If you are new to 3D laser scanning you will likely soon find yourself exposed to lots of new and unfamiliar terminology. In general, 3D laser scanner manufacturers are notorious for throwing lots of new and sometimes confusing terminology at you, the consumer.
Take the term “accuracy”. You might think that it is an easy thing to compare the accuracy of one manufacturer’s laser scanner to another’s. You would be wrong because most manufacturers don’t publish the accuracy of their 3D laser scanner. (Leica does, but we think you probably guessed that by now. Our accuracy out to a 50m range is either 3mm or 6mm depending on the model of ScanStation.) The thing about the word accuracy is that it is unambiguous. Accuracy means accuracy. You can define it at one sigma or two, or use the GUM definition but at the end of the day it will be defined.
In looking over other vendor’s performance specifications (and you must look there and not at the marketing fluff) you will find impressive sounding terms like “ranging noise” and “ranging error” with values shown that seem very small, but they don’t tell you anything about the accuracy of the laser scanner. Only stating the distance accuracy is another popular way of avoiding stating the 3D positional accuracy. It is after all a 3D laser scanner.
Imagine yourself shopping for a blood alcohol content measuring device for your agency and you live in a state where the difference between a driver blowing .07 versus .08 is the difference between going to jail or not. You’d probably be pretty interested in knowing how accurate that device was before purchasing it, wouldn’t you?
Now imagine yourself at an evidentiary hearing in court for the first time a year or two down the road after purchasing a 3D laser scanner from a manufacturer that doesn’t tell you (publish) how accurate their laser scanner is. Don’t you kind of expect to get asked that key question? Doesn’t Daubert require that the trier of fact be educated on the known or potential error rate?
Shouldn’t this give you pause?
When you choose the Leica ScanStation you are getting a very accurate instrument from an almost 200 year old company that has been in the business of producing accurate instruments for generations. We understand the importance and we clearly publish our accuracy and we explicitly state that this accuracy is achieved under all operating conditions (meaning we don’t change our specs because the sun came out).
This is another one of those issues that you need to decide how important it is to you as you select a vendor because all 3D laser scan data is not created equal. There are many stakeholders who will be impacted by your decision. One of them is your prosecutor’s office.
Validation studies are an important part of deploying 3D laser scanning in the post-NAS report ISO world and this section covers some of the work done in this area with the Leica ScanStation.
The California Department of Transportation (CalTrans) in conjunction with the University of California at Davis undertook a comparison of the major 3D laser Scanners available and issued a report in June 2007 detailing their testing and their conclusions. The Leica Laser Scanner tested was the ScanStation and the report concluded that the Leica system exhibited the highest elevation and range accuracy of all scanners evaluated. After this study was concluded and the report created, CalTrans purchased a significant number of Leica ScanStation systems (five) where they continue to be deployed to large construction projects and mapping projects. Projects such as the new San Francisco-Oakland Bay Bridge with very demanding accuracy requirements in challenging conditions.
This UC Davis report is regularly cited as an example of a peer-reviewed white paper which clearly establishes the accuracy of the Leica ScanStation. It is just one example of the many documents we frequently provide to prosecutors who are preparing to go to court with Leica scan data for the first time. We are happy to provide it to defense attorneys as well because we are all about finding the truth.
Download: White Paper
Validation for Shooting Reconstruction
Leica Geosystems developed our shooting reconstruction software tools and best practices by working closely with the Albuquerque Police Department Crime Laboratory which is accredited to ISO/IEC 17025:2005 under the ASCLD/LAB-International Supplemental Requirements for Testing Laboratories (2011).
Mike Haag is the Physical Unit Supervisor for the lab who assisted us with our development and then validated it as being at least as accurate as manual methods. He is a Distinguished Member of the Association of Firearm and Tool Mark Examiners (AFTE) and past Member of the Year, and one of the few in the field to hold AFTE certifications in all three areas offered: firearm examination and identification, tool mark examination and identification, and gunshot residue / distance determination.
He is the author of “Shooting Incident Reconstruction” and he regularly teaches classes in the use of the Leica ScanStation for bullet path reconstruction, including at our annual Hexagon Conference.
AFTE Article: “The Accuracy and Precision of Trajectory Measurements”
Video: Mike Haag discusses trial methodology
Mike Haag is a forensic scientist with the Albuquerque Police Department’s Crime Laboratory where he is the Physical Identification Unit Supervisor. This includes the supervision of the Firearms and Tool Marks section of the lab where he encourages his team to undertake controlled scientific experiments to advance the greater understanding of forensic science.
In the fall of 2011 Mike and his team put together a plan for a series of experiments involving using the Leica ScanStation C10 to document bullet deflections based upon several variables. In this video he describes his methodology. Click on the link above to watch the video.