A javascript package that aims to bring styling from a sld document to popular mapping tools. The project consists of two parts:
- An SLDReader that parses an SLD document into a style object.
- A function createOlStyleFunction that converts the parsed style object into a function that you can use in OpenLayers to style features.
The OpenLayers style converter tries to be as efficient as possible by recycling OpenLayers Style instances whenever possible.
CONTRIBUTIONS WELCOME!
More information about the standards:
See docs/examples folder, to serve them locally
npm start
- OpenLayers version 6.15 or higher.
- An up-to date browser. If you need to support older browsers, you have to compile SLDReader yourself with a different
browserslistsetting inpackage.json.- The browsers supported by SLDReader can be found here: https://browsersl.ist/#q=defaults .
- If you want to build and/or run SLDReader, NodeJS v18.18 or higher is required.
The SLDReader library can read both SLD v1.0 and SLD v1.1 documents, but not every part of the SLD standard is (or can be) implemented by the SLDReader and OpenLayers style converter (y 8000 et).
Marks with well known symbol names are supported: circle, square, triangle, star, cross, x, hexagon, octagon. ExternalGraphic icons are supported.
Two custom marks are also supported: horline for a horizontal line through the center and backslash for a line from the top left to the bottom right. Use backslash instead of horline if you want to have diagonal hashing as a polygon graphic fill.
Wellknown names that reference a symbol library, like ttf://CustomFont#42 are not supported. The Size and Rotation elements may be dynamic by using the PropertyName element.
Only one Graphic per PointSymbolizer is supported. Each Graphic can only have one Mark or one ExternalGraphic.
External graphics can be used with an OnlineResource linking to a valid image url.
<se:ExternalGraphic>
<se:OnlineResource xlink:type="simple" xlink:href="assets/img/flag-nl.png"/>
<se:Format>image/png</se:Format>
</se:ExternalGraphic>A valid image url can also be a base64 url:
<se:ExternalGraphic>
<se:OnlineResource xlink:type="simple" xlink:href="data:image/jpeg;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=="/>
<se:Format>image/jpeg</se:Format>
</se:ExternalGraphic>Instead of using base64 urls inside an OnlineResource, external graphics can also be embedded as base64 string using InlineContent with encoding="base64".
<se:ExternalGraphic>
<se:InlineContent encoding="base64">iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==</se:InlineContent>
<se:Format>image/jpeg</se:Format>
</se:ExternalGraphic>Inline content can also be SVG with encoding="xml".
<se:ExternalGraphic>
<se:InlineContent encoding="xml">
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" width="100" height="100">
<path d="M50,3l12,36h38l-30,22l11,36l-31-21l-31,21l11-36l-30-22h38z" fill="#0F0" stroke="#040" stroke-width="2"/>
</svg>
</se:InlineContent>
<se:Format>image/svg+xml</se:Format>
</se:ExternalGraphic>Important notes:
- SLDReader does not support
ColorReplacementinsideExternalGraphics. - Do not include the
<?xml ... ?>header for inline SVG content. - Make sure that inline SVG has
widthandheightattributes. Without it, (most?) browsers cannot properly load the SVG as an image.
SLD's with parametric embedded SVG's exported by QGIS should be able to be used in SLDReader.
Support for this functionality is quite hacky and experimental, but appears to work for simple examples.
Only these svg-parameters are supported:
- stroke
- stroke-width
- stroke-opacity
- stroke-linejoin
- stroke-linecap
- stroke-dasharray
- stroke-dashoffset
GraphicStroke with Mark or ExternalGraphic is mostly supported.
GraphicFill and PerpendicularOffset are not supported.
- It's not possible to use property-dependent values inside a GraphicStroke symbolizer.
- ExternalGraphic is mostly supported with these caveats:
- Always add a Size-element, even if using an ExternalGraphic instead of a Mark.
- SLD V1.0.0 does not officially support the Gap property. For this, SLDReader implements the same workaround that Geoserver uses. You can use the
stroke-dasharrayparameter to add a gap between stroke marks. To do this, use a dash array with two parameters: the first parameter being the size of the graphic and the second being the gap size. See the " GraphicStroke: ExternalGraphic" example.
