Apart from the noise generated by the capture of lidar data with the L1 sensor, we have detected that the laser passes do not coincide, do not overlap well and there is a difference between them. Any ideas to improve the accuracy error between laser passes?
Working with the FOV very open gives more error in the margins of the passes, can it be? What is the optimal FOV? For the same reason it would be better to fly with a 50% of lateral overlap between passes than to do it with one of 70%, right?


On the other hand, I suppose it would be very convenient to calibrate the L1 Sensor but in Terra it only gives me the option to do so if the version is the Pro, the paid one. Maybe?
Does It exist another form to calibrate L1? Am I doing something wrong?


And finally, what would be the best workflow to process good point clouds, minimizing this lag in overlaps? Or that other programs can or should be used in addition to DJI Terra.


We usually work in the forestry sector and also touch some power lines and topography.


Thank you, very much.

Here I show you an image of the error between passes

Hi Jaboar, as i can understand, you haven't the DJI Terra PRO version, which include the "Points optimization", which is the command for strip alignment. If you're not using DJI Terra PRO for alignment, you should use TerraMatch.
As i can see in the screenshot, it looks like the paths are not aligned at all, as this is a raw data out of the L1 sensor. This misalignment is absolutely normal in Lidar data, it's necessary to align the paths in order to have good terrain points.

If you cannot align paths, because you haven't any licence of any software, the only thing you can do is to use PPK processing with a RINEX file, this will increase GPS accuracy and minimize the errors.

Panph Posted at 8-21 23:03
Hi Jaboar, as i can understand, you haven't the DJI Terra PRO version, which include the "Points optimization", which is the command for strip alignment. If you're not using DJI Terra PRO for alignment, you should use TerraMatch.
As i can see in the screenshot, it looks like the paths are not aligned at all, as this is a raw data out of the L1 sensor. This misalignment is absolutely normal in Lidar data, it's necessary to align the paths in order to have good terrain points.

HI Panph.
You are right, we haven't the pro version.

We asked DJI some time ago to know if Dji TERRA PRO improved the results in the point cloud, but from "DJI" they only said that it improves the optimization of points but didn't explain how much, how, what improvement there was.
In the forums most people who work in the forestry sector commented that Terra free was enough.
Now seeing that difference between paths and the noise that gets us into the calculation models we use, we wonder if the Pro version would really improve the result of the point cloud.

But we don't know if with versio Pro the paths get aligned or we'll need a program , like Terramach, to have good results.
What is your opinion, or your experinece?

In another kind of works like topography,  powerlines , ...  DJI Terra pro is good?  Do we have to forget about Dji Terra/Terra Pro  and buy another program?

Thank you for your patience  

Panph Posted at 8-21 23:03
Hi Jaboar, as i can understand, you haven't the DJI Terra PRO version, which include the "Points optimization", which is the command for strip alignment. If you're not using DJI Terra PRO for alignment, you should use TerraMatch.
As i can see in the screenshot, it looks like the paths are not aligned at all, as this is a raw data out of the L1 sensor. This misalignment is absolutely normal in Lidar data, it's necessary to align the paths in order to have good terrain points.

Hi again
Sorry  for my ignorance
Where can I do the PPK procesing with Rinex file? In DJI Terra?

https://forum.dji.com/thread-285647-1-1.html

Hello, there. Sorry for the inconvenience. We will consult your issue with our engineers and get back to you later.

Jaboar Posted at 8-22 01:31
HI Panph.
You are right, we haven't the pro version.

In my experience, DJI Terra PRO is not enough for any purpose.
I bought the lifetime version which was included with the Kit i bought with the M300, i used its features as newbie in lidar survey, but once you understand how it works, you won't use it any more.

If you don't use the DJI Terra PRO "oint Optimization" you won't have the paths alignment, but if you align it without GCP you'd occur big absolute errors.

Now i only use DJI Terra to create the Point Cloud out of the L1 and i always use PPK with Rinex if available to increase data accuracy. After creating the Point Cloud without GCP and Alignment in DJI Terra, i use at first TerraMatch to align paths and TerraScan to chech the cloud with GCP.
In my case, TerraScan was included with my M300kit, and then i bought TerraMatch at full price, but i can guarrantee it's a very good alignment software, specially in the last V23 version, with some "automatic feature" designed for the L1.
about the PPK processing with DJI Terra, you can watch this video.

but i can guess you don't know what a Rinex file is, and where to get one of these..

Hello, there. We received a response from our engineers. We will put it below:
According to your description, when comparing the point cloud generated by the L1 lidar with the point cloud reconstructed by the L1 visible light camera, there is a problem in that it cannot be overlapped.
This problem needs to check the data accuracy of the L1 point cloud reconstruction.
Please confirm whether the aircraft has performed warming up, calibrated flight, and if the RTK module was in FIX state all the time.
It is recommended that turn on the "Optimize Point Cloud Accuracy" switch to see if there is any improvement

In addition, since the point cloud true-color coloring switch is turned on, there is no distortion parameter in the visible light photos taken, and when RGB is used to reconstruct las data, the deviation will also be large.

In addition, the L1 self-calibration function is a paid function, you can apply for a full-featured trial version, or use this function after purchasing a certificate

LV_Forestry Posted at 8-22 10:31
https://forum.dji.com/thread-285647-1-1.html

Thankyou!!

Panph Posted at 8-24 04:08
In my experience, DJI Terra PRO is not enough for any purpose.
I bought the lifetime version which was included with the Kit i bought with the M300, i used its features as newbie in lidar survey, but once you understand how it works, you won't use it any more.

Thank you!
We'll take a look at Terrascan and we'll value it