Register several scans into one

What you'll do

Several scans of one place (each from its own scanner position) start in their own coordinates. Register them: give each scan one placement so they all sit in one frame, then save that as a project and write the registered cloud as one LAS or E57 file.

Place the scans

1. Open the dialog (Register scans… on the start panel, or Show › Register scans… once a model is open). Add scans… takes LAS, LAZ, E57, PLY, PCD, PTX, PTS or XYZ files, or drop them on the dialog. Scans that use different units are refused with a note: convert one first.
2. Choose Scan to move and Place against. The picture shows every scan in the frame as it is now, one color each: Plan, Front or Side; drag to pan, use the wheel to zoom.
3. By point pairs. Click Pick a pair, then a point on the scan to move, then the same place on another scan (a corner, a target, the foot of a column). Do this at least three times, with points that are not in one line and are spread apart. Click Place by pairs: the scan is placed by a least-squares fit, and Left over shows how far each pair still misses. A pair with a large number is a bad pick: remove it with the cross and place again.
4. By targets. If a point's true coordinates are known (surveyed targets), click Pick, then type target, click the point on its scan, and type the target's X, Y and Z in the row. Pairs and typed targets mix freely.

Refine with ICP

Pairs give a rough placement. Refine moves the scan until its surfaces sit on the other scan's: first point to point, then point to plane. The table lists every step with its error and how many points matched; the line above it draws the error falling. Stop ends the run after the step in progress and keeps what it reached. Undo takes the whole run (or the last placement) back; Reset puts the scan back at its file coordinates.

To keep it quick on a laptop, ICP works on a decimated share of the points (Points used, 5,000 to 60,000) and ignores matches farther than Largest match distance (by default 5% of the scan's size, shrinking as it settles). It needs a rough placement first: scans that barely overlap report that they cannot be matched. Surfaces that are only flat or only straight cannot fix a position along themselves; add pairs in that case.

Save and export

• Save project writes a small .ccscans.json file: each scan's name, size and a fingerprint of its first 64 KB, with its transform. It holds no points. Open project… finds the scan files by those references (the files must be added first) and puts every transform back.
• Export LAS and Export E57 write one file with every scan in its registered place. Points are never rewritten in the originals; the transform is applied on the way out. With Read every point from the files on, each file is read again for every point (up to 20 million per scan); off, only the points shown in the viewer are written.
• Show registered cloud (BimCraft) writes the LAS and opens it in the 3D view beside the model, like any cloud.