Minimal Python S2 Geometry cell ID, token and lat/lon conversion library.
This library does conversion between S2 cell ID, S2 token and latitude/longitude and was written as a method to understand the way the S2 cell system works; hopefully this is useful to others as a single-file reference on the process, where tracing the relevant parts from the reference C++ implementation can be somewhat daunting. All steps in the conversions are well commented and written to be understandable and functional rather than strictly fast, although little is different from the reference implementation.
The library is checked against a test suite generated from the reference C++ implementation to ensure conformity with the standard.
Should you need more complete S2 Geometry functionality or a fast C-based implementation, please consider using the Python extension included in the s2geometry repository or the pure-Python s2sphere implementation.
Issues and PRs are very welcome to improve the implementation, descriptions or to correct any misunderstandings of the S2 cell system. Please note that this library strives to be an easy to read reference rather than aiming for peak performance (it is in Python after all), so PRs which reduce readability of the implementation (such as for Python specific speed optimisations) are generally discouraged. However, if you have optimisations that are applicable to S2 implementations across many languages and can be described easily, please do consider making a PR.
This package can be installed from PyPI with pip or any other Python package manager:
pip install s2cellThe full documentation, including the API Reference, is available at docs.s2cell.aliddell.com. Below is a quick start guide for the most common uses.
The library is designed to be minimal, predictable and purely functional. Conversion from lat/lon (in degrees) to a cell ID or token can be done with the following two functions:
s2cell.lat_lon_to_cell_id(-10.490091, 105.641318) # -> 3383782026967071427
s2cell.lat_lon_to_token(-10.490091, 105.641318) # -> '2ef59bd352b93ac3'By default, these conversions will give you a level 30 leaf-cell as output. If you require a lower precision level, you can specify this:
s2cell.lat_lon_to_cell_id(-10.490091, 105.641318, 10) # -> 3383781119341101056
s2cell.lat_lon_to_token(-10.490091, 105.641318, 0) # -> '3'Conversion from a cell ID or token to lat/lon (in degrees) can be done with the following two functions:
s2cell.cell_id_to_lat_lon(3383781119341101056) # -> (-10.452552407574101, 105.6412526632361)
s2cell.token_to_lat_lon('3') # -> (0.0, 90.0)The lat/lon returned will be the center of the cell at the level available in the provided cell ID or token.
There are also a few other useful functions for inspecting or converting a cell ID/token:
# Conversion between cell ID and token
s2cell.cell_id_to_token(3383781119341101056) # -> '2ef59b'
s2cell.token_to_cell_id('3') # -> 3458764513820540928# Level extraction
s2cell.cell_id_to_level(3383781119341101056) # -> 10
s2cell.token_to_level('3') # -> 0# Parent cell calculation
s2cell.cell_id_to_parent_cell_id(3383781119341101056) # -> 3383782218852728832
s2cell.cell_id_to_parent_cell_id(3383781119341101056, 2) # -> 3386706919782612992
s2cell.token_to_parent_token('2ef59b') # -> '2ef59c'
s2cell.token_to_parent_token('2ef59b', 2) # -> '2f'# Token canonicalisation
s2cell.token_to_canonical_token('2ef59BD352b90') # -> '2ef59bd352b9'A list of useful links for S2 related concepts and projects can be found here.
This project is released under the same license as the reference C++ S2 Geometry implementation, namely the Apache 2.0 License.