In-Depth with the VFR Lightboard – Watch the Webinar!
The VFR Lightboard has quickly become one of our favorite tools here at iNPUT-ACE. That’s why we are devoted to consistent development of the Lightboard and to the delivery of training materials.
To better support the quickly growing user base, we wanted to share specific examples of how the VFR Lightboard works and some best practices for Investigators who want to calculate vehicle speed from video.
In this post:
- What is the VFR Lightboard?
- Why use the VFR Lightboard?
- What is a variable frame rate and how does it affect my speed calculations?
- What is a rolling shutter?
- How to calculate vehicle speed with the VFR Lightboard
- How to use the VFR Lightboard in iNPUT-ACE
- Taking your speed calculations to court
- Additional resources and tutorials
What is the VFR Lightboard?
The VFR Lightboard provides a method to accurately calculate timing from video, primarily for vehicle speed calculations and use of force matters.
By placing the VFR Lightboard in front of any video camera and then bringing the recording into the VFR Lightboard Tool in iNPUT-ACE, users can generate a report of precisely calculated frame timing intervals that can be used to measure the minimum and maximum speeds of vehicles or other objects.
The VFR Lightboard uses a specific pattern of LED lights that spiral inward towards the center. The special pattern allows for calculating the effect of the rolling shutter and any variable frame timing intervals created by the recording device.
This VFR Lightboard shows the LED pattern slowed down significantly and spiraling towards the center of the board before it repeats.
Why Use the Lightboard To Calculate Speed?
Every camera/DVR system works differently, and not all recording devices are created equal. Let’s take a look at some of the common issues that occur with a recording device and why counting frames or driving a test vehicle through the scene can often result in inaccurate measurements:
#1 – Timing metadata isn’t always accurate
Video analysts know that many recording devices simply get the frame rate wrong, and while some systems offer frame level metadata, some recording devices store inaccurate frame times. Due to these limitations, many video analysts testify in court seeking to dismiss speed calculations performed by untrained investigators or forensic experts. The VFR Lightboard provides an accurate methodology and creates dynamic output reports which protect you and your evidence.
#2 – Timing between frames
When a recording device captures an event (especially at slower frame rates), it is important to understand that the activity between frames is missed. These unsampled durations are particularly relevant when analyzing events such as muzzle flashes.
The event in the animation below shows a single muzzle flash. However, the video cannot be used to asses how many shots were fired based on the sampled data alone.
It is entirely possible that additional muzzle flashes occurred in between frames (the unsampled duration) and were therefore not captured to video.
To better understand the timing from the video evidence, experts use the VFR Lightboard to measure the unsampled duration to understand how much time can pass between what we see on the video and can be used to statistically measure the likelihood of capturing a muzzle flash in a particular recording.
In this illustration, multiple muzzle flashes could have occurred despite only one being captured to video. Any activity that happens during the unsampled time between frames will not be captured.
3 – What is a Variable Frame Rate (VFR)?
While frame rate is referenced as a static number in the metadata, many recording devices do not record consistent intervals.
The VFR Lightboard provides a methodology to analyze these cameras and report on any variations in the sampled and unsampled durations (the time it takes to capture a frame and the time between each frame).
Variable frame rates are often misunderstood and investigators who want to calculate vehicle speeds should not use a file’s frame rate to assess timing because the file will often simply report an average frame rate, and even then, that frame rate can be wrong. The VFR Lightboard unlocks the ability to calculate speeds for every file types.
Watch the webinar for more in-depth information on how a variable frame rate works.
#4 – What is a rolling shutter?
Some cameras use a rolling shutter to capture each frame. This means that the shutter starts capturing the frame at the top (or bottom) of the image and continues capturing as it “rolls” over the image.
Since the entire frame is not captured instantly, the first part of the image is captured at an earlier point in time than the last part of the image. In some cases, the data is not even recorded linearly and will cause a phenomenon where the top of an image is recorded at the same point in time as the bottom of the previous frame.
In the animation below, the car actually crossed the line after the light turned red. How can this be? Watch the webinar for a more detailed description of the effects of a rolling shutter.
With these challenges in mind, it is important for investigators and forensic experts to consider many factors when performing speed calculations from video evidence.
How to Calculate Vehicle Speed from video with the VFR Lightboard
In order to calculate vehicle speed from video evidence, you need a reliable method to determine both distance and timing because speed = distance/time.
The speed calculation workflow starts by using iNPUT-ACE to interrogate your video files and ensure you are working with the best evidence.
Next, investigators can use the reverse projection process in the Camera Match Overlay tool to measure the distance.
Then, the VFR Lightboard is used to measure the minimum and maximum amount of time that can pass when recording frames for a specific recording device.
Finally, investigators can use the reported distance and time ranges to calculate a range of speeds within a defined margin of error.
How to Use The VFR Lightboard in iNPUT-ACE
To get started, take the VFR Lightboard to the scene and set it up as close as possible to the camera.
