Hallo CC community
Is anyone could explain to me how to (related the procedures) correct the intensity values based on distance and the incident angle in CC?
Thanks a lot in advance
Intensity values
Re: Intensity values
Hi mikmik,
very good question. So you are after correcting the intensty value of laserscan data in order to use the value as a proxy for differentiating material properties of the scanned object (such as lithologies in rock outcrops). First, this can only work on an individual scan , not on a pointcloud build from multiple scans. The main problem is that the different scanners use filters to enhance or reduce the intensity for different ranges, so the intensity versus distance ratio is not linear but very complex. However, people do aply such corrections and I believe they probably use only selected distance ranges where the ratio is linear. So it would be usefull for you to find out if there is specific distance ranges where your device behaves linear. For example for me it is 10-40m distance from scanner to object. So essentially this is not realy a CC issue. Once your data behaves linear, you can simply calculate the corected intensity in a new scalar field. Maybe also have a look at "Geological mapping and fold modeling using Terrestrial Laser Scanning point cloud: application to the Dents-du-Midi..." Battista Matasci, Dario Carrea ..., European Journal of Remote Sensing 2015, 48, 569-591 - there is a section on LIDAR intensity correction. Also, I heart that more expensive scanners+software allow to correct this value automatically and give you the choice not to use filters. But for us regular folks with ordinary scanners it is a bit harder.
I hope this helped a bit
cheers
mat
very good question. So you are after correcting the intensty value of laserscan data in order to use the value as a proxy for differentiating material properties of the scanned object (such as lithologies in rock outcrops). First, this can only work on an individual scan , not on a pointcloud build from multiple scans. The main problem is that the different scanners use filters to enhance or reduce the intensity for different ranges, so the intensity versus distance ratio is not linear but very complex. However, people do aply such corrections and I believe they probably use only selected distance ranges where the ratio is linear. So it would be usefull for you to find out if there is specific distance ranges where your device behaves linear. For example for me it is 10-40m distance from scanner to object. So essentially this is not realy a CC issue. Once your data behaves linear, you can simply calculate the corected intensity in a new scalar field. Maybe also have a look at "Geological mapping and fold modeling using Terrestrial Laser Scanning point cloud: application to the Dents-du-Midi..." Battista Matasci, Dario Carrea ..., European Journal of Remote Sensing 2015, 48, 569-591 - there is a section on LIDAR intensity correction. Also, I heart that more expensive scanners+software allow to correct this value automatically and give you the choice not to use filters. But for us regular folks with ordinary scanners it is a bit harder.
I hope this helped a bit
cheers
mat
Re: Intensity values
Thanks a lot Mat for the answer.
It helps me a lot. I understand the point of distance correction.
According to your explanation, could you elaborate more the meaning of the ratio is linear (when you're talking about distance range?
My second question is would it be possible to define the incident angle from raw point cloud data in CC? How's the procedure to reach this part?
I do appreciate any answers from anyone.
Best,
miktha
It helps me a lot. I understand the point of distance correction.
According to your explanation, could you elaborate more the meaning of the ratio is linear (when you're talking about distance range?
My second question is would it be possible to define the incident angle from raw point cloud data in CC? How's the procedure to reach this part?
I do appreciate any answers from anyone.
Best,
miktha
Re: Intensity values
Hi Miktha,
below is a graph showing intensity versus distance of the scanner to the scanned object. What I have done is that I used a box with four different surfaces and placed it at different distances to the scanner. For each distance I took a scan and plotted the average intensity for each surface (material). As you can see from the plot, the intensity changes with the distance. The "ratio" or curve is very complex in the distance range between 0.6m to 10 m, but becomes semi-linear between 10 m and 40 m. For this range it is possible to calculate a simple function which you could use in CC to recalculate the intensity . Please be aware that this function might change slightly when your scanner gets re-calibrated during a service for example.
Re incident angle - I have to admit that I have not paid too much attention to this - there is several papers that suggest that for natural rock outcrops the incident angle does not have a significant influence on the intensity depending on the roughness of the scanned surface, but personally I am not sure.
I too would appreciate if there is others that can share their experience with intensity corrections.
cheers
mat
below is a graph showing intensity versus distance of the scanner to the scanned object. What I have done is that I used a box with four different surfaces and placed it at different distances to the scanner. For each distance I took a scan and plotted the average intensity for each surface (material). As you can see from the plot, the intensity changes with the distance. The "ratio" or curve is very complex in the distance range between 0.6m to 10 m, but becomes semi-linear between 10 m and 40 m. For this range it is possible to calculate a simple function which you could use in CC to recalculate the intensity . Please be aware that this function might change slightly when your scanner gets re-calibrated during a service for example.
- Intensity.jpg (118.74 KiB) Viewed 5164 times
I too would appreciate if there is others that can share their experience with intensity corrections.
cheers
mat