1. Mapping in GeoServer with SLD and CSS
Ing. Andrea Aime
GeoSolutions

2. GeoSolutions Founded in Italy in late 2006
Expertise
Image Processing, GeoSpatial Data Fusion
Java, Java Enterprise, C++, Python
JPEG2000, JPIP, Advanced 2D visualization
Supporting/Developing FOSS4G projects
GeoServer, MapStore
GeoNetwork, GeoNode, Ckan
Clients
Public Agencies
Private Companies
FOSS4G 2015, Seoul
14th-19th September 2015

3. SLD vs CSS GeoCSS Styled Layer Descriptor OGC standard
XML based, verbose, hard to hand edit
Only showing relevant bits of the SLD
GeoCSS
CSS with extensions for map rendering
Simple, Compact, designed for human beings
Not a standard (several incompatible variants for mapping, GeoServer one has nothing to do with CartoDB/MapBox one)
Today I’m going to showcase some of the map styling abilities of GeoServer, comparing the SLD and CSS syntaxes for bothl
FOSS4G 2015, Seoul
14th-19th September 2015

4. Point styling FOSS4G 2015, Seoul 14th-19th September 2015
Let’s start our dive into map styling with point styling
FOSS4G 2015, Seoul
14th-19th September 2015

5. Simple symbol * { mark: symbol(triangle); } :mark { fill: maroon; }
This simple example uses the well known «triangle» mark to display a mountain peak. Notice the compactness of the CSS syntax. The one maybe weird bit is that to specifiy the color inside the mark, we need to create a special rule with the :mark selector, as using fill directly in the top level rule will make the renderer treat the points as polygons instead.
FOSS4G 2015, Seoul
14th-19th September 2015

6. One symbol per point class (SLD)
We want a different symbol per landmark type
600 lines of XML for 6 different points types
Too much repetition
We can also render point maps with external graphisc, referring to an external image, could be a png, jpeg, svg and so on.
Let’s also say we want to use six different symbols, and add labels to them. We then have to resort to add filters in rules, expressed in OGC filter syntax (XML).
FOSS4G 2015, Seoul
14th-19th September 2015

7. One symbol per point class (css)
This is the same with CSS, in which the we can just setup the common rendering details for labels and marks, and then override the point symbol in more specific rules, using a filter expressed in CQL sytanx. This is much shorter, but still 70 lines of CSS.
Still an excerpt
But 70 lines total
Power of cascading
FOSS4G 2015, Seoul
14th-19th September 2015

8. Embedding attribute in url (css)
Moved the image name in the feature attributes
Down to 15 lines
The style is all here
If we can push the name of the symbol to use as an attribute of our data called ‘IMAGE’, then we can redue it all to 15 lines of CSS, by expanding the attribute in the URL using the ${IMAGE]} syntax
FOSS4G 2015, Seoul
14th-19th September 2015

9. Using TTF fonts as marks
The well known symbolis and graphics are not the only way to add symbols in GeoServer, the mark names are actually pluggable and extensible by everybody, for example, we have a special syntax to pull symbols out of fonts filled with graphic icons, such as Webdings, by specifying the font name and the symbol code, which you can get using the charmap application
FOSS4G 2015, Seoul
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10. Wind barbs mark WMO compliant wind barb mark
Accounts for speed and emisphere
Examples:
windbarbs://default(100)[kts]
windbarbs://default(15)[m/s]emisphere=s
Another example of custom marks is our ability to render wind barbs, just provide in the name the wind strenght, the unit of measure, and in case you need that, if the point is located in the northern or southern emisphere. I’m not going though all the possibilities, but there are more mark types, such as customizable arrows and the ability to specify the mark shape as a WKT geometry
Full example available online in the GeoSolutions ND training material
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14th-19th September 2015

