Hi Andrea:
Thanks for the detailed background - stuck between a rock and a hard place.
I would prefer the defaults to be chosen for speed; rather then pretty (but
perhaps that is me).
In this case I don't like the idea of changing rendering on something that
is already deployed everywhere.
So although I usually consider following the standard strictly as the default
setting; I think we should resist and maintain current behaviour.
Always fun when a user reads the standard more carefully (or in a different
manner)
then we have.
Jody
On 28/06/2010, at 6:08 PM, Andrea Aime wrote:
> Hi,
> following a report from a user I was checking the SLD/SE specifications
> about the meaning of PerpendicularOffset
>
> ------------------------------------------------------------------
>
> The PerpendicularOffset element of a LinePlacement gives the perpendicular
> distance away from a line to draw a label. It is defined simply as:
> <xs:element name="PerpendicularOffset"
> type="sld:ParameterValueType"/>
> The distance is in pixels and is positive to the left-hand side of the
> line string. Negative
> numbers mean right. The default offset is 0.
>
> -------------------------------------------------------------------
>
> By implementing the spec to the letter it seems that a horizontal
> road labels would appear either above or below the line depending
> on the orientation of the line.
>
> What we do instead considers the eventual label flipping, that
> we do to keep the label readable, and flips the offset as well.
> In other words, if you consider a horizontal line oriented
> from east to west with positive offset, the natural position
> of the label would be below the line, and upside down,
> but in order to keep it readable we flip both the label and
> the offset and end up with a label that is above the line
> and readable.
>
> Now, for road labeling this is what I would honestly expect
> from a positive value ("positive must mean above, right?")
> yet that is not what the spec says for lines oriented from
> east to west.
>
> Now, the user in question has a legit case for want the
> labels below: he wants to label the border or a polygon
> the way google does it for state/province borders.
> See the Wisconsin/Iowa border here for an example:
> http://maps.google.com/?ie=UTF8&ll=42.599598,-90.702095&spn=0.185244,0.445976&z=12
>
> Besides that, we're not really respecting the spec...
>
> So, what shall we do? I was thinking to provide a
> new vendor options "absoluteOffset" true/false that
> would control if we adjust the offset or follow the
> spec by the letter (anyone with a better name?)
>
> The bigger question is, what will be the default.
> Do we follow the spec by the letter by default, even if
> it does not make much sense and it will break backwards
> compatibility for uDig/GeoTools/GeoServer users, or
> we default on our current behavior?
>
> Or we roll a global flag to determine what the default
> would be (a rendering hint?)
>
> Cheers
> Andrea
>
>
> --
> Andrea Aime
> OpenGeo - http://opengeo.org
> Expert service straight from the developers.
>
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