Lock the scan position

Pin where a 3D capture starts, by averaging a new point or using a marker you already surveyed, so the scan lands in the right place.

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A 3D scan is only placed as well as the point it starts from. The phone's AR tracking measures how the camera moves and turns during the capture, but only relative to where the session began. So before the camera opens, the app asks you to lock that starting point. "The lock fixes the origin; ARKit carries the camera path and direction from there."

This step appears after you choose Points or Photogrammetry in New capture. The screen is titled Start the points capture or Start the photogrammetry capture, with the preflight banner at the top.

Before you start

  • Stand where the scan will begin.
  • For the best origin, connect an RTK receiver and wait for a fixed solution. Phone GPS works, but the scan is then placed to metre-level accuracy.

Choose how to anchor the scan

There are three options, from best to least.

Lock this position

This creates a new 3D Scan point where you stand and anchors the capture to it. The card shows your current position source, accuracy and fix type.

With phone GPS:

  1. Tap Lock position (30 s average). The screen changes to Locking position.
  2. Hold the phone upright and steady. The bubble shows whether you're plumb ("Level the bubble — hold the phone upright"). The countdown runs from 30, and the line underneath shows the sample count and spread.
  3. When the countdown ends, the position locks and the camera opens. To stop early with what you have, tap Collect now. Cancel takes you back to the choices.

In a hurry? Tap Quick lock (single fix) to lock a single position straight away.

With a receiver connected:

  • Tap Lock position. A single RTK epoch is already survey grade.
  • Tap Average multiple samples… for an averaged occupation instead. It works the same way as the 30-second average above.

If there's no position yet, the card shows Waiting for a position fix… and the lock buttons don't appear.

The new 3D Scan point gets a suggested name and is saved to the project like any other point. You won't find 3D Scan in the collect type picker. It's only created this way, because a scan anchor without a scan is just a position.

Use an existing marker

This anchors the capture to a point you've already surveyed, such as a control point or a manhole. Stand at it and scan from there.

  1. Tap Use an existing marker. The card shows how many assets the project has.
  2. Pick the asset from the Anchor to list.
  3. For a line or area, choose the vertex under Which vertex?.

The marker's height is treated as the ground, not as the phone in the air. The app puts the scan's own floor at that height instead of adding a pole.

Skip the lock

Tap Skip the lock at the bottom to go straight to the camera. As the app puts it: "The scan takes whatever fix is live when you finish, and you'll be asked where to file it." The capture has no deliberate origin, and its details show Live fix at capture as the origin.

Skip the lock is unavailable when the project has no assets, because the scan would have nothing to be filed against. In that case, lock a new point instead.

Why the lock matters

The scan itself is recorded in a local frame, in metres from the starting point, with up aligned to gravity. Two more things are needed to put it on the ground:

  • An origin: where the local zero sits on the earth. The lock provides it.
  • A heading: which way the local frame faces. For a point cloud, this starts from the compass and, once you've walked a few metres, can be replaced by a heading solved from your GNSS track. For photogrammetry, it comes from fitting the camera positions to the GPS fix logged for each photo.

The capture's details show where the origin came from under Georeference → Origin:

Origin Meaning
GPS lock at capture start You used Lock this position
Existing marker You used Use an existing marker, or started the capture from an asset's details
Fitted from shot positions A photogrammetry model whose position came from the photo fixes
Live fix at capture No lock. The origin came from the fix available at the time.

Camera offset

With a receiver on a handheld grip, the antenna isn't at the camera. It's a few centimetres to the side, above and behind it. If you don't tell the app, that gap becomes unmodelled error in the scan's origin. The preflight check flags Camera offset: Not set whenever a receiver is connected.

  1. Go to Settings → Camera offset (handheld).
  2. Under Mount, choose Left or Right for the side the receiver sits on. These presets match the Emlid RX2 capture grip: 7.9 cm to the side, 10.7 cm above and 2.9 cm behind the camera.
  3. Or enter your own measurements under Offset (m): X — right of camera, Y — above camera and Z — behind camera. Measure from the camera lens to the antenna phase centre. Negative values mean left, below or in front. Editing a value switches the mount to Custom.
  4. Tap Done.

How the offset is used:

  • Point clouds anchored with a fresh lock or a live fix: once a heading is known, the origin is moved from the antenna to the camera using this offset.
  • Captures anchored to an existing marker: no offset is needed, because the marker describes the ground.
  • Photogrammetry: the offset is recorded with the model but not applied. At under 15 cm, it's absorbed into the photo fit.

The camera offset is separate from the pole height. The pole height, set in the receiver sheet, applies to surveyed points. For a fresh lock, the app adds the pole back so the origin describes the device at capture height.