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I have a big list of locations with their coordinates in a city that is fully divided by a river that's running from north to south. Now I want to determine for each location if it is located east or west of that river. If it was possible to get the coordinates of the river in a granular enough manner, I could achieve that goal by comparing coordinates between location and the river. I have not found a way to get these coordinates so far. I'm new to OSM, however, and would be thrilled if someone could point me in the right direction here. |
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If you use osm2pgsql to load the OSM data into PostGIS database (based on postsql) then you can use use the ST_closestpoint() function to find the closest point on a way (your river) to a point. You can then take the two points (one on the river and the one you are interested in) and use the ST_Azimuth() function to determine the direction of travel between the two points. If the the river is serpentine you may get a result other than what you wish for (if the point is within a loop or near a curve in the river the azimuth could be quite different than you want). I don’t have enough experience with this stuff to suggest a way around that issue though. |
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I ended up using @stf's suggestion of using the ST_AZIMUTH() function.
Making the left/right distinction at 180 degrees worked out perfectly in this case. @Frederik Ramm's suggestion of splitting the map in two using the river would've lead to a more robust solution but the river had some arms with the same name which made it inconvenient in my case. |
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Another computational option would be: 1. Create polygon around whole city. 2. Get river geometry as a line. 3. split polygon in two along that line. 4. for every point, ask "is this point in the left-land polygon", if not it'll be on the right. If I understand the question correctly, the main issue is extracting the river's coordinates. This could potentially be done in PostGIS if the data is loaded (something along the lines of |
