The difference between the ArcGIS tool output and the WhiteboxTools output is the result of the ways in which they identify points belonging to different flightlines. The ArcGIS Classify LAS Overlap tool uses the Point Source ID property to determine each point's associated flightline. By comparison, both the WBT ClassifyOverlapPoints and the FlightlineOverlap tools identified the condition of points belonging to different flightlines based on a threshold time difference. This technique does generally work well, but unfortunately I had hard-coded the time difference threshold value, rather than making it user-specified. It's likely the case that the value used was not well conditioned for your particular data.
In fairness, the approach of using the Point Source ID to infer the flightline is more conventional. The main reason that I did not adopt this approach when I first wrote these tools was that sometimes the Point Source ID information is either omitted or lost from files. However, I have recently added the new RecoverFlightlineInfo tool, so that when this condition occurs, users have a mechanism in place to update their Point Source ID with relative flightline information. As a result, I have just committed updated versions of the two flightline overlap tools to use the Point Source ID instead, similar to the ArcGIS solution. The ArcGIS tool flags all points in a grid cell that have the same Point Source ID as the point with the maximum (absolute) scan angle. I have included this option, however, I have also added three other flagging criteria for conditions when scan angle information is unavailable or inadequate. These include:
Criterion |
Overlap Point Definition |
max scan angle |
All points that share the PSID of the point with the maximum absolute scan angle |
not min point source ID |
All points with a different PSID to that of the point with the lowest PSID |
not min time |
All points with a different PSID to that of the point with the minimum GPS time |
multiple point source IDs |
All points in grid cells with multiple PSIDs, i.e. all overlap points. |
I have also updated the help documentation for these two tools so that they better describe the operational characteristics of the new method. These new versions of the tools will be available in the next public release of the WhiteboxTools open-core, which I am planning sometime towards the end of April or beginning of May. If you cannot wait until then, you may either build from source code, or contact me for an pre-release binary, which I will be happy to provide.