[pdal] Chunking/streaming support

[Andrew Bell]

On Mon, May 23, 2016 at 5:02 PM, Jason Overland <joverland at lizardtech.com>
wrote:

> Hi,
>
> I’m trying to use PDAL’s C++ API to read BPF files and integrate it into
> our existing API.  In our API we expose an iterator called PointIterator
> which is constructed from a file and a region (bounding box).  Our
> PointIterator has a getNextPoints() method which walks the specified region
> of the point cloud until there are no more points to extract.  To work
> within this existing API we would like to use a
> chunking/streaming/stripping/iteration mechanism, i.e. read at most n
> points at a time from the file, stop and return execution to our API user’s
> code, and then continue where we left off on the next call to
> getNextPoints(), rinse and repeat until we’ve read all the points we’re
> interested in.  I’ve been looking at the Streaming support as exemplified
> in StreamingTest.cpp but haven’t quite been able to wrap my head around
> whether or not what I’m trying to achieve is currently possible.
>

The issue is that PDAL's API works in a manner opposite to yours.  PDAL
expects to call your code when a point has been read, rather than the other
way around.  PDAL handles the point buffering and so on, relieving your
code of the burden.  PDAL wants to run an entire pipeline -- it's not
intended as a stand-along point-by-point reader.  Without seeing your
processing code, I can't provide any advice on how to make it work with the
existing API.

That said, I understand that this doesn't meet your model and your model
isn't unreasonable.  I don't know where doing something like this might fit
in our current priority list, but it's probably not too large a task.

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