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I know that, linestring is a vector and if i want to check that, if point coordinates are between linestring beginning and ending coordinates then i need to use vector comparison (x2 > x && x2 < x1 && y2 > y && y2 < y1) that comparison show me if x2(Point) coordinate is between a linestring(vector) codrinates.

But I don't know how do compare linestring coordinates and point coordinates,

I wonder if somebody can give me some tips on how do compare if a point corodinate is between linestring coordinates?

  • y=mx+c where m = y1-y0/x1-x0 and c is the intercept – Ian Turton Mar 16 '15 at 15:50
  • Are you trying to find the shortest distance from a point to a set of connected line segments (aka "linestring")? With the special case that if the distance is zero then the point is "on the line"? – Spacedman Jan 1 '16 at 16:38
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If you are trying to solve a point in polygon problem, there are plenty of examples just within a google's reach.

If it is simply to find out whether the point coincides with one of the linestring vertices, a simple in operator (for Python) can do the job pretty well - or you can iterate the vertices and compare using abs() to introduce some coordinate precision tolerance.

If you want to know if the point lies on a polyline, iterate through the segment in the following way (Pythonic pseudocode):

function lies_on_polyline(point, vertices):
  for i from 0 to vertices.length - 2: // finish on last-but-one
    if lies_on_segment(point, vertices[i], vertices[i+1]):
      return True
  return False

function lies_on_segment(point, start, end):
  deltax = end.x - start.x
  if deltax == 0:
    liesInXDir = (point.x == start.x)
  else:
    t = (point.x - start.x) / deltax
    liesInXDir = (t >= 0 and t <= 1)
  if liesInXDir:
    deltay = end.y - start.y
    if deltay == 0:
      return (point.y == start.y)
    else:
      t = (point.y - start.y) / deltay
      return (t >= 0 and t <= 1)
  else:
    return False
  • im using javascript, but i only need to find that if point C is on the line segment of AB, but how i find if C is not on the line segment but near that ? I need to make two cases one is if C is on the line and second is if C is near a line. – Kevin Laanemägi Mar 17 '15 at 13:17
  • Edited. Should fulfill your needs. – Jan Šimbera Mar 19 '15 at 17:38

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