Re[2]: [HACKERS] GSoC 2015: SP-GIST for geometrical objects

On Mar 27, 2015 11:08 AM, "Dima Ivanovskiy" <dima-iv@mail.ru> wrote:
>
> Hello, I am Dmitrii, student of Moscow Institute of Physics and Technology
>
> Abstract:
>
> I chose project "Indexing prolonged geometrical objects (i.e. boxes, circles, polygons, not points) with SP-GiST by mapping to 4d-space".
> According to the presentation
> https://www.pgcon.org/2011/schedule/attachments/197_pgcon-2011.pdf
> SP-GIST 3 times faster than GiST in some cases. But GIST supports geometrical data types:
> box, circle, polygon with operators: && &> &< &<| >> << <<| <@ @> @ |&> |>> ~ ~=
> Popular spatial extension PostGIS doesn't include SP-GIST, but has a lot of geometrical features.
>
> Project details:
>
> After meeting with Alexander Korotkov, I wrote some plan.
> Using of K-D-tree and Quadtree in building index for geometrical data types can increase speed of search in some cases.
> The main idea is representing 2-D geometrical objects in their bounding box. Set of 2-D boxes is 4-D space.
> New _ops will work with points from 4-D space, for example kd_box_ops, quad_circle_ops and will support all geometrical operators.
> After conversion object to their bounding box algo has set of tuples (x1, y1, x2, y2).
> Our goal is separate this space the most equally. If we talk about K-D-tree, on first step K-D-tree algorithm will split space in 2 parts by the first coordinate, in next step by the second coordinate etc., after 4-th coordinate we repeat this procedure.
> At the end we have index at geometrical objects and use traversal tree for every search operator.
>
> Postgresql has already has realization ideas of MBR in gist/gistproc.c. So I will transfer this realization to other type of tree.
>
> Of cource, I assume that SP-GIST can be not the best decision of this problem. So after testing this clear methods, I will try to find more effective way. Maybe with using combination of different spatial tree structures.
>
> Project Schedule:
>
> until May 25
>
> Read documentation and source code, clarify details of implementation.
>
> 1st month
>
> Implement new '_ops' with all geometrical operators for box, circle, polygon
>
> 2nd month
>
> Research new methods for increase speed of geometrical query
>
> 3rd month
>
> Final refactoring, testing and submitting a patch.
>
>
> Links:
>
> http://www.sai.msu.su/~megera/postgres/talks/gist_tutorial.html - about GIST
> https://toster.ru/q/27135#answer_110197 - people need SP-GIST for cubes
> http://www.slideshare.net/profyclub_ru/o-lt - presentation about indexes
> http://pgconf.ru/static/presentations/2015/korotkov_spatial.pdf - working with geo objects
>
Nice proposal.

Dynamic Kdtrees can perform badly as the splitting median can get way off as updates are coming. What are your thoughts about that?

Also what's up with the 4d space? I don't quite get it. These types are 2 or 3 dimensions.