11. Filling polygons
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12. Solid filling * { fill: lightgrey; stroke: black; stroke-width: 0.5; }
Simple solid filling is relatively simple in both CSS and SLD, although of course the lack of boilerplate and being able to use named colors is a great advantage.
FOSS4G-EU 2015, Como
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13. Filling with repeating images
A more interesting way of filling is by repeating the same image or symbol over and over. In SLD this is called using a graphic fill, in CSS you just pass a url to the target symbol in the fill property.
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14. Marks for Hatches shape://vertiline shape://horline shape://slash
shape://backslash
We can also fill with marks, and there is a set that is designed for hatching, that is, a set of vertical, horizontal and diagonal lines that are filling the polygon, while still allowing you to see though it.
shape://plus
shape://times
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15. Filling with hatch marks
This is one example in CSS and SLD, using the «times» mark to create a cross hatch fill. Notice how we use the :fill pseudo-selector in the second css rule to control the size and color of the cross hatch.
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16. Using TTF fonts as marks8 8
Sometimes when filling with repeated symbols you need to add some space in between them, this can be done via the graphic marging vendor option. In SLD we have the special tag VendorOption for all the vendor options, in CSS they all start with the –gt prefix instead.
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17. Painting lines
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18. Solid lines * { stroke: darkOrange; stroke-width: 5; }
Switching to lines, we can see again a simple solid line, the advantanges of CSS are pretty much the same as with fills.
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19. Dashes FOSS4G-EU 2015, Como 14th-17th July 2015
The first variation we can do is to add a dasharray, which in this case specifies an alternation of 2px lines, 2px space, 2px line, and so on. In this example we can also see how scale denominator gets controlled, with tag in XML, with a filter on the the scale pseudo property in CSS
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20. Dashes with marks (SLD)
Using GraphicStroke with dash array to draw spaced circles, and then use dasharray with a dashoffset to interleave a line.
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21. Dashes with marks (CSS)
* {
stroke: darkRed, symbol('circle');
stroke-dasharray: 10 14, 6 18;
stroke-dashoffset: 14, 0; }
:stroke {
fill: darkRed;
size: 6;
In CSS if one wants to apply twice the same type of symbolzer, it’s possible to just add a second value to the property, by separating them with a comma
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22. Labeling
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23. Vendor options Priority labelling, static or attribute based
16 other vendor options to control in detail labelling:
group
labelAllGroup
spaceAround
followLine
maxDisplacement
repeat
maxAngleDelta
maxAngleDelta
autoWrap
forceLeftToRight
conflictResolution
goodnessOfFit
polygonAlign
graphic-resize
graphic-margin
partial
Labelling is a rather complex topic, let me just show the vendor options that allow GeoServer to produce better labelling.
FOSS4G-EU 2015, Como
14th-17th July 2015

24. Point labels FOSS4G-EU 2015, Como 14th-17th July 2015
When labelling points, we often want to add the auto-wrap option to make sure the labels do not get too long
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14th-17th July 2015

25. Line labels FOSS4G-EU 2015, Como 14th-17th July 2015
Labelling a road network normally requires a small halo to increase readability, but also a number of GeoServer extensions to make it look good:
Followline to get curved labels
Repeat to get the long lines labelled multiple times
Group to form a single line out of small separated segments of the same road
maxDisplacement to allow the labeller to search for better positions in case a candidate one is busy
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14th-17th July 2015

26. Polygon labels FOSS4G-EU 2015, Como 14th-17th July 2015
Anchor point to center horizontally
High priority to make them stand on top (default priority is 1000)
Autowrap long labels
Make sure 90% of the label is inside the polygon, allow for some search around the centroid
FOSS4G-EU 2015, Como
14th-17th July 2015

27. Label Obstacles FOSS4G-EU 2015, Como 14th-17th July 2015
Make a point symbolizer into a label obstacle, so that it cannot be covered with a label
FOSS4G-EU 2015, Como
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28. Support for pre-laid-out labels
IGN has custom engine to lay out labels at all zoom levels
Need to disable GeoServer own one
Two new vendorOptions:
conflictResolution=false
partials=true
Finally, if you have an engine or a human that pre-laid out the labels to achive maximum quality, you can add these two vendor options to make GeoServer stop deciding where to put the labels. These examples are courtesy of the national french geographic agency, which uses GeoServer for all the mapping purposes, but has a separate algorithm to lay out the labels once and for all for all the zoom levels they are publishing, at high quality, producing a map quality rivalling the one of printed atlases.
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14th-17th July 2015

