How GNSS with Visual Positioning Makes Scene Investigations Fast and Failproof

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The use of high-precision GNSS RTK technology has a long history in land surveying. In public safety, the technology been used to support quick clearance of traffic incidents, the setting of ground control points for drone use, and efficient documentation of challenging outdoor crime scenes such as the Boston Marathon bombing and a stray-bullet homicide in Washington. Early adopters have highlighted the ability to work much faster than with other scene documentation methods in real-world coordinates with high accuracy.


A point cloud data set captured with the Leica GS18 I GNSS RTK rover.

But there have been some drawbacks—most notably, the need for a clear, unobstructed view to the sky, direct access to the measurement point with the pole tip, avoidance of areas with potential magnetic interference, and adherence to time-consuming leveling procedures. Because of these limitations, total stations remain the predominant scene documentation technology for many agencies.

Innovations such as the integration of inertial measurement unit (IMU) sensors with GNSS eliminate magnetic interference and allow the sensor to be tilted, removing the time-consuming leveling procedure. This development has expanded the use of GNSS RTK technology in public safety within the last couple of years.

Now, a new level of sensor fusion has removed all remaining barriers to using GNSS RTK in scene documentation. With the introduction of visual positioning technology in addition to an IMU in the new Leica GS18 I GNSS RTK rover, you can work even faster, reach previously inaccessible points, and capture points from a safe distance, all with a simple workflow.

Investigating the Real-World Potential of the GS18 I GNSS RTK Rover

Ryan Rezzelle, who served as a CSI and Forensic Specialist for nearly 16 years before stepping in to manage the public safety group for Leica Geosystems, was intrigued by the possibilities of this new technology development. A recognized expert in forensic laser scanning, Rezzelle has scanned hundreds of crime scenes and has experienced the power of a fully digital scene mapping workflow firsthand. “I’m a scanner guy at my core,” he explains. “So when I first started learning about the GS18 I, I wanted to know how the technology works. What are the limits? What are the advantages?”


Ryan Rezzelle with the GS18 I.

To answer these questions, Rezzelle took the new GNSS sensor to a local baseball diamond, a location that would provide a relatable reference. He had two objectives: capture coded points for linework, and capture image sets for measurement.
The first thing he noticed was how quickly he was able to get to work. “When you pull this equipment out, it only takes about a minute to be ready to shoot points and start coding data. There's great value there. The startup time when you get to a scene is amazing.”

Within a few minutes, Rezzelle had walked around the entire field capturing points and image sets—a series of photographs captured with the technology’s innovative visual inertial system (VIS) camera that allowed him to obtain accurate GNSS coordinates from the images on scene or create point clouds in the office.

“I was able to measure from the images right there in real time with the real-world coordinates.” Rezzelle says. “The ability to tilt the rover meant I didn’t have to mind the bubble or make sure my shot was level—coding all my points was really fast.”

“For investigators on a scene,” he explains, “this means increased safety while clearing the scene faster and being able to see that you’ve captured all the data without missing anything. It’s a significant advantage.”


It only took a few minutes for Rezzelle to walk around the entire field capturing points and image sets.

The Real Value of Creating Point Clouds from Images

A key question for Rezzelle, with his background in laser scanning, was what the quality of the point clouds from visual imaging would be. To test this capability, he captured additional image sets around a nearby bus and building and took all the data back to his office. “I was really surprised at how great the point clouds looked,” he says.


The visual positioning capabilities of the GS18 I provide another tool that is highly versatile and can help you visualize the measured points you located on the scene.

This isn’t reality capture, he cautions, and laser scanning is still the standard best practice for comprehensive, fast and accurate data capture on any scene. But the visual positioning capabilities of the GS18 I give you another tool that is highly versatile and can help you visualize the measured points you located on the scene.

“Photogrammetry needs structure and geometry, so it doesn’t capture everything,” Rezzelle explains. “I don’t think I would just export the point cloud and provide that as a deliverable. But it does give you another layer of flexibility for how you capture, measure and ultimately share what you’ve done at any given site. You can measure from that point cloud, but you can also combine it with other datasets, such as orthos from drones or point clouds from laser scanners, to give a complete picture that can be extremely powerful in a courtroom or case file. And all the data is placed accurately to survey-grade measurements within that scene. That’s the real value.”

Cutting On-Scene Time in Half

Within the last several years, advances in GNSS RTK rover technology have overcome many of the previous limitations of using GNSS for scene documentation. Even some of the most basic rovers now have the capability to work reliably in more areas with fast startup times and easy data transfers. The ability to work in rain, snow, and other challenging environmental conditions, as well as in the dark, makes GNSS an attractive solution for investigators.

Add tilt capabilities and visual positioning, and you now have a high-value tool that you can use 95% of the time to quickly capture accurate, complete scene data outdoors. “The startup time from when you arrive to when you're shooting and gathering data is amazingly fast,” Rezzelle says. “You can move quickly through the scene because you don't have to watch the bubble and level the instrument—you just touch the probe and record the point. And then you have the flexibility to capture areas with images that you can’t reach and measure them right there in the data collector or after the fact from point clouds.

“All these capabilities give you amazing flexibility that can reduce your time on scene by 50% or more. With the latest technology advances, GNSS is now an indispensable tool for public safety.”

To talk to a public safety expert who can guide you on the technology that will help your agency maximize efficiency and effectiveness, contact the Leica Geosystems PSG team.

 
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