[postgis-users] segmentize lines with order

[Pedro Costa]

Hi Rémi,

Thanks for your awnser.
My problem is that the draw order isn't equal in all lines so the path 
of st_dumppoints sometimes return ascend order and another times 
descend. I need to make a loop to make a reverse...

Em 25-02-2014 08:33, Rémi Cura escreveu:
> Hey,
> I don't understand your problem.
>
> If you have multilinestring, you need to break it to linestring with 
> an id per multilinestring.
> If you have linestring, you just need to keep an id for each line and 
> an id per point (given in path).
>
> Then you have several option to generate a ordered set of point (use 
> the ORDER BY and the row_number() postgres function).
>
> If you give some detailled example maybe we could help better.
>
> Cheers,
> Rémi-C
>
>
> 2014-02-24 19:27 GMT+01:00 Stephen Woodbridge <woodbri at swoodbridge.com 
> <mailto:woodbri at swoodbridge.com>>:
>
>     On 2/24/2014 11:33 AM, Pedro Costa wrote:
>
>         Hi guys,
>
>         I'm trying to use lines from postgis to google maps android.
>         To do that, I'm converting the lines to points with
>         St_DumpPoints and,
>         in gmaps, I make the lines. My problem is that I cannot create
>         a correct
>         sequence to order the points in android and so i get wrong
>         lines (see ss
>         atached). I'm already try to use st_dumpPoints path column and
>         generate
>         a serial but doesn't result.
>
>         Anybody knows a solution to resolve that?
>
>
>     You probably need to write function that re-orients you lines
>     before you dump them to points. The algorithm is like this:
>
>     1. for the first edge, if the start point match the the start or
>     end of the 2nd edge, if it does then st_reverse() the first edge.
>
>     2. for the rest of the edges, if the edge point of the current
>     edge matches the end point of the last edge, then st_reverse() the
>     current edge.
>
>     You might be able to st_union all the edges into one large edge
>     and that should create a new reorder edge.
>
>     No you can dump them and the order will be correct.
>
>     -Steve
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