zfxyu-spec: ZFXYU specifications (Work in Progress)

Definition

Four-dimentional spatial identifier candidate ZFXYU of a point with longitude lng [decimal degrees], latitude lat [decimal degrees] (lat_rad in radians), elevation h [m], and unix time t [s] shall be encoded {z}/{f}/{x}/{y}.{u} when a zoom level z is given as an integer and f, x, y, u are given in the following formulae:

• f = floor(n * h / H)
• x = floor(n * ((lng + 180) / 360))
• y = floor(n * (1 - log(tan(lat_rad) + (1 / cos(lat_rad))) / PI) / 2)
• u = floor(t / 1800)
• where n = 2 ^ z, Z = 25 and H = 2 ^ Z [m].

Definitions of z, x, y are the same as ones in the industry standard Slippy Map Tilenames.

Characteristics

• Height of a voxel represented by a ZFXYU with z=Z is 1 [m].

Future considerations

• More compact encodings of ZFXYU may be considered in future.
• The value of Z is still subject to change.