The following QGIS vendor options are supported on line symbolizers with a graphic stroke:
<VendorOption name="placement">firstPoint</VendorOption><VendorOption name="placement">lastPoint</VendorOption>
See the demo page for an example.
Polygons with static fill and stroke style parameters are supported. See LineSymbolizer above for supported properties for the polygon outline.
For polygon graphic fills, both ExternalGraphic and Mark graphic fills are supported. The Marks supported here are the same as for a point symbolizer, with the additional restriction that feature-dependent value cannot be used.
The following WellKnownNames used by QGIS simple fills can be used as well:
- x
- cross
- line
- horline
- slash
- backslash
- brush://dense1 (till dense7)
Note: It's not possible to use property-dependent values for inside a GraphicFill element.
Dynamic Labels (with PropertyName elements), Font and Halo are supported. No vendor-specific options are supported. LabelPlacement or PointPlacement are supported. Graphic elements to display behind the label text are not supported.
- For PointPlacement, Displacement is supported1.
- For PointPlacement, Rotation is supported1. PropertyName as rotation value is supported.
- For PointPlacement, AnchorPoint is partially supported. Since OpenLayers does not support fractional anchor points, the label anchor is snapped to the alignment closest to left/right/top/bottom/center alignment. For instance: an
AnchorPointXof 0.1 is snapped to 0, corresponding to left alignment in OpenLayers. - For LinePlacement, PerpendicularOffset is not supported.
[1]: according to the SLD-spec, label rotation takes place before displacement, but OpenLayers applies displacement before rotation. Beware when combining rotation and displacement inside a single text symbolizer.
According to the SLD spec, most values can be mixed type (a combination of plain text and Filter expressions). This means that most values can depend on feature properties.
SLDReader supports dynamic values in these cases:
- PointSymbolizer Size
- PointSymbolizer Rotation
- TextSymbolizer Label
- SvgParameters used for styling:
strokestroke-opacitystroke-widthfillfill-opacityfont-familyfont-stylefont-weightfont-size
Note: dynamic parameter values currently have no effect on Marks used inside GraphicStroke or GraphicFill and will use SLD defaults instead.
Operators Add, Sub, Mul, and Div are implemented by converting them to function expressions.
The following units of measure are supported on symbolizers, as uom attribute:
http://www.opengeospatial.org/se/units/pixel
http://www.opengeospatial.org/se/units/metre
http://www.opengeospatial.org/se/units/foot
Values can be forced to pixels by appending px:
<se:PointSymbolizer uom="http://www.opengeospatial.org/se/units/metre">
<se:Graphic>
<se:Mark>
<se:WellKnownName>circle</se:WellKnownName>
<se:Fill>
<se:SvgParameter name="fill">#88aa88</se:SvgParameter>
</se:Fill>
<se:Stroke>
<se:SvgParameter name="stroke">#004000</se:SvgParameter>
<!-- Override symbolizer uom with pixels by appending px to the value. -->
<se:SvgParameter name="stroke-width">2px</se:SvgParameter>
</se:Stroke>
</se:Mark>
<se:Size>10</se:Size> <!-- in metres, as per uom attribute -->
</se:Graphic>
</se:PointSymbolizer>Restrictions:
- Units of measure are not supported for
GraphicStrokeandGraphicFill. - Units of measure are not supported on
stroke-dasharray. - Units of measure are not supported within or as return value of
Functionelements. The return type ofFunctionsis always treated as dimensionless or pixels, depending on context. - Values will always be treated as pixels where units of measure are not supported.
When converting metres (or feet) to pixels, SLDReader assumes that the resolution passed to the style function by OpenLayers is in metres/pixel. This is only true for some map projections. If you care about (approximately) correct sizes in metres, you have to pass a function that calculate the true point resolution in metres per pixel from the view resolution.
See the convertResolution option in the API example here.
The use of a Geometry element to point to a different geometry property on a feature to use for styling is not supported.
