README.md

postgres-angle-avg

A C-Language function for PostgreSQL allowing to average angles in degree.

This can be useful for e.g. component averaging of wind directions (not taking the wind speed into account) directly in the database.

Setup

version 0.1.1

Compilation

This was tested against PostgreSQL 12, 13, 14, 15 and 16. The function has to be compiled into a shared object.

Pre-compiled binaries can be found here: https://github.com/jkittner/postgres-angle-avg/releases/tag/0.1.1

On Linux:

compile the intermediate object file. The PostgreSQL development files (Header files) need to be present and included e.g. postgresql-server-dev-12 on debian based OS.

cc -fpic -c angle_avg.c -lm -I /usr/include/postgresql/16/server

create the shared object file

cc -shared -o angle_avg.so angle_avg.o

For other platforms see Compiling and Linking Dynamically-Loaded Functions

SQL Function Creation

The angle_avg.so needs to be placed in a directory, which can be accessed by PostgreSQL. Ideally /usr/lib/postgresql/16/lib/angle_avg.so or what pg_config --pkglibdir returns.

Execute the angle_avg.sql file and now the function avg_angle is available.

Example

CREATE TABLE wind (wind_direction NUMERIC);
INSERT INTO wind VALUES (355), (15);

SELECT wind_direction FROM wind;

 wind_direction
----------------
            355
             15
(2 rows)

SELECT avg_angle(wind_direction) FROM wind;

     avg_angle
--------------------
 4.999999999999996

running the tests

This repo uses pytest for testing the C and sql code. For running the tests you will have to have docker and the compose plugin installed. Then install the python requirements using:

pip install -r requirements-dev.txt

finally run the tests using:

pytest tests