29. Raster styling
FOSS4G 2015, Seoul
14th-19th September 2015

30. A DEM and a color map SRTM from USGS Standard color map
No-data natively transparent in 2.8.x thanks to JAI-EXT
Raster styling is almost always required when mapping raster surfaces of some kind, this one is a digital elevation model, but it could be also concentration of a pollutant, ambient noise in urban environment, and so on: in all cases we’ll want to associate colors to specific values of the phenomenon, and have GeoServer linearly interpolate between them.
CSS:
FOSS4G 2015, Seoul
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31. Expressions in ColorMap
Standard ColorMapEntry accepts only static values
Not anymore (GS 2.8.0)
Useful with env function, picking values from the GetMap
As you can remember when the zoom level we see a DEM. The DEM is based on the SRTM data set, and depcited with a elevation color map that excludes the nodata values setting their opacity to 0. As you can see it’s a bit dull, we miss hillshade
&ENV=low:10;medium:100;high:500
FOSS4G 2015, Seoul
14th-19th September 2015

32. Hillshading incoming
The only part of SLD 1.0 we have never had support for
In the works, scheduled for GeoServer (might be backported sooner)
raster-channels: auto;
raster-color-map:
color-map-entry(darkBlue, 0)
color-map-entry(darkGreen, 1)
color-map-entry(green, 300)
color-map-entry(yellow, 1800)
color-map-entry(maroon, 4000)
color-map-entry(white, 5000);
raster-relief-factor: 20;
raster-relief-brightness-only: false;
We are currently working on supporting hillshading, aka shaded relief, the one SLD 1.0 feature that we were still missing. Here is an example of its application on Korea, using the CSS syntax.
FOSS4G 2015, Seoul
14th-19th September 2015

33. Contrast enhancement <sld:RasterSymbolizer>
<sld:ContrastEnhancement>
<sld:Normalize>
<sld:VendorOption name="algorithm">
StretchToMinimumMaximum
</sld:VendorOption>
<sld:VendorOption name="minValue">50</sld:VendorOption>
<sld:VendorOption name="maxValue">800</sld:VendorOption>
</sld:Normalize>
</sld:ContrastEnhancement>
</sld:RasterSymbolizer>
We recently also updated the constrast stretching code, adding support for controlling which algorithm is used, and the range of data on which it operates. This is an example using the SLD syntad
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14th-19th September 2015

34. Transformations
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35. Geometry transformations
Dropping a shadow by offseting the building outline a bit using a «geometry transformation», that is, calling a filter function that takes the geometry and transforms it. This is applied on the single feature geometry, and its available both via SLD and CSS
FOSS4G-EU 2015, Como
14th-17th July 2015

36. Rendering transformations
CSS
WPS + WMS + rendering optimizations
In this slide, on the fly contour extraction
Extract on the fly contour lines from the DEM calling a process using the custom «Transformation» element, which operates at the layer level. There is still no equivalent functionality in CSS
The raster is tranformed into a set of lines with an elevation attribute which is then styled as vector
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37. RT: from raster to wind barbs
Two banded raster, U and V, extracted as a set of points with two attributes (subsampling possible)
In this one we extract the actual values of each cell as a set of points, controlling subsampling so that only a subset of the pixel values are extracted, and then assuming this is a two band wind raster map, we can build windbarbs out of it.
CSS
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14th-17th July 2015

38. Color blending and compositing
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39. Color blending and compositing
Support for alpha blending and compositing between Layer/FeatureTypeStyle
Alpha compositing:
copy
destination
source-over
destination-over
source-in
destination-in
source-out
destination-out
source-atop
destination-atop
xor
Color blending
multiply
screen
overlay
darken
lighten
color-dodge
color-burn
hard-light
soft-light
difference
exclusion
Color blending and compositing is a new feature in GeoServer 2.7, which allows for taking two layers in your map, and either masking them, with alpha compositing, or mix their colors, with color blending.
This is controlled by a vendor option at the FeatureTypeStyle level in SLD,
composite: multiply, 0.5;
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14th-17th July 2015

