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3-2-1 Align sets both the orientation and the position of a part in the global coordinate system. You define three references on the part, one after another: a plane, a direction (vector) and a point. Use it when a part must sit in the same, explainable position every time, for example to compare a scanned part with its CAD model or to prepare it for inspection and manufacturing. To put just one face onto a plane, the quicker tool is Align to Plane.
What 3-2-1 Means
The name comes from the classic way to locate a part with datums:
- 3 points or more define the Plane. It fixes the tilt of the part and its position along one axis, like a part lying on a table.
- 2 points or more define the Vector, a direction in that plane. It fixes the rotation of the part on the table and its position along the second axis, like a part pushed against a fence.
- 1 point defines the Point. It fixes the position along the third axis, like a stop at the end of the fence.
For example, on a machined part you pick the base face for the Plane, a straight edge of the base for the Vector and a corner for the Point.
Open the Tool
Select the part (one object) in the Scene tree and click Transform › 3-2-1 Align. The 3-2-1 Align panel opens, and MeshInspector at once moves the part so that the centre of its bounding box is at the global origin and fits the view. This move is expected: the alignment starts from the origin. The global axes are shown while the panel is open.
The panel has the Mode list, a block for each step (Plane, Vector, Point) and the Apply button. Only the current step is active; the next one becomes available after you click Accept.
Modes
Mode sets which global axis each step defines. The letters say which axis is perpendicular to the plane of each step, and how many points the step needs.
| Mode | Plane (3 points) becomes | Plane through the vector becomes | Plane through the point becomes |
|---|---|---|---|
| ZZZ-YY-X (default) | XY plane (perpendicular to Z) | ZX plane (perpendicular to Y) | YZ plane (perpendicular to X) |
| ZZZ-XX-Y | XY plane | YZ plane | ZX plane |
| YYY-XX-Z | ZX plane | YZ plane | XY plane |
| YYY-ZZ-X | ZX plane | XY plane | YZ plane |
| XXX-ZZ-Y | YZ plane | XY plane | ZX plane |
| XXX-YY-Z | YZ plane | ZX plane | XY plane |
In the default mode ZZZ-YY-X, the base face goes into the XY plane, an edge picked on that face ends up along the X axis, and the point gets X = 0. The origin is where the three planes meet. Choose another mode when your drawing or CAD model uses another axis as "up", for example YYY-XX-Z for a Y-up system.
Controls of Each Step
| Control | What it does |
|---|---|
| Fit Samples / Feature (under Select Pick Mode) | Pick points on the model, or click a feature created in advance |
| Offset | Shifts the result along the axis of this step by the given distance. Type a value or drag the field |
| Accept | Confirms the step and makes the next step active |
| Flip | Turns the part to the other side of this step's plane (Plane and Vector steps only) |
| Reset | Clears this step and all the steps after it |
| Apply | Available after the third Accept. Closes the panel; the part stays where it is |
Step 1: Define the Plane
With Plane Fit Samples selected, click the model to place points; you can drag a point to move it. MeshInspector fits a plane through the points, so at least three are needed; more points on a noisy scan give a better plane. Spread them over the face: points that lie almost on one line do not define a plane well.
The part is placed on the positive side of the plane (above the XY plane in the default mode). Click Flip to put it on the other side, then click Accept.
Step 2: Define the Direction Vector
In the Vector step, pick at least two points, for example along a straight edge. MeshInspector fits a line through them; together with the plane of step 1, it sets the rotation of the part. If the part faces the wrong way, click Flip: it reverses the direction without changing the points.
Before flipping
After flipping
Using Offset
Offset shifts the reference by a distance along the axis of the step. Use it when the zero of your coordinate system must not lie on the picked geometry, for example a set distance from the edge. Type a value for precise control, or drag the field and watch the part move. Then click Accept.
Step 3: Define the Point
In the Point step, pick one point, for example a corner. If you pick several, MeshInspector uses their average position. Click Accept, and then Apply. The part is now fixed along all three axes.
Step 4: Check the Result
Look at the part from different sides with the navigation cube to make sure it is aligned with the global axes. To check the position with numbers, turn on the bounding box or read Translation in the Transform section on the left, below Information.
Aligning by Features Created in Advance
Instead of picking points, you can use features: a plane, a line and a point fitted to the part on the Inspect tab (see how to create features). This is useful when the references must be exact, for example a plane fitted to a whole face of a scan.
- Create a Plane, a Line and a Point feature on the part.
- Click Transform › 3-2-1 Align.
- In each step, select Plane Feature, Vector Feature or Point Feature and click the feature itself in the viewport, not its name in the Scene tree. Click Accept.
- After the third Accept, click Apply. You can then hide the features and check the position of the part.
Typical Mistakes
- Accept is unavailable: the step does not have enough points yet (3 for the Plane, 2 for the Vector, 1 for the Point).
- Apply is unavailable: one of the three steps is not accepted.
- The part is tilted after step 1: the plane points are too close together or almost on one line. Click Reset and spread the points over the face.
- The part is upside down or turned by 180°: click Flip in the Plane or Vector step.
If you only need to centre a model or to turn it by one feature, the quicker tools are Move to Zero and Make X, Make Y, Make Z. Do not use Move to Zero after 3-2-1 Align: it moves the centre of the part to the origin and loses the zero point you have just set.