The SLDReader library supports the following operators inside Filter elements:
- PropertyIsEqualTo
- PropertyIsNotEqualTo
- PropertyIsLessThan
- PropertyIsLessThanOrEqualTo
- PropertyIsGreaterThan
- PropertyIsGreaterThanOrEqualTo
- PropertyIsNull
- PropertyIsLike
- PropertyIsBetween
- And
- Or
- Not
- FeatureId
SLDReader can parse <Function> elements, but the support for functions is vendor specific. Geoserver supports different functions than QGIS does. Since it's not feasible to support all possible vendor specific functions, SLDReader only supports a handful of them, listed below.
-
geometryType(geometry) -> string- Returns OpenLayers geometry type for the input geometry: (Multi)Point, (Multi)LineString, (Multi)Polygon, LinearRing, Circle, or GeometryCollection.
-
dimension(geometry) -> integer- Returns the dimension of the input geometry. 0 for points, 1 for lines and 2 for polygons.
- Returns -1 for GeometryCollection.
- Returns -1 for null geometry or unknown geometry type.
- For a multipart geometry, returns the dimension of the part geometries.
- See the dynamic styling demo for an example of dimension-based styling.
<Filter>
<PropertyIsEqualTo>
<Function name="dimension">
<PropertyName>geometry</PropertyName>
</Function>
<Literal>1</Literal>
</PropertyIsEqualTo>
</Filter>-
substr(string, start, [length]) -> string- Returns part of a string, starting from start index, starting with 1 (!!).
- Runs until the end if length is not given.
- A negative start index
-Nmeans startNcharacters from the end. - If length is negative, omit the last
lengthcharacters from the end of the string. - See QGIS docs for more info.
-
strSubstring(string, begin, end) -> string- Returns a new string that is a substring of this string. The substring begins at the specified begin and extends to the character at index endIndex - 1 (indexes are zero-based).
-
strSubstringStart(string, begin) -> string- Returns a new string that is a substring of this string. The substring begins at the specified begin and extends to the last character of the string.
- A negative
beginindex means: start at that many characters from the end of the string.
-
in(test, ...candidates) -> boolean- Returns
trueiftestvalue is present in the list ofcandidatesarguments, using string-based, case sensitive, comparison. - Example:
in('fox', 'the', 'quick', 'brown', 'fox') --> true. - Example:
in(2, '1', '2', '3') --> true.
- Returns
-
in2..in10- These are aliases for the
infunction, coming from (older) GeoServer versions that required a different function for different parameter counts.
- These are aliases for the
It's possible to add support for a specific function yourself, using SLDReader.registerFunction(functionName, implementation).
Example:
SLDReader.registerFunction('strSubstringStart', (text, startIndex) =>
text.slice(startIndex)
);After registering your function implementation, you can use it for example in a filter expression:
<Filter>
<PropertyIsEqualTo>
<Function name="strSubstringStart">
<PropertyName>title</PropertyName>
<Literal>2</Literal>
</Function>
<Literal>LLO WORLD</Literal>
</PropertyIsEqualTo>
</Filter>The registered function will be called with the value of its child expressions as parameters.
Important notes:
<Literal>expression parameters are always passed as string. If your function expects numeric parameters, convert accordingly.- The type of
<PropertyName>expressions depends on the feature. Typically, when serializing from GeoJSON, integer values are actual integers. - SLDReader does not check if the functions are called with the correct number of parameters. Make your function robust against receiving fewer parameters than expected.
- Geometry-valued expressions will always be OpenLayers Geometry instances.
- Unless specifically set for your features, the geometry property name is
'geometry'for OpenLayers features by default. - Make your functions as lenient as possible regarding possible inputs. Do not throw errors, but try to return a value that makes sense in that case. If you return
nullfrom a function implementation, the function fallback value will be used if one is specified in the SLD.<Function name="someFunction" fallbackValue="42">
Please include an example sld and if possible an example feature as GeoJSON.
Before starting on a pull request, please raise a Github issue first to prevent starting work on something we're already planning/working on.
When making a pull request, please:
- Address only a single issue or add a single item of functionality.
- Create a test for your functionality.
- Follow eslint rules and apply prettier.
- Update or add an example.
To install dependencies, test, build and document
npm install
npm test
npm run build
npm run docs
docker-compose up (runs doc website on :4000)