Below we present an ad posted by FARO wherein a laser cloud scanner was used simply to present pictures of a crash. It included an incomplete crash reconstruction which apparently a driver agreed was OK.
- Our summary, which is also repeated below is:
- Laser Cloud Scan Devices for crash reconstruction by
and others are excellent for memorializing and presenting crash scene data and vehicle crush measurements.
However- As scientists, engineers and accident reconstructionists, we should not let the impressive presentation abilities of data from these scanners obscure our duty to perform a careful and detailed engineering analysis while also continually testing and evaluating the applied techniques, including computer programs, to achieve the most accurate reconstruction possible
- Laser Cloud Scan Devices for crash reconstruction by
and others are excellent for memorializing and presenting crash scene data and vehicle crush measurements.
FARO AD PRESENTATION:
- Saw a post on Linkedin Today on FARO's Linkedin Page which included:
- "Calling all #TrueCrime and #ForensicScience fans: If all evidence from a fatal crash scene pointed to one driver being at fault, but the second driver had a very different story to tell...who would you believe?"
- "In our case study, one forensic scientist decided to use FARO technology to solve the mystery. Find out the twist ending: https://bddy.me/34Ok7tv
With a link to FARO web page Modern Day Scherlock Holmes 3D Scanning Meets Forensic Science
That page includes a link to a PDF report
which includes the following additional quotes:- "At the scene of the accident, Survivor B’s car ended up on the wrong side of the road, facing oncoming traffic, while Party A’s car remained in its lane. The traffic police determined that Survivor B’s husband, who was driving at the time, should bear full responsibility for the accident.
- "The 3D point cloud data enabled Prof Zhao to obtain accurate measurements and perform a precise deformation analysis on a computer. "
- "Using the software, Prof Zhao found the positions of the two vehicles prior to the collision by pulling them apart. With this, the positional changes between the two cars (prior and after collision) were reconstructed. By substituting the trace data on the ground, Prof Zhao placed both vehicles in their relative positions.
- "Taking the collision point as the center, and calculating with an equation, he deduced that the intersection angle for the collision was 16 degrees."
Which included the following quote:
- "In our case study, one forensic scientist decided to use FARO technology to solve the mystery. Find out the twist ending: https://bddy.me/34Ok7tv
- "Calling all #TrueCrime and #ForensicScience fans: If all evidence from a fatal crash scene pointed to one driver being at fault, but the second driver had a very different story to tell...who would you believe?"
- Apparently the 'driver' of the adverse vehicle "agreed with Prof Zhao’s "deduction" that it was indeed the truth of what happened"
- We wonder if the driver 'agreed' or simply didn't know due to injuries, etc and once presented with the impressive scientific looking graphics felt they had no choice but to agree.
- The analysis MAY have been correct, HOWEVER it may have been WRONG...
- We find reprehensible that any crash analyst would use ONLY A SINGLE EQUATION to reconstruct a crash.
Also shocked that an international company, FARO, would irresponsibly ADVERTISE THIS BLATANT INCOMPETENCE!!!
- No doubt some variation of a 'instantaneous momentum exchange' simplification which is an elementary and crude when applied as a SINGLE 'equation'
- I guess WE need to add another Beginners Error#1 in Crash Reconstruction 101 and state:
- USE MORE THAN A SINGLE ELEMENTARY EQUATION TO PERFORM A PROFESSIONAL RECONSTRUCTION!
- DO a sensitivity study! Vary some of the simplifying assumptions!
But no...he only did ONE EQUATION!
Zhao must have know that no competent crash reconstruction analyst was going to review his sloppy work!
THAT is simply unacceptable - I guess WE need to add another Beginners Error#1 in Crash Reconstruction 101 and state:
Fancy Graphics and Bluster many times mask inappropriate and incomplete collision investigations and analyses.
- Cloud scan technology is amazing and being used in crash reconstruction to create great demonstrative documentation of crash scene details and vehicle damage details....however as with any new technology one must be careful to not let the 'pretty pictures' obscure the duty to fully and completely investigate and reconstruct a crash...
- What is the singular "equation" Zhao used?
