Creating stunning maps with GeoServer With SLD and CSS Ing. Andrea Aime GeoSolutions 1 

GeoSolutions Enterprise Support Services Deployment Subscription Professional Training Customized Solutions GeoNode • Offices in Italy & US, Global Clients/Team • 40+ collaborators, 30+ Engineers • Our products • Our Offer 

Affiliations We strongly support Open Source, it Is in our core We actively participate in OGC working groups and get funded to advance new open standards We support standards critical to GEOINT 

Quick tour of styling languages 4 

Languages SLD 1.0 core SLD 1.1 core YSLD extension MBStyles community GeoCSS extension SLD 1.0 inspired object model, with extensions parse parse parse parse and translate parse and translate 5 Map rendering 

Shared concepts ● Layers (the styles applies to) ● Rules ● Filters/selectors (what should be painted) ● Scale dependencies (zoomed in, zoomed out?) ● Symbolizers (how should it be painted) – Point – Line – Polygon – Text 6 

Styled Layer Descriptor 1.0 and 11 ● OGC styling standard, XML based ● Was meant for machine export but ended up being edited a lot by hand ● Can be generated by external tools and imported (with some hand tweaking) 7 

SLD 1.0 example … type alpine_hut 100000.0 image/png Filter Scale dep. Symbolizer 

YSLD ● SLD in YAML syntax ● Filtering by CQL ● Can define reusable variables and blocks ● Verbosity it’s between SLD and CSS ● Has a notion of zoom levels, if needed feature-styles: - rules: - filter: type = 'alpine_hut' scale: (,100000.0) symbolizers: - point: symbols: - external: url: symbols/alpinehut.p.16.png format: image/png 9 

GeoCSS ● Compact syntax, familiar for web developers ● CQL based filtering, rule nesting and cascading keeps styling compact ● Does not get any more compact than this: ● Cons: some are confused by “rule cascading” 🡪 can now be turned off [type = 'alpine_hut'][@sd < 100k] { mark: url('symbols/alpinehut.p.16.png'); } 10 

MBStyles (aka MapBox GL) ● Symbols as “sprites” (symbol collections) ● Can be applied both on the client side and the server side ● Online editors available, complex expressions still require writing JSON ● JSON based, designed for GUI editing (like SLD) instead of hand editing ● Scale control based only on Web Mercator zoom levels ● 

MBStyles (aka MapBox GL) { "version": 8, … boilerplate omitted here "name": "mountain huts" , "sprite": "https://my.sever/sprite" , "layers": [ { "id": "huts", "type": "symbol", "minzoom": 9, "filter": [ "==", "type", "alpine_hut" ], "layout": { "icon-image" : "alpinehut", "icon-size": 1, "icon-allow-overlap" : true } } ] } Filter (in postfix notation!) Scale dep. Symbolizer The sprint contains various images, like in videogames 

Styling concepts: Scale dependencies 13 

Scale dependency Filters ● SLD: ● 1000 ● 1000000 ● CSS ● [@sd > 1k][@sd < 1M] Compact expression of large numbers makes them readable at a glance, e.g., 100k, 1M , 10M Show buildings as user zooms in 

Unit of Measure ● Real world measures, sizes grow as one zooms in … #0000FF 5 ... … stroke: blue; stroke-width: 5m; SLD CSS 

Transformation functions ● Use a different value depending on the current scale/zoom level ● For non linear scaling [class = 'highway’ and type in ('motorway’, 'motorway_link’)] [@sd < 25M] { stroke: #e66e89; stroke-width: categorize(@sd, 2, 400k, 1.9, 800k, 1.4, 1.5M, 1, 3M, 0.8, 6M, 0.5); ● Less than 400k 🡪 2px ● [400k, 800k] 🡪 1.9px ● [800k, 1.5M] 🡪 1.4px ● [1.5M, 3M] 🡪 1 ● [3M, 6M] 🡪 0.8 ● Above 6M -> 0.5 CSS 

