tile_math.hpp¶

file src/app/map/tile_math.hpp · Applications

Web Mercator (EPSG:3857) tile arithmetic for slippy maps, the scheme OpenStreetMap uses.

Source src/app/map/tile_math.hpp

Tile coordinates at zoom z run from 0 to 2^z along both axes, with (0, 0) at the north-west corner of the world (latitude kMaxLatitudeDeg, longitude -180) and y growing southwards; the integer part names a tile and the fraction is the place inside it. Pixel coordinates are tile coordinates times kTileSize, so a widget only needs to know where its centre lies in pixels at the current zoom. All functions here work on whole zoom levels; MapWidget scales their results for fractional zoom.

See also

https://wiki.openstreetmap.org/wiki/Slippy_map_tilenames

Namespaces¶

Namespace	Description
`nmeasim::app::map`	The slippy-map view of the desktop application, part of `nmeasim::app`.

Types¶

Type	Description
`TileKey`	Address of one tile: its zoom level and its column and row at that level.

Namespace members¶

Declared or defined in this file and documented on the page of their namespace.

Member	Description
`nmeasim::app::map::kTileSize`	Edge length of a square raster tile in pixels, as served by OpenStreetMap-style servers.
`nmeasim::app::map::kMinZoom`	Lowest zoom level the map widget allows; at level 1 the world is 2 by 2 tiles.
`nmeasim::app::map::kMaxZoom`	Highest zoom level the map widget allows, the deepest level the OpenStreetMap standard tile layer serves.
`nmeasim::app::map::kMaxLatitudeDeg`	Northern and southern limit of Web Mercator in degrees, `atan(sinh(pi))`.
`nmeasim::app::map::tiles_at`	Returns the number of tiles along one axis at a zoom level, 2^`zoom`.
`nmeasim::app::map::tile_coordinates`	Returns the fractional tile coordinates of a position at a zoom level.
`nmeasim::app::map::pixel_coordinates`	Returns the pixel coordinates of a position at a zoom level.
`nmeasim::app::map::position_of_tile`	Returns the position at fractional tile coordinates at a zoom level, the inverse of `tile_coordinates`.
`nmeasim::app::map::position_of_pixel`	Returns the position at pixel coordinates at a zoom level, the inverse of `pixel_coordinates`.
`nmeasim::app::map::tile_at`	Returns the tile containing fractional tile coordinates, with x wrapped around the antimeridian.
`nmeasim::app::map::parent_of`	Returns the tile one zoom level up (one level less detailed) that contains a tile.
`nmeasim::app::map::wrap_longitude`	Wraps a longitude into [-180, 180), as the world repeats east and west.
`nmeasim::app::map::metres_per_pixel`	Returns the ground distance one pixel covers at a latitude and zoom level.