Calibrate XVision speed using radar, timed drives, or GPS tracking. Adjust calibration factor to convert px/s into accurate km/h for better traffic insights.
XVision calculates speed by tracking the movement of objects in the camera’s field of view, measured in pixels per second (px/s). To make this data meaningful and usable in real-world applications, it must be calibrated against known real-world speed values such as meters per second (m/s) or kilometres per hour (km/h).
This guide outlines how to calibrate speed data in XVision using real-world observations, such as radar measurements, vehicle tests, GPS tracking, and timing methods. Accurate calibration improves the reliability of speed data for traffic monitoring, safety analysis, and operational planning.
How XVision Measures Speed
XVision tracks how many pixels an object moves per second across the camera’s video frame. This measurement—pixels per second (px/s)—is the raw output provided by the system.
To convert this into real-world units like m/s or km/h, a calibration factor must be applied based on actual speed observations in the camera’s field of view.
Conversion Formulas:
Meters per second (m/s):
Speed (m/s) = Speed (px/s) ÷ Pixels-per-Meter
Kilometres per hour (km/h):
Speed (km/h) = Speed (m/s) × 3.6Calibration Methods Using Real-World Observations
To determine the correct calibration factor, you’ll need to compare the raw px/s data from XVision with known real-world speed values. Below are common methods for doing this:
1. Speed Radar Gun (Recommended Method)
Use a calibrated speed radar gun to measure actual vehicle speeds passing through the camera’s view. Compare this speed with XVision’s reported px/s value and adjust the calibration factor accordingly.
2. Vehicle Dashboard Speed Method
Drive a vehicle at a constant, known speed (e.g., 30 km/h), then review the XVision speed readings during the same period. Compare the dashboard value with XVision’s px/s and calculate the required calibration factor.
3. Fixed Distance Timing Method
Mark two points a known distance apart (e.g., 20 meters) and time how long it takes a vehicle to pass between them. Calculate speed with the formula:
Speed (km/h) = (Distance in meters ÷ Time in seconds) × 3.6
Compare this result with the system output to calibrate px/s to km/h.
4. GPS Tracking with Sensor or Smartphone
Use a GPS tracker or smartphone app to log speed data while driving through the camera’s view. Export the speed data from the GPS tracker (e.g., GPX, CSV) and compare the actual speed at the time of camera detection to XVision’s px/s.
Suggested GPS tools:
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GPS Logger for Android
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GPX Tracker (iOS)
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Commercial vehicle GPS sensors
This method offers a practical alternative when radar guns are unavailable and provides timestamped speed records for high accuracy.
Steps to Perform Calibration in AlphaX
Assuming the following speed channels
Step 1: Navigate to the Device Menu
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Go to "Devices" in the AlphaX Left Menu Bar.
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Filter on your device and then click edit to navigate to the device settings.
Step 2: Filter speed channels
- Go to the "Channels" Section on the device manage page
- Filter by "Speed" to shortlist speed channels.
Step 3: Determine Speed Reference Data
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Highlight to the "Last 50 Readings" by hovering over the chart.
- Find the last (or known) measurement and use this value as your reference.
HINT: Performing multiple measurements and using average speed will reduce margins of errors typically found in real-world scenarios.
Step 3: Adjust the Calibration Factor
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Locate the settings for the speed channel you wish to calibrate. The settings button is the cog icon on the end each line in the "Channels" section.
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In the Modal Pop-up, update the calibration factor to scale the px/s output to match real-world observations. Leave Calibration Offset at 0.
Example: If real-world speed is 25 km/h and XVision reports 300 px/s, then:
25 (km/hr) / 300 (px/s) = 0.08333 (Calibration Factor)
HINT: Aim for realistic speed readings. For instance, if the typical speed on the road is 20 km/h, ensure your results fall in the speed range you expect.
Step 4: Fine-Tune the Calibration
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Continue adjusting the calibration factor based on observed discrepancies.
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Compare the updated values against your field data.
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Repeat this process until the speed readings accurately reflect real-world conditions.
Best Practices for Accurate Calibration
✔ Use the most accurate field method available—radar guns or GPS provide the best results.
✔ Calibrate using average vehicle movement through the center of the frame, where perspective distortion is minimal.
✔ Perform calibration during typical traffic conditions to ensure data reflects actual usage.
✔ Document your calibration factor for future reference and consistency across devices.
✔ Recalibrate periodically to account for changes in camera angle, environment, or traffic behavior.
Advantages of Real-World Calibration
✅ Highly accurate alignment with real-world speeds
✅ Adaptable to different environments and camera positions
✅ Cost-effective—uses existing infrastructure and tools
✅ Enhances the quality of data used for decision-making
✅ Supports compliance, analytics, and performance monitoring
Limitations and Considerations
⚠ Real-world methods (timing, GPS, dashboard readings) can introduce human or device errors
⚠ Environmental changes such as camera tilt, shadows, or lighting can affect pixel tracking
⚠ Calibration is based on a typical object depth—aim to calibrate for the center of the screen for best accuracy
⚠ Results can vary slightly between day/night or low/high traffic conditions—validate periodically
Summary
XVision calculates speed in pixels per second, which must be calibrated using real-world references to produce accurate km/h or m/s data. Use methods like radar, dashboard observation, timing over fixed distances, or GPS tracking to determine true vehicle speeds, then adjust the calibration factor in AlphaX accordingly. Accurate speed calibration enhances data quality, improves decision-making, and ensures your AI system delivers maximum value.