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So, I have groups of polylines returned from google map API (Green, Red and Yellow), some starting point p (blue one), and a radius r. I need to find all routes whose distance from p is no greater than r (in this case red and yellow) enter image description here

I know that I can calculate it manually (find equation of each line and compare it to the equation of the circle) but it can be inefficient for many routes. So my question is:

Is there builtin function in PostGIS which will help me accomplish this task?

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1 Answer 1

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A better (much faster) solution is to use

ST_Dwithin(pointgeom, linegeom, maxdistance)

Also see manual

The ST_Distance function will calculate the exact distance whereas ST_DWithin stops when it knows it is in range, making it easier and faster to calculate.

Bonus: be careful to use the correct projection here, since lat-lon calculations will be in degrees, not meters.

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  • I am not sure if it works for me. Following query should return true, but returns false. pastebin.com/yV8fxWKC
    – mkuligowski
    Jun 1, 2017 at 13:07
  • The distance between these two geometries is more than 2000 meters. So the answer 'false' is corrrect. Why do you think it should return true?
    – tilt
    Jun 1, 2017 at 13:14
  • Because, according to google maps, from this point to nearest edge of the polyline is about 200 meters.
    – mkuligowski
    Jun 1, 2017 at 13:28
  • You must have missed a decimator somewhere, because I just double checked it, and google tells me more than 2 km. How did you measure in google maps?
    – tilt
    Jun 1, 2017 at 13:47
  • It seems that I made a mistake previously, because now I double checked it and it is correct. Thanks man!
    – mkuligowski
    Jun 1, 2017 at 16:04

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