Calculates shading based on a theoretical ambient light source to create general areas of shadow on your model. Ambient occlusion calculations can be used both with hardware shading and software renderings.
The calculated information is saved to the wire file, and after it has been calculated, it can easily be turned on and off without requiring a large overhead of calculations again.
Ambient occlusion requires
that all surface normals are unified. When you first compute ambient
occlusion, the tool and display will change to the Unify Surface
Orientation tool. For further information about unifying
normals, see Surface Edit > Orientation > Unify Surface Orientation 
.
Ambient occlusion works best when intersecting geometry is trimmed to the shared edge. Intersecting geometry causes confusion because the algorithim tries to average between dark sample points on the interior and light sample points on the exterior. Raising the Detail (resolution) minimizes the problem but does not completely get rid of it.
There is a distinction between geometry that is the "occluder" and geometry that is "occluded;" only spline surfaces can be occluded - not meshes. Hardware shading tessellation is used for the calculation. You must have hardware shade turned on.
Choose whether all surfaces are to have their occlusion textures calculated, or only the picked (active) surfaces in the scene.
All geometry that isn't set as invisible, template, or reference will occlude, regardless of the switch.
All transparent surfaces should be hidden (or templated, or referenced) before calculating ambient occlusion, to ensure that the surfaces are not obscured during rendering.
If you have a few surfaces that are much larger than any others (like the floor or walls of an environment), compute occlusion separately for these large surfaces with a lower resolution. If you have a few small details that you want higher quality on, compute those separately with a higher resolution.
Occlusion texture resolutions are computed automatically in order to balance the quality evenly across the model and provide a reasonable resolution for models of any scale. The Detail slider lets you scale these resolutions up or down.
Increase this value to ensure that small details are calculated and included in the ambient occlusion. If the scene does not have small details, the number can be left low.
Imagine that it works this way: the scene bounding box is computed and a 512 by 512 texture is mapped onto that box. A measuring tape checks the distance between those texture pixels. The "Detail (resolution)" slider is multiplied into that distance. This scheme ensures that the initial result is satisfactory, whether you're modeling a cufflink or a passenger jet, without having to change any settings at all .
Now forget about the bounding box and the imaginary 512 by 512 texture. We take the distance we've measured and multiplied and use it to measure the occlusion texture onto each surface in proportion to its own worldspace length in u and v. This is so that (1) there's a consistent level of detail across the whole model and (2) none but the most dramatic changes to the model will have the side effect of altering the level of detail you're getting with any given slider value.
Increase this value if your image is speckled or spotty to create a smoother, more uniform image.
The value is the number of rays traced per pixel of occlusion texture. A higher value takes longer to compute but reduces the contrast of the noisyness of the resulting texture.
The algorithm used for the smoothness calculation rounds the number of rays to a multiple of 4, so try to use a multple of 4 for this value.
Controls the smoothing of occlusion textures.The slider range is 1-4, however, you can enter values in the range of 0 to 7.
Activates a distance limit for objects occluding a point on the surface to be shaded. Objects further than this distance (Decay Distance) will have no effect on the Ambient Occlusion of the surface at that sample point.
The distance (in scene units) from a sample point at which objects no longer occlude the sample point.
In the event that a surface is both sufficiently concave and very coarsely tessellated, you might see some black spots or streaks in the model. Usually, the problem can be solved by computing occlusion with Hardware Shade set to a finer tessellation than before. If it still has spots and streaks, the Self Shadow Correction value can be increased, and those surfaces recomputed to fix the artifact.
Self-shadowing can be confirmed as the cause of an artifact by turning on Show Triangles in the Hardware Shade settings and observing whether the dark spots line up with the tesselation grid.
Causes the surfaces to use a mapping technique that ignores the UV parameterization of the spline-based surface, and instead maps according to surface distances (measured in world space units). This can help to distribute occlusion detail evenly over surfaces regardless of how they are constructed. Seam artifacts are sometimes produced because of highly uneven detail distribution.
Calculations can be halted
by pressing 
. It may take a few seconds before
the calculations stop.
