Ensure milestone zeros work correctly (#497)

Fixes #494

Followup of #481

Part of #392

Changes:
- Match exact positions against non-exact positions. If exact positions
do not have a corresponding non-exact position, they are used as is.
- Use textual position (not exact position) for determining if a
milestone is a zero.

(https://openrailwaymap.app/#view=10.39/49.5818/11.4117&style=signals)

Before:
<img width="1418" height="1110" alt="image"
src="https://github.com/user-attachments/assets/2f26bb69-58b7-4545-988c-8c4c82ac613b"
/>

After:
<img width="1417" height="1113" alt="image"
src="https://github.com/user-attachments/assets/23e64517-4986-406a-8bf9-db51c51a3b02"
/>

Author: hiddewie

import/openrailwaymap.lua

@@ -393,6 +393,7 @@ local railway_positions = osm2pgsql.define_table({
     { column = 'railway', type = 'text' },
     { column = 'position_numeric', type = 'real' },
     { column = 'position_text', type = 'text', not_null = true },
+    { column = 'position_exact', type = 'text' },
     { column = 'type', type = 'text', not_null = true },
     { column = 'zero', type = 'boolean' },
     { column = 'name', type = 'text' },
@@ -698,37 +699,58 @@ function name_tags(tags)
   return found_name_tags
 end
 
+function position_is_zero(position)
+  return position:find('^%-?%d+$') or position:find('^%-?%d*[,/.]0*$')
+end
+
 function parse_railway_position(position)
   if not position then
     return nil
   end
 
   if position:find('^mi:') then
+    local stripped_position = position:gsub('^mi: ?', '')
+    local position_with_dot = stripped_position:gsub(',', '.')
+
     return {
-      text = position:gsub('^mi:', ''),
+      text = stripped_position,
+      numeric = tonumber(position_with_dot),
       type = 'mi',
+      zero = position_is_zero(stripped_position),
+      exact = nil,
     }
   elseif position:find('^pkm:') then
+    local stripped_position = position:gsub('^pkm: ?', '')
+    local position_with_dot = stripped_position:gsub(',', '.')
+
     return {
-      text = position:gsub('^pkm:', ''),
+      text = stripped_position,
+      numeric = tonumber(position_with_dot),
       type = 'pkm',
+      zero = position_is_zero(stripped_position),
+      exact = nil,
     }
   else
+    local position_with_dot = position:gsub(',', '.')
+
     return {
       text = position,
+      numeric = tonumber(position_with_dot),
       type = 'km',
+      zero = position_is_zero(position),
+      exact = nil,
     }
   end
 end
 
 function parse_railway_positions(position, position_exact)
-  -- Parse one or more positions from a position or exact position
+  -- Collect positions, from both normal and exact positions, eliminating duplicates
 
-  if position_exact then
-    local parsed_positions = {}
-    local found_positions = false
+  local parsed_positions = {}
+  local found_positions = false
 
-    for part in string.gmatch(position_exact, '[^;]+') do
+  if position then
+    for part in string.gmatch(position, '[^;]+') do
       local stripped_part = part:gsub('^ ', '')
       local position = parse_railway_position(stripped_part)
 
@@ -737,38 +759,48 @@ function parse_railway_positions(position, position_exact)
         found_positions = true
       end
     end
-
-    if found_positions then
-      return parsed_positions
-    end
   end
 
-  -- Fall back to non-exact positions
-
-  if position then
-    local parsed_positions = {}
-    local found_positions = false
-
-    for part in string.gmatch(position, '[^;]+') do
+  if position_exact then
+    for part in string.gmatch(position_exact, '[^;]+') do
       local stripped_part = part:gsub('^ ', '')
       local position = parse_railway_position(stripped_part)
 
       if position then
-        table.insert(parsed_positions, position)
-        found_positions = true
-      end
-    end
+        local found_existing_position = false
+
+        if found_positions and position.numeric ~= nil then
+          for _, existing_position in ipairs(parsed_positions) do
+            -- Verify if the position is close to another position. Note that this matches slightly outside the first decimal's precision.
+            if existing_position.numeric ~= nil and math.abs(existing_position.numeric - position.numeric) < 0.1 then
+              existing_position.numeric = position.numeric
+              existing_position.exact = position.text
+              found_existing_position = true
+            end
+          end
+        end
 
