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Forensic tec midterm
forensic tec midterm
| Question | Answer |
|---|---|
| legal considerations for the use of Lidar in criminal justice | user must be qualified, data gathered must be verified, peer reviewed, if used as reconstruction judge must admit as expert evidence |
| legal considerations for new technology, A Judge will decide if demonstrative evidence is admissible based on: | o Relevance of the demonstrative evidence to the issue o Accuracy in representing the facts o Fairness and absence of any intention to be mislead (unbiased) o Verification on oath by user Prejudicial effect does not outweigh probative value |
| precision describes | how well the performance of the device can be replicated |
| The accuracy of a measuring device or technique describes | how close the reported distance is to the true absolute distance |
| sources of tech error | improper calibration, malfunction, damage |
| source human error | Improper communication • Reported the wrong number • Skipped a measurement • Combined technologies |
| MINIMIZING ERROR – AT THE OFFICE | • Before leaving complete a mini-calibration check, Use standard distance (height of door frame, width of a hallway) Measure with multiple measuring device (especially if using digital devices), Ensure that all measuring devices are in the same units |
| MINIMIZING ERROR RATES AT THE SCENE Ensure that: | sufficient scans are taken to locate significant item structures, Use Targets for registration, Use a Scan Plan for reference, Ensure there is a reference measurement |
| If an error is found in your datasets | you must identify it, record it, and if possible, re-measure / re-scan. |
| LASER SCANNING | Process of capturing millions of data points (to create a point cloud), which produces an unbiased virtual replica of the scene |
| Data sets can then be used to produce: | • 3D models • Maps • Analysis and Reconstructions (shooting, Traffic, Bloodstain Pattern) |
| LASERS | Light amplification by stimulated emission of electromagnetic radiation |
| Various light sources ca be used as the basis of the laser for LiDAR | • Infrared – Does not interfere with other sensors (cameras, human eye), narrow emission width • Green Light – underwater LiDAR – reduction of scatter (less noise), penetrates further |
| LiDAR | light detection and ranging |
| Lidar works by | Pulsed light emitted, calculating distance either by Time of Flight or Phase Shift calculation |
| data captured by | Laser pulses emitted, collection millions of‘points’ per revolution. Laser is emitted on a 270 ° revolution on axis, while also rotating 360°. As pulse emits, the return is calculated by either time of flight, or phase shift calculations. |
| Phase shift | has a higher accuracy in determining distance than time of flight |
| Each scan is | its own entity that then gets ‘stitched’ together at the end. Panoramic photos are applied to each scan independent of the laser scan data collected |
| Scan plan | • Create a sketch with rough positioning of your scanner • Allows you to visualize what your blind spots will be • Acts as a verification that all areas will be covered • Can always modify ‘the scan plan |
| covering your blind spots | 360 coverage • Blind spot diameter below = the height of the machine • Ensure that you’re covering your blind spots • Different heights might be required to fully capture the scene |
| Quality and resolution | Detail of photo capture – increased quality reduces noise, takes longer • Points collected (resolution) • Overall scene, blood spatter, shooting reconstruction |
| setting up the scene | set up targets, recognize if there are reflective surfaces |
| Targets are specifically calibrated by companies for software to | ‘lock-in’ and recognize a unique feature • Help provide unique features that allow for the ‘stitching’ of scans together. • Not always required for indoor scenes, ideal for outdoor scence |
| back at the office | processing, registration, post processing, court deliverables |
| back at office | Decontaminate equipment • Back-up files • Review Data • Process • Register • Verify Data • Create Court Deliverables |
| Processing Scans | • Setting up the software to create initial data parameters • Stray Point Filters • Distance Filters “To infinity and beyond” • Target Identification • Edge Artifact Filter |
| Registering Scans | • Stitching the scans together • Top – Down / Cloud to Cloud • Geometric Referencing • Target Based Registration |
| post processing and registration | Clean Up • Review Registration results • Remove false rooms created by mirrored surfaces • Add a “Clipping Box” to isolate scene • Apply additional filters • Moving Object Filter |
