Hey Andrea, All of your changes sound good to me. Only question I have is whether your proposed change will replace what is there? Or is your thought to add some config parameter that would trigger the histogram / approximation based method?
As for moving the code to jai-text definitely makes sense to me. -Justin On Wed, Nov 14, 2018 at 10:00 AM Andrea Aime <andrea.a...@geo-solutions.it> wrote: > Hi, > I'm looking into extending the GeoServer SLDService API to work against > raster data too. > The current code in that module works off the vector classification > functions for equal intervals, natural breaks and quantiles. > > When looking at extending it for rasters, I stumbled into > the ClassBreaksOpImage and its subclasses, which > does more or less what I need... with a hitch though: the rasters that I'm > playing with can be large and have floats/doubles > > Looking at the implementation for quantilies and natural breaks I've > noticed that all input values get collected > either in a List<Double> or a Map<Double, Integer>, where the doubles are > the values and the integer is a pixel count. > Mind, this is the same as vector code is doing, but getting to a million > of those in raster space only requires a 1000x1000 > image... and millions of double values (or map entries) take up a lot of > space. I could look into using non boxed > variants, but the issue is not really that one, it's just that keeping > track of all values requires too much space. > > So I'd like to add an approximate calculator instead that collects > histograms, and the works off the result applying the > same logic as today. Ideally, these would be new entries in > the ClassificationMethod enumeration, say > QUANTILE_HISTOGRAM and NATURAL_BREAKS_HISTOGRAM, and ClassBreaksOpImage > would have an > extra optional parameter to decide the bucket count (with some reasonable > defaults, e.g. 256 for byte data, > 1000 for any other type). > Working off histograms has a clear benefit, the size of the working memory > is fixed at the start, and it's possible > to use primitives in the data structure, of course it also means the > resulting classification won't be exact, but > should be close enough. > The downside is that the min/max values need to be known in advance to > build the buckets, so for the histogram > based methods the "extrema" parameter in the ClassBreaksOpImage will be > mandatory (exception thrown if not provided). > > How does that sound? > > Cheers > Andrea > > PS: most operations are in jai-ext, mind if the ClassBreaksOpImage gets > moved there, in its own module? > > -- > > Regards, Andrea Aime == GeoServer Professional Services from the experts! > Visit http://goo.gl/it488V for more information. == Ing. Andrea Aime > @geowolf Technical Lead GeoSolutions S.A.S. Via di Montramito 3/A 55054 > Massarosa (LU) phone: +39 0584 962313 fax: +39 0584 1660272 mob: +39 339 > 8844549 http://www.geo-solutions.it http://twitter.com/geosolutions_it > ------------------------------------------------------- *Con riferimento > alla normativa sul trattamento dei dati personali (Reg. UE 2016/679 - > Regolamento generale sulla protezione dei dati “GDPR”), si precisa che ogni > circostanza inerente alla presente email (il suo contenuto, gli eventuali > allegati, etc.) è un dato la cui conoscenza è riservata al/i solo/i > destinatario/i indicati dallo scrivente. Se il messaggio Le è giunto per > errore, è tenuta/o a cancellarlo, ogni altra operazione è illecita. Le > sarei comunque grato se potesse darmene notizia. This email is intended > only for the person or entity to which it is addressed and may contain > information that is privileged, confidential or otherwise protected from > disclosure. We remind that - as provided by European Regulation 2016/679 > “GDPR” - copying, dissemination or use of this e-mail or the information > herein by anyone other than the intended recipient is prohibited. If you > have received this email by mistake, please notify us immediately by > telephone or e-mail.* >
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