- No doubt a simplified momentum analysis which assumes "instantaneous momentum exchange" which sometimes is OK,but can be a problem as it is EASY to GET ANY RESULT WITH SOME IMPACT CONFIGURATIONS, LIKE WRONG SIDE OF ROAD TYPE QUESTIONS. (see below for links)
- What is the "precise deformation analysis on a computer"
- A damage analysis of some sort? That would indicate more than one equation was used and many assumptions (what did he assume for each vehicle's stiffness characteristics? etc.)
- We have a Forum section on Damage Analysis which presents and discusses the limitations and preliminary characteristics of all CRASH type damage analysis procedures.
- Given the ad includes the statement that he used a 'single equation' one must conclude that NO DAMAGE ANALYSIS was performed except a geometric manual analysis.
- He visually and arbitrarily "pulling the vehicles apart" at some random rate and angle "on the computer" which is merely a fancy way to pretend there was some scientific calculation procedure aka "computer method" behind what he did to determine the approximate impact positions and orientations.
- To scientifically 'pull the vehicles apart" is a much more complicated process than that.
- He got lucky or the driver didn't know and so simply agreed with his determination.
- The paper does not present any scaled roadway evidence such as tire marks, debris, etc from which others might be able to check his work.
- A damage analysis of some sort? That would indicate more than one equation was used and many assumptions (what did he assume for each vehicle's stiffness characteristics? etc.)
For example:- Zhao's "deduced intersection angle for the collision of 16 degrees" is rather high.
Did he perform any analysis to determine whether and how the 16 degrees was created?- Using a program like SMAC which actually mathematically models the forces and moments of the collision interaction as they happen over 50-150 ms of the collision.
The SMAC program can also be used to model the pre-impact movement which might have allowed Zhao to determine if the 16 degrees was possible- He should have determined as a minimum how much lateral distance was required to create 16 degrees with something like the Barrier impact angle Equation.
16 degrees is a HIGH angle to produce in a single maneuver in the lateral space available.- Note that the ability of a vehicle to change its direction of motion is dependent upon its forward speed, the utilized roadway friction and the lateral space available for the maneuver. Were any pre-impact tire marks documented? where relative to the center of each lane was the approximate collision area? And relative to that where did the vehicles come to rest?
- He should have determined as a minimum how much lateral distance was required to create 16 degrees with something like the Barrier impact angle Equation.
- Using a program like SMAC which actually mathematically models the forces and moments of the collision interaction as they happen over 50-150 ms of the collision.
Programs like PC-CRASH, Virtual Crash, Planar Impact Models, and others:
- There are many great programs out there with amazing options/graphics.
This is just a word of warning to be very careful as momentum and momentum crash simulation programs include the simplifying assumption of an 'instantaneous exchange of momentum' which requires the user select a subjective 'point and angle' for that instantaneous exchange (begs question: Why isn't it automatic?)
These programs are useful however they can be very sensitive in many impact configurations. CHECK FOR SENSITIVITIES IN RESULTS!
Here are some related articles:
- Some Momentum Misconceptions
- PC-CRASH: How Many % May An Investigator Be Wrong with pc-crash? response to a question posed on another forum
- More Discussion on PC-CRASH type simplified momentum solutions review of a $100 pc-crash training video
- Does Momentum Analysis Requires COM Common Velocity? Some alleged 'experts' run fast and loose with science
- Planar Impact Model assumptions planar impact models have issues with simplifying assumptions and subjective inputs
- What is the singular "equation" Zhao used?
- Laser Cloud Scan Devices for crash reconstruction by
and others are excellent for memorializing and presenting crash scene data and vehicle crush information.
However- As scientists, engineers and accident reconstructionists, we should not let the impressive presentation abilities of data from these scanners obscure our duty to perform a careful and detailed engineering analysis while also continually testing and evaluating the applied techniques, including computer programs, to achieve the most accurate reconstruction possible
- As scientists, engineers and accident reconstructionists, we should not let the impressive presentation abilities of data from these scanners obscure our duty to perform a careful and detailed engineering analysis while also continually testing and evaluating the applied techniques, including computer programs, to achieve the most accurate reconstruction possible
Here are items from the PDF report by Zhao: - No doubt some variation of a 'instantaneous momentum exchange' simplification which is an elementary and crude when applied as a SINGLE 'equation'
- We find reprehensible that any crash analyst would use ONLY A SINGLE EQUATION to reconstruct a crash.