Understanding the Role of Points in Inventor Sketches

When drawing in an Inventor sketch, you work with lines, circles, arcs… But behind the scenes, all these entities rely on a more fundamental element: points.

Understanding how Inventor manages these points helps you better understand geometric constraint behavior and avoid many frustrations.

Every entity is built on points

When you draw a line with the dedicated tool, Inventor doesn't just draw a stroke: it creates two points and connects them with a segment. Similarly, when you use the Rectangle tool, Inventor creates four points and connects them with lines.

The same principle applies to all entities:

• A circle is defined by a center point and a radius.
• An arc is defined by a center point, a start point, and an end point.
• An ellipse is defined by a center point and two axes.

These points are the foundation on which everything else is built.

Why points?

Inventor uses a constraint solver, a mathematical engine that solves a system of equations to determine the position of each entity. This solver doesn't work directly with lines or circles: it works with points and relationships between those points.

Each constraint you apply (coincidence, tangency, perpendicularity, dimension…) adds an equation to the system. When the sketch is fully constrained — meaning the degrees of freedom are zero — the system is solved and each point has a defined position.

This is why Inventor must create these points: without them, the solver would have nothing to work with.

Points are managed automatically

You have no direct control over these points. You cannot create, delete, or move them independently from their entity. Inventor manages them automatically.

However, you can use them: they are what you target when you apply a coincidence constraint between two entities, or when you snap a dimension to the center of a circle.

Example: the corners of a rectangle

When you hover over the corner of a rectangle, you can select the point located there. Upon examining it, you'll see it carries two coincidence constraints, one for each line:

• Point ↔ End of line 1
• Point ↔ End of line 2

This shared point is what binds the two lines together. The chain is as follows:

Line 1 ↔ Point ↔ Line 2

If you delete one of these constraints, Inventor creates a second point. You then get:

• Point 1 ↔ End of line 1
• Point 2 ↔ End of line 2

The chain is broken: the two lines are now independent. This is exactly the same mechanism as when you "break" a link between any two entities in a sketch.

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