Fishbones for the TN NG911 Address Server

Feb 19, 2020 | 911, address, postgis, QGIS

It’s been a bit since I’ve talked about the TN address server. I’ve been slowly adding more functionality to it and some of that functionality has been more difficult than others.

If you’ve played in the address space any length of time you’ve heard of fishbones – and that is simply drawing a line from the address point to it’s “spot on the street”. Granted if you’ve ever done an addressing project from scratch (I had the joy to do that a few years ago in the Caribbean) it makes a lot of sense. You can quickly see problems where lines cross over other lines or where addresses have no lines at all.  Please read up here if you are so inclined.

There are probably multiple ways to do this  but I’ve gotten fishboning (if that’s a word) running in the TN NG911 Address Server. In PostGIS with less than 25 lines of SQL (and I’m quite proud of myself – 5 years ago I sucked at SQL. I still suck at it – but way less).  While it’s not quite ready for prime time it’s close – I’m just trying to figure out what I can pull out of this that makes the County’s job easier in the addressing realm. I’d love to move it to python at some point – and it’s probably doable (well I know it is – it’s just doing it).

Three things happen:

  1. I join the address point to the closest road using ST_LineLocatePoint
  2. Does the closest point fit the address range on the street (double bonus I also check left and right).
  3. Finish it up with ST_Makeline to join the spot closest to the street to the address point.

Which quickly shows something is wrong here:

Bonus for this one as is it’s not incredibly obvious what the problem is at first glance….UNTIL you see you have an addressing issue where you have 2, 3, and 4 on the same side of the street.

Hurrah for misspelled street names by leaving a W off

Anyway – there will be more announcements coming like this “running in the cloud” and other things. I’d like to get the fishbones running once a night or realistically run the one for the new address. Why not both probably. Anyway – pretty nice for an ArcView/FGDB Replacement.

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