We recommend you mount the lightboard on a light stand because most of our cameras tend to be mounted pretty high. Make sure to secure your light stand to protect your VFR Lightboard!
Capture a recording of the lightboard flashing in front of the camera, and remember to keep the lightboard still for the recording (note – some movement is ok).
Tips and Tricks: The How to use this step button within the VFR Lightboard Calculator Tool opens a pop out window containing instructions and tips and tricks to ensure that your workflow is streamlined and efficient. Please read these steps prior to starting any workflow in the VFR Lightboard Calculator Tool.
Step 1: Load the Data
Add the recorded video of the Lightboard to the File List and open the VFR Lightboard Calculator from the Tools Tab.
Drag and drop the file, Subclip, or stream from the File List into the white space of the tool. Alternatively, select the file by clicking on it > click Load VFR Lightboard Video
Click and drag to create a green crop region that surrounds all of the lights on the VFR Lightboard. iNPUT-ACE will use this region to automatically calculate the light positions.
Step 2: Identify the Light Locations
iNPUT-ACE will automatically identify all the light positions and will create an image showing all lights illuminated.
Make sure that every light is illuminated, and then click “Next” to continue to Step 3.
Step 3: Select the Illuminated Lights
Next, iNPUT-ACE will step through the video frames and highlight the LEDs that were illuminated on each frame. It is important to advance through (at least) 400 frames to verify that the automatic selection process correctly identified the lights that are on.
Making changes is easy. Simply click a light to add a selection, click and drag to add multiples or right click to remove a selection.
Step 4: Final Report
After validating your frames, it’s time to generate some reports. Get started by choosing the Excel/CSV report or the PDF report from the drop down.
The Excel/CSV format provides a detailed spreadsheet of all timing measurements across all frames in the dataset. This output is most suitable for analysts who want access to detailed records, or for users who want to determine which frame timing intervals should be generated in a PDF output.
The PDF format provides a summary of the selected timing intervals. The PDF output contains visual charts that are easier to understand for non-technical users and are more suitable for final forensic/investigative reports that may be referenced by the trier of fact in court matters.
Use the sliders to set the minimum and maximum timing intervals to be displayed in the final report.
For example, to create a PDF output that contains the frame timing intervals for “2, 3, 4, and 5 intervals”, set the lefthand box to 2 and the right-hand box to 5. The numbers can be entered by typing directly into the box or by clicking/dragging the sliders to reach the desired number.
It is important to note that the Lightboard calculates the minimum and maximum amount of time that can elapse for a particular frame interval.
For example, to measure the speed of a vehicle between frame 1 and frame 10 of a particular recording, we need to assess or measure how much time can elapse during any 9 frame interval. Note, between frame 1 and frame 2 is a single frame interval.
Between frame 1 and frame 3 is a 2 frame interval. Between frame 1 and frame 10 is a 9 frame interval. For any measurement, we need 400 samples of our desired frame interval size. To learn more about frame intervals and sample size requirements, you can go watch the webinar.
How to Calculate the full range of Vehicle Speeds
The camera match overlay tool provides a methodology to calculate the minimum and maximum distance.
The VFR Lightboard tool provides a methodology to calculate the minimum and maximum time.
In the example below, our distance measurement is between 14.2 and 14.6 feet and our time measurement is between 0.166 and 0.169 seconds.
To get the slowest speed, divide the shortest distance (14.2ft) by the longest time (0.169 seconds) = 84.02 ft/second (or, 57.31 mph)
To get the fastest speed, divide longest distance (14.6ft) by the shortest time (0.166 seconds) = 87.95 ft/second (or, 59.99 mph)
This means the minimum and maximum speeds for this example are 57.31 mph to 59.99 mph.
Taking Speed Calculations to Court
The team at iNPUT-ACE has developed products for years based on our experiences of testifying in court. With this experience, we create products that are held to a forensic standard, repeatable, peer reviewed, contain a reported margin of error, and are intuitive for investigators and forensic video analysts.
That’s why we calibrate every VFR Lightboard to a 99.99% confidence interval with margins of error less than 1%. We recommend the boards get recalibrated every two years so that you can continue to testify with confidence.
Additional Resources
Become a Certified Metrologist
The iNPUT-ACE Metrologist Certification gives students the foundational knowledge needed to get accurate measurements of distance and time from video evidence.
Instructors will use the iNPUT-ACE VFR Lightboard to diagnose common errors that can come from counting frames. In the second course, students will go in-depth with using the Camera Match Overlay Tool for overlaying the video evidence on top of point cloud data for accurate measurements and calculations within a documented margin of error.
The certification track includes one 4-hour and one 5-hour course including Calculating Speed From Video and Reverse Projection: Camera Match Overlay.
Calculate Speed From Video On-Demand Training
Learn more about the methods used by Investigators and Accident Reconstruction Specialists to calculate vehicle speed from video in this on-demand training series. Consisting of 5 different 90 minute videos, this track will help you to learn about proven methods for more accurate calculations.
