Great Stella Manual

Last updated 2nd August 2008.
The latest version of this manual can be found online at http://www.software3d.com/StellaManual.php?prod=great.

Contents

Getting Started

This manual contains instructions to get you started using Great Stella. It covers most features, and after reading this document you should be able to find your way around most of the interface. A description of how to use various features will be found here, but for a more detailed explanation of what is possible and what the features can be used for, please see my paper "Stella: Polyhedron Navigator".

If you get stuck, feel free to ask questions on the Stella forums at http://www.software3d.com/Forums.

Built-in Polyhedra

The program includes all the uniform polyhedra (which includes the Platonic, Archimedean and Kepler-Poinsot solids and more), the Johnson solids, some Stewart toroids, compounds, and other polyhedra.

The default window layout has two views side-by-side, showing the base polyhedron on the left and its net (or one of its nets) on the right. The default base model is the icosahedron.

Use the Right and Left arrow keys to change to the next/previous model in the built-in list (or the menu items "Poly->Next Polyhedron" and "Poly->Previous Polyhedron", or the green left and right arrow buttons on the main toolbar or at the top of some views). Note: if you have loaded a .stel file, then the arrow keys move forward and backward through files in the same folder instead. Furthermore, the arrow keys, unlike the green arrow buttons and menu items, are context sensitive. That is, they behave differently depending on what type of view is currently active. If the current view has yellow arrow buttons at the top, then they performs the function of those instead. See more about yellow arrow buttons later. You can also use Ctrl+Left and Ctrl+Right to go to the previous/next model, regardless of the selected view (they behave exactly like the green arrow buttons).

The built-in list is divided into categories. You will see the current category and model name displayed in the main toolbar. Clicking on either of these names opens a list of other categories or models to choose from, providing another way to select a model.

You may also open a separate window for looking through the built-in list and choosing a specific model. To open the list, use menu item "File->Polyhedron List...", hit Ctrl+N, or click the equivalent button on the main toolbar. A window opens showing a list of categories on the left, and a list of models from the current category on the right. Select a category, then select a model, and click OK or hit Enter. The selected model and its net should appear on the screen. The categories are as follows:

Finally, if you know the symbol or name of the model you want, you can enter it directly. Again, open the polyhedron list ("Poly->Polyhedron List...") and you'll find a text entry field at the top. Type in the symbol or name of a polyhedron. Symbols for uniform polyhedra may be any of the following:

Other models use different notations. For example, enter "J4" for the square cupola, one of the Johnson solids. This provides a very quick way to jump to a particular Johnson solid if you know its number.

You may also enter the name of a polyhedron. It can be either the full name (including known alternative names and dual names), a substring in the name, or an abbreviation for the name using either the first letter from each word, or the first letter from each part of each word. Some examples:

Dual Polyhedra

Every polyhedron has a dual, which won't be explained fully here, but you may think of it as the model's opposite. It has the number of faces and vertices swapped with respect to the original model, and the same number of edges. The dual of the dual brings us back to the original model again.

Hit "d" to switch between the base polyhedron and its dual. The net will also change.

The closer a facial plane passes to the centre of a model, the further away from the centre the corresponding dual's vertex will be. If the facial plane passes right through the model's centre, then the dual vertex will be infinitely far away (in a direction perpendicular to the face). Although Great Stella doesn't allow base polyhedra to have infinite parts, their duals can. In the dual view you can see these as faces that extend out towards infinity, but stop after a fixed distance. You can control this distance interactively with Ctrl+Left-drag. Try it, moving the mouse left and right, to show more or less of the infinite dual faces. This will only work if the dual model does indeed have infinite parts of course.

Mouse Tips

The mouse does many different things, depending on what mode you're in, which view you're in, whether you're holding down the left/right/both mouse buttons, and whether you're holding down Shift/Ctrl/Neither/Both/Space. Watch for the tips in the bottom right hand corner, which show you what the mouse buttons do in the current mode. The tips change when you hold down Shift/Ctrl/Neither/Both/Space. They may also change when you move the pointer from one view to another. Even I forget what the mouse can do in some modes, so these on-screen tips help a lot!

Sometimes just clicking is required (e.g. Shift+Left-click to select a face). Sometimes dragging in 2D is required (e.g. Left-Drag to tumble the polyhedron). And sometimes dragging in 1D is required (e.g. Right-Drag to zoom in/out).

Navigation

All basic navigation is done with the mouse and no need to touch the keyboard, except for some less common movements. These mouse controls generally continue to work in different modes too.

In a 3D view:

Tumbling and twisting both have mouse inertia, so you can release the mouse buttons while dragging and the model will continue to tumble or twist.

Similarly in a 2D view:

With 2D views, zooming zooms in on the point where the mouse was when you first clicked the right button, so you can zoom in on a specific point. As with 3D views, twisting has mouse inertia.

