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In the picture below I am finding the bearing of two close lines. This is the picture of two complete lines. The brown line might be a bit large from the blue line.

Should not be the bearing of these two lines should be close to each other with a difference of may be few degrees?

I am checking whether they are equal or not by getting the difference of both lines bearing. I am using python to calculate the bearing and get the difference between there bearing. The code I am using to get out the bearing is:

def calculate_initial_compass_bearing(pointA, pointB):
    """
    Calculates the bearing between two points.
    The formulae used is the following:
        θ = atan2(sin(Δlong).cos(lat2),
                  cos(lat1).sin(lat2) − sin(lat1).cos(lat2).cos(Δlong))
    :Parameters:
      - `pointA: The tuple representing the latitude/longitude for the
        first point. Latitude and longitude must be in decimal degrees
      - `pointB: The tuple representing the latitude/longitude for the
        second point. Latitude and longitude must be in decimal degrees
    :Returns:
      The bearing in degrees
    :Returns Type:
      float
    """
    if (type(pointA) != tuple) or (type(pointB) != tuple):
        raise TypeError("Only tuples are supported as arguments")

    lat1 = math.radians(pointA[0])
    lat2 = math.radians(pointB[0])

    diffLong = math.radians(pointB[1] - pointA[1])

    x = math.sin(diffLong) * math.cos(lat2)
    y = math.cos(lat1) * math.sin(lat2) - (math.sin(lat1)
            * math.cos(lat2) * math.cos(diffLong))

    initial_bearing = math.atan2(x, y)

    # Now we have the initial bearing but math.atan2 return values
    # from -180° to + 180° which is not what we want for a compass bearing
    # The solution is to normalize the initial bearing as shown below
    initial_bearing = math.degrees(initial_bearing)
    compass_bearing = (initial_bearing + 360) % 360

return compass_bearing

In the end what I am doing is calculate there difference like that:

DifferenceInBearing = abs(BlueLineBearing - BrownLineBearing)

My problem is that the difference between them is huge just around 179.71922333147256 degrees.

The WKT values of blue line is:

LINESTRING (327854.7919419953 6809188.658530097, 327854.2288694207 6809187.856443238)

The Wkt value for brown line:

LINESTRING (327854.139971 6809187.723519, 327854.714599625 6809188.541579125)

Shouldn't the bearing be close enough?

enter image description here

  • @BERA that is what the problem the difference between there bearing is huge approximately 179. Do you have some idea why is it? – mimetype Sep 27 '17 at 8:58
2

One line starts at bottom left and one starts at top right so a diffence of about 180 should be correct.

I use this calculation, taken from Find the bearing angle between two points in a 2D space:

import math

def calculate_initial_compass_bearing(pointA, pointB):
    startx,starty,endx,endy=pointA[0],pointA[1],pointB[0],pointB[1]
    angle=math.atan2(endy-starty, endx-startx)
    if angle>=0:
        return math.degrees(angle)
    else:
        return math.degrees((angle+2*math.pi))

Which for the first line gives:

calculate_initial_compass_bearing((327854.139971,6809187.723519), (327854.714599625,6809188.541579125))
54.91470758400356

And second line:

calculate_initial_compass_bearing((327854.7919419953, 6809188.658530097), (327854.2288694207, 6809187.856443238))
234.93078130214872
  • why you changed your code? – mimetype Sep 28 '17 at 10:12

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