From BlenderWiki

A mesh is a set of connected Vertices, sometimes thousands of vertices for the more complex objects. Blender allows you to group these vertices for several main reasons:

• Re-using parts of a mesh for making copies
• Hiding "everything else" while you work on details
• Documentation and explanation to others
• Armatures deformation
• Generating particles from only the group
• Controlling the velocity of particles emitted

Armatures: Vertex Groups can be automatically created for each bone in an armature. However, that process is pretty involved and for more information on Armatures and Bone Vertex Groups, click here. The rest of this section will focus on user-defined vertex groups.

Why use Vertex Groups?

You want to re-use part of your object if that object has or maybe will have many of those parts. For example, a cabinet has many hinges and may have many knobs and doors; a chair or table has four legs; a fence has many posts. While you could model each of these parts independently as separate objects and parent them all together, sometimes you may wish to simply think of them as parts of an integral whole. While similar to each other, you may wish to alter each one slightly. For example, put a nick in one of the chair legs, or make some knobs larger or more ornate that others.

Use Vertex Groups to identify sub-parts of your model so that you can easily select and work on only that part. Especially using the hide function, vertex groups make it very easy to select a part of your model and hide everything else so that you can concentrate on only that part.

Vertex groups also make it easy to cull out and duplicate a part of the mesh many times. Consider modelling a Lego(tm) block. The most simplest block consists of a base and a nipple. To create a four-nipple block, you would want to be able to easily select the nipple vertices, and, still in edit mode, duplicate them and position them where you want them.

Another use for vertex groups is for skinning an armature. If you want to animate your mesh and make it move, you will define an armature which consists of a bunch of invistible bones. As a bone moves, it deforms or moves the vertices associated with it. Not all of the vertices, but some of them; the ones assigned to it. So, when you move the bone "Arm", the arm bone moves the Arm vertices, and not the Leg vertices. In this way, parts of the mesh can stretch and move around, while other parts remain stationary.

By entering the name of the group in the VGroup: field in the Particle and/or Particle Motion panels, the weight painting of the group will define how much particles come out. Recall that hair is a static particle; so define a Vertex Group called "Scalp" and use it to tell Blender to emit hair from the Scalp.

Creating a Vertex Group

By default, an object does not have any groups, and all of its vertices are hanging out there in cyberspace as loners. The image to the right highlights the Vertex Groups buttons in hot pink. These buttons are located in a Buttons window in the Editing F9 buttons group on the Link and Materials panel. They are shown when an object with vertices is selected AND being edited (Tab). You can tell when an object is in Editmode because your 3D window cursor is a crosshair.

Only Groups are for Vertices: Vertex Groups are only available for objects that have vertices. Text objects, for example, cannot have vertex groups and the panel is not shown when that kind of object is selected. Vertex Groups are only shown when an object with vertices is being edited.

To create a vertex group, LMB click the New button. When you do, a new group (named, surprisingly, "Group") is created, all the selected vertices are assigned to it, and the panel shows you a Weight numeric slider/entry/scroll box.

Naming Vertex Groups

To name a group something other than the creative "Group", Shift LMB click into the name field, and delete or overtype your new creative name.

For example, consider the model of a kitchen cabinet. The cabinet consists of three vertical walls (two sides and a back), a floor and countertop, a door frame, a door, a knob and two hinges. You may or may not, at some point, to be able to model the door opening. You may want to make the cabinet a single door or later easily modify it to be a double door (with two knobs). You may wish to copy the knob design and use it for the drawers which you will be modeling later. In this case, you would want to define at least three vertex groups: Base, Door, and Knob. If you were writing a user manual, you would want your example to contain each possible group for maximum re-use and selection, as shown.

Access the group list by clicking the list selector button next to the group name. Select a group by clicking on any named group.

Assigning Vertices to a Group

To add vertices to a group you do the following:

1. Select the group you want to work with from the group list.
2. Use your mouse to Shift RMB select more vertices that you want in that group.
3. LMB click the Assign button

Keep in mind that a vertex can be assigned to multiple groups.

Seeing a Vertex Group

From experience, we have found that is is best to start first by seeing the existing vertices in a group, before adding more or removing some. To do this, de-select all vertices by pressing A once or twice in the 3d window until the User Preferences header shows Ve:0-x, where x is the number of vertices in your mesh. This means that zero (0) vertices are selected. The Vertice count is located just to the right of the Blender Version.

Then, with the appropriate group active, press the Select button. In your 3D window, the vertices that belong to the active group will be highlighted.

Removing Vertices from a Group

To remove vertices from a group:

1. Select the vertices you want to remove from the vertex group.
2. Select the group you want to work with from the group list.
3. LMB click the Remove button.

