Leica SPL100
This section tries to outline at a higher level the suggested workflow for the SPL 100 and some of the steps that are unique for this sensor. The major steps to process raw Leica SPL100 data are listed below:
Per each flight, create new HxMap calibration files
To do so, pick an Area of Interest (as described in the Calibration section below) from dedicated flight lines and perform a calibration using HxMaps Calibration tool following similar steps as LiDAR misalignment calibration
With the updated calibration files in place, run Ingest of raw data for the whole collect
Perform LiDAR QC to check for the for/aft and line/line registration
If required, create a block and run the LiDAR matching tool
Compare the point cloud against the control points
If required, run product generator on the block to colorize the LiDAR point with the imagery
An isometric view of the solar noise in SPL is shown below:
The ingest process for SPL100 chains multiple algorithms that are used to filter out the noise and clean up the data. Some of the current filters include:
Noise Reduction - denoising algorithm that estimates the density of each point in the 3D point cloud to remove the solar noise
Decimation - reduces a flight line's greater edge densities to match the rest of the data
Outlier Removal - removes noise while preserving features
Intensity Averaging - multiple intensity averaging algorithm from simple spatial averaging to computationally intensive local edge preserving averaging.
The different parameters for these filters that are specific for this sensor are found in the advanced section of the HxMap INI file.
Raw Data Organization
The SPL100 "Raw_Data" directory to be selected at Ingest time has both Imagery and SPL LiDAR data in sub directories:
TOF_Raw - raw LiDAR data
Logs_Raw - LiDAR sensor logs files
Images_Raw - RCD30 raw data
GPS_Raw - GPS/IMU data from the flight management system
The data from SPL100 for the time being comes in two sets of disks. One set of two SSD disks from the LiDAR part of the sensor and the other two set of MMs from the Imagery. For the data to be processed in HxMap it needs to be copied to a common root directory as specified above. User should be very careful in copying raw data since simply using Window Explorer Copy functionality to copy such large files could result in files that are not exactly identical and very difficult problems to diagnose. For this reason, HxMap comes with HxMap Data Copy tool that is included in each installation. The HxMap Data Copy tool should ALWAYS be used to copy raw data to the file server with checksum validation. The steps to copy SPL100 data are:
Create the root destination directory on the file server using Windows Explorer
(For example: "Z:\Flight_2017\Easton")Create the required sub directories: "TOF_Raw", "Images_Raw", "Images_Raw\20170316" manually
Use the HxMap Data Copy tool to copy Imagery Raw
Add one of the MMs from the set to the "Data Directory" list of the Copy Tool
Copy tool should Identify the other MM and add it to the list
Select the "Images_Raw\20170316" as the destination for the Images
(For example: "Z:\Flight_2017\Easton\Images_Raw\20170316")Tool should start copying and create the "MM1".."MM4" sub directories
Use the HxMap Data Copy tool to copy LiDAR Raw
Add one of the disks that contain the LiDAR data (*.tof) files and select the top root directory
(For example, "G:\")System will not be able to recognize it as a Raw disk (accept with a "yes" to add the disk to the copy list)
Select the "TOF_Raw" directory you created as the destination for the raw LiDAR data
(For example: "Z:\Flight_2017\Easton\TOF_Raw")Tool should start copying all the files and verify that files are correct
Repeat the process for the second Disk
Calibration
There are 14 calibration parameters for the SPL100: 3 boresight angles, 1 wedge angel bias and 10 coefficients for Fourier Model for describing wedge angle variation. Prerequisite for a good calibration is a cross-pattern flight over varying terrain. However, occasionally calibration from the boresight pattern does not converge as well as desired. In this event, use production flight lines for calibration. Ideally pick an area with terrain relief, buildings and a crossing flight line.
Empty or small size of *.hexshot files
Empty or small size of *.hexshot files have been reported on some projects and that has caused the failure of the calibration tool. To resolve this issue there are a few things that need to be checked or set to handle the situation:
Check if the selected AOI is over the vegetation, water, or other locally smoothed area (low vegetation, small size of man-made structures (i.e. cars)), if so, change the AOI and select some areas with a good terrain variation and large man-made structures and less vegetation.
If the *.hexshot files contains good quality of points from a bright surface that is difficult to differentiate it from the vegetation and water objects, then change of the AOI doesn't help. In this case, it is better to expand the AOI to use a larger enough area which will result in a reasonable size of calibration data and small enough not to slow down the calibration process significantly.
If the above two methods still don't help to get a reasonable amount of calibration points, then that may indicate the project is over some vegetation area or mostly dark objects. This may require a slight decrease in the threshold of "Min_Num_returns_in_largest_quad_bin". The default for this parameter is 20, a slight reduction to 15 or 10 would boost the filter and bring more points. Noted here, the desired calibration points are from hard surfaces and locally smoothed objects, like buildings and bare grounds. If this parameter is set too low, that will also bring the vegetation into the calibration and will degrade the calibration performance. Therefore, it is recommended to decrease this parameter in steps, for example, try 18, 16, 14... until you see a good amount of points are generated.
If the calibration is performed on high relief area, it is expected to slightly increase the parameter "Quad_bin_width_meter" to 6, 7, 8 until you see a good amount of points are generated. However, one needs to be cautious as the larger bin width will introduce more vegetation points and it will contaminate the calibration result.