Add statistics.

[abellgithub]

No description provided.

[wonder-sk]

Tested with PDAL 2.2 and it seems to work fine!

But I am having issues compiling it with PDAL 2.0.1

First I got

../bu/Processor.cpp: In member function ‘void untwine::bu::Processor::flushCompressed(pdal::PointTableRef, pdal::PointViewPtr, const untwine::bu::OctantInfo&, untwine::IndexedStats&)’:
../bu/Processor.cpp:378:28: error: invalid use of incomplete type ‘class pdal::PointViewIter’
  378 |         for (PointRef p : *view)
      |                            ^~~~
In file included from /usr/include/pdal/PipelineManager.hpp:38,
                 from /usr/include/pdal/Kernel.hpp:44,
                 from /usr/include/pdal/PluginHelper.hpp:43,
                 from /usr/include/pdal/Stage.hpp:45,
                 from /usr/include/pdal/StageFactory.hpp:38,
                 from ../bu/Processor.cpp:19:
/usr/include/pdal/PointView.hpp:61:7: note: forward declaration of ‘class pdal::PointViewIter’
   61 | class PointViewIter;
      |       ^~~~~~~~~~~~~
../bu/Processor.cpp:378:28: error: invalid use of incomplete type ‘class pdal::PointViewIter’
  378 |         for (PointRef p : *view)
      |                            ^~~~
In file included from /usr/include/pdal/PipelineManager.hpp:38,
                 from /usr/include/pdal/Kernel.hpp:44,
                 from /usr/include/pdal/PluginHelper.hpp:43,
                 from /usr/include/pdal/Stage.hpp:45,
                 from /usr/include/pdal/StageFactory.hpp:38,
                 from ../bu/Processor.cpp:19:
/usr/include/pdal/PointView.hpp:61:7: note: forward declaration of ‘class pdal::PointViewIter’
   61 | class PointViewIter;
      |       ^~~~~~~~~~~~~

Then after adding #include <pdal/PointViewIter.hpp> to Processor.cpp I get another error:

../bu/Processor.cpp: In member function ‘void untwine::bu::Processor::flushCompressed(pdal::PointTableRef, pdal::PointViewPtr, const untwine::bu::OctantInfo&, untwine::IndexedStats&)’:
../bu/Processor.cpp:380:28: error: conversion from ‘pdal::PointIdxRef’ to non-scalar type ‘pdal::PointRef’ requested
  380 |         for (PointRef p : *view)
      |                            ^~~~

Which I am not sure how to fix - there seems to be a change in API - PDAL 2.2 returns PointRef from the iterator, while PDAL 2.0 returns PointIdxRef.

[wonder-sk]

Looks good to me - please feel free to merge.