[postgis-users] segmentize lines with order

[Pedro Costa]

thanks Remi.
I'm tying to make a stored procedure to use st_reverse when draw order 
is wrong.
Now, my difficult is in writing the loop.
I can't find something like that to guide me...



Em 25-02-2014 11:11, Rémi Cura escreveu:
> You can use
> http://postgis.refractions.net/docs/ST_Reverse.html
>
> Or simply ORDER BY DESC for your path
>
> Cheers,
>
> Rémi-C
>
>
> 2014-02-25 11:49 GMT+01:00 Pedro Costa <pedrocostaarma at sapo.pt 
> <mailto:pedrocostaarma at sapo.pt>>:
>
>     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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