Ball
Ball analysis
Margin over the net, depth, speed, in or out and the landing map of your strokes. What’s measured, what’s a projection and how far to trust it.
On this page
With the court calibrated, Racketlens follows the ball of each of your strokes and works out its flight in 3D: how far over the net it goes, where it lands, how deep, how fast it leaves the racket and whether it went in.
Before you start#
- The court calibrated with a good or fair fit.
- Your strokes recognised. Scan the session in the Session tab. With the court already calibrated, the scan follows the ball of up to 4 strokes of each kind.
Analyse your strokes#
- Open Tools → Ball. Under The ball of my strokes press Analyse the ball of my … strokes (or Analyse the remaining … if the scan already did some).
- Wait or keep working. It takes about 5 seconds per stroke and the page stays responsive. Stop keeps what’s been measured.
- Read the summary. Sentences like “You clear the net by 0.62 m on average” or “3 of 20 went into the net”, per kind of stroke.
- Click a stroke in the table to see its flight, net crossing and bounce drawn on the video, with all its numbers.
What each number means#
| Number | What it measures |
|---|---|
| Margin over the net | The distance between the bottom of the ball and the net tape, where it crossed. The tape is 0.914 m high at the centre and 1.07 m at the posts. Under 30 cm is risky. |
| Depth | How many metres inside the baseline it landed. Negative = long. On a serve it’s measured against the service line. |
| Speed off the racket | The ball’s real speed as it leaves the racket, in km/h, measured in 3D on the court. |
| In or out | Whether it landed in. When it’s too close to the line to say, it reads on the line?. |
| Launch angle | The ball’s angle above the horizontal as it leaves the racket. |
| Contact height | How high you hit it. |
| Spin (estimate) | topspin, flat or backspin, read from the curve of the flight. |
Every number comes with its ±: the margin of error of that measurement. A wide ± means read it with care.
Measured or projection#
- Measured: the camera saw the ball cross the net (or reach the bounce). The most reliable result.
- Projection: the camera only saw the start of the flight. The rest is worked out from how the ball left the racket, without knowing its spin, hence the wide ±. It happens mostly when filming from the side.
The landing map#
The court seen from above, with a dot where each ball landed:
- Solid dot = measured; hollow dot = projection.
- Green = in; red = out; grey = too close to call.
- An × = into the net.
Hover a dot for its numbers; click it to go to that stroke.
How far to trust it#
On synthetic videos with known answers, when the flight is seen to the bounce, the net margin comes back within about ±10 cm, the landing within ±0.6 m, the speed within ±5 % and the angle within ±1°. Projections from the side: ±20 cm, ±1.5 m and ±7 %. On a real court expect a bit more: it’s one camera, the body is estimated and the ball’s spin isn’t known.
When the ball wasn’t found#
ball not followed means the ball wasn’t seen leaving the racket on that stroke: hidden, too blurred or out of the picture. It helps to film with the whole flight in the picture, in good light, with the camera still.
Manual tools#
For one stroke at a time, or when automatic tracking misses, open Manual tools: scale and marking the ball by hand:
- Go to a few frames before contact, choose Mark ball (B) and click the ball: the video steps forward a frame per click. Shift-click marks contact.
- Keep going through contact and a few frames after, or press Auto-track (T) to follow it automatically.
- With the court calibrated, Measure this track on the court turns that track into the same numbers in metres (it needs at least 4 frames after contact).
Without a court calibration, these tools measure speed in the picture plane against a reference line (Scale): accurate when the ball crosses the picture at that line’s distance, and they underestimate motion towards or away from the camera.
In your history#
Net clearance, depth, the share of balls in and speed are charted session by session in History, with each session’s landing map.