[Geoserver-devel] Re: Priority Labeling (Lite/SLD)

[Amit K. <ami...@ya...>]

Dave,

Cole is talking about something called "Label by Scale" in Geomedia.
ArcGIS handles it better than Geomedia by some automatic scale calc.
This is real important as it clutters up the whole graphics if rendered
without zoomed in scale. Rendering labels takes a horrible amount of
time otherwise. I think most people here know about it.

Thansk

--- Cole Markham <mar...@gm...> wrote:

> This is very interesting to me. I would also like to see some concept
> of turning off all labels based on the zoom level.
> 
> I'm a little confused as to whether this works with all feature
> types,
> and if so how would you specify the constraints (e.g. from a PostGIS
> database).
> 
> The data we are labeling is primarily roads and buildings, so it
> would
> make the most since to prioritize based on feature size. This leads
> to
> the simple inclusion of the zoom concept since you could tell it not
> to label if the feature is below some threshold.
> 
> What changes would need to be made to uDig in order to support this?
> Or should I direct that to the uDig list?
> 
> I will be happy to do some testing, and might have some time to help
> with the uDig side as well.
> 
> Cole Markham
> 
> On 8/23/05, db...@op... <db...@op...> wrote:
> > After talking with James, I've decided to start improving the
> Labeler
> > (again).
> > 
> > My first improvement will be to add "priority labeling".  Right
> now,
> > labeling order is random (ie. based on the hashtable).  I'd like to
> > change it so I can give features different "priority" values so
> they
> > show up "first".
> > 
> > Here's a simple example;
> > 
> > I have a city DB (point, population, name) and, on my map, i want
> "New
> > York" (population 8,000,000) to be drawn before "Yonkers"
> (population
> > 200,000).  These 2 cities are very close, so if only one can be
> drawn I
> > want New York to be drawn instead of it being "random".
> > 
> > Another example would be to use "<Function name='geomArea'>" to so
> you
> > can have "Central Park" labeled instead of "The Pool" (a little
> lake in
> > the middle of the park.
> > 
> > This isnt too difficult a change;
> > 
> > 1. add an expression "labelPriority" to TextSymbolizer
> >       + default = 1,000 (or what have you)
> > 
> > 2. Modify the HashTable so that it also stores the priority value
> >       + for items-with-the-same-label-grouping I think we should
> use an
> > "add" priority strategy for the group.  In the future, we'll have
> ways
> > of turning off grouping.
> > 
> > 3. Modify the labeler so instead of just grabbing stuff from the
> > hashtable, it sorts it on the priority value
> > 
> > 4. modify the SLD parse so it has a "<Priority>" tag with an
> > <Expression> inside it
> > 
> > 5. update the geoserver SLD validator so the .xsd reflects the
> extra
> > Priority tag.
> > 
> > 
> > You'll notice that the results will be the same as they are now if
> > people dont put a "<Priority>" tag in, so this is backwards
> compatible.
> > 
> > There could be some layer-to-layer conflicts, but thats up to the
> people
> > writing the SLDs deal with.
> > 
> > 
> > I believe the PMC already gave an okay to these changes a while
> ago, I
> > (or anyone else) havent had a chance to do them.
> > 
> > Other improvements will be things like:
> > * grouping - on/off
> > * always render (for people who dont care if the label overlaps)
> > 
> > I'd like to see the labeling get pretty good, since its probably
> one of
> > the top "missing pieces" in Geotools (apart from really good raster
> > support - which others are currently working on).  Does anyone have
> any
> > comments or other things that they want supported?  Anyone willing
> to
> > help (ie. programming, testing, giving feedback, trying it on their
> > data  to see how the results look)...
> > 
> > NOTE: THE BIGGEST PROBLEM ABOUT THIS IS THAT OUR SLD FILE WILL NO
> LONGER
> > BE 100% OGC 1.0 COMPATIBLE.
> > 
> > We've already discussed this and noone (except me) has had a
> problem
> > with it.  But, we really dont have any other way of doing this.
> > 
> > 
> > dave

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