[postgis-users] segmentize lines with order

[Stephen Woodbridge]

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