Re: [mapserver-users] RE: How to label only largest displayed areas?

Fri, 03 Feb 2012 08:24:26 -0800 

Hi Jukka,
The labelcache could be extended to handle this, we already create and entry for each label, by name and by priority, if we priority was set to -1 or 02 for largest or smallest, and a size slot was added to the cache then all the rendering code would need to do isi compute the rendered (ie clipped) size in pixels or whatever. Database queries don't work if you are using shapefiles or other datasources. While postgres connections do support a !BOX! as Steve L mentioned not all databases have this coded. Size could be trivially computed as the number of pixels drawn for the polygon when it is rendered, although this might not be easily accessible given some of the newer rendering engines we support now. 

-Steve

On 2/3/2012 10:03 AM, Rahkonen Jukka wrote:

Hi,

But still in this certain case the final select should sort by
clipped size AND group by state name AND select the biggest feature
from each group. Doesn't it feel easier to do with a database query
and addional label layer? But how to pass the WMS BBOX for the
database so it could do polygon intersections for getting the areas?
And attributes should be transferred too so that clipped areas could
be sorted by state name.

-Jukka Rahkonen-


-----Alkuperäinen viesti----- Lähettäjä:
[email protected]
[mailto:[email protected]] Puolesta Stephen
Woodbridge Lähetetty: 3. helmikuuta 2012 16:44 Vastaanottaja:
[email protected] Aihe: Re: [mapserver-users] RE: How
to label only largest displayed areas?

Phil,

In theory, it might be possible to do this by extending the
labelcache code to save the clipped area size of each polygon or a
clipped length of a line and then sort the labelcache items by size
and label them. MINDISTANCE could be applied to limit the number of
labels using the existing code. This behavior would need to be
triggered by a new LABEL keyword maybe like PRIORITY
[LARGEST|SMALLEST]

If you want to write an enhancement ticket for this in the bug
tracker you can add my comment above, but I suspect that you would
have to fund the development of this or provide a patch.

Best regards, -Steve W

On 2/3/2012 8:59 AM, Anzel, Phil - NRCS, Fort Collins, CO wrote:

Hi, Jukka and Steve,

Thanks for your replies. Jukka is correct, I do not believe it
is simple. Steve, your approach sorts all areas and then filters
by those visible in the layer's extent. I'm looking for ranking
by the clipped area. For example, if the current map and layer's
extent shows the a small sliver of the mainland of California and
a larger visible part of an island that is part of California,
only

the island

would be labeled, as its visible area is larger than that of the
sliver.

- Phil

-----Original Message----- From: Rahkonen Jukka
[mailto:[email protected]] Sent: Thursday, February 02,
2012 4:01 PM To: Lime, Steve D (DNR); Anzel, Phil - NRCS, Fort
Collins, CO; [email protected] Subject: Re: How to
label only largest displayed areas?

Hi,

I understood that meaning was to put exactly one label per
state. Each state, even tiny ones, should be labeled. But one
state should get only one label even if the map window is
splitting the state polygon into two or more intersections. Those
intersections may be bigger than the tiny state. Not extremely
simple.

-Jukka-

________________________________________ L Lime, Steve D (DNR)
wrote:


I'd do this by sorting features based on area (ascending
order). This would draw the smallest polygons first, but would
put the labels for the shapes with the largest area into the
label cache last (where they would be placed and drawn first).
I've done this with labeling lakes and it works fine.


Steve

-----Original Message----- From:
[email protected]
[mailto:[email protected]] On Behalf Of
Anzel, Phil - NRCS, Fort Collins, CO Sent: Thursday, February 02,
2012 1:43 PM To: [email protected] Cc: Anzel, Phil
- NRCS, Fort Collins, CO Subject: [mapserver-users] How to label
only largest displayed areas?

Hi, All,

How can I label only the largest displayed areas within an
extent? For example, if I'm labeling states of the United States
and my extent covers a small region around the Maine, New
Hampshire and Massachusetts junction, I only want a single label
for each state, chosen by the largest displayed area (within the
current map extent) in each state.

I'm using spatial data stored in Microsoft's SQL Server 2008.

I've created an enhancement request ticket (#4173: Define a
current layer extent's WKT string for use in Data statement) as
one possible approach, but this approach requires a change to
MapServer.

Is there a better way?

Thanks.

- Phil Anzel Vistronix Inc for USDA/NRCS/ITC

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