How to display labels for Staircase Locks ?

[pyrog]

Example : Newlay Locks

• Zoom 18
  
• Zoom 16
  display one label : Newlay Locks
  

The map could have a better reading with this lock gate logo :

[yohanboniface]

See mapnik/mapnik#1682

[pyrog]

To avoid this problem, it's possible to map the lock only once (N+1 gates, only 1 line for a N basins lock).
In the example of Newlay, the lock_name could be simply "Newlay Lock".

Example : Lock of Picquigny

[PetrDlouhy]

Hi, I am not sure, if this issue is just about rotating point symbolizer along the line or something more. If it's just that, I was able to solve that in Prague Green map (github) for highway crossings. I used "point-transfor" with SVG icon:

#crossings[zoom >= 16] {
  point-placement: interior;
  point-transform: 'rotate([angle])';
  point-allow-overlap: true;
  point-ignore-placement: true;
  point-file: url('symbols/SVG/crossing_small.svg');
}

And counted the angle in PSQL query:

(
  select distinct on (p.way) p.way as way,
    p.crossing,
    degrees( ST_azimuth(coalesce(ST_Line_Interpolate_Point(l.way, ST_line_locate_point(l.way,p.way) * 0.99), p.way),
    coalesce(ST_Line_Interpolate_Point(l.way, (1 - (1 - ST_line_locate_point(l.way,p.way)) * 0.99)), p.way))) as angle

   from planet_osm_point p
   join planet_osm_line l
    on ST_DWithin(p.way,l.way,0.1)
   join (values
    ('motorway',1),
    ('trunk',2),
    ('primary',3),
    ('secondary',4),
    ('tertiary',5),
    ('unclassified',6),
    ('residential',7),
    ('living_street',8),
    ('service',9),
    ('cycleway',10)
   ) as v (highway,prio)
    on v.highway=l.highway
   where p.highway='crossing'
   order by p.way,v.prio
 ) as crossing