Thursday, 15 May 2014

S-57 Styling ENC Group 1 Classes (Skin of the Earth) for #GeoServer #ECDIS

Class LNDARE (Land area) requires a simple color fill with color token LANDA.

The S-52 Specification for ECDIS Display consists of 64 color tokens, in three (or five - depending on the version of the Spec) color palettes for DAY (DAY BRIGHT, DAY WHITE, and DAY BLACK), DUSK, and NIGHT displays. The differing color palettes enables the ECDIS to behave in a similar fashion to how a GPS Navigator in your car turns from a bright white display into a dark navy display in order to preserve your night vision during night time driving.

These color tokens are provided as CIE Yxy colors, and need to be converted into RGB colors by the ECDIS manufacturers.

For the DAY BRIGHT palette, LANDA maps to a soft yellow/light brown color. This shifts to a very dark e brown tone for night time use.

The next Class we want to show s DEPARE (Depth area) – this is the water, essentially. The DEPARE can be rendered in either 2 (default) or 4 distinguishing shades (of greyish blue for DAY BRIGHT palette, and dark violet/black for NIGHT) - DEPDW (deep water), DEPMD (medium deep water), DEPMS (medium shallow), DEPVS (very shallow), plus DEPIT (intertidal).

The NIGHT palette can only distinguish three shades – deep (using DEPDW), shallow (DEPVS), and intertidal (DEPIT). Note that deep and shallow are in reference to the safety contour.
The S-52 Specification recommends that the ECDIS allow the mariner to select a deep contour (default 30 metres) and a shallow contour (default 2.0 metres) in addition to safety contour (default 30 metres).
The actual contour lines are handled by the Class DEPCNT which is a Line Geometry. We shall look at this later.

In order to show the WRECKS layer with the LNDARE and DEPARE layers, we need to create a Layer Group, and this brings up the issue of the order of layering. The S-52 Specification consists of a field called Display Priority which is a number between 0 and 9, with the lowest priority 0 being laid down first and higher numbers being displayed on top. In cases where the Display Priority is the same, Geometries of type Point go on top of Lines, which go on top of Areas.

To facilitate this layering, I have developed a naming convention for these SLD Style files like so:

LNDARE_A1.sld – this signifies that style LNDARE is for Area Geometry, Display Priority 1
DEPARE_A1.sld – also for Area Geometry, Display Priority 1
WRECKS_P4.sld – this is for Point Geometry, Display Priority 4 (goes on top of the other two)

Putting all this together, we now have this for Cell US5FL24M:

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