# Normals¶

## Introduction¶

In geometry, a normal is a direction or line that is perpendicular to something, typically a triangle or surface but can also be relative to a line, a tangent line for a point on a curve, or a tangent plane for a point on a surface.

In the figure above, each blue line represents the normal for a face on the torus. The lines are each perpendicular to the face on which they lie. The visualization can be activate in the Mesh Display panel.

Reference

Mode: Object Mode
Panel: Tool Shelf ‣ Tools ‣ Edit ‣ Shading:

Reference

Mode: Edit Mode

### Flat¶

As seen in the previous sections, polygons are central to Blender. Most objects are represented by polygons and truly curved objects are often approximated by polygon meshes. When rendering images, you may notice that these polygons appear as a series of small, flat faces. Sometimes this is a desirable effect, but usually we want our objects to look nice and smooth.

### Smooth¶

The easiest way is to set an entire object as smooth or faceted by selecting a mesh object, and in Object Mode, click Smooth in the Tool Shelf. This button does not stay pressed; it forces the assignment of the “smoothing” attribute to each face in the mesh, including when you add or delete geometry.

Notice that the outline of the object is still strongly faceted. Activating the smoothing features does not actually modify the object’s geometry; it changes the way the shading is calculated across the surfaces (normals will be interpolated), giving the illusion of a smooth surface.

Click the Flat button in the Tool Shelf’s Shading panel to revert the shading back (normals will be constant) to that shown in the first image above.

#### Smoothing Parts of a Mesh¶

Alternatively, you can choose which edges to smooth by entering Edit Mode, then selecting some faces and clicking the Smooth button. The selected edges are marked in yellow.

When the mesh is in Edit Mode, only the selected edges will receive the “smoothing” attribute. You can set edges as flat (removing the “smoothing” attribute) in the same way by selecting edges and clicking the Flat button.

The Auto Smooth filter is an quick and easy way to combine smooth and faceted faces in the same object.

## Editing¶

### Flip Direction¶

Reference

Mode: Edit Mode
Menu: Mesh ‣ Normals ‣ Flip or Specials ‣ Flip Normals

Well, it will just reverse the normals direction of all selected faces. Note that this allows you to precisely control the direction (not the orientation, which is always perpendicular to the face) of your normals, as only selected ones are flipped.

### Recalculate Normals¶

Reference

Mode: Edit Mode
Hotkey: Ctrl-N and Ctrl-Shift-N