There are three main types of inferences: point, linear, and planar. SketchUp often combines inferences together to form a complex inference.
A point inference is based on the exact point of your cursor in your model. Following is a list of point inference types:
Endpoint: The Endpoint inference indicates the end of a Line or Arc entity. The Endpoint inference is represented by a green circle. Following is an image of an Endpoint inference.
Midpoint:The Midpoint inference indicates the middle point on a line or edge. The Midpoint inference is represented by a cyan circle. Following is an image of a Midpoint inference.
Intersection: The Intersection inference indicates an exact point where a line intersects another line or face. The Intersection inference is represented by a red x. Following is an image of an Intersection inference.
On Face: The On Face inference indicates a point which lies on a Face entity. The On Face inference is represented by a blue diamond.
On Edge:The On Edge inference indicates a point that lies along an edge. The On Edge inference is represented by a red square. Following is an image of an On Edge inference.
A linear inference snaps along a line or direction in space. In addition to a tooltip, a linear inference sometimes displays a temporary dotted line while you draw.
On Red Axis: The On Red Axis inference indicates a linear alignment to the red drawing axis. The On Red Axis inference is represented by a red line.
On Green Axis: The On Green Axis inference indicates a linear alignment to green drawing axis. The On Green Axis inference is represented by a green line.
On Blue Axis: The On Blue Axis inference indicates a linear alignment to the blue drawing axis. The On Blue Axis inference is represented by a blue line.
From Point: The From Point inference indicates a linear alignment from a point along the drawing axes directions. The From Point inference is represented by a dotted line whose color corresponds to the axis direction (red, green, or blue).
Perpendicular: The Perpendicular inference indicates perpendicular alignment to an edge. The Perpendicular inference is represented by a magenta line.
Parallel: The Parallel inference indicates a parallel alignment to an edge. The Parallel inference is represented by a magenta line.
Tangent at Vertex: The Tangent at Vertex inference indicates an arc whose vertex is tangent to a previously drawn arc's vertex. The Tangent at Vertex inference is represented by a cyan arc
SketchUp indicates half circles, squares, and golden sections, using unique inference indicators. These indicators follow.
Half Circle: The Half Circle inference indicates an arc that is exactly one half of a circle.
Square: The Square inference indicates a rectangle whose sides are all the same size.
Golden Section: The Golden Section inference indicates a rectangle whose properties match the Golden Ratio as found in mathematics and the arts.
Drawing Plane Inference
SketchUp will snap to the planes defined by the Drawing Axes or your view when it cannot snap to geometry in the drawing area. For example, SketchUp will draw on the ground plane when the point of view is that of the ground plane.
Component and Group Inferences
All inferences apply on geometry inside Component entities or Group entities. Group and Component inference indicators are the same shape, but are magenta color. Group and component tooltips also indicate that the inference is in a Group or Component entity by appending the phrase 'in group' or 'in component' to the end of an inference tooltip.