Count people crossing a line

A counting line is the simplest measurement in CV-Scope. Each time a tracked person crosses the line, CV-Scope counts the crossing and records its direction and time.

CV-Scope places each object at the bottom centre of its box, about where the feet touch the floor. Draw lines on the floor where people walk, not at head height.

Step 1. Add the corridor video

Skip this step if you did guide 01. The camera Corridor then exists already. Open it from Cameras and click Open scene builder.

1. Open Cameras and click Add camera.
2. Set Camera name to Corridor and pick a Project. If the list is empty, create a project on the Projects page first.
3. Set Connection type to Video file.
4. In Or use a file already on this computer, type the full path of samples\videos\people-detection.mp4 and click Use file. To copy the file into CV-Scope’s data folder instead, use Upload a video file.
5. Click Add camera. The first frame of the clip appears on the right.
6. Click Open scene builder.

Step 2. Draw the counting line

1. Drag the slider at the bottom of the Scene Builder to about 00:03 and release it. The frame shows a person walking across the room. A frame with people in it shows where they walk. Any frame works for drawing.
2. Press L, or click Line in the tool column on the left.
3. Click on the floor at the foot of the back wall, halfway across the picture. Then click at the bottom edge of the picture, straight below the first point. A point close to the edge snaps onto it.
4. The inspector on the right now shows the new line. Set Name to Middle line.
5. Under Object to track, keep Person ticked.
6. Under Direction, keep Both. The solid arrow on the line points forward. The short, faint arrow points in reverse.
7. Under When an object crosses, keep both boxes ticked: Count the crossing and Record an event with time, direction and track.
8. Click Save in the top bar, or press Ctrl+S.

Step 3. Create the experiment and run it

1. Click New experiment in the top bar of the Scene Builder.
2. Set Name to Count the middle line. The project and the camera are already filled in. Under Objects to track, keep Person. Click Create experiment.
3. The new experiment is now selected in the top bar. Click Start.
4. The picture switches to the run. You see a box around each person, their anonymous track number and a short trail. Counters such as Middle line forward and the newest events appear in the bottom bar.
5. Wait for the run to finish. A video file is processed as fast as the computer allows, so the 50-second clip takes from a few seconds to a few minutes. The status in the top bar then reads stopped, and the bottom bar shows Last run … completed with a Results link.

Step 4. Read the counts

1. Click Results at the bottom of the Scene Builder.
2. On the Summary tab, the Line crossings panel lists Middle line.
3. Open the Events tab. It lists every crossing with its Media time, Direction and Track number. Click a row to see all its fields, and Jump to video to watch that moment.

With the recommended detector we counted 3 crossings on the sample: 2 forward and 1 reverse. Another detector can differ by one or two.

Why someone was not counted

• The person walked along the line rather than across it.
• The person was hidden behind someone else while crossing. The tracker must see a person on both sides of the line.
• The person appeared right on the line. A track has to be 2 frames old before it can count. You can change this under Advanced in the inspector, as Minimum track age (frames).
• The same person crossed back within a second. Debounce (seconds) under Advanced ignores such repeats.

Next

Guide 05 uses the direction to count people coming in and going out. Guide 17 checks the counts against your own.