Transformation functions in SLD #e66e89 wms_scale_denominator 2 400000 1.9 800000 1.4 1500000 1 3000000 0.8 6000000 0.5 SLD 

Point styling 18 

Simple symbol [type = 'alpine_hut'][@sd < 100k] { mark: url('symbols/alpinehut.p.16.png'); } type alpine_hut 100000.0 image/png SLD CSS 

SVG as a scalable, fillable shape [type = 'bank'][@sd < 6k] { mark: symbol('file://symbols/bank.svg'); :mark { fill: #734a08 }; mark-size: 14; } type bank 6000 file://symbols/bank.svg #734a08 14 CSS bank.svg 

Marks composition and override [type = 'fountain’] { [@sd < 6k] { mark: symbol(circle), symbol(circle); :nth-mark(1) { fill: #b5d0d0 }; :nth-mark(2) { fill: #576ddf }; mark-size: 10, 3; }; [@sd < 3k] { mark: symbol('file://symbols/fountain.svg'); :mark { fill: #576ddf; }; } } CSS 

● Here are some examples: ● From TTF fonts using the name ttf://#charcode ● Windbarbs, e.g.: windbarbs://default(15)[kts] ● WKT specification, e.g. wkt://MULTIPOLYGON(((-0.25 -0.25, -0.125 -0.25), (0.125 -0.25, 0.25 -0.25)), (-0.25 0.25, -0.125 0.25), (0.125 0.25, 0.25 0.25) …… ) ● Build your own, pluggable system ● Full docs at: http://docs.geoserver.org/latest/en/user/styling/sld/exte nsions/pointsymbols.html Other mark options 

Filling polygons 23 

Solid filling * { fill: lightgrey; stroke-width: 0.5; } #d3d3d3 0.5 SLD CSS 

Overlap solid fills with repeated icons fill [@sd < 800k][type in ('cemetery', 'grave_yard')] { fill: #aacbaf; [religion = 'jewish'] { fill: #aacbaf, url('symbols/grave_yard_jewish.png'); }; [religion = 'christian'] { fill: #aacbaf, url('symbols/grave_yard_christian.png'); }; [religion = 'INT-generic'] { fill: #aacbaf, url('symbols/grave_yard_generic.png'); }; } CSS 

Hatching shape://times #ADD8E6 8 [@scale < 10000] { fill: symbol('shape://times'); fill-size: 8; :fill { stroke: #ADD8E6; } } SLD CSS 

Line symbology 27 

Solid lines (OSM admin borders) [type = 'administrative'] { [admin_level <= 4], [admin_level = 5 or admin_level = 6][@sd <= 400k], [admin_level = 7 or admin_level = 8][@sd <= 200k], [admin_level = 9 or admin_level = 10][@sd <= 100k] { stroke: #ac46ac; stroke-opacity: 0.4; } } CSS 

Dashes/Marks/images along a line * { stroke: darkRed, symbol('circle'); stroke-dasharray: 10 14, 6 18; stroke-dashoffset: 14, 0; :stroke { fill: darkRed; size: 6; } } ● Two coordinated dashed lines ● One made with lines ● One made with circles ● The offset shifts them to have one appear in the empty spaces of the other CSS 

Labeling 30 

Vendor options • Priority labelling, static or attribute based • Deluge of vendor options to control in detail labelling: • group • labelAllGroup • spaceAround • followLine • maxDisplacement • repeat • maxAngleDelta • autoWrap • forceLeftToRight • conflictResolution • goodnessOfFit • polygonAlign • graphic-resize • graphic-margin • partials • underlineText • strikethroughText • charSpacing • wordSpacing 

