polygons is a fabulous method for creating windows
with window sills. Simply select the central polygon
that will become the window pane and duplicate it.
Scale it down slightly in X and Z to create a window
frame. Duplicate it again but this time translate
it in negative Y so that it becomes recessed into
the frame (see Figure 7.20).
the polygon at the base of the window frame and
duplicate it. Then translate it in positive Y so
that a window ledge extends a short distance from
the base of the window.
you have a bunch of windows on a building face,
select every other window and execute these commands
on them as a group. It works because none of the
polygons shares an edge with another. Then go back
and repeat this for the windows you excluded the
first time around.
7.20 A simple polygonal window with frame
Of course, you
sometimes want to remove a polygon while keeping the vertices
and edges that it shares with neighbors.
When in POL mode,
choosing the Delete->Selection command permanently removes
the selected polygon from the object (see Figure 7.21). The
edges it used to share now become open, and you can build
new polygons to share them. This polygon delete function is
a great way to knock holes in an object .
in the Model mode while deleting polygons, or the
entire object disappears.
7.21 The Delete->Selection menu cell.
shapes can also be extruded, with often interesting results.
To accomplish this task, you must be working in POL mode,
have some polygons selected on an object, and then use the
standard Surface]Extrusion command in the Model module. When
in POL mode, all the extrusion details in teh Extrusion dialog
apply only to the selected polygons on the selected onject!
You can extrude polygons along a path, and you can apply a
transformation to the polygon at each step of the extrusion,
making the resulting polygons smaller, revolved slightly,
or offset in space (see Figure 7.22).
7.22 An object with some polygons selected and
The polygon Extrude
Along a Path option in the Extrusion dialog gives you the
power to draw a path, and then have the Y direction of the
polygon (the normal) oriented along this path during the extrusion.