[pgpointcloud] Nature of patches

[Howard Butler]

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.