A couple of more advanced navigation controls are available in 3D views. Hold down the Space bar and you'll notice the mouse-tips in the bottom right corner change:

You may also switch each view between perspective and orthogonal projections by ticking/unticking "View->Orthogonal View" (keyboard shortcut: o). Perspective views are what we see in the real world, where things closer to the camera appear to be larger. Orthogonal views are like architectural plans, where distance from the camera does not affect the apparent size of objects.

Finally, you can use items on the "View->Camera" submenu to store and recall camera positions. The field-of-view and perspective/orthogonal setting are also stored.

Selecting Faces and Vertices

In the default mouse selection mode (see below), faces and vertices may be selected with the mouse.

Faces may be selected by pointing the mouse at them and double Left-clicking or doing Shift+Left-click. The selected face is highlighted in white and will partly show through other faces (try rotating the model so that the face is on the other side). Only one face may be selected at a time. Many operations work on the current face, which is either the selected face, or the most recently selected face if no face is selected. If you have not yet selected a face, then the first face is the current face.

Vertices may be selected by pointing the mouse at them and double Right-clicking or doing Shift+Right-click. The selected vertex is highlighted with a white dot, and half of each surrounding edge is also highlighted. These show partly through other faces. This also selects the corresponding face of the dual model, which will also become highlighted if you have a dual view open. Selecting a vertex is useful in a few situations, such as when you have a vertex figure view open and want to choose which vertex figure to look at.

Faces and vertices can also be selected via the Info window.

Toolbars

There are four toolbars arranged in three rows, with two in the last row. They may be dragged and docked to different sides of the window, or dragged away into a separate window. Their positions will be remembered between sessions. The toolbars are:

The buttons all have tool-tips, so if you place the mouse over a button and don't move for a moment, a small description of the button appears.

In addition, there are further buttons in the top right corner of each view. The buttons that appear depend on the type of view. Yellow left or right arrow buttons are for changing to the previous or next item that this view type can display. For example, in the 2D net view, these buttons cycle through the various nets required. If the current view has yellow arrow buttons, then you can use the left and right arrow keys on the keyboard to perform the same function. Occasionally you will also see tick and cross buttons, which are used to accept or reject something. For example, these buttons appear in facet-creation mode, and can be used to accept or cancel a partially completed facet.

Polyhedron Information

There is a special window for displaying information about the current polyhedron. There are three ways to open or close it: via the "View->Model Info" menu item; via the equivalent toolbar button on the options toolbar; or by simply hitting "i" on the keyboard.

Information includes number of faces, vertices and edges, number of edges that must be cut/folded/glued to make the model, alternative names for the model (if any) and lots of other info. It is presented in a tree structure, where collections of similar data are grouped together. A small "+" or "-" sign beside each item may be clicked with the mouse, allowing each section to be expanded to show all the data in that group, or collapsed to hide the data. Which groups are expanded or collapsed is remembered between sessions, so the data presented will always be the data of most interest to you.

You can Right-click on information that may be edited to edit that item. Most items can't be edited, but ones that can include the model's name, the dual's name, comments about the model, the radius, and the volume.

Open the face types or vertex types sections to see a list of these types. You can Left-click on a type to select a face or vertex of that type in the main view. Similarly, when a face or vertex is selected another way, the matching entry in the Info window will be highlighted.

This window starts off docked to the right hand side of the main window, but like the toolbars, it may be dragged to dock elsewhere in the main window, or dragged away into a free-floating window of its own. The position is remembered between sessions.

Views and Layouts

By default there are two views, one showing the base polyhedron, and one showing its net. You may choose a different layout by using Ctrl+1 to Ctrl+6, depending on how many views you want. For example Ctrl+4 will give you a four-view layout. Repeatedly hitting Ctrl+4 will cycle through all the different four-view layouts available.

Once you have the layout you want you can choose what kind of views are shown by selecting each view in turn (by clicking in them or on their title bars) and hitting one of the buttons on the view toolbar (or choosing from the bottom section of the View menu).

You may expand any view temporarily to become full-screen using F2 or "View->Full Screen". The active view then takes over the screen and all menus, toolbars and borders are hidden. It can be nice to view models this way with no other distractions. To exit this mode, hit F2 again, or hit Esc. Any operation that opens a dialog box will also force an exit from full screen mode (e.g. opening a file with Ctrl+O).

When you save a .stel file (not available in the demo) your layout and view types are also saved, and restored when the file is opened another time. If you wish to open a file without changing the current view layout, use "Options->Keep Layout when Opening Files". Once ticked, you may continue to open further files without the layout being affected.

Dual Morphing

There are six types of view which show smooth morphing between a model and its dual. Select one of these view types from the view toolbar, or from the "View->View Duals Morphing" submenu. Use Ctrl+Left-Drag to morph between the two in these views. There's also mouse inertia on this function, so you can release the mouse button while dragging and the morphing will continue on its own. To create nets for a morphed model, you first need to make it the new base model. Do this by clicking the left-and-down arrow button on the morph view's title bar.

