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

[Bradley Chambers]

Michael,

You are correct that there is no out of the box LAS point type, although
you could in theory create one [1].

Various PCL modules provide methods such as "getInliers" to get a vector of
indices [2]. PCL treatment of inliers varies somewhat from module to
module, so one has to read the docs carefully.

For an example of acting on the indices, you can look at the OutlierFilter
where we start by processing a PointView to obtain (in this case) two
vectors of PointIds, the inliers and the outliers [3]. We later create a
new output PointView by appending only the inliers from the input PointView
[4].

No need to sort. The PDAL to PCL conversion [5] is order preserving, so
unless your PCL code is doing something to the order, you should be good.

Brad

[1]
http://pointclouds.org/documentation/tutorials/adding_custom_ptype.php#how-to-add-a-new-pointt-type
[2] http://docs.pointclouds.org/1.7.1/classpcl_1_1_sample_consensus.html
[3] https://github.com/PDAL/PDAL/blob/master/filters/OutlierFilter.cpp#L159
[4]
https://github.com/PDAL/PDAL/blob/master/filters/OutlierFilter.cpp#L203-L209
[5]
https://github.com/PDAL/PDAL/blob/master/plugins/pcl/PCLConversions.hpp#L127-L191


On Tue, Mar 14, 2017 at 6:27 PM Michael Rosen <michael.rosen at gmail.com>
wrote:

> 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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