Inference

SketchUp features a geometric analysis engine, called the inference engine, allowing you to work in 3D space using a 2D screen and input device. This engine helps you draw very accurately by inferring points from other points as you draw while also providing you with visual cues.

Inference Cues

The inference engine uses tooltip cues, appearing automatically while working on the model, to identify significant points or geometric conditions. These cues make complex inference combinations clear to you as you draw

Additionally, the inference engine uses specific colors to indicate its type of inference (covered further in Inference Types).

Inference Types

There are three main types of inferences: point, linear, and planar. SketchUp often combines inferences together to form a complex inference.

Point Inference

A point inference is based on an exact point of your cursor in your model.

Endpoint: The green Endpoint inference identifies the end of a Line entity or Arc entity.

Midpoint: The cyan Midpoint inference indicates the middle point on a line or edge.

Intersection: The black intersection inference indicates an exact point where a line intersects another line or face.

On Face: The blue On Face inference identifies a point which lies on a Face Entity.

On Edge: The red On Edge inference identifies a point that lies along an edge.

Equi-Distant On Edge: The Equi-Distant On Edge inference indicates an equidistant point, or a chamfer, when a magenta line appears between two connected edges.

Half Circle: The Half Circle inference appears when drawing an arc to indicate the point that creates an exact half circle.

Linear 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 Axis: The On Axis inference indicates a linear alignment to one of the drawing axes. The solid line is drawn in the color associated with the corresponding axis (red, green, or blue).

From Point: The From Point inference indicates a linear alignment from a point along the Drawing Axes directions. The dotted line is drawn in the color associated with the corresponding axis (red, green, or blue).

Perpendicular: Tie Perpendicular magenta line indicates perpendicular alignment to an edge.

Parallel: The Parallel magenta line indicates a parallel alignment to an edge.

Tangent at Vertex: When drawing from the endpoint of an Arc entity using the Arc Tool.

Planar Inference

A planar inference snaps to a plane in space.

Drawing Planes: SketchUp will snap to the planes defined by the Drawing Axes and 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.

On Face: A blue On Face inference identifies a point which lies on a face. Although initially a point inference, On Face can also serve as a planar alignment by using inference locking (described below).

Encouraging an Inference

At times, the inference you need may not come up immediately or SketchUp might choose alignments with the wrong geometry. In these cases, you can increase the chances of a particular alignment by pausing your mouse cursor over the particular location that you want SketchUp to infer from. When the tooltips appears, SketchUp will briefly prioritize that alignment as you continue drawing. For example, to encourage SketchUp to create a line to match another, parallel, line (such as when drawing the third line of a rectangle):

1. Create the first two edges of a rectangle with the first edge being parallel to the red axes.
2. Click on the start point of the third edge and move the line tool as though you were creating the third line parallel to first line. As you begin to move the Line Tool, the line should appear in red.
3. Mid-line creation, move the Line Tool over the start point of the start point of the first line you created for the rectangle. Your line will extend diagonally to this point.
4. Leave the tool over this point until the Endpoint tooltip displays.
5. Move the Line Tool to the approximate location where the end of the third line should appear. A dotted line, with the color of the corresponding axes (green) will follow the Line Tool to indicate you are directly inline with the start point of the first line.
6. Click when the line you are drawing is indicated by an axes color (red) and is directly perpendicular to the green dotted line.

Component Inferences

All normal geometry inferences can be obtained from geometry inside Component entities or Group entities. Group and Component inferences are all indicated by magenta dots.

Inference Locking

At times, geometry might interfere with your ability to infer points from other points, making it difficult to draw accurately. Use an inference lock, which tells SketchUp not to waver from the direction it is currently inferring from, to solve this problem. To use the inference lock, hold down the Shift key when SketchUp infers the desired alignment (the inference line will bold). The alignment will remain locked, even as you move the mouse and/or pick a secondary inference point. The following image shows the inference locked in the blue direction to ensure that a new line is exactly perpendicular to the face.

Any of the inference conditions may be locked; along an axis direction, along an edge direction, on a face, from a point, parallel or perpendicular to an edge, and so on.