[pdal] Migrating from libLAS

[Andrew Bell]

On Wed, Sep 2, 2015 at 8:39 AM, Vaclav Petras <wenzeslaus at gmail.com> wrote:
>
> On Wed, Sep 2, 2015 at 8:15 AM, Newcomb, Doug <doug_newcomb at fws.gov> wrote:
>>
>> Does this mean that with the new version of r.in.lidar using pdal that the
>> file size that can be read in will be limited by the amount of memory on my
>> computer?
>>
>>  I currently use r.in.lidar with liblas and can process aggregated las
>> files with up to 4.2 billion points with memory usage limited by the amount
>> of map in memory parameter. ( The type of the analysis cell size and extent
>> also affect memory usage)
>
>
> I meant v.in.lidar, sorry for confusion. But what you are saying applies
> even more for v.in.lidar. It always holds in memory just one point as it
> doesn't combines the points in any way. There might be some issues on GRASS
> site like counting the points but that's a different story.

If you're only using PDAL to read the data from LAS as in your example
code, then using the callback mechanism and a custom PointBuffer will
result in less memory usage and faster run times.  I thought there was
a good example around, but I don't see it, so I'll write one.

PDAL is slower than the libLAS when all you're doing is reading data.
We've spent quite a bit of time looking at this, and have squeezed
most of what we think we can out of it without changing the
architecture.  PDAL isn't intended to be a super-fast LAS reader.
It's made for doing analysis work and handling multiple types of
input/output datasets.  Most of the the time difference you see
between libLAS and PDAL isn't iteration, but data copying.  You can
iterate the data very quickly on most modern computers with sufficient
memory.

Note that PDAL will do a bunch of the work that you're doing in your
code for you.  You can filter based on geometry, do reprojection,
perform classification filtering, etc., without writing code or
writing much less than what you have done.  It will be somewhat slower
than your own code if all you're doing is reading the data and
throwing it away after doing some calculations, but you don't have to
write the code :)

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