-    if found_positions then
-      return parsed_positions
+        if not found_existing_position then
+          table.insert(parsed_positions, position)
+          found_positions = true
+        end
+      end
     end
   end
 
-  return nil
+  if found_positions then
+    return parsed_positions
+  else
+    return nil
+  end
 end
 
 function format_railway_position(item)
-  return item.text .. ' (' .. item.type .. ')'
+  if item.exact then
+    return item.text .. ' @ ' .. item.exact.. ' (' .. item.type .. ')'
+  else
+    return item.text .. ' (' .. item.type .. ')'
+  end
 end
 
 local railway_station_values = osm2pgsql.make_check_values_func({'station', 'halt', 'tram_stop', 'service_station', 'yard', 'junction', 'spur_junction', 'crossover', 'site'})
@@ -926,16 +958,14 @@ function osm2pgsql.process_node(object)
 
   if railway_position_values(tags.railway) and (position or position_exact) then
     for _, position in ipairs(parse_railway_positions(position, position_exact)) do
-      local position_with_dots, _ = position.text:gsub(',', '.')
-      local position_numeric = tonumber(position_with_dots)
-
       railway_positions:insert({
         way = object:as_point(),
         railway = tags.railway,
-        position_numeric = position_numeric,
+        position_numeric = position.numeric,
         position_text = position.text,
+        position_exact = position.exact,
         type = position.type,
-        zero = position_numeric ~= nil and ((math.abs(position_numeric) % 1) < 0.001),
+        zero = position.zero,
         name = tags['name'],
         ref = tags['ref'],
         operator = tags['operator'],

import/sql/tile_views.sql

@@ -492,6 +492,7 @@ CREATE OR REPLACE VIEW railway_text_km AS
     way,
     railway,
     position_text as pos,
+    position_exact as pos_exact,
     zero,
     round(position_numeric) as pos_int,
     type,

martin/configuration.yml

@@ -188,6 +188,7 @@ postgres:
         osm_id: integer
         railway: string
         pos: string
+        pos_exact: string
         pos_int: integer
         zero: boolean
         type: string

proxy/js/features.mjs

@@ -513,6 +513,9 @@ const features = {
       pos: {
         name: 'Position',
       },
+      pos_exact: {
+        name: 'Exact position',
+      },
       type: {
         name: 'Type',
       },

proxy/js/styles.mjs

@@ -4658,6 +4658,7 @@ const legendData = {
           zero: true,
           pos_int: '47',
           pos: '47.0',
+          pos_exact: '47.012',
           type: 'km',
         },
       },
@@ -5251,6 +5252,7 @@ const legendData = {
           zero: true,
           pos_int: '47',
           pos: '47.0',
+          pos_exact: '47.012',
           type: 'km',
         },
       },
@@ -5475,6 +5477,7 @@ const legendData = {
           zero: true,
           pos_int: '47',
           pos: '47.0',
+          pos_exact: '47.012',
           type: 'km',
         },
       },
@@ -5714,6 +5717,7 @@ const legendData = {
           zero: true,
           pos_int: '47',
           pos: '47.0',
+          pos_exact: '47.012',
           type: 'km',
         },
       },
@@ -6083,6 +6087,7 @@ const legendData = {
           zero: true,
           pos_int: '47',
           pos: '47.0',
+          pos_exact: '47.012',
           type: 'km',
         },
       },
@@ -6153,6 +6158,7 @@ const legendData = {
           zero: true,
           pos_int: '47',
           pos: '47.0',
+          pos_exact: '47.012',
           type: 'km',
         },
       },
@@ -6223,6 +6229,7 @@ const legendData = {
           zero: true,
           pos_int: '47',
           pos: '47.0',
+          pos_exact: '47.012',
           type: 'km',
         },
       },
@@ -6301,6 +6308,7 @@ const legendData = {
           zero: true,
           pos_int: '47',
           pos: '47.0',
+          pos_exact: '47.012',
           type: 'km',
         },
       },