Questions, answers, and a person at the end.

Any iPhone with a LiDAR scanner running iOS 18 or later: iPhone 12 Pro and Pro Max, and every Pro model since. Non-Pro iPhones have no LiDAR and cannot scan.

iPhone only, deliberately. An iPad Pro has the same LiDAR scanner, but GreenScanner is built to be held upright in one hand while you walk a putt, and we have not built or tested the landscape layouts an iPad deserves. We would rather leave it out than ship a version we cannot stand behind.

The app checks at launch and tells you straight away if the device is not supported.

No. Rule 4.3 of the Rules of Golf prohibits using a device to measure slope or elevation during a round, and restricts green-reading aids. GreenScanner is for practice: the practice green, a casual round where your group agrees, or studying a course beforehand.

Saved greens are yours to study at home. What you remember on the day is entirely legal.

Once, to sign in. GreenScanner asks you to sign in with your Apple account before you use it, and that first sign-in needs a connection.

After that, scanning, viewing and saving a green are computed entirely on the phone and work with no signal at all — which is just as well on a course.

Course names, hole numbers and green outlines come from the course database, which needs a connection at the moment you save. Without one, the scan is named by date and place and you can rename it later.

It is built for mown putting surfaces. On a green the LiDAR sees a dense, even canopy and the per-cell scatter settles to about a millimetre. Fringe and fairway scan too, though noisier. Rough, long grass and bare soil are not what it is for.

Walk slowly along the putt with the phone pointed at the surface about a metre ahead, roughly a 45° tilt. Go out to the hole and back to the ball: re-observing the early cells is what lets the app cancel drift.

Keep some background in the frame now and then, such as the flag, the fringe or a bunker edge. The camera tracks position from texture, and an unbroken carpet of green gives it little to hold onto.

Aim for 45 to 75 seconds. The app suggests finishing at around 75 seconds so drift stays bounded.

No, the corridor of the putt: from the ball to the hole plus a couple of metres either side. Typically 3 to 15 metres long. It is faster, more accurate, and it is where the answer lives.

Scan the same green again later and the app extends the saved entry with the new coverage instead of adding a duplicate, as long as the two scans line up convincingly.

Honest answer: good at shape, not yet trustworthy on absolute slope.

A single LiDAR frame is good to about ±1 cm. GreenScanner fuses around 15 frames a second into a grid of 1.5 cm cells, so each cell collects a hundred-plus samples and its random noise averages down to roughly 1 mm. That part works, and it is enough to see a slope change of half a percent over half a metre.

What has not been solved is systematic error. Scan a floor we know to be level and the map currently reports 2.5–3.6 % of slope that is not there, and bows by 12–27 mm across the scan. The cause is under investigation. A constant tilt does not change the shape of a break — which is why the contours and the relative fall of a green are useful today — but it does move the absolute uphill-or-downhill reading.

So use it to understand how a green runs, and keep your own read for how much. A quality report after every scan shows coverage, drift and a plain verdict, and the accuracy section of How it works publishes the current numbers, including the test that is failing.

The small top-down map paints each cell brighter as it collects samples. You are literally painting the surface. Pale patches need another pass; the arrow is your phone.

LiDAR works in shade, cloud and dusk. Bright sun is fine. Standing water and very wet, shiny grass reflect poorly and lower the number of samples the app accepts; the quality report will tell you.

Slope. Green is under about half a percent, yellow around 2 %, orange around 4 %, red 6 % and steeper. Contour lines are every 1 cm of height, bold every 5 cm, so tight lines mean a fast break.

Switch to the elevation view for blue (low) to red (high) when you want to see where water would run.

Height is exaggerated on screen, 2.5× by default, because true-scale undulation on a green is almost invisible. Drag the slider to 1× for true proportions or higher to hunt for subtle breaks. The data underneath never changes.

The real outline of the green, from the course database, placed at its true size and orientation using the compass reading taken during the scan. It is a level reference plane so you can judge tilt against the whole green. Without a database match you get a plain rectangle instead.

A ball is rolled over the measured surface in simulation: gravity along the slope, rolling resistance from the green speed, a thousand steps a second. For the speed you choose, the app searches the aim that brings the ball to the cup and shows the resulting path.

Move the speed slider and the aim re-solves live. The app also shows the range of speeds that hole the putt from that spot.

Stimp is green speed: how far a ball rolls from a standard release, in feet. Slow greens are around 7 to 8, tournament greens 11 to 13. It sets the rolling resistance, which decides how much a putt breaks.

The guided calibration takes a minute: putt a real ball and watch where it stops, recreate the same line and speed on the panel, then drag the Stimp slider until the simulated rollout matches. That value is saved and used for every green until you change it.

Four usual suspects. Green speed not calibrated for today's conditions. Ball or hole marker a few centimetres off, so drag them exactly. A pace different from the slider, since the line only holds for that speed. And grain or wind, which the scan cannot see.

If a line looks wrong on a green you know, send us the scan from the library share sheet and we will look at it.

During the scan the app watches the camera for a bright, ball-sized blob and a dark, cup-sized disc, checks their size against the LiDAR distance, and clusters the sightings. Candidates appear as ghost markers you confirm with a tap; nothing is placed without you. Place them by hand whenever you prefer.

From OpenStreetMap, via a small database of Dutch courses that is refreshed nightly. When you save a located scan, the app finds the green you are standing on and prefills a name such as “De Rotterdamse — Hole 7”. Where the hole is drawn and numbered on the map, the green gets its number; where it is not, the scan is called “— Green” and you can rename it.

Either the course's greens are not drawn on OpenStreetMap yet, or you had no connection when saving. Check the coverage page. Mapping a course on OSM is straightforward and it appears in the database the following night.

On your device only, in the app's documents folder, each with a thumbnail. Nothing is uploaded. You can export a scan from the library as a file to share or back up.

If a new scan resolves to a green already in your library, or lands within 30 m of one, the app tries to align the two. When the shapes match convincingly it merges the new coverage into the saved entry and tells you how many square metres were added. When it cannot confirm they are the same green, it saves separately and says so. Ball and hole always come from the latest scan.

Two things. A course lookup: your approximate position when you save a located scan, sent to find the nearest green. And the scan itself, uploaded in the background and kept with your account — either the full measured surface or just its details (which green, where, when, how good), depending on a setting we control. No images ever leave the phone; the camera frames the detectors use are discarded during the scan. Sign in with Apple gives us your email (or Apple's private relay address) and Apple's identifier for you, and nothing else. Deleting your account deletes your uploaded scans with it. See the privacy policy for the full picture.

Three things, all about the green you are standing on. It looks up which green and course that is, so the scan is named after the course rather than the date. It fetches that green's outline and draws it around your scan, so you see where your scan sits on the green. And it lets your uploaded scan be pooled with other golfers' scans of the same green, which is how the collective slope data everyone benefits from gets built. Location is read only while the app is open. Decline it and scanning, viewing and putt reading still work; scans are named by date, there is no outline, and your scans stay out of the pool.