[postgis-users] Intersect ???

Basques, Bob (CI-StPaul) bob.basques at ci.stpaul.mn.us
Thu Jul 30 09:30:34 PDT 2015

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 . . .



On Jul 30, 2015, at 11:06 AM, Eduardo Bieñkowski <edukoski at gmail.com<mailto: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

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