Note: the demo version will not allow morphing for certain models.

This morphing may not act perfectly between all pairs of models. Some methods cause parts to get flatter and flatter until they disappear, which appears to be an error, but isn't really. Also, morphing between hemi-polyhedra and their infinite duals won't work perfectly, which probably isn't surprising!

Nets

Another type of view is the Unfolded Net view. Use PageUp and PageDown to move through the list of nets required. Hit Ctrl+P to print the net (or to print any other view type, but make sure you have the appropriate view selected first!). The demo version will only allow you to print nets for the five Platonic solids, but it will still let you see a print-preview of nets for any model. Nets are laid out differently for printing from how they appear on the screen, in an attempt to fit as many nets onto each page as possible. You get a dialog full of options for printing nets, but you can ignore most of these to start with and just click on "Preview" (or hit Enter).

Folding Nets

There's also a Folding Net view. This can show you the nets in 3D, folding up into the final model and unfolding again into separate flat nets. Use Ctrl+Left-drag to interactively fold and unfold the nets. Mouse inertia applies here too, which means if you release the left mouse button while still moving the mouse, the folding/unfolding will continue on its own at the current rate.

When unfolding, first the folded nets move apart from each other, then they each unfold individually. Ctrl+Right-click jumps to the point between these two stages, or just folds the net half-way if there is only a single net.

The "Nets->Nets Shown in 3D View" submenu gives you control over what is shown in the Folding Net view. Your options are:

Submenu: "Nets->Net/Paper Color Mixing"

This submenu contains the following options:

When mixing of colors is not permitted within nets, only nets of a single color will be printed at any one time. For example, if there are red, yellow, and blue pieces, and you are currently viewing a yellow piece in the Unfolded Net View, then printing will only print yellow nets. It will print all the yellow nets though, not just the one you are viewing, and it will try to pack them all together as best it can. The print-preview lets you see how many pages there are, so you just put that many pieces of yellow paper in the printer tray (use manual feed for thicker paper and to reduce curling). Then you use PageUp or PageDown to change to a net of another color in the Unfolded Net View, and print again with different colored paper, and so on for each different color.

Scale

Before printing out nets, you are going to want to decide how big to make your model. This is what the items on the "Scale" menu are for. They let you change the scale of the whole model by specifying the length of certain features, such as edge length or radius. Note: the model does not get bigger or smaller on the screen, but printed nets or exported models will reflect the change in scale. Here's what the items on this menu do:

Undo/Redo

Most operations can be undone and redone, including changing to a new model, changing the scale of the model, and changing face colors and images. Use "Edit->Undo" (keyboard shortcut: Ctrl+Z) to undo, and "Edit->Redo" (keyboard shortcut: Ctrl+R) to redo. Both operations are also available on the main toolbar. If you Right-click on either button, you'll see a menu of the last 20 operations that can be undone/redone. Select one to perform multiple undos/redos in a single step.

See also "Edit->Undo Settings" for various options that control the undo mechanism. You may limit the amount of memory used, and the number of undo levels available.

Advanced Topics

Showing Vertices and Edges

The following options are available for controlling the display of vertices and edges. They are found on the "Display->Vertex & Edge Options" submenu. All settings are remembered after you exit the program for next time.

Hiding Faces

The Display menu includes a group of items for hiding or showing faces. Most of these require you to select a face first (see Selecting Faces and Vertices). Note, the hidden attribute of a face can also be copied quickly between faces using the mouse. See Color/Hide Faces Mode.

Colors

Models may be colored in various ways. This section describes the items on the Color menu.

Images

Images may be put on faces. You may want photos of your pets on the faces of a dodecahedron, or you may want a model to look like it's made of wood. This section describes the items on the Image menu (see also Image mode below).

Polygon Filling and Overlapping Colors

Use "Display->Polygon Filling Options..." to open a dialog box with various options for polygon filling. It is a modeless dialog box, meaning that you can leave it open while you use other features of Great Stella.

An image is displayed which shows a preview of the current settings. See how it changes as you select different options. The following options are available.

Note: cross-sections will always use the "Auto" filling method, and always allow coplanar faces to cancel each other out, regardless of the above settings. Otherwise some areas may be filled incorrectly.

Cross-Sections

Select a view and use "View->View Diagrams->Cross-Section" or the matching toolbar button to switch to the Cross-Section view. This shows a 2D cross-section (or slice) through the current polyhedron. The cross-section is made with a slicing plane, which can be controlled in various ways. Any edge of the original model passing through the plane is sliced to become a vertex. Any face crossing the plane is sliced to become one or more edges (nonconvex polygons can lead to more than one edge). And a whole polyhedron is sliced to create one or more polygons. So each entity loses one dimension as a result of the slicing process. Note: many edges and faces may lie entirely on one side of the slicing plane, and so do not contribute at all to the cross-section.

