Leaving off here for the night.

joydivision.sql

DROP FUNCTION IF EXISTS Faraday_JoyDivision(
  field TEXT,
  grid_tolerance FLOAT,
  offset_mult FLOAT,
  offset_correction FLOAT
);
 
CREATE FUNCTION Faraday_JoyDivision(
  field TEXT,
  grid_tolerance FLOAT DEFAULT 0.002,
  offset_mult FLOAT DEFAULT 0.00004,
  offset_correction FLOAT DEFAULT 0.06
) RETURNS TABLE(
  the_geom GEOMETRY
)
AS $$
DECLARE
  query TEXT;
BEGIN
  query := '
  WITH
 
  grid AS (
    SELECT
      -- note transform here
      ST_SnapToGrid(ST_Transform(the_geom, 4326), $1) the_geom,
      '|| field ||'
    FROM
      joydivisiontest
    WHERE
      '|| field ||' IS NOT NULL
  ),
 
  stats AS (
    SELECT
      the_geom,
      avg('|| field ||') avg_field,
      ST_Y(the_geom) pulserow,
      ST_X(the_geom) pulseorder
    FROM
      grid
    GROUP BY
      the_geom
  ),
 
  offsets AS (
    SELECT
      pulserow,
      pulseorder,
	  CASE WHEN ST_Y(ST_Translate(the_geom, 0, (avg_field * $2)-$3)) > pulserow THEN ST_Translate(the_geom, 0, (avg_field * $2)-$3)
      ELSE the_geom
	  END AS the_geom
    FROM
      stats
  ),

  lines AS (
    SELECT
      pulserow,
      ST_MakeLine(the_geom ORDER BY pulseorder ASC) the_geom
    FROM
      offsets
    GROUP BY
      pulserow
  ),
 
  hulls AS (
    SELECT 
      round(pulserow::numeric,1)::text || round(pulseorder::numeric,1)::text groupHULL, 
      St_Buffer(ST_ConcaveHull(ST_Collect(the_geom), 0.99),0.01) the_geom
    FROM 
      offsets
    GROUP BY 
      groupHull
  )
 
  SELECT 
    st_intersection(a.the_geom, b.the_geom) the_geom
  FROM 
    hulls a, lines b
  WHERE 
    st_intersects(b.the_geom, a.the_geom)';
  RETURN QUERY EXECUTE query USING grid_tolerance, offset_mult, offset_correction;
END
$$ LANGUAGE 'plpgsql' STABLE;