[mapserver-users] Mapserver tile edge rendering behaviour

[Johannes Paul]

Hi Steve,
thanks for your answer.
Basically, I have the planet emerged lands that are cut-off in square
polygons. These polygons are stored in postgis, and I use mapcache with a
mapserver WMS source to tile the layer.
When I have a polygon ending exactly on the tile edge and the polygon does
not have adjacent polygons on the top or on the left hand tile, I miss my
polygon border.
As explained I made a simple test with a mapserver WMS request where the
requested bbox would be exactly the bbox of a square polygon, and mapserver
doesn't render top and left borders of the polygon...
Could you please tell me more about the options that could be used within
mapcache or mapserver conf ?
Thanks,
Johannes

On Thu, 12 Mar 2020 at 05:08, Steve Lime <sdlime at gmail.com> wrote:

> MapServer uses the center of the pixel but does compensate for models
> defined by other specs (e.g. WMS, which defines an extent as outer edge to
> outer edge. Straight CGI (mode=map) will adjust the requested extent based
> on the image size to ensure that square cells are being used. WMS allows
> for non-square cells.
>
> It’s possible you’re seeing the effect because the requested extent and
> image size are off just a bit. Would need a little more info to be sure.
>
> When tiling you can set edge buffers to deal with this sort of thing.
> Generally you’d choose a value to match your widest symbol. How exactly
> you’d deal with this depends on how you’re generating tiles (mapcache,
> mode=tile, etc...).
>
> —Steve
>
> On Wed, Mar 11, 2020 at 8:59 AM Johannes Paul <johannespaul92 at gmail.com>
> wrote:
>
>> Hello,
>> I use a data source (postgis or shapefile, it doesn't matter, the
>> behaviour is the same), that is made of a simple polygon created from a
>> bbox, on which is applied a simple 'outlinecolor'.
>> When calling my URL with a bbox that is *exactly* the size of that
>> polygon, mapserver only renders the bottom and the right hand edges; top
>> and left hand egdes are not drawn on my output image!?
>> When forcing 'WIDTH 2', I do get a thin (1 pixel) outline on the top and
>> left hand edges, and a thick (2 pixels) on the bottom and right hand edges.
>> I expect this is related to where mapserver is taking the coordinate
>> within the pixel (center? corner?), but I'm not sure ? Any option to
>> overcome that behaviour ?
>> Thanks in advance.
>> Johannes
>> _______________________________________________
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>> mapserver-users at lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/mapserver-users
>
>
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