pg_eviltransform

Overview

Version

Build

You can build the RPM / DEB packages for pg_eviltransform using pig build:

pig build pkg pg_eviltransform         # build RPM / DEB packages

Install

You can install pg_eviltransform directly. First, make sure the PGDG and PIGSTY repositories are added and enabled:

pig repo add pgsql -u          # Add repo and update cache

Install the extension using pig or apt/yum/dnf:

pig install pg_eviltransform;          # Install for current active PG version

pig ext install -y pg_eviltransform -v 18  # PG 18
pig ext install -y pg_eviltransform -v 17  # PG 17
pig ext install -y pg_eviltransform -v 16  # PG 16
pig ext install -y pg_eviltransform -v 15  # PG 15
pig ext install -y pg_eviltransform -v 14  # PG 14

dnf install -y pg_eviltransform_18       # PG 18
dnf install -y pg_eviltransform_17       # PG 17
dnf install -y pg_eviltransform_16       # PG 16
dnf install -y pg_eviltransform_15       # PG 15
dnf install -y pg_eviltransform_14       # PG 14

apt install -y postgresql-18-eviltransform   # PG 18
apt install -y postgresql-17-eviltransform   # PG 17
apt install -y postgresql-16-eviltransform   # PG 16
apt install -y postgresql-15-eviltransform   # PG 15
apt install -y postgresql-14-eviltransform   # PG 14

Create Extension:

CREATE EXTENSION pg_eviltransform CASCADE;  -- requires: postgis

Usage

Sources:

• Official v0.0.4 README
• v0.0.4 release notes
• v0.0.4 control file
• v0.0.4 upgrade SQL

pg_eviltransform extends PostGIS with coordinate transformations involving China’s GCJ-02 and BD-09 systems. Version 0.0.4 also adds exact Jenks natural-break classification through ST_JenksBins array and aggregate overloads.

Coordinate Transformation

CREATE EXTENSION postgis;
CREATE EXTENSION pg_eviltransform;

-- WGS84 to GCJ-02 using a readable coordinate-system name.
SELECT ST_EvilTransform(
    ST_SetSRID('POINT(120 30)'::geometry, 4326),
    'GCJ02'
);

-- BD-09 to Web Mercator.
SELECT ST_EvilTransform(
    ST_SetSRID('POINT(120.011070620552 30.0038830555128)'::geometry, 990002),
    3857
);

Custom SRIDs are 990001 for GCJ-02 and 990002 for BD-09. When neither endpoint uses a custom system, ST_EvilTransform delegates to PostGIS ST_Transform; otherwise it converts through WGS84 (4326) when necessary.

Jenks Natural Breaks

-- Array form; NULL elements are ignored.
SELECT ST_JenksBins(ARRAY[1, 2, NULL, 10, 11]::numeric[], 2);

-- Streaming aggregate form for a large table.
SELECT ST_JenksBins(value, 7)
FROM measurements;

-- Return lower rather than upper bin edges.
SELECT ST_JenksBins(value, 7, true)
FROM measurements;

Array inputs support numeric, double precision, real, bigint, integer, and smallint. Aggregate inputs are numeric or double precision; cast other numeric columns when needed.

API Index and Caveats

• ST_EvilTransform(geometry, integer|text) and ST_EvilTransform(geometry, text, integer|text): four overloads corresponding to the PostGIS ST_Transform interface.
• ST_JenksBins(values[], breaks [, invert]): classifies an array and returns double precision[] edges.
• ST_JenksBins(value, breaks [, invert]): streaming aggregate that avoids materializing array_agg.
• PostGIS is a runtime prerequisite and must be installed before pg_eviltransform.
• Jenks inputs must be finite and breaks must be at least one. numeric values are converted to finite f64, so returned edges are floating-point values.
• When the distinct value count does not exceed breaks, the result is the sorted set of unique values; no valid input rows return NULL.