Google S2 geometry library extension for kdb+/q.
You may need to init git submodules:
git submodule update --init --recursive
- Requires
libcryptoto be installed (eg:brew install opensslorapt-get install libssl-dev)
$ make {m32,m64,l32,l64} [USE_CLANG=1] [NO_OPENMP=1]
$ cp qrapidjson_{m32,m64,l32,l64}.so /path/to/q/bin
USE_CLANGwill use Clang instead of GCC-7 on MacOS. OpenMP will be disabled.NO_OPENMPwill disable OpenMP (not recommended).
NOTE: By default, on MacOS, qs2 will use gcc-7 in order to get the performance benefits of OpenMP.
You will need to: brew install gcc-7.
q) \l s2.q
NOTE: You might need to set DYLD_LIBRARY_PATH or LD_LIBRARY_PATH environment variables
(Mac and Linux respectively) to the directory where the .so lives before running q.
The x{name} family of functions provided by qs2 work with tables.
Tables must have lat, lon and can have cid columns.
The cid column can be generated from lat/lon using .s2.xcid and
arranged for optimal lookup using .s2.xcidpart.
If for some reason you do not wish to part your table by cid (or even have cid present),
you should only use .s2.xcontains. This will perform a bounding clip without culling via cid.
plat and plon parameters to functions represent lat and lon points respectively.
That is, a single list of latitudes and a single list of longitudes. A single point could be (lat[0], lon[0]).
When a plat/plon pair has exactly 2 points, it will be interpreted to be a rectangle,
with the first point representing the top-left and the second point representing the bottom-right of the rectangle.
A plat/plon pair is considered to be a polygon when it has 3 or more points.
Because it is treated as a closed loop, the last point must not be the same as the first point.
Be aware that polygon lookup is fairly slow compared to lat/lon rectangles.
NOTE: Polygon point order must be counter clockwise ordering. Use .s2.clockwise to check this.
To lookup all entries in a table which are within a rectangle:
// Define rectangle (in this case, Australia)
rect: flip ((-10.349484; 111.297704); (-44.269108; 154.888309));
// Lookup
.s2.lookup[rect 0;rect 1;] table
To increase performance, pass through a table containing only the columns you need, for example:
.s2.lookup[rect 0;rect 1;] select lat, lon, cid, blah from table
This techique is particularly performant when the rectangle or polygon has a small area (eg: a few square kilometres).
When the bounds is large (eg: the size of Victoria or greater), it may be faster to use .s2.contains directly (no pre-cull).
LGPLv3. See LICENSE and COPYING.LESSER.
Copyright (c) 2016 Lucas Martin-King.
Other parts of this software (eg: RapidJSON) are covered by other licences.