[pdal] PCLBlock drops non-XYZ dimensions & what to do about

[Michael Rosen]

Picking up on a conversation started on Gitter:  https://gitter.im/PDAL/PDAL

One problem we have with the PCLBlock filter is that we currently drop all
non-XYZ dimensions because when we marshal point cloud data from PDAL -->
PCL we needs to specify a PCL-compatible point type and we pick XYZ.  As a
result, when we marshal the result back, we there is nothing except XYZ.

One workaround suggested was to create a PCL point type that fits the
data.  My quick look suggests there is not such point type, even for the
simplest of LAS files.  Can someone confirm this?  These, I think, are the
options http://docs.pointclouds.org/1.5.1/point__types_8hpp_source.html ?
So, For example, no way to carry Classification to say nothing of LAS
metadata like the array of "Number of points by return."

The other suggestion was to return just the indices of the desired points.
Can someone say a little more about what PCL API would enable this?  Once
we had it, how can we get PDAL to remove all the points except those
returned?

One thought I had would be to sort the point cloud before marshaling it to
PCL and similarly sort the result from PCL.  Create the desired result set
by marching through the point clouds in parallel removing anything from the
original point cloud that isn't in the PCL result.



msr
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