Cross-sections have a beauty all of their own, especially when animated by altering the slicing depth (keeping the plane parallel, but moving it through the model). The slicing depth is a value between 0.0 and 1.0, each representing a plane at opposite ends of the model.

Each polygon of the 2D cross-section is surrounded by edges formed by slicing faces. The edges are shown in the color of their corresponding face, and the polygon itself is filled with a color obtained by averaging the colors of its surrounding edges, weighted by their edge-lengths. This can produce some pleasing results, with the polygon colors changing smoothly into other colors as their edges get longer or shorter. When multiple polygons overlap, the overlapping colors are also blended, making even more interesting images.

More colorful cross-sections can be obtained by using "Color->Basic Color Scheme->Color Along Cross-Section Direction", especially for regular polyhedra, which would normally be shown all in one color. When all faces have the same color, the detail of the cross-section can be lost since all edges and filled regions become the same color. With this option, cross-sections become much more colorful, but still retain full color symmetry.

The mouse may be used in the following ways.

The Section menu offers further cross-sectioning options:

The yellow left/right buttons in the title bar of the Cross-Section view also serve a purpose. They skip the slicing depth forward or backward to all the values where the slicing plane passes through a vertex of the original model. These are often quite interesting points in the transition.

Finally, the slicing plane can be tumbled interactively in a free-form style. See Cross-Section Tumble Mode for the details.

Zonohedra

Use "Poly->Zonohedrify" (keyboard shortcut: z) to create a zonohedron based on the current polyhedron. The vertex positions of the current model are used as a star, that is, they represent the directions of edges in the zonohedron. Note: all edges in the resulting polyhedron will have the same length, even if vertices were at different radii.

Geodesic Spheres

Use "Poly->Create Geodesic Sphere" (keyboard shortcut: Ctrl+G) to create a geodesic sphere based on the current model. Traditionally geodesic spheres are based on an icosahedron, octahedron, or occasionally a tetrahedron, but here any model may be used as a starting point. Try starting with one of the Stewart Toroids for interesting results!

You will be prompted for the frequency of the geodesic sphere, which is the number of subdivisions along each edge of the original polyhedron. Faces having more than three sides are also subdivided into triangles first. Once the faces are subdivided, all vertices are projected onto a sphere.

You can also just subdivide the faces without projecting onto a sphere by using "Poly->Subdivide Faces". In this case the result will generally have the same shape as the original model, but each face will actually be made up of many smaller faces.

Stellated Polyhedra

A stellation of a polyhedron is a new polyhedron which has faces that lie in the same planes as the faces of the original model. Typically you start with a convex polyhedron and build stellations out from it, but the seed polyhedron does not have to be convex. Great Stella is able to find all the possible stellations of a given polyhedron.

For models which may be stellated (a small set in the demo, but not restricted in the full version of Great Stella), use the Up and Down arrow keys to visit each valid stellation (same as "Stellation->Next Stellation" and "Stellation->Previous Stellation", or the up and down green arrow buttons on the options toolbar or at the top of a stellation view). You can hold the keys down to see all the different stellations racing past. Note however that you won't see anything happen in the base polyhedron view though. The default views show the base polyhedron and its net. Instead you need to change one of them to a view of a stellation, by selecting either the View Stellation or View Dual Stellation buttons from the view toolbar.

What counts as a valid stellation depends on your settings. The default is that only fully supported stellations are counted as valid. Choose a different criterion by selecting a different item from the top section of the "Stellation->Stellation Criteria" submenu. This affects what stellations you will encounter when hitting the Up and Down arrow keys, and which stellations will be counted when you do an enumeration ("Stellation->Enumerate..."). For a description of the different stellation criteria, see my paper "Stella: Polyhedron Navigator".

To create a new stellation manually, you need to select and deselect cells. Cells are the smallest volumes enclosed by sets of planes in which the original model's faces lie, and are the 3D building blocks of stellations. Actually, all cells of a certain type are usually referred to as a single cell, and together they maintain the same rotational symmetry group as the original model being stellated. A stellation is made up of some set of all the possible cells for a given set of planes. There are a number of ways to select/deselect cells, that is, to include them in or exclude them from the current stellation.

In any situation where you can select stellation cells using Shift+Left-click, you can also use the following.

You can also stellate using an arbitrary set of facial planes, rather than starting with the faces of a given polyhedron. This is more maths-intensive for the user though, as you need to know the plane equations required. Use "Stellation->Stellation Planes". A dialog box opens with various options, initialised with values taken from the current polyhedron. At the top you can select the symmetry group for the stellation, and below that you can enter as many plane equations as you wish. Each plane will be repeated over the symmetry group though, so you only need to enter an equation for one of each type of plane. The X, Y and Z fields represent a normal to the plane (a unit vector perpendicular to the plane). This vector will be normalised if it is not already unit length. The final parameter to define each plane is Radius, which gives the distance of the plane from the centre of symmetry. It may be zero to define a plane that passes through the centre. Each field may be given as a decimal value, or an equation like "4 + 2r3", where 2r3 means 2 times the square root of 3. You may also use g as shorthand for the golden ratio. It is very important that the values are as accurate as possible, so use an exact equation where possible. If entering a decimal value, I recommend 17 or 18 significant figures.

