Service · Speed, height and distance
Speed, height and distance measured from video
Forensic photogrammetry measures real-world speed, height, distance and position from video and still images. We relate points in the footage to measurements of the scene, verify the frame rate, and report every result with its margin of error.
Expert Witness Code of Conduct
Reports prepared in line with court rules on expert evidence
SWGDE best practice
Recognised methods for digital and multimedia evidence
Repeatable methods
Documented workflow that another examiner can reproduce
Hash-verified custody
SHA-256 recorded on receipt and at every hand-off
Strictly confidential
Encrypted transfer and secure storage of evidence
Overview
What is forensic photogrammetry?
Forensic photogrammetry is the science of taking real-world measurements from images. Applied to video, it can establish how fast a vehicle was travelling, how tall a person is, how far apart two objects were and where something was at a given moment.
A camera turns a three-dimensional scene into a flat image, so sizes and distances in the frame depend on perspective, lens distortion and the camera’s position. Photogrammetry reverses that process. We identify fixed reference points that are visible in the footage, such as road markings, kerbs and doorways, and measure them at the scene or from plans. Those measurements let us map positions in the image to positions in the real world. Combined with a verified frame rate, the same mapping gives distance travelled over time, and therefore speed. Every result is reported with its margin of error, because no measurement from video is exact, and the court needs to know how precise each figure is.
What we can measure
Measurements we can provide from video
Each measurement starts from the question that matters to your matter. We then choose the method that can answer it and report the result with its uncertainty.
Vehicle speed
Distance travelled between frames, divided by the verified time between them.
Height of a person
An estimated height range, allowing for posture, footwear and camera angle.
Distance and position
Where people, vehicles and objects were, and how far apart, at a given moment.
Timing and duration
How long an event lasted, measured from verified frame timing rather than on-screen clocks.
Reverse projection
Recording a known object from the same camera position to compare it directly with the footage.
Scene survey
Measuring fixed reference points at the scene, or from plans, to anchor every calculation.
Camera and lens geometry
Correcting lens distortion and establishing the camera’s position and field of view.
Margins of error
A stated uncertainty for every result, so the court knows how precise each figure is.
What accuracy depends on
What makes a measurement reliable
The accuracy of any measurement from video depends on these six factors. We check each one before starting, and tell you early if any of them limits what can be measured.
Fixed reference points
Features visible in the footage that can be measured, linking the image to the real world.
Watch out: roadworks, new signage or moved furniture can remove reference points. Record the scene as soon as possible.
Verified frame rate
The real time between frames, which every speed and duration calculation relies on.
Watch out: the frame rate in the settings is often not what was recorded, and phones vary it. We measure it from the file.
Lens and camera geometry
How the lens bends straight lines, and where the camera sits relative to the scene.
Watch out: wide-angle lenses distort most at the edges of the frame, where measurements need extra care.
A clearly visible subject
The points to be measured, such as the top of the head and the feet, must be visible.
Watch out: footwear, headwear, posture and walking all change apparent height, so results are given as a range.
An unchanged camera
The camera in the same position, angle and zoom as when the footage was recorded.
Watch out: if the camera has been moved or replaced, reverse projection is harder. Avoid adjusting it.
Enough frames
Frames that show the subject at known positions, such as entering and leaving a measured area.
Watch out: at low frame rates the subject moves further between frames, which widens the margin of error.
Related video forensic services
Services often used with measurement
Measurement usually forms part of a wider examination of the footage. Each of these services has its own page.
CCTV Footage Analysis
Event reconstruction and multi-camera timelines that place each measurement in sequence.
CCTV footage analysis →
Forensic Video Enhancement
Clarification that makes reference points and subjects easier to locate in the frame.
Forensic video enhancement →
Video Decoding
Recovering frame timestamps from proprietary files, so timing can be verified.
Video decoding →
Common questions
What lawyers and insurers ask us about measurement
Short, direct answers to the questions that most often decide how a measurement from video can be relied on.
How is vehicle speed calculated from CCTV?
By measuring how far the vehicle travelled between two frames and dividing by the verified time between those frames. Distance comes from surveyed reference points in the scene; time comes from the frame rate, measured from the file rather than taken from the settings.
We repeat the calculation across several pairs of frames and positions, and combine the uncertainty in each distance and time measurement into one margin of error. The worked example below shows the structure of the result. In a report, every input is listed so another examiner can check the arithmetic.
How accurate is height estimation from video?
It is reported as a range, not a single figure. Under good conditions the range can be narrow, but posture, footwear, camera angle and image resolution all add uncertainty. We state each source of error and how it affects the result.
| Factor | Effect on the estimate |
|---|---|
| Posture and gait | A person walking is shorter at some points in their stride, and leaning or slouching lowers apparent height. |
| Footwear and headwear | Shoes, hats and hairstyles add height that must be estimated and allowed for. |
| Camera angle | High cameras look down on the subject, making the top of the head and the feet harder to locate exactly. |
| Image resolution | Each pixel may cover several centimetres at the subject, which sets a limit on precision. |
| Lens distortion | Uncorrected distortion stretches or compresses the subject, especially near the edges of the frame. |
What is reverse projection?
