[mapserver-users] Label text always clipped by tiles

[Jean-François Gigand]

I'm not sure if the issue is related to the renderer.
My issue is met on both AGG and GD, and is perfectly understandable:
MapServer requests vector data only within the BBOX. So the rendered
image misses symbols which are drawn from outside feature, even though
they should be visible on the image because of their size.
Same for labels: they are incomplete because missing on the tiles
whose BBOX do not contain the geometry they were created from.

TileCache is the solution. Set "metaBuffer" to the double of the maximum
size in pixels of your symbols.

A youger project following TileCache concepts is mod-geocache. It
seems to support metaBuffer and metaTiles (haven't tested it yet):
http://code.google.com/p/mod-geocache/

Jeff

2011/1/26 Mike Stoddart <stodge at gmail.com>:
> Thanks Jean-François, I'll try your solution.
>
> Is this clipping issue only a problem in the AGG renderer or does the
> original GD(?) renderer have the same problem.
>
> Thanks
> Mike
>
> On Wed, Jan 26, 2011 at 11:00 AM, Jean-François Gigand
> <jean-francois at gigand.fr> wrote:
>> Hi,
>>
>> I met the edge issue when I had to produce statistics maps with
>> proportional symbols.
>>
>> TileCache addressed the issue indeed, with the "metaBuffer" option
>> (see http://tilecache.org/docs/README.html#configuration).
>> It means that MapServer will be called to generate larger tiles which
>> are then cropped by TileCache, which has a time processing cost.
>>
>> The "metaTile" is meant to optimize this by rendering multiple tiles
>> as a single one.
>>
>> Jeff
>>
>> 2011/1/26 Gregor at HostGIS <gregor at hostgis.com>:
>>>> I was using TileCache, but I switched it off to debug this problem. If
>>>> TileCache generates larger tiles, will there still be clipped labels?
>>>> Just fewer clipped labels? I don't think this is a workable solution
>>>> for me, but if I have the time I'll try it.
>>>
>>> Correct; there would be FEWER labels clipped (if you force them and allow
>>> partials) or missing (if you disallow partials).
>>>
>>> How many fewer, depends on how large you make your meta-tiles. If they're
>>> 5x5, that's a significant reduction in the number of tile edges. If you
>>> really turn up your MAXSIZE in your mapfile, you could potentially make
>>> 10x10 meta-tiles; that's 1% as many tile edges.
>>>
>>> You could also make your tiles larger. If you have 512x512 tiles, and 10x10
>>> meta-tiles, that's a HUGE reduction in the number of tile edges over single
>>> 256x256 tiles.
>>>
>>> The only method I know that would eliminate ALL tile-edge artifacts, would
>>> be to eliminate tiling, e.g. singleTile:true in OpenLayers. Not that that's
>>> a great solution either, but it is sometimes the only way.
>>>
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>>
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