Deselecting Vertices

Sometimes you will want to see if any vertices are still loners. To do so, select All the vertices in the 3D window. For each Vertex Group, LMB click the Desel. button to de-select the vertices in that group. Repeat the de-selection for each group. When you run out of groups, any vertices left highlighted are the loners. Sort of like picking baseball teams.

Deleting a Group

To delete a vertex group, select it from the list and click Delete. Yes, it's as simple as that. Any vertices that belonged to that group are unassigned from that group. However, please keep in mind that vertices can belong to many Groups. When they are unassigned from one group, they still belong to their other groups.

Using Vertex Groups in Practice

Assume you have defined the groups used in our cabinet example. Here are some examples of common things you might want to do involving Vertex Groups.

Duplicating Parts

You now want to make that cabinet a double door model:

1. Select the cabinet object ( RMB ) and enter Editmode (Tab).
2. Ensure that NO vertices are selected (Ve:0 - remember?).
3. Select the "Knob" vertex group from the dropdown menu.
4. Click the Select button.
5. Move your mouse into the 3D window.
6. Duplicate that sub-mesh by pressing Shift D. The vertices are copied, selected, and grabbed.
7. Move the mouse over to position the new knob.
8. LMB to drop the sub-mesh.

The duplicated vertices belong to the same group(s) as their originals.

To assign this new knob to its own group, click New, name it something like "Knob.L" and click on Assign. See #Creating a Vertex Group and #Assigning Vertices to a Group.

Left and Right naming convention: Certain features of Blender can perform related actions on groups that are left and right counterparts of each other. If you end a name in ".L" or ".left" and its counterpart ".R" or ".right", Blender may be able to easily mirror its actions for you. You can read more about the naming convention in Manual/Editing Armatures: Naming conventions. The convention for armatures/bone apply here as well.

Simplifying a Vertex Group

You may have correctly surmised that the original Knob group now has both sets of vertices: the original and the duplicated ones. You've created a "Knob.L" group, but there is no corresponding 'right' group. The Knob group really needs to be renamed and contain only the vertices for the right knob. To correct this,

1. Ensure the new "Knob.L" vertices still selected (the ones that don't belong)
2. Select the original Knob Vertex Group from the list
3. Click the Remove button

To test your work, deselect all vertices and click the Select button. Only the vertices from the original knob should highlight. Rename this group "Knob.R"

Repeat the above for the "door" and "hinge" group, and you now have a two-door cabinet model. Note that you will have to either make the doors narrower or cabinet wider to accommodate the new door.

Combining Groups

To create a Knobs (plural group), you could:

1. Ensure that no vertices are selected.
2. Select the "Knob.L" group (select its name from the list and click Select)
3. Select the "Knob.R" group (ditto).
4. Observe that selecting one set of vertices does not deselect the others; the selection process adds on vertices to the selection.
5. Click the New button, and name the group "Knobs"

Focus on a part of your model

You want to make an inset panel on the door. To work on the door sub-mesh without cluttering up your screen with all the other vertices, you would:

1. Ensure that ALL vertices are selected. (You can use A for that.)
2. Deselect the "door" group by selecting its name from the Vertex Group list and clicking Desel. (for DeSelect), leaving everything BUT the door selected.
3. With your cursor in the 3d Window, Hide the selected vertices. Poof! They disappear.

Separating a part into its own

Now, the patent lawyer calls and says that you must patent your hinge design to keep anyone else from copying it; you need to separate the hinge out from the cabinet mesh:

1. Ensure that NO vertices are selected.
2. Select the Hinge vertices (select the name from the Vertex Group list, and click Select)
3. With your cursor in the 3d Window, seParate them into their own object.
4. The remaining cabinet vertices are left. Tab out of editmode and RMB click the floating hinge object. Note that it is conveniently called "Cabinet.001", and has all the same Vertex Groups as the original. Delete those groups you do not need, rename the object "Hinge".

Parent it to the original (and now hinge-less) "Cabinet" object (include the parent by Shift RMB clicking the Cabinet, and pressing Ctrl P). Now, when you move your cabinet, the hinges move with it.

About Weight

By default, every vertex in a group has a weight of 1.00. If a vertex belongs to multiple groups, it has a combined weight. When influenced by a bone or other object, it is moved by an amount proportional to its weight; heavier vertices move less. So, a middle vertice belonging to two groups (each with a weight of 1.00) would move half as much as a left vertice that only belonged to one group. This weighting system provides realistic deformation of a mesh when bones move, for example, around the shoulder area, where some of the vertices belong to both the chest and the arm groups.

You can set the weight of all vertices in a group using the Weight numeric control. For more advanced weighting, please read Weight Painting. Weight Painting allows you to smoothly blend individual vertex weights so that meshes deform smoothly.

Previous: Manual/Edge and Face Tools Contents Next: Manual/Weight Paint