The X3P file format is simply a container for the efficient transfer of 3D surface topography data. X3P can be used by any system capable of generating or analyzing surface topography data measured in standard units. X3P therefore allows for the exchange of 3D surface topography data between such systems. The X3P format enjoys the following advantages:
- X3P is described in ISO Standard 25178-72, approved in 2017 and amended in 2018.
- X3P was initially developed and supported by the openGPS community to efficiently support surface metrology. The format conforms to ISO 25178 and ISO 25178-72 regarding geometry and XML-based file exchange format. It is therefore a natural fit for the storing and transfer of microscopic surface topographies in firearm and toolmark examination.
- X3P is a non-proprietary file format which can be read or written by any manufacturer or researcher.
- X3P is an efficient means of storing 3D surface topographies that have been measured in standard units. X3P files store data in a binary format and are approximately 10x smaller than a text file version of the same data.
- X3P format contains metrology-specific data including information on the instrument used to collect the data (manufacturer, model, serial number), the hardware's last calibration date, the lab which collected the data, the date on which the data was collected, and the scan sampling resolution.
- X3P contains an internal MD5 hash key which is a validation code for the included surface topography. The MD5 hash allows the recipient of the X3P data to verify that the data has not been corrupted during file transfer.
- X3P format allows for the storing of an unlimited amount of secondary data. That is, manufacturers can store scanner specific details within the X3P format. This feature allows OpenFMC to specify a Firearm Specific meta-data record containing forensic specific details of the contained surface (see below).
- X3P is being adopted by academic, industry, and government labs within the United States and abroad.
- X3P facilities the sharing of data between labs and systems. Successful exchange of data has been demonstrated by several vendors of 3D surface metrology hardware and software. X3P-based data exchange is in routine use within the United States.
- X3P allows time-critical data to be shared between labs. Access is essentially instantaneous. Because X3P is a digital copy, the source lab does not need to worry about potential damage to the source specimen which could occur during transfer or exam. Chain-of-custody documentation is minimized. Multiple labs can examine copies of the same source scan at the same time.
Example X3P Use Case
X3P is a storage container for 3D surface topographies measured in standard units. This data can be exchanged between laboratories using either the same or different 3D scanning systems. The following represents a typical example of X3P data exchange:
- Lab A and B are coordinating on a case in which Lab A has evidence cartridge cases and Lab B has test fires from a suspect's firearm.
- Lab A acquires scans of the evidence cartridge cases using their 3D scanner (Scanner Model X). This scanner measures surfaces at 1.5 micrometers / pixel.
- Lab B collects and scans test fires from the suspect's firearm using their 3D scanner (a different machine, Scanner Model Y, from a different company). Lab B's scanner measures surfaces at 1.9 micrometers / pixel.
- Lab A exports their scan in X3P format. These X3P files contain the measured 3D surface and meta-data regarding the caliber and material of the cartridges cases scanned. Lab A electronically transfers these X3P files to Lab B.
- Lab B imports the received X3P files into their comparison software. They are able to compare the evidence cartridge cases from the crime scene to the test fires from the suspect firearm. The software scales the images appropriately and displays the two surfaces side-by-side. That is, the software accounts for the fact that one system scanned at 1.5 micrometers / pixel while the other system scanned at 1.9 micrometers / pixel. Meta-data for each scan is made available to the examiner.
- Based on lab SOPs and completed validation work, Lab B may decide that they can issue a final conclusion based on the virtual comparison microscopy examination. Alternatively, Lab B may decide that the scanned surfaces are sufficiently similar that it is worth requesting the physical specimens from Lab A for comparison using traditional light comparison microscopy.
Open FMC Data Record
OpenFMC adopted the specification for a firearm specific data record to be included in the X3P data file. The use of a common agreed-upon format for this firearm specific data record is an important component of data exchange within the discipline. The OpenFMC record contains four sections.
- Admin : The admin section contains details about the originating agency, lab name, and type of data.
- Firearm : The firearm record contains details about the firearm serial number, item number, brand, model, and caliber
- Cartridge Case : The cartridge case section includes information such as ammunition brand, caliber, primer and casing material, firing pin class, breech face class, and regions of interest
- Bullet : The bullet section includes information such as ammunition brand, number of lands, twist direction, caliber, weight, material, LEA or GEA number, and scanning rotation direction