Updated: Sep 12, 2018
So you’ve done the survey. You’ve flown the airborne LiDAR collection, wrapped up the mobile survey or finished up with the terrestrial project. You’ve been very thorough, and now you’re buried in data — what are you going to do with it all?
The tools you’ll use for processing LiDAR data are typically the same for all LiDAR providers, depending on make and model of the system you’re using. The techniques may vary somewhat from one provider to another, but the steps are pretty much the same.
The Recipe for Raw Data:
Before you do anything else, you need to extract the raw data. This process is sometimes called pre-processing. You’ll be pulling the data in its raw format from the system — first the laser data and the positional raw data, then the ground base station data, and finally the raw GPS and IMU data, which is extracted from the positional information. But while raw is great for vegetables and sushi, when it comes to LiDAR you need to spend some more time in the kitchen.
First, you’ll process the GPS data, using the airborne GPS data if you have it, as well as the ground GPS information. You’ll need to determine the coordinates for the ground GPS data, and how you do that is based on the type of points being used. Once you have processed the GPS data, you’ll combine it with IMU data, processing the two sets of data into trajectory files.
A trajectory file includes the GPS location information as well as the attitude information from the IMU. You’ll also want to do additional analysis on the accuracy of the gyro and accelerometer to make sure they’re functioning correctly, along with the positional components.
With that step down, the recipe moves on. You’ll combine the processed trajectory file with the laser data, and carefully stir in the software calibration files that were adjusted during system calibration as well as the intensity tables provided by the manufacturer. If it sounds like a tricky operation, you’ll feel better knowing that the LiDAR hardware manufacturer usually provides software to handle the slicing, dicing, and mixing.
Once this pre-process is completed, the project calibration is accessed and adjustments to the calibration files will be made. The LiDAR is calibrated and output in LAS format, the standard format for most LiDAR systems, used almost universally throughout the industry. Then, you’ll move on to the post-processing.
Young, James. LiDAR for Dummies. Hoboken: Wiley Publishing, Inc., 2011.