[postgis-users] Intersect ???

[Rémi Cura]

Hey,
answered a few weeks ago :
http://comments.gmane.org/gmane.comp.gis.postgis/38249
Cheers
Rémi-C

2015-07-30 18:30 GMT+02:00 Basques, Bob (CI-StPaul) <
bob.basques at ci.stpaul.mn.us>:

> I’ve done this with a SQL statement in the past.  (it’s been a few years
> now.)
>
> It was dependent on the lines actually intersecting each other
> (diagrammatic lifework) vs physical representations.  We had to manually
> end the line work at the intersections, and in some instances divide lines
> that need a break at the intersections.
>
> You can still do the intersection extract without all this work by using a
> gap tolerance in the search, but this may lead to more errors depending on
> number of short street segments, etc in the dataset.
>
> Another way to approach this is by matching up street attributes like
> names.  You can then derive a street intersection name index for zooming-to
> in a map.  you’ll also likely need to use a self join of some type.
>
> Lastly, you can use a straight tabular method, that uses a cartiesian
> coordinate equation and check every line segment again every other (Hint:
> a^2 + b^2 = c^2) You don’t even need POSTGIS for this is you have the end
> points of each line segment as coordinates.  In most cases this type of
> search is very fast.
>
> I would look at the ST_INTERSECTS and possibly ST_CROSSES functions to
> start with, but they don’t actually give up a point.
>
> Also, this may help get you started . . .
>
>
> http://gis.stackexchange.com/questions/20835/identifying-road-intersections-using-postgis
>
>
>
> bobb
>
>
> On Jul 30, 2015, at 11:06 AM, Eduardo Bieñkowski <edukoski at gmail.com>
> wrote:
>
> I have one and only one layer lines (they are city streets)
> How I can get a point layer where the lines cross? and so have a layer of
> crosspoints
>
> Apologize for my English
>
> --
> Eduardo
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