Reverse projection means recording a known object, such as a measuring pole or a person of known height, from the same camera in the same position. Comparing the new recording with the original footage gives a direct visual measurement.
It is one of the most persuasive methods in court, because the comparison can be seen rather than calculated. It does depend on the camera being in the same position, angle and zoom as when the original footage was recorded, so we ask that the camera is not moved or adjusted before the site visit. Where the camera has changed, we can often still measure from surveyed reference points instead. More on CCTV footage analysis.
Can speed be measured from dashcam footage?
Often, yes. Speed can be calculated from how quickly fixed objects, such as lane markings or poles of known spacing, pass the dashcam vehicle. Where the dashcam records GPS speed, that data can be checked against the video.
Dashcams usually have wide-angle lenses, which need distortion correction, and many record at variable frame rates, so timing must be verified from the file. Embedded GPS speed is useful but not automatically reliable, because it is averaged and can lag behind the vehicle’s actual speed. We compare it with the video-based calculation and report both. More on video forensics.
Instructing us
What to send us, and what you receive
Measurement depends on the footage and on the scene. Please contact us before sending footage so we can arrange a secure transfer.
What to send us
- The original export or native video file, with any player software
- The exact location of the camera and the incident
- Whether the scene or camera has changed since the incident
- The camera make and model, if known
- Photos of the camera’s position and the area it covers
- Which subject, vehicle or event you need measured
- The specific questions you need answered
If the scene has changed, tell us early. Plans, older photos or street imagery can sometimes replace a site visit.
What you receive
An independent expert report, prepared in line with the Expert Witness Code of Conduct, that sets out:
- InstructionsThe questions we were asked to address
- Materials examinedEvery file, with its hash value
- Scene surveyReference points and how they were measured
- Method and calculationsEvery input, so the arithmetic can be checked
- ResultsEach measurement with its margin of error
- LimitationsFactors affecting reliability and interpretation
- ExhibitsAnnotated frames, plan diagrams and reverse projection images
Our process
How a measurement examination works
We tell you whether the footage can be measured before you commit. You receive a written scope and quote before any work begins.
Initial assessment
We review the footage and tell you whether the measurement is possible.
Secure evidence transfer
Encrypted transfer or original media by courier. SHA-256 hash recorded on receipt.
Frame rate and camera checks
Timing verified from the file, and lens and camera geometry established.
Scene survey and analysis
Reference points measured, often on site, then calculations peer reviewed.
Report and testimony
Results with margins of error, diagrams, and court attendance if required.
Simple distance or timing questions can often be answered within days. Speed and height analysis that needs a site visit takes longer, and urgent court deadlines can be accommodated.
See the full process7–30
days to overwrite
Secure the footage and the scene early
Measurements rely on the footage and on the scene staying as it was. Secure a native export now, as many recorders overwrite within 7 to 30 days, and ask that the camera is not moved or adjusted.
Frequently asked questions
Speed, height and distance FAQs
Answers to the questions we are asked most often about measurements from video.
See all FAQsAccuracy depends on the frame rate, the image resolution, the number and quality of reference points and how far the vehicle travels in view. We calculate a margin of error for every result from the uncertainty in each input. Higher frame rates and well-surveyed reference points give the narrowest margins.
Often, yes, for speed and height analysis. A site visit lets us measure reference points and, where possible, record a reverse projection from the same camera. If the scene has changed or cannot be accessed, plans, older photos or street imagery can sometimes be used instead.
Usually, but the result is a range. Walking changes apparent height through each stride, so we measure across several frames and select the most upright positions. Posture, footwear and headwear are allowed for in the stated margin of error.
Sometimes, but it is far less reliable. Filming a screen adds its own distortion and loses the original frame timing, which speed calculations depend on. Wherever possible, obtain the native export from the recorder before the footage is overwritten.
Simple distance or timing questions can often be answered within days. Speed and height analysis that needs a site visit, a reverse projection or several cameras takes longer. We confirm a timeframe in writing before work starts, and urgent court deadlines can be accommodated.
Fees depend on the measurements needed, the number of cameras, whether a site visit or reverse projection is required and whether court attendance is needed. We offer fixed-fee and hourly engagements, and you receive a written quote before any work begins.
Related services
Other video and image forensic services
Measurement matters often raise questions about authenticity, still images or expert evidence. These services are provided by the same team.
Video Forensics
Analysis of CCTV, dashcam, body-worn and phone video.
All video forensic services →
Video Authentication
Testing footage for editing, deleted frames and altered timestamps.
Video authentication →
Digital Image Forensics
Measurement and authentication of photographs and still images.
Digital image forensics →
Expert Witness
Independent expert reports and court testimony on measurements from video.
Expert witness services →
Get expert advice
Find out what your footage can measure
Tell us what the footage shows, what you need measured and any deadlines. We will give you a candid view of what can be established, and how precisely, before you commit to any work.
Freecall
1800 865 190
Hours
Monday to Friday, 9.00 am to 5.30 pm
All enquiries are treated in strict confidence. Please contact us before sending any footage so we can advise on the most appropriate transfer method. If you do share footage with us, always use a secure method to protect the integrity of your evidence.