I will begin by stating that I am hardware neutral. I have processed data from both the Velodyne 32 with a good STIM IMU and the Riegl mini VUX with an even higher end FOG IMU. Both for “survey grade” uses. I can say that although the Riegl produces better results, the Velodyne was accurate enough for the same purposes with some extra but minimal processing. Our supplier did some extra work to calibrate the individual lasers, so that might explain the different opinion I have. Our current Riegl system supplier has software that makes it easier to calibrate the multiple lasers of the Velodynes.
UAV lidar is not as simple as attaching a lidar to a drone and looking at the resultant point cloud. The industry is following the same evolution as did (is) UAV photogrammetry and SFM software. I think at one time everyone thought they could buy a cheap drone and a camera and pull it out of the trunk of their car to fly for survey data. Eventually the wake up call came.
Good GNSS, IMU, and flight parameters are needed. Some of that costs money, more than most are willing to invest. Then there’s the know-how to post process and the software needed. More investment, but worthwhile. The survey people are by nature accuracy freaks. And they have formed much of the world with their work. We need to give them what they need.
Unless for research, educational uses, or just playing around with the technology for fun, my advice is to stay with a supplier who has put his business reputation on assembling a turn-key package that is already proven to yield a deliverable result that will not put your own business reputation at risk. Many of our potential clients have been through and experience with someone who gave them bad data. Their attitude is difficult to overcome to sell them the real thing.
Too much coffee, I digress. Main point here is no differential corrections, question re: IMU, and individual laser calibrations for my two cents.
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Having been advised by different lidar hardware suppliers as well as surveyors, 30KM is too long of a baseline to rely on for CORS corrections, that is if it is the sole source. We go no more than 5-6 miles.
For fluctuation corrections (they are extremely minor with the system we fly with) we use Terramatch as a routine part of the workflow.
Sam, I’m afraid my source is commercial and would likely not share their proprietary work. I know that LidarUSA, the supplier of the previous system I worked with, somehow calibrated the lasers in a more manual and tedious way. But they are also commercial and I suspect guarded about sharing things. They are great people and I wouldn’t hesitate to contact them. They have a lot of experience with Velodyne for surveying. I am a bit out of my league with the research and educational world of lidar. I am a true turn-key end user that relies mostly on GUIs and only strives to learn what I need to produce the best data for my clients. I am in awe of what it takes behind the scenes for all this to work. God bless the developers and code writers! Swapping is uncommon in this world. LOL
I would like to add that it is very difficult to learn proper operation of these systems without in-depth, hands-on training. I hope I did not come off as rude in my previous comment. Have a good weekend everyone!
Martin, do you have the boresight information for your platform?