Monday, November 8, 2010

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.

Thursday, November 4, 2010

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.

Wednesday, November 3, 2010

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.