Mobile LiDAR & GIS: Background of a Service Provider

I have the pleasure of being a contributing author to LiDAR News - a new electronic newsletter by Spatial Media.  My specific focus will be Mobile LiDAR and GIS - with a host of other contributers addressing Aerial LiDAR, Static Scanning and Processing.

My first article is now available and is a basic introduction of things to come.  It may be accessed through this link.  I will be collaborating with other authors when appropriate to address processing, animation and sensor fusion.

Should you have a topic for discussion, please leave as a comment.

Thanks.

Coloring the Cloud

Nearly a year ago, I wrote a posting titled Measurement Systems Part 2 - Lasers and Cameras.  In it, I first presented how the combination of the Mobile LiDAR data and imagery from the system's on board cameras are combined to create colorized point clouds.  Having a broad static scanning background, I often went through great lengths to recapture pictures to improve the colorized cloud. We face similar challenges with the Mobile LiDAR system.  With proper planning, patient operators, creative scheduling and a little bit of luck, the results can be impressive.

Below is an image captured from one of the cameras positioned on the rear of the platform and facing backward.  As you can see, the trees cast shadows across the road surface. Collecting multiple passes down the road would create additional shadows at different angles.

The image below is the colorized point cloud.  We colorized one pass (two strips) down this rural road.  The cross hatch pattern created by the two sensors is clearly visible at the bottom of the image. 

The below image clearly shows the concrete/asphalt transition, pavement markings and other roadway characteristics.

Wikipedia states: "The adage "A picture is worth a thousand words" refers to the idea that a complex idea can be conveyed with just a single still image. It also aptly characterizes one of the main goals of visualization, namely making it possible to absorb large amounts of data quickly."  I'm curious how a colorized point cloud would be described. 

In the coming posts, I will present how else we are utilizing the images captured by our Mobile LiDAR system.

Enjoy!

Stephen

Mobile LiDAR Podcast

Recently, I had the pleasure of being interviewed by Matthew DeMerritt of Esri.  The interview was part of Esri's Speaker Series and is available online through their website or Apple's iTunes as a Podcast.

Titled Streetview Lidar, the interview briefly explains Mobile LiDAR and how it can compliment Aerial LiDAR.

West Virginia - Preliminary Information

As we finish the final products for the bridge we collected a couple weeks ago, I want to share some of the preliminary information.  As mentioned in the posting titled "On the Water with the Baker Navy", we performed a collection with the unit on a barge (SBET shown below in blue) and a collection from the vehicle (SBET shown below in red).  Since we utilized the same GPS base, the collections were seamlessly integrated and adjusted.

We exported both SBET's to a Google Earth KMZ file to visualize the vehicle trajectory. An interesting feature of Google Earth is the Elevation Profile tool.  The below image shows the land collection SBET and elevation profile.  The profile pulls the Z value from the KMZ file - rather than clamping the information to the ground.  Notice that our Mobile LiDAR crew made 4 passes over the bridge.  The position of the red arrow represents the vertical line in the profile - showing elevation, slope and distance from start along the drive.

Next, the preliminary LAS data was processed.  The two images below show the intensity values from the LAS data from both collections.  No adjustment was performed up to this point.

Since this is unadjusted LAS data, there is "noise" in the data due to inaccuracies in the SBET - primarily caused by loss of GPS. Using the ground control established using the Trimble S6 reflectorless total station we carry on-board the vehicle, the point cloud was adjusted to be coincident and to meet the localized coordinate system for the project.

Mississippi River Levee

Given my recent travels and work assignments, it's been hard to find time to update Baker's Mobile LiDAR blog with new content.  Aaron stepped in a couple weeks ago for the Revisiting Yazoo post.  And now that products are being finalized for some recent collections, new postings will be forthcoming.  In the meantime, one of our technicians compiled a brief fly through of the Mississippi River Levee collection.

The below animation shows an intensity and colorized point cloud of a two mile stretch of levee along the east bank of the Mississippi River outside Baton Rouge.  Areas not colorized do not appear in the photographs taken by the on-board cameras.

Some of the challenges we face in colorizing point clouds include:

• Changes in sun angle during collection
• Orientation of the vehicle with respect to the sun (vehicle shadow in images)
• Saturation of the upper portions of tree canopies
• Vehicles and other extraneous objects in the images

Again, project planning comes into the "picture."  If a colorized point cloud of a roadway corridor is required, it would prove more wise to perform two shorter collections during off-peak hours (perhaps a Saturday and Sunday morning) to improve the final product.