“There are people who look at a point cloud and
say they can’t see the details,” Green said. “That
is usually because it wasn’t scanned or processed
correctly. We want to avoid the trap of not seeing the
evidence for the cloud. We do not want just a huge
cloud; we want better management of the cloud.”
The solution comes from integrating the processes,
from collection through final reports.
That integration begins in the field, where WSP
uses a Trimble TX5 scanner. The scanner simplifies
the work for scene investigators by providing preset
scanning modes that capture data at different levels of
resolution. Green has developed guidelines for WSP
investigators that recommend the appropriate mode
for capturing different types of details and evidence.
“We like the presets,” he said, “because we can
teach our people what mode to use in a given situ-
ation without having to calculate resolution. [For
example,] I might need to capture shell casings or faint
tire marks; for that we might scan at high resolutions.
But for other setups we can run at lower resolution,
which is much faster.”
Data from the scanner goes to the office, where
detectives use Trimble Real Works software to com-
bine the scans and begin analyzing the scenes. The
software can use “plane-based” and “cloud to cloud“
registration to merge multiple scans—the technique
helps reduce the need for on-scene investigators to
handle the spherical targets commonly used in many
scanning projects. Although target spheres are needed
in some situations, Green said the plane-based and
cloud to cloud approach is much simpler and faster
for field investigators—so much so, it’s become the
Eliminating the targets is just one way the software
component of the integrated system helps make the
job of on-site personnel and office faster and easier.
For example, even when working at low resolution the
scanner may collect thousands of points on a road—
far more than needed to correctly depict the surface.
The software can reduce the density of the points
to preserve the accuracy of the information while
eliminating clutter that could potentially distract or
confuse a jury.
As soon as the main point cloud is in place, the office starts creating reports and diagrams. Using reconstruction software, Green can draft maps and models
in 3-D. Points that are superfluous or irrelevant to the
case can be moved to separate layers that are switched
off, but are still preserved to meet the essential chain
of evidence requirement and maintain integrity of the
scene’s data. When the point clouds are completed,
the clouds and analyses can be supplied to prosecution
Investigators can add evidence markers, vehicle
models, trajectories and more—the software can
even simulate how cars are crushed in a collision.
The information can be used to produce diagrams
and animations for courtroom presentations or can
be sent for specialized analysis. The result is a concise
representation of the scene and events—all backed by
detailed, defensible data.
One of scanning’s most valuable features is the
ability to preserve a scene while it is fresh so officers
can “virtually” revisit it after the fact. For example, an
object not deemed pertinent early in an investigation
may turn out to be important. By using the point
cloud, investigators can return to the virtual scene at
any time. They can use the virtual return visits to extract or confirm details on the object and its location
long after the on-scene events and investigation.
What’s key to Green’s success is his understanding
of what goes on at the scene and beyond. By using a
holistic approach to reconstruction data collection
and analysis, he is helping to simplify the work of
officers in the field as well as in the office. The result is
faster, safer work with better results. ●
Chad McFadden is the Forensics Business Area Manager
for the Geospatial Division of Trimble, Inc. He has over
20 years’ experience in Land Surveying and GIS projects,
including field, office and business development.
An example of a point cloud of a collision scene. Parasite
images of troopers are caused as they move through the
scene during scanning.