Hello! I have created a patch for GeoTools which implements whole layer transparency (for layers and labels) and allows to skip label rendering for a layer. The patch is submitted as a github pull request https://github.com/geotools/geotools/pull/32
Andrea asked me to explain what I try to do, so I will try to describe what is being done and why. We had to implement in our product a feature which would allow user to easily adjust layer transparency (by using a slider or some other input control - this is irrelevant). I think (correct me if I'm wrong) that this is not possible to achieve by means of SLD only. The picure "layer opacity.png" (which was produced by a patched version of GeoTools) shows desired result. Trying to mimic it with following SLD style renders output as in "sld opacity.png" image. =======8<===================== <StyledLayerDescriptor xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xmlns="http://www.opengis.net/sld"; xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd"; version="1.0.0" > <UserLayer> <LayerFeatureConstraints> <FeatureTypeConstraint/> </LayerFeatureConstraints> <UserStyle> <FeatureTypeStyle> <Rule> <PolygonSymbolizer> <Fill> <CssParameter name="fill">#0000FF</CssParameter> <CssParameter name="fill-opacity">0.5</CssParameter> </Fill> <Stroke> <CssParameter name="stroke">#000000</CssParameter> <CssParameter name="stroke-opacity">0.5</CssParameter> </Stroke> </PolygonSymbolizer> </Rule> </FeatureTypeStyle> </UserStyle> </UserLayer> </StyledLayerDescriptor> =======8<===================== This is a very simple use case. When layer style contains multiple symbolizers using different values for opacity, it would be really difficult to adjust them (if possible at all - opacity could be specified as a feature property) to achieve desired transparency at a layer level. But it would still produce bad output for overlapping objects or overlapping symbolizers. This feature (whole layer transparency) is present in ArcMap for example. We also had to implement a feature allowing for quick switching of labels on and off. Theoretically it could be implemented by removing all text symbolizers from layer style and restoring them when needed but it seems overly complicated and I think this is a very common use case for interactive map viewers. Removing TextSymbolizers could lead to an invalid style - when a TextSymbolizer is the only sybmolizer in a Rule. According to SLD schema a Rule is required to have at least one symbolizer. Removing a Rule could lead to invalid rendering - when the rule uses a Filter then the features which matched the filter would be rendered (after the rule was removed) by a rule with ElseFilter. Andrea mentioned that he wants to avoid extra API-s for styling layers. But I could come up with some other ideas (which we already implemented but not in a system which uses GeoTools) for extending GeoTools styling capabilities. Like not drawing features when a label for this feature was rendered. Please see http://msip-mapa.um.gliwice.pl/geoportaltoolkit/map.php?link=2924&skin=gliwice_new_mieszkaniec Near the lower right corner there is Stansława Moniuszki street with some address points marked with a small blue envelope (for those point labels could not be placed). But if the label is placed (Dworcowa street in the middle), the point icon is not drawn. -- Sebastian Graca Institute of Spatial and Cadastral Systems tel: +48 32 301 10 74 fax: +48 32 301 10 77 e-mail: sgr...@ispik.pl http://www.ispik.pl
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