[postgis-users] segmentize lines with order

[Rémi Cura]

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>:

>  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>:
>
>>  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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>
>
>
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