| create court deliverables | Plan Drawings • Maps • 3D Models • Scene to GO • Fly Through Videos • Project Integrations • Eyewitness Perspective • Photogrammetry • Suspect Height Analysis |
| Tripod-Mounted Scanners: | High-precision, long-range, durable, ideal for accurate measurements in critical scenes |
| SLAM Scanners: | Portable, field-based devices for large- scale data capture, less focused on high accuracy. |
| Handheld Scanners: | Compact, short-range (<2m), ideal for detailed measurements in small areas. |
| Even though the system is self calibrating | it still requires to be sent in for calibration. • Nonetheless follow the manufactures recommend calibration policy for your instrument |
| Periodic Calibration Verification | If possible, check your, equipment for accuracy before you leave the office. Cross reference your measurements with known references |
| Operator | Captures TLS data suitable for specific analysis, Selects appropriate settings and placement • Qualified to testify on instrument operation and data capture methods. • Maintains instrument and ensures calibration at regular intervals |
| Operator Training Requirements | Must complete a manufacturer prescribed training course, Demonstrate competency in TLS instrument operation. Ex # of training exercises, assessments • Participate in ongoing proficiency testing as part of a quality assurance program 12 |
| Technologist | Has Operator qualifications + additional expertise. Processes TLS data with software. Integrates TLS data with other data sources to create demonstrative exhibits with measurements. • Qualified to testify on software use and data processing method |
| technologist training requirements | operator training + additional training in non-TLS device Demonstrate competency integrating TLS and non-TLS data sources. Software training. Produce demonstrable renderings of scenes. Ongoing proficiency testing in: Instrument operation Software usage. |
| Analyst | Possesses Technologist qualifications plus additional expertise. • Conducts forensic analysis and creates reconstructions from TLS data. • Provides expert opinions and explanations of reconstruction methodologies |
| analyst training requirements | • In addition to the Operator and Technologist Training Requirements • Specialized forensic analysis training related to drawing conclusions from data |
| proficiency testing | operators, techs and analysts are recommended yearly testing based on their role, should be represented on casework where results are known and monitor by someone of the same or higher level, results should be maintained yearly and stored with the agency |
| TLS used for | Critical measurements: that require a high level of accuracy i.e. bloodstain pattern analysis, crush analysis and trajectory analysis. |
| TLS used for | General Analysis: used to take overall measurements where a rigorous level of accuracy is not required. |
| TLS used for | Demonstrative Use: measurements are not primary consideration, the data is used to display the crime scene. |
| scanning should be done | after Photos have been taken • The evidence markers have been placed § Evidence can be picked up prior to scanning to prioritize integrity. |
| Scene environment will be a factor dependent on | • Lighting, • Limited space, • Rain, • Fog • and other weather conditions will all dictate scan settings |
| Reflective objects | can produce artifacts due to reflection or refraction |
| how to prep reflective surfaces | A large mirror covered by paper. • Covering a reflective surface with fingerprint powder, aerosol deodorant that contains baking soda and dry shampoo |
| if altering scene for reflective surface | take photos and notes first |
| scenes that require precise measurements | require higher resolution |
| Measurement precision error increases | when the angle between the laser beam and the surface is small (beam is less perpendicular |
| Measurement error decreases when | the laser beam is more perpendicular to the surface |
| Point spacing: | the distance between individual points in the point cloud |
| Critical Measurements: | Point spacing should generally be between 1–3 mm at the location of measurement |
| General Indoor Analysis: | Point spacing should be less than 3 cm at the measurement location. |
| General Outdoor Scenes: | Point spacing should not exceed 15 cm at the reference point |
| Scanner Settings: | Operators must ensure point spacing aligns with or exceeds the manufacturer’s guidelines |
Created by:
skyep25