- by Brian McHenry, originally created 2009, last updated 07/01/2013
Also available on the McHenry Software website
- Background,m-hvosm,PC-CRASH,HVE, WHAT YOU NEED to Evaluate an 3-D reconstruction/animation
Background
- Today, on a PC or MAC laptop or desktop, anyone can easily and affordably make 3-Dimensional animations which can rival Hollywood's best. See Lightwave for THE state-of-the art animation software all for less than $2500 (see our News! page for more information). And with this newfound capability, it is very easy to make anything imagined look very realistic.
For example, a sample application which is included with the Lightwave animation program is how to make a cow fly! By following the example, anyone can create an animation of a cow flying. And very quickly and easily someone could create a very realistic animation such that upon viewing the animation you might believe that cows do indeed fly! So now let's say there is a court hearing to determine whether cow's fly. And at the court, an expert with an advanced degree from an esteemed university and years of experience testifies that 'cows can fly!' and as part of the testimony the expert offers a video to prove it! Well everyone know that cows don't fly, yet, when the expert, impressive in his academic credentials, counters that argument and supplements it with a realistic animation of a cow flying, the jury may be swayed to believe something that is obviously not true. [attachment=1]pigsfly.gif[/attachment]- (Please look at Youtube video of ad with pigs flying for Time Warner Cable. It includes images of realistic looking Pigs flying! The above example could have also been for flying pigs!)
In the field of accident reconstruction there is an increasing use (and abuse) of animation techniques for demonstrative evidence purposes. So you may find yourself, either as an expert or attorney, being faced with a reconstruction which is supplemented with a 3-Dimensional animation. Or perhaps you are an expert who would like to add a 3-Dimensional reconstruction capability to your tool chest.
This page and links are being created to assist interested parties in evaluation of the existing "3-Dimensional" software. With this page we will explain the origins, capabilities and limitations of programs which are available which claim '3-D' analysis and/or simulation'.
- The HVOSM mathematical model consists of up to 15 degrees of freedom; 6 for the sprung-mass, and up to 9 for the unsprung-masses. The mathematical model is based on fundamental laws of physics (i.e., Newtonian dynamics of rigid bodies) combined with empirical relationships derived from experimental test data (i.e., tire and suspension characteristics, load deflection properties of the vehicle structure). The balance of forces occurring within and applied to components of the system are defined in the form of a set of differential equations which constitute the mathematical model of the system. The HVOSM includes the general three-dimensional motions resulting from vehicle control inputs, traversals of terrain irregularities and collisions with certain types of roadside obstacles.
In addition to the substantial effort in validation of the mathematical model, the HVOSMwas also uniquely tested by designing an automobile stunt which was used both in a traveling auto-stunt thrill show and in the 1974 James Bond Movie, “Man with the Golden Gun” produced by United Artists Corporation. [attachment=0]spiral computer v live 50pct.gif[/attachment] For additional discussion on research performed by the McHenrys on HVOSM, Please also see the following:- "Simulation Models of Vehicle Dynamics", B.G. McHenry, This paper contains a summary of some of the research and development McHenry Consultants, Inc has performed with the HVOSM computer program. presented November 1987, National Conference on Future Improvements to and Supplemental Guidance for AASHTO Policy on Geometric Design of Highways and Streets; Published April 1992, Transportation Research Board Circular "Beyond the Green Book".
- "HVOSM-87", SAE Technical Paper No. 880228, This paper contains research McHenry Consultants, Inc performed on Concrete Median Barrier (CMB) simulations. Presented at the International Congress and Exposition, Detroit, Michigan, March 1988 B.G. McHenry, R. R. McHenry
PC-CRASH
- PC-CRASH is a momentum based collision reconstruction program
- 3-D - The limitations and sensitivities of 2-D PC-CRASH are dramatically increased and compounded when applied to 3-D.
- Multi-Body Option -A multi-body ability was added to PC-CRASH for use in pedestrian/vehicle impacts and simulations. (The multi-body option appears to be basically the ATB program). For more information on limitations of ATB and any occupant simulation models, please see "Occupant Kinematics in Forensics: Evaluating the Appropriateness and Applicability of an ATB Application".
- MADYMO -A 'starter version' of the MADYMO program has been added as an option. MADYMO is a research tool and is subject to the same limitations as ATB for occupant kinematics in accident reconstruction. Please see "Occupant Kinematics in Forensics: Evaluating the Appropriateness and Applicability of an ATB Application".
- Kinematics Calculations - PC-CRASH also includes the ability to create Post-impact, Pre-impact and Acceleration/Braking sequences. These sequences 'can be used for the simulation' (from user manual). Therefore a careful analysis of any animation created with PC-CRASH should include the determination of whether the kinematics calculation option was used.
- Cost: From ~$2500 (2D) to ~$4000 (3-D) with an additional ~$3000 for the MADYMO option.
- One company which markets a '3-D Reconstruction and Simulation' package is the Engineering Dynamics Corp (EDC). What they originally marketed was basically a 'value-added' SGI graphics hardware and software package. SGI is Silicon Graphics which is an industry leader in 3-D computer graphics which require dedicated graphics systems. With the advent of Pentium PC's, the need for SGI workstations diminished and Lightwave for the PC provides a low-cost state-of-the art capability all for less than $2500. In 2001, EDC began marketing a Windows based version of their HVE.
