[pdal] Reading only specific fields from LAS files to improve performance.

[Andrew Bell]

Hi,

You should look at

this:
https://github.com/PDAL/PDAL/pull/3311/commits/db2d4a2539ad4551b62fee9711c51f0e0cbb939b

This change allows a user to limit what gets loaded when using `pdal
translate` or `pdal pipeline`, but the code that's there can serve as an
example for your own.

Note that this doesn't change what gets read from a file, just what gets
stored. We don't currently support the selective reading of data, though
this probably only much matters for LAZ with point formats 6-10.

On Mon, Mar 15, 2021 at 6:32 PM Leona Swift <leonaswift80 at gmail.com> wrote:

> When using PDAL as part of a C++ codebase to read a large LAS/LAZ file
> from which we are only interested in the XYZ position of each point, import
> with PDAL is very slow. It looks like all of the other attributes in the
> PDAL file are being parsed. Additionally that parsing is very slow due to
> many type conversions, although the documentation is clear that PDAL is
> more concerned with genericity than efficiency.
>
> Is there any example in C++ of how to say "Only read the XYZ data from
> this file" to make things quicker?
>
> I assume that it is possible to do something (prepare the table
> differently) prior to calling execute() (which is where the time is spent.)
> However, there don't seem to be any code examples of doing this.
>
> las_reader.setOptions(las_opts);
> las_reader.prepare(table);
> pdal::PointViewSet point_view_set = las_reader.execute(table);
>
> (Actually, I haven't found any C++ examples at all other than
> https://pdal.io/api/transition/index.html).
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-- 
Andrew Bell
andrew.bell.ia at gmail.com
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