Thursday, April 21, 2011

No Place for Survey Crews

Earlier this year, we were tasked to perform a Mobile LiDAR collection of an Interstate tunnel (2 lanes in each direction - measuring 0.8 miles in length).  The tunnel is in a heavily trafficked urban corridor where closures required by traditional surveying, even in the early morning hours, were completely out of the question.

Due to the constant, unrelenting traffic, we performed the collection shortly after midnight.  We collected each of the 4 travel lanes at or slightly below posted speed limits - slowing down or speeding up to minimize laser shadows from other vehicles.  Following the collection, our LiDAR processing staff and Applied Technology Group produced the final products.

First, our LiDAR processing staff adjusted the passes to ensure coincidence.  Then they made quick work of removing other vehicles from the point cloud.  Then, they turned over the tiled point clouds for modeling.

An image of the point cloud with vehicles removed, but tractor trailer model added.  Notice the pothole in the bottom left hand corner of the image. 

Our Applied Technology Group utilized the cleaned point cloud to create a rendering of the tunnel in MicroStation.
In the article I wrote for LiDAR News last week I made the statement "if you can’t see it, the system isn’t measuring it." The below image is directly disputing that statement - which I don't quite mind in this case.  

The image shows a cross-section of the tunnel.  Notice the arc above the "box" tunnel.  The arc represents returns from the actual tunnel ceiling (extent of bore) that were measured through small (1") joints in the false ceiling.
Perhaps what is most fascinating to me is not that the system captured this information, but how it will be exploited by our client.

Cheers!
Stephen

Monday, April 18, 2011

Knowing your Limitations

I have recently prepared another article for LiDAR News titled Knowing your Limitations.  Understanding what a technology does not do is equally, if not more, important than understanding what it does do.  Where those limitations can affect the successful outcome of a project, other methods, tools or techniques are needed to compensate.  The article addresses some of the larger topics.  In upcoming posts, I'll provide additional items to consider when pursuing a Mobile LiDAR project.

The images presented in the article are shown below with captions:

Manholes:  In a span of 40' along a roadway, there are 6 manholes and two water valves.

Grass on Bare-Earth/DEM:  A random non-Federal levee shows the difficulty dense vegetation adds to determine bare earth along the bank.

Obscured Areas:  The area behind two parallel parked cars is obscured in comparison to the open area between them.  The shape of the voids depicted, represents the orientation of the lasers and varies based upon heading.
As always, please let me know if there are any topics you would like to see discussed.

Cheers!
Stephen

What is Mobile LiDAR?

Mobile LiDAR (Light Detection and Ranging) systems are comprised of vehicle-mounted lasers, cameras and GPS/INS navigation systems to capture highly-detailed and accurate three-dimensional (3D) topographic information for surveying and engineering applications. Michael Baker International became an early adopter of Mobile LiDAR technology by acquiring our first system in 2009, with further expansions in 2014 and 2015 that increased our fleet to four (4) Optech Lynx SG1 Mobile LiDAR systems. Over that period our systems have completed more than 300 projects throughout 29 different U.S. States (and multiple countries), and encompassing hundreds of thousands of miles. Our project portfolio includes applications in roadway design, 3D modeling, railroad corridors, signaled intersections, utility infrastructure, asset management, pavement condition assessment and airport infrastructure.