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
phone: +39 0584 962313
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