Measuring with the camera

On a field that a designer set to Measure, you can read a length straight from a photo instead of typing it. Like everything in the voice assistant, it proposes a value that you confirm, so a photo never commits a length on its own.

Who can do this

This needs the Member or Admin role.

Measuring is part of AI-assisted collection, included on the Professional plan and above.

Why a card or marker has to be in the photo

A photo has no built-in scale. If the app measured raw pixels, the same fish would read a different length depending on how close you held the camera, which is useless for a record. The fix is to put something of known size in the same photo, lying flat in the same plane as the specimen: a credit card, or a printed marker. Because the reference and the specimen are the same distance from the camera, the app can work out the real length from the two together, and the answer no longer depends on distance or on a slight camera tilt.

The one habit that matters

Keep the reference and the specimen flat and in the same plane (both on the board or table), and take the photo roughly from above. A reference propped at a different height, or a specimen bulging up toward the lens, is the main source of error.

Set your reference once (admin)

An admin opens Settings for the organization and finds Measurement reference. Choose one:

• ID or credit card (recommended to start): any standard card is a fixed, worldwide-standard size, so there is nothing to measure or enter. Most crews already have one.
• Printed marker: a square marker you print and lay beside the specimen. It lets the app find the reference automatically, so you tap fewer points. Enter its side length in millimetres (the black square’s edge).

This is your organization’s default, and it syncs to every device, including the mobile app, so a whole crew measures against the same reference. A field user can still switch the reference during a single measurement.

Printing a marker (optional)

If you choose the marker, print one straight from the Measurement reference settings (the Print a marker at this size link), or open the /measure-marker page. It is a ready ArUco marker (dictionary ARUCO MIP 36h12, id 0), the exact one the tool reads, so there is nothing to configure. Print on matte white paper at 100% / actual size (not “fit to page”), keep the white border around it, and laminate it for the field. Then measure the printed black square to confirm it really is the size you chose (100 mm by default), and set that same number as the marker side length in Settings.

Measure a specimen

1. On a Measure field, tap Measure (or say open the camera).
2. Lay the specimen flat, with your card or marker beside it in the same plane, and both fully in the frame.
3. Tap Capture to freeze the photo.
4. Mark the reference. With a card, tap its four corners (clockwise from the top-left). With a marker, the app finds the corners for you, so you can skip straight to the next step; if it cannot, it asks you to tap the four corners.
5. Tap the two ends of the specimen (for a fish, snout to tail fork).
6. Drag to fine-tune. On the mobile app every point you placed is a draggable handle. Touch one and drag it exactly onto the tip; a magnifier pops up showing what is under your fingertip, so your finger never hides the spot. A plain tap only places a point, so nudging a handle never happens by accident.
7. The proposed length appears. Confirm it, or tap Clear points to redo the taps, or Retake for a new photo.

Check it yourself

The quickest way to trust the tool: measure the same item twice from very different distances. The two readings should agree closely. If they do, the reference is doing its job.

Tips for accurate results

• Press the specimen flat and keep it in the same plane as the reference.
• Fill a good part of the frame with the scene; a reference that is tiny in the photo is read less precisely.
• Avoid glare and hard shadows on the card or marker.
• Tap the specimen’s true end points, then drag them to fine-tune. On the mobile app the magnifier makes it easy to land on the exact tip.
• Expect accuracy within about a couple of percent (a few millimetres on a hand-sized fish), comparable to a measuring board. For a legal or dispute-sensitive length, a physical board or calipers is still the arbiter.

Where it works

Measuring runs on the device, offline, and works in any modern browser including on iPhone. It never uploads the photo; the image stays on your device unless you separately attach it to the record.

Related

• AI-assisted data collection
• Field settings