Reprojecting LiDAR

Article by Paul Fuller, sales and drainage consultant

December 2018

I have been using Lidar for drainage planning since I first learned about it back in 2010.  Is Lidar perfect?  No, it is not, but once you understand the weak parts of it, it can be a valuable tool.  That thought will have to wait for another day.  Be watching for a future discussion about the good and bad of Lidar.

Before Lidar can be used in GK Technology Inc’s Ag Data Mapping Solution or any other GIS software, you need to know how it is projected and the requirements for your specific software package.  There are several different ways of projecting Lidar.  None of them are wrong, they are just different.  ADMS requires it to be in a UTM projection.  One of the most common other projections I have run across is State Plane.

UTM Zones

My primary source for LiDAR has been https://earthexplorer.usgs.gov/ Much of the currently available US LiDAR is downloadable from the site.  Specific areas have their own websites some of which are listed here. Data Links

After downloading and unzipping the Lidar tiles, some will have to be reprojected to work in your software package.  I have recently been working with Lidar for Illinois, Indiana, Mississippi, and Michigan.  These have been projected in State Plane Feet.  How did I know that?  There are 2 different ways to determine the projection they are in.  Option 1 is to look in the .XML Metadata file that is included with the .LAS file when unzipped.  The .XML file will open in Internet Explorer or Notepad.  In this example from Gibson county Indiana, I can determine that this tile is projected in State Plane Indiana West Feet using the NAVD88 vertical datum.  This all required information to reproject to UTM for use in ADMS software.

Option 2 is to look at the Metadata on EarthExplorer.  After selecting the location and searching the datasets, click on the Show Metadata and Browse button for an individual tile.

Now that we have the tiles downloaded, unzipped and have determined the current projections, we are ready to reproject them.  One note of caution, I learned from this project in Indiana.  Make sure that if there are multiple collection projects within the area you have downloaded that they are all projected the same.  In Gibson county Indiana, some are projected in State Plane and some are in UTM-16. 

The only tools I have used for reprojection are from https://rapidlasso.com/  This a powerful set of tools that I have only scratched the surface of.   The LAS2LAS program will reproject and convert from .LAS to .LAZ.  This results in about a 10x compression for saving hard drive space.  If you only have a few tiles, it is not a big deal, but if you have counties or states of Lidar it becomes a huge space saving step.

A word of caution before you start.  Throughout this process, it will appear that LAS2LAS has stopped working and appear nonresponsive.  Let it do its magic.  You cannot rush it and need to be patient. You need to select the source folder that you are working with and select the tiles to reproject.  Load the tiles via the browse tab and it will show the tiles selected in the main window.

The next step is to select the current projection on the left side toolbar. Selecting the correct measurement units for your project is very important.  Here is an example for a project.

Now we can move to the right side toolbar to set our outputs.  First select the destination directory.  If converting from .las to .laz, you can put it in the same folder.  However if converting .las to .las or .laz to .laz, create a new folder to export to. 

Set your Target Projection, zone and units.  For UTM projections meters will select by default.

Select the format you want to export in and click RUN.

Click Start on the next screen and be patient.  It will show as not responding.  You can always go into the destination folder to make sure that the process is working.  I reprojected a county in Illinois that had 7000 tiles and it took about 7 hours.  After everything is processed, I would highly recommend that you do a test against a known area.  If something did not reproject correctly, you get to do it all again.  I keep my original dataset until I know it works correctly.  Once you have verified that everything is correct, you can delete the original dataset.  Hopefully this will help you with reprojecting Lidar to work in ADMS or your preferred GIS software package.