[postgis-tickets] [PostGIS] #2444: Wrong example in asTopoJON manual

[PostGIS]

#2444: Wrong example in asTopoJON manual
---------------------------+------------------------------------------------
 Reporter:  tilt           |       Owner:  robe         
     Type:  enhancement    |      Status:  new          
 Priority:  medium         |   Milestone:  PostGIS 2.1.1
Component:  documentation  |     Version:  2.1.x        
 Keywords:  astopojson     |  
---------------------------+------------------------------------------------
 TopoJson seems to require delta values in the coordinates instead of pure
 coordinates given in the example. Additionally, the indexing in arcs is
 wrong and some comma's are missing in the example.

 A better output example would be:

 {{{
 { "type": "Topology", "transform": { "scale": [1,1], "translate":
 [0,0] }, "objects": {
 "P3P4": { "type": "MultiPolygon", "arcs": [[[0]],[[1,2,3,4,5,6]]]}
 }, "arcs": [
 [[25,30],[6,0],[0,10],[-14,0],[0,-10],[14,0]],
 [[35,14],[0,-8]],
 [[35,6],[12,0]],
 [[47,6],[0,8]],
 [[47,14],[0,8]],
 [[47,22],[-12,0]],
 [[35,22],[0,-8]]
 ]}
 }}}


 To get the deltas from the coordinates is a bit tricky. Here's a
 suggestion that works but it's open for improvement:

 {{{
 WITH points as (
         SELECT nextval('mycounter') as id, m.edge_id as groupid,
 (st_dumppoints(geom)).geom
         FROM edgemap m, <yourTopoTable>.edge e WHERE e.edge_id = m.edge_id
 ),
 compare as (
         SELECT id, groupid,
                 first_value(geom) OVER (PARTITION BY groupid ORDER BY id )
 geom0,
                 (geom) geom1,
                 (lead(geom) OVER (PARTITION BY groupid ORDER BY id ))
 geom2
                 FROM points
 )
 SELECT
         '[[' || ST_X(geom0) || ','||ST_Y(geom0)|| '],' || string_agg('['
 || ROUND(ST_X(geom2) - ST_X(geom1)) || ',' || ROUND(ST_Y(geom2) -
 ST_Y(geom1)) || ']',',') || '],' as arc
 FROM compare
 }}}

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/2444>
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