[pdal] Fwd: Change the pdal container

[Andrew Bell]

On Tue, Mar 15, 2016 at 11:40 AM, Helimap Postmaster <postmaster at helimap.ch>
wrote:

>
> Hello all,
>
> This is a follow-up on a discussion started on liblas-devel mailing list
> with subject 'How to use a cached reader (c++)'.
>
> The question it has come to is, how can I change the pdal cloud container?
> The cloud container, not the point container, that is, the container that
> stores all the points.
>
> I've seen that pdal uses a std::set as a container
> <https://github.com/PDAL/PDAL/blob/master/include/pdal/PointView.hpp#L66>
> for the cloud, but std::set doesn't play with the parallel access of an
> openmp 2.0 for loop, which can only handle std::vector or std::queue.
>

Well, not exactly.  By default PDAL has a set of buffers that contain the
points.  You're welcome to implement a class derived from BasePointTable
and arrange the data as you like.

Is it possible to re-implement PointView class to use a
> std::vector<PointViewPtr>? Is it possible for me to access this vector?
>

If what you're wanting to do is simply loop through points that you read,
you'd only have a single view into a single table.  The access is direct
from the view to the table. The table, by default, stores data in a vector
of blocks, the blocks being memory containing points.

The first simple scenario is that I read the full pointcloud and store it
> into a std::vector<PointViewPtr>, then I process each point in parallel in
> an openmp for loop, and finally I save the modified std::vector to a new
> las file. The process is roughly adding color to each las point.
>

I'm not sure why you need openmp, but I won't question.  If your colorizing
algorithm is slow, then perhaps some threading system will be helpful.  But
I'm not sure that you're worrying anything that is necessarily a problem
given what you've said so far.  I certainly can't see any reason for a
vector of point views.  If you're reading a single file, one PointView
should suffice and be all that is normally created.  All points should be
accessible through the one PointView.

The normal way to attack these problems is to first come up with a
single-threaded solution and then optimize through threading as necessary.
Writing the base code will clarify issues and allow others to help you
better than we can at this time.

Best,

-- 
Andrew Bell
andrew.bell.ia at gmail.com
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