Data & licence

Time zone boundaries

Celeris works out the time zone of a place from data it carries rather than from a network service, so the times are right for the point under the crosshair even with no connection. The boundaries are under ODbL 1.0, and so is the grid made from them.

The boundaries come from timezone-boundary-builder by Evan Siroky, built from OpenStreetMap data, © OpenStreetMap contributors. They were rasterised to a grid of one twentieth of a degree, run-length encoded and compressed. The source is available under the Open Database License (ODbL) 1.0, and so is this derived database.

The file is raw deflate, no zlib header. Unpacked it starts with the four bytes CTZ1, then the width, the height and the number of zones as unsigned 16-bit integers. Then that many zone identifiers, each a length byte followed by UTF-8. Then height + 1 unsigned 32-bit row offsets into the runs, and finally the runs themselves: pairs of unsigned 16-bit integers giving the column a run ends before and the index of the zone it holds. Everything is little endian. Row 0 is the north pole, column 0 is 180° west, and a cell holds the zone at its centre.

The other data Celeris carries have pages of their own: the star catalogue, the points of interest and the elevation data.

The orbital elements the space station is drawn from have no page, because nothing about them is changed: they are read exactly as CelesTrak publishes them.