Looks clear to me, thanks for getting the headers correct (sigh!).
I had one general question about the design of JDBCAggregateFunctionTest (
https://github.com/aaime/geotools/blob/b7f66c845acc3ee456cdc2db174e5f1578ddf41d/modules/library/jdbc/src/test/java/org/geotools/jdbc/JDBCAggregateFunctionTest.java
).
Why does the test cases create a subclass to test (i.e. MyNearestVisitor
extends NearestVisitor)?
Jody Garnett
On Sun, Mar 9, 2014 at 10:27 PM, Andrea Aime
<[email protected]>wrote:
> Hi,
> in a GeoServer pull request we have an implementation a NearestVisitor
> whose objective was to find the closest value to a given reference value in
> the domain of a feature attribute whose value was a Number, a Date or
> String:
>
> https://github.com/ilkkarinne/geoserver/blob/master/src/wms/src/main/java/org/geoserver/wms/dimension/NearestVisitorFactory.java
>
> In essence, this is similar to a max/min visitor, and not so similar
> instead to
> a KNN search (find the N closest features to a given point), in that it
> searches
> for the closest value, not for the closest features.
>
> I've started backporting that code to Geotools and adding unit tests, a
> JDBC optimized
> implementation, and then moved to make it more general, so that it could
> work
> against Geometry and generally speaking Comparable objects as well, with a
> small twist there if you want, that if we are dealing wit a Comparable
> that's not
> a Number or a Date, we end up with the two closest values (unless the
> reference is
> above or below the domain), and then we basically arbitrarily pick one.
>
> I did not add a String based implementation, but if we had one, it would
> probably have to
> use some reliable string distance (e.g. the Levenstein distance for
> example,
> http://en.wikipedia.org/wiki/Levenshtein_distance)
>
> During the implementation I've also noticed that what we are searching a
> value in
> the attribute domain, which is not necessarily of the same type as the
> reference
> value (e.g., domain made of integers, with the reference being a double)
> so
> had the code make sure to handle that.
> The overall visitor code is here:
>
> https://github.com/aaime/geotools/blob/nearest/modules/library/main/src/main/java/org/geotools/feature/visitor/NearestVisitor.java
>
> The JDBC optimized implementation turns the nearest visit into two visits,
> basically finding the closest value to the reference in the half below the
> reference (the max in that interval),
> and then the closest value to the reference in the half above (the min in
> that interval) and then
> picks the closest of the two. If the domain is indexed this should be
> quite a bit
> faster than scanning the whole domain, if not, it's still going to be
> faster than loading
> all the features from the database in the in memory visitor:
>
> https://github.com/geotools/geotools/pull/386/files#diff-5e45fc0686088e1fbeea65365775a1fbL678
>
> The pull request is here, comments welcomed:
> https://github.com/geotools/geotools/pull/386
>
> Cheers
> Andrea
>
> --
> == Our support, Your Success! Visit http://opensdi.geo-solutions.it for
> more information ==
>
> Ing. Andrea Aime
> @geowolf
> Technical Lead
>
> GeoSolutions S.A.S.
> Via Poggio alle Viti 1187
> 55054 Massarosa (LU)
> Italy
> phone: +39 0584 962313
> fax: +39 0584 1660272
> mob: +39 339 8844549
>
> http://www.geo-solutions.it
> http://twitter.com/geosolutions_it
>
> -------------------------------------------------------
>
>
> ------------------------------------------------------------------------------
> Subversion Kills Productivity. Get off Subversion & Make the Move to
> Perforce.
> With Perforce, you get hassle-free workflows. Merge that actually works.
> Faster operations. Version large binaries. Built-in WAN optimization and
> the
> freedom to use Git, Perforce or both. Make the move to Perforce.
>
> http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk
> _______________________________________________
> GeoTools-Devel mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/geotools-devel
>
>
------------------------------------------------------------------------------
Subversion Kills Productivity. Get off Subversion & Make the Move to Perforce.
With Perforce, you get hassle-free workflows. Merge that actually works.
Faster operations. Version large binaries. Built-in WAN optimization and the
freedom to use Git, Perforce or both. Make the move to Perforce.
http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk
_______________________________________________
GeoTools-Devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/geotools-devel
