[pdal] tweaking parameters in filters.smrf

[Karl North]

Greetings PDAL'ers.

I'm new to PDAL, and have recently begun the testing of a PDAL pipeline in hopes of improving an existing automated workflow which uses a TerraScan macro to classify ground points in raw Lidar point clouds.  My pipeline is based on the SMRF filter.

By including the ELM and OUTLIER filters, and then juggling the cell size, scalar, slope, threshold, widow size and the cut grid parameters in the SMRF filter, I can achieve a final point cloud that is mostly equivalent to the TSCAN result in many terrain/vegetation/feature scenarios.  Of course, I would like to use PDAL to surpass the TSCAN results.  The main issue that I currently have with my PDAL result is the presence of too much high frequency "noise" visible in the surface defined by the ground classified points.  A lesser issue is the delicate balance, when using the cut grid parameter to help eliminate building points, between the removal of building features and preserving sufficient terrain detail.

I should point out that we've invested several years (off and on) in tweaking our TSCAN macro with the help of paid support staff to achieve the current excellent result, and that the macro includes 40+ individual steps to achieve this result.  In comparison, to date we have only devoted a couple of weeks to testing/tweaking the PDAL filter parameters.

I've searched on-line for tutorials/suggestions/experiences that users have had with tweaking the SMRF parameters in various terrain types, vegetation density/types, and cultural feature density/types but have really not found a definitive guide.

Is there anyone out there on the mailing list that can suggest such write-ups, or would be willing to share their insights?

Perhaps there are other (as yet undiscovered) PDAL filters that I might include in my pipeline either before or after SMRF that would be better suited to the remaining cleanup than tweaking the SMRF parameters themselves.

I can share sample LAZ data illustrating a SMRF-vs-TSCAN comparison of current my state-of-the-art, if this will help clarify the current issue(s).  To do so, I could use some guidance on reasonable limits on file size for sharing such a sample.

Thanks in advance for any/all suggestions.

Karl
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