Field guide

Getting a clean, stable overlay — and what to do when it drifts.

Almost every bad first experience with a body-tracking app is a setup problem, not a software one. Sixty seconds of framing gets you a solid overlay.

Set the shot up

1. Stand the subject 1–3 metres away

   Whole body in frame — head to feet if you can, and at minimum the full torso and head. Cropping either end degrades the underlying skeleton estimate, and everything else is built on it.

2. Let the floor into the shot

   Corpus 4AR uses the floor plane to work out how tall the person is. A clear view of the ground in front of them is the single biggest factor in getting the anatomy scaled correctly.

3. Face the camera

   Front-on tracks best. Extreme side profiles and large yaw angles confuse body tracking, and the overlay will wander.

4. Light the room, not the lens

   A reasonably well-lit room works; a bright window directly behind the subject does not. Backlight is the most common cause of a body never being detected at all.

5. Wear something plain

   Fitted, plain clothing with contrast against the background is easiest to track. Loose robes, and clothing that camouflages against the backdrop, can defeat detection entirely.

6. Give it a second

   First detection usually takes 1–2 seconds, and accuracy keeps improving for a moment after that as the proportions settle. If it stalls, have the subject shift their weight slightly.

Read the tracking pill

The pill at the top of the screen tells you how much to trust what you're seeing. Tap it in the app for the full explanation, including the scale caveat.

• Searching
• Approximate
• Strong

• Searching — no stable body yet. Check framing, distance and light before anything else.
• Approximate — tracking, but the fit is still settling or the view is compromised. Usable for orientation, not for pointing at a specific small structure.
• Strong — locked on. This is the state to teach from and to record in.

When it drifts

• Re-frame first. Nine times out of ten the subject has drifted out of the ideal 1–3 m window, turned side-on, or the floor has left the shot.
• Reset Tracking. In settings. Restarts ARKit's world tracking and reloads the meshes — the right move when the skeleton has slowly walked away from the body over a long session.
• Drop a layer on older devices. Muscles are the heaviest mode by a wide margin. On A12 and A13 iPhones, turn bones or organs off while muscles are on, and close other apps to free memory.
• Check permissions. If the camera was denied by accident, re-enable it in Settings → Corpus 4AR. The camera is required; the microphone is only needed for narrated clips.

Using it to explain something

• Focus instead of hiding. Search for the structure and tap it — everything else disappears, so you get the kidney alone, inside the body, instead of a cluttered abdomen. Focus several at once when you want to show a relationship.
• Turn the opacity down. Around 50–70% keeps the person visible underneath, which is what makes the overlay read as their anatomy rather than a floating model.
• Dim the camera, not the anatomy. The camera-dim slider darkens only the camera feed. In a bright room this is how you make the structures pop without losing colour accuracy.
• Filter organs by system. Showing only the digestive or respiratory system removes most of the visual noise from an explanation.
• Move the model beside them. Two-finger drag on the camera view stands the rendered skeleton next to the person instead of inside them — useful when you want to compare, or when the subject would rather not have organs drawn on their chest. Two-finger double-tap snaps it back.
• Switch to Latin when you're quizzing someone, and back to English when you're explaining to a patient.

Recording a clip

• Clips run up to 60 seconds. The toggles, search and shutter drop away while recording — the record button, its progress ring and a small “Made with Corpus 4AR” watermark stay in frame.
• Narrate as you go if you want — the microphone is optional, and denying it simply produces a silent clip.
• You review the clip in the app before keeping or sharing it. Nothing reaches your Photos library until you say so.
• If you're recording another person, get their consent first. That's on you, not on the app — see section 7 of the Terms.

Something else wrong?

The FAQ covers device support, accuracy and privacy. If neither page helps, email [email protected] with your iPhone model, iOS version and app version.