Polygon labels FULLNAME Arial 14.0 bold 0.5 0.5 #000000 50000 100 200 0.9 SLD 

Point labels and obstacles [@sd < 200k] { label: [FULLNAME]; label-anchor: 0.5 1.0; label-offset: 0.0 -14.0; font-fill: #000033; font-family: Arial; font-size: 12; halo-color: white; halo-radius: 1.5; label-priority: 200000; label-auto-wrap: 100; mark: url('./img/landmarks/${IMAGE}’); mark-label-obstacle: true; } «FULLNAME» attribute Auto wrapping label with halo. Data driven symbol URL Labels won’t overlap the symbol CSS 

Line labels [@sd < 200k] { label: [LABEL_NAME]; font-fill: #000000; font-family: Arial; font-size: 13; font-style: normal; font-weight: bold; halo-color: #FFFFFF; halo-radius: 1; label-follow-line: true; label-repeat: 400; label-group: true; label-max-displacement: 200; } Draw «LABEL_NAME», black, with white halo Draw them along lines, fuse segments with same label, repeat CSS 

Raster styling 35 

A DEM and a color map ● SRTM from USGS ● Standard color map ● Also shaded relief (not shown in the css below) [@sd > 75000] { raster-channels: auto; raster-color-map: color-map-entry(#00BFBF, -100.0, 0) color-map-entry(#00FF00, 920.0, 0) color-map-entry(#00FF00, 920.0, 1.0) color-map-entry(#FFFF00, 1940.0, 1.0) color-map-entry(#FFFF00, 1940.0, 1.0) color-map-entry(#FF7F00, 2960.0, 1.0) color-map-entry(#FF7F00, 2960.0, 1.0) color-map-entry(#BF7F3F, 3980.0, 1.0) color-map-entry(#BF7F3F, 3980.0, 1.0) color-map-entry(#141514, 5000.0, 1.0); } CSS 

Contrast enhancement http://docs.geoserver.org/latest/en/user/styling/sld-reference/rastersymbolizer. html#contrastenhancement StretchToMinimumMaximum 50 800 GeoServer vendor extension SLD 

Other assorted features 38 

Color blending and alpha compositing multiply color-burn difference Source Destination https://docs.geoserver.org/latest/en/user/styling/sld/extensions/composite-blend/index.html More info at: Mask with alpha compositing multiply, 0.5 

Z ordering https://docs.geoserver.org/latest/en/user/styling/sl d/extensions/z-order/syntax.html#z-ordering-acros s-layers [class = 'motorways'] { stroke: #990000, #ff6666; stroke-width: 8, 6; stroke-linecap: round; z-index: 0, 2; } [class = 'railways'] { stroke: #333333; stroke-width: 3; z-index: 1; } [class = 'railways'] { stroke: #ffffff; stroke-width: 1.5; stroke-dasharray: 5 5; z-index: 2; } * { sort-by: "z_order"; sort-by-group: "roadsGroup"; } CSS 40 

Rendering transformations • WPS + WMS + rendering optimizations • In this slide, on the fly contour extraction * { transform: ras:Contour(levels: 1100 1200 1300 1400 1500 1600 1700 1800); stroke: black; label: [GRAY-INDEX]; font-fill: black; font-family: Sans; font-size: 12; halo-radius: 2; halo-color: white; label-follow-line: true } CSS 41 

Jiffle map algebra * { transform: ras:Jiffle(script: ‘ nir = src[7]; vir = src[3]; dest = (nir-vir)/(nir+vir);’); raster-channels: auto; raster-color-map: color-map-entry(#00BFBF, -100.0, 0) color-map-entry(#00FF00, 920.0, 0) … } CSS On the fly NDVI computation from Sentinel 2 images 

Point and click editors 43 

QGIS SLD export • Basic vector and raster styling covered • Much advanced bits missing though • Needs sponsoring on both ends (QGIS and GeoServer) 

GeoStyler https://geostyler.github.io/geostyler-demo/ 

MapStore styler https://mapstore.readthedocs.io/en/latest/user-guide/layer-settings/#visual-editor-style 

That’s all folks! Questions? [email protected] 47