[pgpointcloud] Nature of patches

[Stephen Mather]

OK, yes, I could see how a 3D chip could be an issue. You start to throw
away the efficiencies that you gain with chipping in the first place.

Would it make sense to implement some sort of sub-chip for a 3rd dimension?
I'm thinking of use cases where I want to understand both the 2D spatial
distribution and the vertical as a series of slices 2D slices.

https://smathermather.files.wordpress.com/2014/07/chipping.png

I'm thinking along the lines of chip in xy (or xz, or whatever) to a known
number of points, but then have a sub-chips which further sub divide each
xy chip into vertical components (pre-set or otherwise).

Best,
Steve





On Mon, Jul 14, 2014 at 11:49 AM, Howard Butler <howard at hobu.co> wrote:

>
> On Jul 10, 2014, at 9:21 PM, Stephen Mather <stephen at smathermather.com>
> wrote:
>
> > Hi Howard,
> >
> > An octree as in a 3D octree? That could be very powerful, It would still
> arrange the points in a chip close to each other vertically, while allowing
> for vertical stratification.  I think I could definitely see uses for that.
>
> The design of the chipper http://www.pdal.io/stages/filters.chipper.html
> is such that it allows the storage of point patches to be predictable and
> efficient. It is not necessarily what you want when you're doing searching
> operations, however.
>
> An octree or quadtree allows for better and more natural searching, but
> the leaf nodes do not have predictable point counts. In the database world,
> this means that some of your rows are filled to 100% capacity, while others
> might only be 10% or 2%. Because the cost of a row is fixed, the database
> storage efficiency can be low.
>
> >
> > 3D indexing is pretty good, I think, in the limited tests I've done with
> it. Makes me wonder what a 3D r-tree looks like, actually.
> >
> > "We could add some functionality to the chipper to allow you to set
> which dimensions you want to use as the X and Y. This would allow you to
> flip the orientation of the data as it is chipped."
> >
> > I understand the first sentence-- that would be brilliant. I'm not sure
> the meaning of second.
>
> The idea would be to allow you to chip in different projections -- not
> just XY, but XZ, and YZ too.
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