The HVE has the following components:
- HVE SMAC = EDSMAC = NHTSA SMAC, circa 1974, (see SAE paper 97-0947 and SMAC-type programs for some related discussion.) EDC also refers to their use of EDSMAC in the HVE environment as '2.5-D' because the vehicles can 'drive on and respond to 3-D surfaces' however they 'do not include degrees of freedom for roll, pitch or Z'.
- EDSMAC4 - EDC claims "more realistic modeling of actual vehicle structural behavior" based on "an A, B stiffness model"?! The "A, B stiffness model" is a "virtual" model equating residual crush to dissipated kinetic energy. The "A, B stiffness model" is not a dynamic model. EDC also mentions that their new model requires a "threshold force to be applied before deformation begins". How is there a force with no deformation? There may be a force without leaving any residual deformation, but there is dynamic deformation. For additional information on EDSMAC4 please see our recent SAE TOPTEC presentation. Please also see our paper Effects of Restitution in the Application of Crush Coefficients, SAE Paper 97-0960 for proposed refinements to the CRASH and SMAC collision models.
- EDVSM = (a subset of) HVOSM 1976 VD2, (see our discussion on HVOSM for references to some extensive research and development that has been performed in the past 20 years on HVOSM, most of which is not included in the EDVSM.).
- PHASE4 - The Transportation Research Institute (formerly the Highway Safety Research Institute) of the University of Michigan (UMTRI) conducted research under the sponsorship of the MVMA and the FHWA to develop a means of predicting and evaluating the directional response characteristics of trucks, tractor-semi trailers, tractor-trailers and triples. In 1980, UMTRI released the PHASE4 program which constitutes a compilation and consolidation of nearly a decade of development of the existing models into a single program. The PHASE4 program includes small angle assumptions. The use of 'small angle assumptions' is a process for simulation models wherein many equations can be simplified and/or eliminated by the assumption that the program will remain in small angles (angles smaller than 10-15 degrees, wherein the angle in radians can be used to roughly approximate the trigonometric functions (sine, cosine, etc.)). EDC incorporated PHASE4 into the HVE and in a SAE paper 1999-01-0103 they announced (on page 4) that "The equations of motion were rewritten and extended to allow complete 3-dimensional motion. The small angle assumption was eliminated". They have provided no other documentation of the procedure they used to 'rewrite and extend' the PHASE4 program to eliminate the small angle assumptions (one has to wonder if it was so simple why did UMTRI use small angle assumptions?!!) Obviously any analyses wherein the HVE PHASE4 is used should to be carefully evaluated.
- GATB - They have added a version of ATB to the HVE environment. For information on limitations of ATB and any occupant simulation models, please see "Occupant Kinematics in Forensics: Evaluating the Appropriateness and Applicability of an ATB Application".
- SIMON - Apparently in a an attempt to establish a single package encompassing all the elements of the HVE, EDC now has merged all the various programs into a single package called SIMON. An unfortunate side effect of the new marketing strategy is that it will further blur and obscure the path for their users to the origins, documentation and validations of the various programs they repackage and market.
- EDGEN - The HVE also includes EDGEN, a '3-Dimensional kinematics spreadsheet' which provides the ability to graphically use spline fits to arbitrarily change the movement of any vehicle being 'simulated'. This means that any 'simulation' and 'animation' created with HVE or SIMON may also include arbitrary changes in the simulated movements and/or arbitrary changes added onto the simulated movements (e.g., for most vehicle rollovers, most or all of the rollover event will probably be created with the SPINE FIT option. Therefore a careful analysis of any animation created with HVE or SIMON should include the determination of whether EDGEN was used.
- Cost: The HVE and/or SIMON system costs between ~$3000 (2-D) up to ~$20,000, depending on options, etc.
- If you are faced with someone using one of these tools (or others), what do you need to evaluate what they have done? These programs cost from ~$3000 up to ~$20,000, so to facilitate the evaluation of an application of any of these programs, you need to obtain complete documentation of the analysis procedure.
- Request complete inputs and outputs for any and all computer programs used
- Printed and in computer form (CD or diskette). (Printed output pages can be saved as text files and copied to a CD to save paper)
- Most of the programs include options for outputs. The outputs should be set with ALL OPTIONS ON to obtain all the outputs and time history data, etc.
- Request the program version, an indication of any add-ons or options used, etc.
- If a video created, request all the files used to create the video: CAD files, Animation files, spreadsheet files, any and all notes, etc.
- Some papers and links written on the subject:
- SAE paper number 1999-01-0101 "Computer–Generated Trial Exhibits: A Post- Daubert Update"
- SAE paper number 940920 "Case Studies in Animation Foundation"
- SAE paper number 980018, "Documenting Scientific Visualizations and Computer Animations used in Collision Reconstruction Presentations" which includes as the Summary:
- "This paper has presented a proposed standard for documenting computer generated images, animations, scientific visualizations, etc. The basic standard is that any still images or videos should be documented such that any qualified analyst can reproduce them. This is the requirement for the scientific community in general and should be adopted in the accident reconstruction community. It is important to note that this standard does not refer to any method of generating these images or videos. There is no implication that any one method or any one program is superior to others. This standard addresses only the images and videos and does not address the analysis or opinions being expressed by an analyst. However, the only way to fully understand the analysis being presented or discussed is to have the ability to duplicate the images or video being presented"