When you record control points and press Station, Dusty rotates and shifts the laser tracker's frame of reference so your scanned points land as close as possible to their CAD positions. That process is called best-fit.
The two sets of points Dusty compares
Best-fit always works with two versions of the same control points:
| Set | Where it comes from | What it represents |
|---|---|---|
| CAD control points | The coordinates in your CAD file and the CSV you upload | Where each point is supposed to be |
| Scanned control points | What the laser tracker measures when you place the reflector on each marked point | Where each point actually is |
The CAD file and the laser tracker each start in their own coordinate system. Best-fit's only job is to bring those two systems into agreement. Use the legend below for the following illustrations.
What happens when you press Station![]()
- Dusty takes both sets of points. You need at least 3 control points that don't all fall on one line. More than 3 is better.
- It finds the geometric center of each set. The center of your CAD points and the center of your scanned points each become a pivot.
- It slides one center onto the other. This is the shift, or translation.
- It rotates the scanned set onto the CAD set. Dusty solves directly for the single rotation that makes the total leftover gap across every recorded point as small as possible — a standard least-squares fit.
- It reports what's left over. Whatever gap remains at each point after the best possible fit is the error you see for that point in the app.
Because the fit is averaged across every point you record, recording more than the 3-point minimum improves accuracy. Extra points give best-fit more samples of the jobsite and dilute the effect of any single point that's slightly off.
Your layout never gets stretched or shrunk
Best-fit only ever applies two moves: a rotation and a shift. It never scales. No matter how large your control point errors are, your layout prints at true 1:1. Errors can rotate or offset where the layout lands on the slab; they can never change its dimensions.
Dusty also never edits your layout. It solves for where the tracker is standing and which way it's facing — your file is untouched.
How this article simplifies the math
This is a deliberate oversimplification. The actual stationing solution is computed in one shot using a well-known technique for rigid-body alignment (the Kabsch algorithm, solved with a singular value decomposition), and anchoring is implemented by giving anchored points an extremely large weight in that same calculation rather than by literally locking them and rotating around them.
The step-by-step here — find the centers, slide them together, rotate — describes what the result looks like and why the tradeoffs behave the way they do. It is not a description of the code. If you need the real derivation, ask your Dusty contact.