What kinds of technology are used to create virtual crime scenes?

Image courtesy Silicon Graphics, Inc.

Detectives swarm over the scene of a recent crime, collecting every bit of evidence they can find in order to figure out exactly what took place, who was involved and how the perpetrator did what he or she did. Unfortunately, many crimes take a long time to solve, and it is rare that the scene of a crime will remain undisturbed for the entire length of the investigation. Police need a way of preserving a crime scene so that it is exactly the same every time they return to it. Hand-drawn sketches and photographs can help establish what a crime scene looks like when police arrive, but these two-dimensional media can miss details, and they can also fail to convey the precise dimensions of the scene.

This is where virtual crime scene technology enters the equation. Some police forces around the world have begun to supplement their photographs and sketches with immersive, three-dimensional simulations of crime scenes that are rendered by computers. There are two common types of virtual crime scene creation: photogrammetry, and three-dimensional rendering based on measurements.

In three-dimensional rendering, investigators have to measure the real crime scene's dimensions and the distance between objects, often using a laser distance meter or a surveyor's total station in order to make sure all measurements are exact. Measurement data is fed into a specialized computer program by a trained operator. After some calculation, the program yields a three-dimensional rendering of the crime scene, which the operator can tweak for accuracy and immersive design.

A photogrammetry system uses a stationary tripod to take a comprehensive series of pictures of an area. This is advantageous when it comes to crime scene imaging because there's no need for trained computer programmers or graphic designers: The photogrammetry machine and computer program can automatically assemble a fully realized, 360-degree digital image of a room with very little help from an operator. Plus, the photogrammetry images are actual pictures of the scene and not just representations. The automatic picture-taking system is much more efficient than a human photographer.

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What are the advantages and disadvantages of virtual crime scenes?

Imagine you're a detective - - you've been called in to investigate a shooting that took place inside a small apartment. You examine the situation, interview witnesses, take photographs and collect physical evidence. Eventually, you have to leave the scene and let the apartment's tenants get on with their lives - - but what if you're not through figuring out how the crime took place?

Traditionally, police would create hand-drawn sketches of crime scenes and return to them later. These days, some police have moved towards virtual crime scene technology. Virtual crime scenes are controlled, digital re-creations of existing crime scenes. They're usually rendered with the help of surveying technology and specialized computer software. Some virtual crime scene software packages use physical measurements or building plans to create three-dimensional models of crime scenes, while other programs take photographic evidence in order to create 360-degree visual simulations.

Virtual crime scenes can help investigators revisit real crime scenes long after they've been cleaned up, altered or abandoned. Detectives can use virtual scenes to aid in data visualization - - if a detective needs to check a bullet's trajectory to figure out an attacker's position, he or she can do so within the three-dimensional model. Investigators can also use virtual crime scenes to imagine various scenarios and test theories about how a crime could have been accomplished. Plus, virtual crime scenes are useful for jogging witnesses' memories and testing witness testimony for accuracy. In addition, virtual crime scenes are outstanding training tools for new investigators. In the trial portion of the case, a virtual crime scene can be shown to a jury to illustrate a crime and demonstrate probable scenarios, or to clarify the testimony of a witness.

One of the biggest disadvantages to virtual crime scene technology is that police departments need someone who knows how to work the computer software that creates and displays the virtual crime scene. Even the simplest virtual crime scene programs require the operator to have some amount of expertise in order to create an accurate rendering of the scene and tweak it for exactness. A second disadvantage is that no matter how good the virtually rendered scene is, it is never a perfect copy of the real crime scene.

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