Menu item: "Stellation->Fill All Inaccessible Cells"

This menu item selects any unselected cells that are totally hidden from external view. For example, when stellating the dodecahedron, you might have the cells selected to create the small stellated dodecahedron. Now whether the central dodecahedron cell is selected or not makes no difference to how the model looks from outside. Generally you want all those hidden cells to be selected; otherwise they will lead to extra nets, for internal parts that won't end up being visible!

Having all parts accessible is also one of Miller's Rules which were used for The 59 Icosahedra.

Once you've made some complicated stellation from various cells, it's often a good idea to fill in the inaccessible cells, since you probably don't want hidden "bubbles" inside your model.

When using this feature, you will not see any difference in the model, but you can see what's going on in the stellation diagram view (if there are any inaccessible parts to fill in of course). You will also see a change in the 2D or 3D nets view.

Submenu: "Nets->Coincident Edge Method"

Exactly one of the items on this submenu may be selected at any one time. The setting only affects "double" or "coincident" edges in stellations, i.e. where two solid pieces touch at an edge. From outside you can see the edge from either side. When building a model you might want to construct the parts connecting at such edges in one of these ways:

These settings generally make subtle differences in the nets produced.

Symmetries

Symmetries are transformations which leave a model looking like it hasn't moved. They mostly come in two types: rotational and reflective. Use "Display->Show Symmetry Axes" to display the rotational symmetry axes (keyboard shortcut: s, also on options toolbar). In 3D views these are indicated by an axis through the model with a small disc at either end. The number of spokes in the disc indicates the order of rotational symmetry. The different types of rotational symmetry axis are shown in different colors. In the stellation diagram view these are indicated as points where the axes intersect with the face plane, using the same colors.

Use "Display->Show Reflection Planes" to display the reflective symmetries (keyboard shortcut: r, also on options toolbar). In 3D views these are represented by great circles around the model in the reflection plane. In the stellation diagram view these are shown as dashed lines where the reflection planes intersect with the face plane.

The symmetry group of a polyhedron is the collection of all its symmetries. The options toolbar has a field that shows the rotational symmetry group (e.g. "Icosahedral"), and another field showing the reflective symmetry group within that (e.g. "Horizontal Reflection").

A good web page showing the different symmetry groups is http://newton.ex.ac.uk/research/qsystems/people/goss/symmetry/Solids.html. The only groups missing here are icosahedral symmetry, both with and without reflections. The h subscripts on that page correspond to "Horizontal Reflection" in Stella, and the d subscripts correspond to "Diagonal Reflection". Notice that the rotational symmetries of a tetrahedron can be combined with either of these reflection types (Th and Td).

Some symmetry groups are subsets of others. Both the symmetry group fields in the toolbar are drop-down lists, which let you see all the sub-symmetry groups available, and choose one. Changing to a sub-symmetry group will affect stellation, faceting, augmentation, and coloring of the model. Note: you can use "Options->Recolor Sub-Symmetries" to prevent the model's color from changing when choosing a sub-symmetry group.

Mouse Selection Modes

Submenu: "Selection->Mouse Selection Mode"

Items in this submenu allow you to enter a different mode, where the mouse behaves differently from normal. Exactly one of the items will be selected at any one time. The first item on the list is the default mode, so to exit one of the other modes, either select this item, or just hit Esc. There is also a toolbar containing a button for each of these modes.

You can tell when you're in a different mode from usual by holding down Shift and seeing what shape the mouse pointer becomes. Navigation with the mouse acts the same in all modes. The difference is what happens when you're holding down Shift and/or Ctrl.

Some of these modes are described in the following sections.

Cut/Uncut Edges Mode

Menu item: "Selection->Mouse Selection Mode->Cut/Uncut Edges"

If you don't like the net created, you can force the program to cut certain edges. This makes it rebuild the nets, connecting different faces together instead. All edges of the selected type are cut/uncut at once. Nothing is really ever "glued", just either forced as a cut or not.

Note that cutting one edge may cause other faces to join together in a net where they were previously not connected. This is because the nets are rebuilt from scratch. So you can use cutting as a way of forcing other faces to join up. If you didn't want those faces to connect, then you can always cut their shared edge too.

For example, use this mode and Shift+Left-click on an edge of the icosahedron. All edges are the same type, so they are all cut, so you end up with only one face in each net.

