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      Understanding How XVision Calculates Speed

      XVision calculates speed in pixels per second; convert to meters using a known reference. Measure near screen center for accuracy.

      Overview

      XVision uses a pixel-based speed detection algorithm to estimate the velocity of moving objects in the camera’s field of view. The system calculates speed as pixels per second, and this can be converted into real-world units (e.g., meters per second) using a simple reference measurement visible in the viewframe. This method offers a flexible, efficient alternative to radar or other physical speed sensors, making it ideal for a wide range of environments.

      How XVision Calculates Speed

      1. Speed = Pixels per Second

        XVision tracks how many pixels an object moves over time and calculates its velocity based on the frame rate. This gives a base measurement of pixels per second (px/s).

      2. Conversion to Real-World Units (Meters per Second)

        To convert this to meters per second (m/s), you need a known reference object or distance in the camera view (e.g., a road line, pole, or other fixed object) to determine how many pixels equal one meter.

        Formula:

        Speed (m/s) = Speed (px/s) ÷ Pixels-per-Meter (px/m)
      3. Converting Speed to Kilometres per Hour (km/h)

      After converting speed from pixels per second (px/s) to meters per second (m/s), you can also express speed in kilometres per hour (km/h) for easier interpretation in many use cases, such as road traffic analysis.

      Formula:

      Speed (km/h) = Speed (m/s) × 3.6

      Example Workflow: 

      Xvision reports 300px/s

      If an object moves at 300 px/s, and you know 100 pixels = 1 meter, then:

      Speed = 300 ÷ 100 = 3 meters per second

      If your converted speed is 3 m/s, then:

      Speed = 3 × 3.6 = 10.8 km/h

      Tip:

      You can create a simple calculator in Excel or in the AlphaX interface (if supported) to automatically convert px/s to m/s and km/h based on your calibration.

      How to Measure Pixels per Meter

      To calculate pixels-per-meter accurately, use a fixed object of known physical length visible in the camera’s view. Tools you can use include:

      • Screen Ruler Tools

        • Examples: Pixel Ruler, ScreenRuler, MeasureIt (browser extension)

        • These allow you to measure the number of pixels directly from an on-screen image or camera feed.

      • Image or Video Software

        • Use tools like ImageJ, VLC Player (pause and frame step), Photoshop, or any image editor with pixel measurement features.

      • AlphaX Interface Tools (if available)

        • Use the interface calibration features to measure distances based on camera feed.

      How Depth and Perspective Affect Speed Accuracy

      XVision calculates speed across the entire camera view, and provides an average speed value based on object movement through the frame. However, due to perspective distortion, objects closer to the camera appear larger (more pixels), while objects farther away appear smaller (fewer pixels).

      To improve accuracy:

      • Choose a reference object or measurement point near the center of the screen, where the object movement is most consistent and representative of average depth.

      • Avoid using measurements from the extreme foreground or background, as these may skew the conversion.

      Advantages of Pixel-Based Speed Calculation

      ✅ Low Cost – No need for expensive radar or physical speed sensors
      ✅ Flexible – Works with a variety of camera positions and angles
      ✅ Easy Calibration – Simple measurement and formula-based adjustment
      ✅ Adaptable – Ideal for monitoring roads, pedestrian areas, pathways, and more

      Limitations and Considerations

      ⚠ Perspective Distortion – The farther an object is from the camera, the fewer pixels it covers. While the system averages speed across the frame, the most accurate conversion will occur when you base your reference measurement around the typical depth where most objects travel—ideally the center of the screen.

      ⚠ Consistent Measurement Reference Needed – Always ensure the same reference is used for consistent results, especially if you’re comparing across multiple sites or cameras.

      Summary

      • XVision measures object speed in pixels per second.

      • To convert to meters per second, divide by the number of pixels per meter (based on a known object in view).

      • The system measures average speed across the camera’s view, so it’s best to base your pixel-per-meter reference around the center depth of the frame.

      • This method is a simple, flexible, and effective way to monitor speed in real-world environments.

      Need Help?

      Refer to the Installation and Maintenance Guide for more setup details, or contact our support team for assistance with calibration and speed tuning.