How it works
RSV Nuyina is Australia's icebreaker. Its underway system logs the ship's position, weather and sea
surface every minute, and the Australian Antarctic Data Centre publishes each voyage as a feature
service. The page reads the voyage you pick and puts the ship on a map at the time on the slider.
Follow the ship centres an azimuthal projection on the ship (+proj=laea +lat_0 +lon_0
at its position), so the map is rebuilt as the ship moves; with heading up it also turns so the
ship's course points up the screen, as a chart plotter does. The Antarctic view is the fixed
EPSG:3031 polar stereographic most Antarctic maps use.
Near the ship. A map centred on the ship is a map of what is close to it, and the choice
of azimuthal says what "close" keeps: aeqd keeps distance and bearing from the ship true, so the
range rings (circles of true distance, drawn as geodesics) are exact circles; laea keeps
area, stere keeps shape, and both pull the rings slightly out of round far out. In EPSG:3031 the
same rings are ovals. The readout gives the nearest place and the nearest ice edge on the map, as
distance and bearing from the ship.
Crow lines run from the ship to a place two ways: the great circle (solid), the shortest
way, whose course changes as the ship goes, and the rhumb line (dashed), one course all the way.
At these latitudes they part by hundreds of kilometres over a few thousand, and the great circle
bends towards the pole and the ice. The readout gives both, and how much farther the ship has
run than the great circle from where the voyage began; the
Rhumb lines page puts the two on four maps.
Two mosaics that overlap. The seafloor comes from two sources: IBCSO v2 (500 m, in its own polar
stereographic, EPSG:9354, south of 50 degrees S) and GEBCO 2026 (15 arc seconds of longitude and
latitude, the whole world). Where both cover a pixel, something has to choose which one is read. The
choice is a plan, separate from either grid: IBCSO first, a cut at a latitude, either alone, or the
difference where both have data. Colour by source paints the plan; IBCSO minus GEBCO
measures what the choice changes. GEBCO builds its Southern Ocean with IBCSO's compilation, so
the two should mostly agree there; the difference shows where they do not, and the ship's
readout gives both depths under the keel.
Cells at the ship draws each source's own cells round the ship: GEBCO's lon/lat cells
(narrow in longitude this far south), IBCSO's 500 m squares and the 25 km sea ice cells, in three
CRSs. The grids never share an edge, so one place is a different cell, and a different (column, row),
in each. Lines are drawn only where the cells are big enough to see.
Sea ice is the NSIDC Sea Ice Index for the day at the slider: concentration on a 25 km polar
stereographic grid, white from 15 percent (the usual ice edge, drawn as a line) to full cover.
Every source is read in its own CRS and resampled per pixel into the map; the polar stereographic
formulas are checked against PROJ for EPSG:3031, 9354, 3412 and 3976 in
test/check-nuyina.mjs.
Hash keys: v (voyage code), t (0 to 1 along it), view
(ship, polar), proj, up, span (log10 km),
plan, cut, src, ice, cells,
coast, rings, by, to (where the crow lines go),
from (wfs, pq) and pq (the parquet file's address).
- Voyage data: RSV Nuyina underway data, Australian Antarctic Data Centre
(CC BY 4.0), each voyage cited by its record (linked under the voyage list). The parquet copy of the
whole record is nuyina-underway, read a few
columns and row groups at a time with hyparquet
and fzstd. The Now entry reads the last
two weeks by time rather than by voyage code, so the page follows the ship between voyages.
- IBCSO v2: Dorschel, B. et al. (2022) The International Bathymetric Chart of the
Southern Ocean Version 2, Scientific Data 9, 275, doi:10.1038/s41597-022-01366-7; read from a
COG copy.
- GEBCO Compilation Group (2026) GEBCO 2026 Grid, from Source Cooperative.
- Fetterer, F. et al. Sea Ice Index, Version 4 (G02135), NSIDC.
- Source addresses from the R package sds (its registry and
nsidc_seaice()). The overlap and grid distinction follows the wxylib design note
m10: overlapping COG mosaics.
- Map projections with proj4js, checked against
PROJ; polar stereographic after Snyder (1987) Map Projections: A Working Manual.
COGs read with geotiff.js. NSIDC's server sends no CORS
header, so the sea ice GeoTIFF is read through a small relay that forwards Range requests and adds
it (nectar,
recipes/relay); coastlines from
Natural Earth; the globe drawn with d3-geo.