Measurement Mode

Menu item: "Selection->Mouse Selection Mode->Measurement Mode"

This mode lets you measure the distance between any two vertices of a model. Use Shift+Left-click on a couple of vertices and the distance between them is shown in the status bar. If you continue to click on other vertices, the value shown is always the distance between the last two vertices chosen. A line is drawn between the vertices so that you can see exactly what distance is being measured. If instead you use Shift+Right-click on a series of vertices, the distance between the first and last one is displayed, rather than the last two. This is convenient if you want to measure the distance from some vertex to several other vertices.

In addition to appearing in the status bar, you can also access the currently measured distance via "Scale->Measured Distance...". This also lets you change the distance, which affects the scale of the model used for printing nets.

Note, in the base or dual view, you may only click on true vertices of the model, not virtual ones caused by intersecting faces, unless you turn on display of stellation vertices (see Showing Vertices and Edges). You may also click on points in the stellation diagram.

Color/Hide Faces Mode

Menu item: "Selection->Mouse Selection Mode->Color/Hide Faces"

This mode lets you easily copy colors, images, or "hiddenness" between faces. Ctrl+Left-click on a face to copy attributes from the previously selected face. Shift+Left-click on a face to change all faces of that type according to the attributes of the previously selected face (use "Options->Maintain Reflexibility" to choose whether reflected faces should also be changed). In either case, hold the left mouse button down and draw the mouse across multiple faces to apply the color/image to all of them, like painting.

If the selected face was hidden, then the "hiddenness" is copied, that is, other faces may be easily hidden too by Ctrl+Left-clicking on them. In this case the color/image of the face is not changed (it is presumed that it is only the hiddenness that you are interested in copying).

Ctrl+Right-click and Shift+Right-click both just select a face without changing its color. This lets you choose a new face to start copying attributes from. In this mode, the face is only highlighted white briefly when you select it, and then returns to its normal color, since it is important to see true face colors in this mode.

If you plan to do a lot of augmentation (see below), this mode can be useful. One of the options when augmenting is to only augment faces of the same color. So select one of the faces you want to augment, then copy that color to all the other faces you want to augment. This lets you quickly and easily select a collection of faces for augmentation.

Image Mode

Menu item: "Selection->Mouse Selection Mode->Image Mode"

If the selected face does not already have an image on it when entering this mode, a file browser will open allowing you to select one. This is the same as if you had used "Image->Load Image" (see Images above). You may cancel the file browser if you wish to use Image mode without loading any new images.

Image mode lets you accurately position images on faces however you want. Use Shift+Left-drag to move an image on a face. Use Shift+Right-drag to scale an image on a face. Use Shift+Left+Right-drag to rotate an image on a face.

Compare these three operations with navigation in a 2D view. Notice the similarity when you don't hold down Shift? This makes it easier to remember which combination of buttons does what.

Use Ctrl+Left-click to select a face without affecting the image on it. And use Ctrl+Right-drag to stretch an image on a face (changes the aspect ratio of the image).

The operations listed above (including Ctrl+Left-click, which doesn't otherwise affect the image) all perform another function too. They change the main face of the image. The main face is the one that is used to control the projection of the image. This only has an effect when "Image->Project onto each Face Separately" is disabled. The image lies parallel to the main face and is projected down through the model in the same way for all faces. So these mouse clicks let you change which face is used for the projection.

Use Ctrl+Shift+Left-click to swap images between two faces. The images are swapped between the face you click on, and the face that was previously selected. This is useful in conjunction with "Image->Load Image List...". You can load a bunch of images at once, then swap them between faces to get the arrangement you want.

Cross-Section Tumble Mode

Menu item: "Selection->Mouse Selection Mode->Cross-section Tumble Mode"

This mode allows you to interactively tumble the slicing plane. See Cross-Sections for more information and ways to choose specific orientations of interest for the plane.

In this mode, the mouse can be used in the following ways.

Faceting Mode

Menu item: "Selection->Mouse Selection Mode->Faceting Mode"

In this mode, you can Shift+Left-click on a series of vertices of a model to create a new polygon. A helpful message will appear when you enter this mode. The points must be coplanar, and you will see the new polygon being drawn as you go (it will show half-transparently through other faces). When you've finished, hit Enter or Shift+Right-click anywhere to accept the polygon (or hit Delete to cancel it). You can also accept or reject the new polygon with the tick and cross buttons at the top of the view. Once accepted, it will appear as another net, on its own (hit PageDown in the Unfolded Net view a few times to find it), and you can print it out. I use this to create supporting pieces to glue inside models for added strength (see my page about the great dodecicosidodecahedron for an example: http://www.software3d.com/GreatDodecicosidodeca.php). You may define more than one such polygon. Creating new polygons in this way is also the first step to creating faceted polyhedra (see next section).

Some other useful controls in this mode are as follows:

Faceting

A faceted form of a model is one which shares the same vertices as that model, but where the faces connecting them are different. Faceting is actually the dual process to stellation, but I won't go into that here!

