What a fun problem, I think the suggestion is a good one.
On Fri, Dec 1, 2023 at 2:31 AM Andrea Aime <
andrea.a...@geosolutionsgroup.com> wrote:
> Hi,
> I'm working with wind maps, where typically the data contains
> (some way to compute) magnitude and directions of the wind vectors.
>
> Now, the "direction" is an angle that is used to rotate a symbol.
> The angle has an assumption... that north is up. However, take a non
> trivial projection, like polar ones, and the assumption goes belly up, the
> direction of north can change point by point.
>
> So my plan is to introduce a function, "northFix", that would provide a
> correction angle
> taking as parameters a CRS and the current point. Something like this:
>
> <Rotation>
> <ogc:Function name="northFix">
> <ogc:Literal>EPSG:3976</ogc:Literal>
> <ogc:PropertyName>theGeom</ogc:PropertyName>
> <ogc:PropertyName>windDirection</ogc:PropertyName>
> </ogc:Function>
> </Rotation>
>
> Parameters in order:
>
> - The current CRS (in actual app, coming from an env variable, e.g
> "wms_crs" in GeoServer)
> - The current point
> - The angle to be fixed
>
> So far, so good, I'd say... but in a general SLD, that might still eat
> quite some time, in cases where it's not needed, e.g., web mercator, WGS84.
> It would be better to recognize the situation right away, and eliminate the
> function, replacing it with the wind direction property name directly.
>
> I have a StyleSimplifier that could do that, but it would also be quite
> ad-hoc. Could we have maybe an interface that functions could implement to
> test if they are simplifyable at all, and offer a replacement? E.g.
>
> SimplifyableFunction {
> Expression simplify(Function function);
> }
>
> Thoughts?
>
> Cheers
> Andrea
> ==
>
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> ==
>
> Ing. Andrea Aime
> @geowolf
> Technical Lead
>
> GeoSolutions Group
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>
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