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-- This config example file is released into the Public Domain.
--
-- This example shows the use of the centroid() and pole_of_inaccessibility()
-- functions. For all named polygons several types of "center" points are
-- calculated that can be used for labelling.
local tables = {}
tables.polygons = osm2pgsql.define_area_table('polygons', {
{ column = 'name', type = 'text' },
{ column = 'tags', type = 'jsonb' },
{ column = 'geom', type = 'polygon', not_null = true },
{ column = 'centroid', type = 'point', not_null = true },
{ column = 'poi1', type = 'point', not_null = true },
{ column = 'poi2', type = 'point', not_null = true },
})
local function add(tags, geom)
tables.polygons:insert({
name = tags.name,
tags = tags,
geom = geom,
-- The centroid is easy and fast to calculate
centroid = geom:centroid(),
-- The pole of inaccessibility can take a bit longer. It calculates
-- the place in the polygon that's farthest away from the boundary.
-- In other words it finds the center of the largest circle that fits
-- completely into the polygon. (Note that due to the time required
-- to calculate this, only an approximation will be calculated.)
poi1 = geom:pole_of_inaccessibility(),
-- The function allows a Lua table with options as parameter.
-- Currently only a single option "stretch" is defined. If you set
-- this to something other than 1 (the default), the functions doesn't
-- use a circle but an ellipse stretched horizontally by the specified
-- factor when calculating the result. This can make sense, because
-- labels are usually written horizontally so you need more space in
-- that direction. (Use a value > 1 to stretch horizontally or values
-- between 0 and 1 to stretch vertically. The value 0 ist not allowed.)
poi2 = geom:pole_of_inaccessibility({ stretch = 3 }),
})
end
function osm2pgsql.process_way(object)
if object.is_closed and object.tags.name then
local geom = object:as_polygon()
add(object.tags, geom)
end
end
function osm2pgsql.process_relation(object)
local relation_type = object:grab_tag('type')
if relation_type == 'multipolygon' and object.tags.name then
local geom = object:as_multipolygon()
-- The pole_of_inaccessibility() function only works for polygons,
-- not multipolygons. So we split up the multipolygons here and
-- calculate the pole for each part separately.
for g in geom:geometries() do
add(object.tags, g)
end
end
end
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