[postgis-users] segmentize lines with order

[Rémi Cura]

I still don't understand what you are trying to do,
if you want to access the next row of a querry, you need to order the row .
So what does "next line" mean? How is this information stored?

It is possible to access other rows using windows function :
http://www.postgresql.org/docs/9.3/static/functions-window.html

However I'm not certain you really need it.

Could you provide a simple test case and an explanation of what you are
trying to do?

(somehting like
create table my_test;
insert into my_test some_geometry_you_have_trouble_with;

--describe the kind of result you want...

--The problem is ..., I want to do ..., I tried ...
)

Cheers,

Rémi-C



2014-02-25 12:59 GMT+01:00 Pedro Costa <pedrocostaarma at sapo.pt>:

>  I was trying CASE before but i doesn't know how to access 'next line
> start point'.
> Example:
>
>
> SELECT
>     CASE
>      WHEN (ST_Intersects(ST_EndPoint(geom),(SELECT ST_StartPoint(geom)
> FROM lines WHERE seq = seq+1)))  <--- I need to get next line geom
>             THEN 1
>     ELSE 0
>     END AS reverse
> FROM lines
>
> Do you understand my problem?
>
> Em 25-02-2014 11:42, Rémi Cura escreveu:
>
>  You don't need a stored procedure,
>  you can simply use pure sql with the CASE WHEN ... THEN .. WHEN .. THEN
> .. .. END.
>
>  doc :
> http://www.postgresql.org/docs/9.3/static/functions-conditional.html
>
> If you still need plpgsql :
> http://www.postgresql.org/docs/9.3/static/plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING
>
> Cheers,
> Rémi-C
>
>
> 2014-02-25 12:17 GMT+01:00 Pedro Costa <pedrocostaarma at sapo.pt>:
>
>>  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>:
>>
>>>  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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