[GRASS-dev] [GRASS GIS] #3038: Decide if validity check in r.in.lidar should be an additional filter or a filter enabled by default

[GRASS GIS]

#3038: Decide if validity check in r.in.lidar should be an additional filter or a
filter enabled by default
-------------------------------------------------+-------------------------
 Reporter:  wenzeslaus                           |      Owner:  grass-dev@…
     Type:  task                                 |     Status:  new
 Priority:  normal                               |  Milestone:  7.2.0
Component:  Raster                               |    Version:  svn-trunk
 Keywords:  r.in.lidar, r3.in.lidar,             |        CPU:  Unspecified
  v.in.lidar, libLAS, PDAL                       |
 Platform:  Unspecified                          |
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 Based on discussion on [http://gis.stackexchange.com/a/187559/10759 GIS
 SE] I wonder if we should make the filtering of lidar points based on
 validity in r.in.lidar, r3.in.lidar, and v.in.lidar optional.

 For us validity is defined by whatever `LASPoint_IsValid(LAS_point)`
 considers valid. [http://www.liblas.org/utilities/las2las.html libLAS
 documentation says]:

 {{{
 removes invalid (according to the ASPRS LAS file format specification)
 points.
 This switch should only be required in a few special circumstances. Points
 that might be invalid include those with larger-than-required scan angles.
 }}}

 ASPRS specification mentions validity of angles and also some numbers but
 otherwise I was not able to find clear information about valid and invalid
 points.

 PDAL does not have any concept like this and either all points are valid
 or application itself must decide what is valid.

 [https://lists.osgeo.org/pipermail/pdal/2015-September/000672.html Andrew
 Bell about PDAL on PDAL mailing list] (see also
 [http://www.pdal.io/tutorial/liblas_to_pdal.html#point-validity migration
 guide]):

 {{{
 Point validity: there is no such concept
 }}}

 I've prepared a patch which turns the validity check into an additional
 filter which needs to be explicitly enabled if user wants it. It also
 removes validity check from scanning mode because no other filters are
 applied at that point. ''This changes the current behavior, so the
 question is if it is acceptable.''

 The alternative is to switch the logic in the patch to disable the filter
 if requested by user but have it on by default (i.e. current behavior by
 default).

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Ticket URL: <https://trac.osgeo.org/grass/ticket/3038>
GRASS GIS <https://grass.osgeo.org>