The previous section described how to make extra polygons, or facets, using the original vertices of a model. When one or more of these facets have been created, you may use "Poly->Create Faceted Polyhedron" (keyboard shortcut: Ctrl+Shift+F) to create a new polyhedron from them. Each facet is repeated over the current symmetry group, and the resulting faces are used as the faces of a new polyhedron, which becomes the new base model (so you can see its nets, dual etc). Not all combinations of facets you might create will lead to a valid polyhedron however, in fact most won't. So you need to be careful when creating the facets. An even number of faces must meet at every edge (and usually you will want exactly two faces).

The Preview Faceting view lets you see how your faceted model is coming along before you've finished it. To use this view, select the view you want to change (by clicking in it) and use "View->View Models->Preview Faceting" (or the toolbar equivalent). Create a facet (using one of the other 3D views and Faceting Mode) and you will see how it is repeated over the symmetry group. Edges with only one face are highlighted in green. These are edges where you need to create another facet to share that edge. Orange edges have an odd number of faces, but at least three. Here you need to either delete one of the facets, or add yet another one. Red highlights edges where an even number of faces meet, but greater than two. These are acceptable, but often undesirable. Finally, if exactly two faces meet at an edge, but they are coplanar, then purple highlighting is used. This is also often undesirable, but not disallowed. Edges where exactly two non-coplanar faces meet are not highlighted at all. Generally you are trying to get rid of all highlighted edges. When you have, create the model with Ctrl+Shift+F, or just click on the left-and-down arrow at the top of the Preview Faceting view.

Use Ctrl+Left-click in the Preview Faceting view to select a facet. Then you can click the "X" button on the title bar to delete that facet. You can also find it in the Unfolded Net view (with PageDown) and delete it using the "X" in that view's title bar.

Since facets are repeated over the symmetry group, you can use the symmetry drop-down lists (see above) to select a different symmetry group, and the facets will be repeated accordingly in the Preview Faceting view. You can also choose whether they should be repeated over reflection symmetries with "Options->Maintain Reflexibility".

For a (very) short faceting tutorial and example, see my web page about the five-dodecahedron compound at http://www.software3d.com/5Dod.php.

You may also find the Faceting Diagram view type ("View->View Diagrams->Faceting Diagram" or the toolbar equivalent). This shows the faceting diagram, which is reciprocal to the stellation diagram. There is a different faceting diagram for each different type of vertex of a polyhedron, so try selecting different vertices in one of the 3D views (by double Right-clicking on them) to see the faceting diagram for that vertex, or use the yellow left and right arrows on the title bar to cycle through them. Each white point in the diagram represents one of the other vertices of the model, all projected back towards the main vertex and onto the plane of the diagram. Each line represents a possible face in a faceted version of the current polyhedron. The big blue point in the middle represents the centre of the model, and the lines are colored according to how far from the centre they pass (yellow near the centre, cyan for the furthest out). You can use double Right-click or Shift+Right-click to select a vertex from the diagram, but otherwise there's not a lot you can do with it for now. It does make pretty pictures though :-)

Memories

Great Stella has nine memories. These are like the memory on a pocket calculator, except instead of storing a number, they store a polyhedron. Quickest way to use memories is to hit m followed by a number from 1 to 9 to store a model in memory, and hit Shift+M followed by a number to retrieve a model from memory. The number indicates which memory slot to use.

You can also deal with memories via the menu:

Augmentation

Use "Poly->Augment Polyhedron..." (keyboard shortcut: a) to augment, excavate, or drill the current polyhedron. These are all basically different aspects of the same function. Augmentation is simply attaching one polyhedron to another at some common face. Excavation is where one model is subtracted from another at some common face, leaving a dent. In either case, any faces that coincide exactly between the two models are removed. The face where the two models were attached always falls into this category, but others may too. When this happens during excavation it is called drilling, as the result is a hole right through the model.

When choosing to augment a model, a dialog box appears with the following sections.

When augmenting with pyramids, the pyramid height may be selected with the following options: When augmenting with prisms, the prism height may be selected with the following options: The Scale setting can be used to scale the height of augmentations when using pyramids, prisms, antiprisms or cupolae. In most cases it scales the height of the augmentation directly, but there are some useful exceptions when augmenting with pyramids. For the "Keep edges same length" and "New edge lengths = 1" options, the scale applies to the edge length used instead of the height. With "Touch model radius", the scale applies to the model radius, then the pyramid height is chosen to touch that new radius.

After clicking OK, an augmentation preview mode will be entered. Here a preview of the result is shown. Depending on your choices above, it will normally show the augmented parts as solid with a wire-frame outline (the wire-frame shows through other faces too, for easy identification). A message at the top indicates how many orientations are possible for the augmentation.

The following controls are available during the augmentation preview.

Augmentation parameters are remembered during a session, so if you augment a lot of times using the same model, you will mostly just have to hit "a" followed by Enter, without having to change anything in the dialog box. This makes it very quick to build up a big structure.