40. Alpha compositing examples
Source
Destination
When using compositing and color blending we always have two layers, what was already drawn so far, called the «destination», and what we want to add now, called the source. So for example, destination-in preserves the destination only if it’s inside the non transparent part of the source, source atop adds the source only on non transparent parts of the destination, and so on. As you can see, this can be used for various types of layer masking.
destination-in
source-atop
destination-atop
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41. Masking via alpha compositing
destination-in
Here is an example of alpha compositing that’s using a mask to generate a «line only on the inside of the polygon» effect
FOSS4G-EU 2015, Como
14th-17th July 2015

42. Color blending examples
Source
Destination
Color blending instead takes the color of both source and destination, and mixes the two with different rules. Multiply is a rather common way to mix in digital elevation models in a vector map for example
multiply
color-burn
difference
FOSS4G-EU 2015, Como
14th-17th July 2015

43. Z-ordering
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44. Z ordering
Added a new sortBy vendor option in SLD (sort-by in CSS), e.g.: <VendorOption name=«sortBy»>z_order</VendorOption>
Allows to sort features before painting them
In a _single_ FeatureTypeStyle
What if one needs to do road casing, or sort across two different layers?
As long as the FeatureTypeStyles involved are side by side, label them with the same sortByGroup property to sort them as one
Finally, a quick tip about z-ordering, a new feature in GeoServer 2.8. With z-ordering one can control, using the sortBy property, in which order the features are drawn, either in a single layer, or across layers. Let’s see an example.
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14th-17th July 2015

45. CSS example
[class = 'motorways'] {
stroke: #990000;
stroke-width: 8;
z-index: 0; }
[class = 'railways'] {
stroke: #333333;
stroke-width: 3;
z-index: 2;
stroke: #ffffff;
stroke-width: 1.5;
stroke-dasharray: 5, 5;
z-index: 3;
stroke: #ff6666;
stroke-width: 6;
stroke-linecap: round;
* {
sort-by: "z_order";
sort-by-group: "roadsGroup";
This is a rather complicated set of intersecting rails and roads somewhere in germany. The layer has a z_order property, and we are creating road casing effects using the z-index property, which controls the creation of featuretypestyles. The catch all rule at the bottom makes sure the features are ordered along the z-order property, and that all the feature type styles created by the z-index property are part of the same group.
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46. Questions? That’s all folks! info@geo-solutions.it
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47. Hidden bonus section ;-)
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48. Dynamic arrow mark Custom WellKnownMark
Arrow symbol with customizable proportions (a Mark size is controlled by the Size element)
extshape://arrow?hr=[hrValue]&t=[tValue]&ab=[abValue]
t: thickness (0-1)
hr: height/width ratio (0-1)
ab: arrow base ratio
The idea of dynamic elements work with marks too, we have custom marks taking parameters, like this arrow where the proportions of height, head size, and thickness, can be controlled.
The parameters can of course be coming from attributes, here too.
FOSS4G 2015, Seoul
14th-19th September 2015

49. Plates (SLD) FOSS4G-EU 2015, Como 14th-17th July 2015
Using GraphicStropke with dash array to draw spaced circles, and then use dasharray with a dashoffset to interleave a line. While nothing in this SLD is out of the standard there is no mention of this approach in the standard itself, it is believed only GeoServer supports this way of building complex strokes out of dashed symbols
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50. Plates (CSS) FOSS4G-EU 2015, Como 14th-17th July 2015
TODO: put all plate related stuff close toghether!
Using CSS we can see the usage of the shield better, notice how the reside and margin vendor options are used to stretch the otherwise square symbol to fit the label, with a bit of margin
FOSS4G-EU 2015, Como
14th-17th July 2015