Hi Andrea,
see responses below...
On Thu, May 22, 2008 at 12:22 PM, Andrea Aime <[EMAIL PROTECTED]> wrote:
> Hi,
> in the project we're following we need to make a couple of variants
> to the sldService, so I guess I'll need to discuss them a bit to make
> sure we don't break FAO users of that module.
>
> The first thing I need, is to change the generated rules so that they
> all use closed intervals, such as:
> 0 <= x <= 10
> 10 < x <= 20
> 20 < x <= 30
> as opposed of today's result:
> x <= 10
> 10 < x <= 20
> x > 20
>
> In order to do that without breaking current users, I was thinking
> of adding a new parameter, closedIntervals=true/false to the POST
> call that generates the intervals.
Even using directly closing intervals won't break FAO implementation, so use
the solution you prefer ... however using the closingIntervals parameter
would give higher control on the rules generation, so in my opinion we
should go for it.
> The second issue is dealing with odd but not uncommon data histograms
> like, for example {0 0 0 0 2 4 6 8}. If you ask the current quantile
> classifier to classify that with 4 intervals, you'll get {0 0}, {0 0},
> {2 4} {6 8}, which would result in very confusing rules (see attached
> screenshot for an example).
>
> One idea I had is to make the quantile function detect the flat areas
> and make it create separate classes for them, and then classify the
> rest using the standard sized classes. The above example would then become:
> {0 0 0 0} {2 4} {6 8}.
> Another example: {0 1 2 3 3 3 4 5}, 2 classes -> {0 1 2} {3 3 3} {4 5},
> that is, first isolate the flat area, then try to build classes of 4
> elements with the rest of the data, accepting the fact that more classes
> than requested may be generated.
>
> Another possible approach, which is easier because we can handle it
> in post processing, that is, when building the rules, would be to simply
> kill subsequent classes that do have the same min and max. With the
> above examples, the rules would become:
> {0 0 0 0 2 4 6 8}
> x = 0 (killing the second x = 0 interval)
> 0 < x <= 4
> 4 < x <= 8
> or if you prefer, {0 0 0 0} {2 4} {6 8}
> and:
> {0 1 2 3 3 3 4 5}
> 0 <= x <= 3
> 3 < x <= 5
> that is {0 1 2 3 3 3} {4 5}
>
> If the latter is good for FAO as well, I can just modify the way
> we build the rules and avoid touching the underlying quantile
> classification function. Opinions?
>
I would prefer that simply the quantile generates the right rules, I don't
think that post-processing would be a good approach. I would prefer to
modify the client behaviour accepting the fact that quantile can generate a
different number of classes than requested.
>
> Cheers
> Andrea
>
>
>
--
-------------------------------------------------------
Eng. Alessio Fabiani
Vice-President /CTO GeoSolutions S.A.S.
Via Carignoni 51
55041 Camaiore (LU)
Italy
phone: +39 0584983027
fax: +39 0584983027
mob: +39 349 8227000
http://www.geo-solutions.it
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