Putting Models on Faces/Vertices

Use "Poly->Put Models on Faces/Vertices" to put any model on the faces or vertices of another model. This is similar to augmentation, but rather than attaching the new model at a face common to the two parts, here the new model is not attached to the original at all, but rather just sits in space on its own. It may intersect with the original model, but there will generally not be any edges connecting the two parts. It is more like a compound in this regard.

A dialog box appears with various options. In the Source section you may choose where to get the new model from (a memory slot, a built-in model or dual, or from a .stel file).

Below this is the Placement section. Here you can choose whether to put the new model on faces or vertices of the original, and what depth to bury the model. At a depth of zero, the model will sit neatly on a face or vertex. At 100% the model will be completely buried inside the other model (at least at the face or vertex where it is attached). Negative values cause the new model to float above a face or vertex. You may also choose whether to put a copy of the new model on just one face/vertex, or all of the same type, shape, or shape and size, or even on all faces/vertices (regardless of shape).

Next is the Size section. Here you can choose how big the added model should be. The size can be based on one of three options:

The above choices are good starting points, but the Scale setting then has the final say. The value you input here is multiplied by the size determined above to get the final size of the added model. For example, set the scale to 0.5 to make the added model half the size it would otherwise be, or 2 for double the size.

The Color section lets you choose how to color the added model. It can use its original colors (e.g. whatever colors it had when you put it in memory), or it can use a single color of your choice. Click on the colored button to select a color.

Finally, there's one more option at the bottom of this dialog bow, Retain original model centre. If this is ticked, then the resulting model will continue to rotate on-screen around the same point it previously rotated around. Otherwise a new model centre is calculated as the centre of mass of all vertices. This may seem off-centre, as it will be dragged closer to the added model, due to the new vertices from that model.

Polyhedron Library

[Not available in demo version]
Great Stella includes a library of over 400 additional models, aside from the many that are built-in. The models in this library were all made using features of the program. They all exist as files on your computer, with the ".stel" file extension, and are located in a folder called StellaLib, under the folder where the program was installed. Feel free to add your own ".stel" files under this folder, and even your own new sub-folders. They will show up in the software.

To select a model from the library you can select the Stella Library option from the category drop-down list on the main toolbar. The sub-categories will then show up in the model drop-down list beside it. Select a sub-category to see the models in that sub-category in the model list, and select one of those to open it.

Alternatively, use "File->Polyhedron List...", hit Ctrl+N, or click the matching toolbar button to open the list of built-in polyhedra. A window opens with a list of all built-in models, including the models in the polyhedron library. If Stella Library in the category list on the left has a "+" beside it, click it to open the list of sub-categories. Select a sub-category to see the list of models in that category on the right, then double-click a model to open it.

Files in the library are organised into the following sub-categories:

Importing Models

If all else fails, and you can't find a way to create your favourite model in Great Stella, fear not! You can always import it from an external file. Currently the only format supported for import is OFF. It's a simple format. You'll find a specification for the format here: http://www.geomview.org/docs/html/geomview_41.html. Please be sure to use as much precision in the vertex positions as possible, or you may run into problems. I recommend using 17 decimal places if you are creating files in this format. The OFF models must also be properly closed surfaces (with an even number of faces meeting at each edge).

To import an OFF file, simply use "File->Open" as you would to open a .stel file. You will find that the file browser also shows .off files.

3D DXF files may be imported in a similar way, but I fear they often lack the accuracy required for Great Stella.

Exporting Models

3D models can be exported in a variety of formats. This is achieved by using items from the "File->3D Export" submenu. Generally the model is exported from whichever view you have selected (e.g. you might export a dual, or a stellation, or even a model morphed between two duals). Available formats are DXF, POV-Ray, VRML, OBJ and OFF. The dimensions of the model exported can be controlled using the Scale menu. Note also that the exported model will be oriented the same as it is on screen. This gives you powerful control over the orientation of the exported model, but can also lead to confusion if you didn't want the model to have a random orientation. I suggest you place the model in a nice orientation before exporting, by using one of the items from the "View->Orientation" submenu.

Exporting Images

2D images can be exported in various formats. To do this, use the "File->Export Image..." menu item. An image of the current view is exported (so make sure you click in the view you want to export first).

A dialog box appears with various options:

Click Export to save the image file.

Credits

Great Stella was written by Robert Webb.

I use FreeImage (http://freeimage.sourceforge.net, under the FreeImage Public License version 1.0) for importing and exporting 2D images, which in turn uses various other libraries. Below is a list of credits regarding these libraries:

Wood and stone textures obtained from http://www.mayang.com/textures

The End!

Hopefully you'll be able to work the rest of the interface out on your own! There are lots of menus to look through. Let me know if you have any problems or can't figure out how to do something. I'll be interested to hear what you think!

Copyright © 2001-2010, Robert Webb ().
Stella Home Page: http://www.software3d.com/Stella.php.