Compare distance between 3 location but the results are not reliable-CodePudding

I trying to create a code that calculate the distance between 2 point. I have 3 point (Point1, Point2, and Point3) and I want to compare each point combination (1 vs 2, 1 vs 3, and 2 vs 3) and find out which combination has the longest distance with expected result:

The distance between PointX and PointY is the longest, with distance {distance_XY}

The code that I used was:

def longest_distance(X,Y,Z):
  a = X[0]
  b = X[1]
  c = Y[0]
  d = Y[1]
  e = Z[0]
  f = Z[1]
  distance_XY = (((a-c)**2)   ((b-d)**2)) ** (1/2)
  distance_XZ = (((a-e)**2)   ((b-f)**2)) ** (1/2)
  distance_YZ = (((c-e)**2)   ((d-f)**2)) ** (1/2)
  if distance_XY > distance_XZ > distance_YZ:
    print(f'The distance between PointX and PointY is the longest, with distance {distance_XY}')
  elif distance_XY < distance_XZ > distance_YZ:
    print(f'The distance between PointX and PointZ is the longest, with distance {distance_XZ}')
  elif distance_XY < distance_XZ < distance_YZ:
    print(f'The distance between PointY and PointZ is the longest, with distance {distance_YZ}')

But that code only worked with some number. When I try using the number below it worked:

X = [0,0]
Y = [5,5]
Z = [10,10]

longest_distance(X,Y,Z)

The distance between PointX and PointZ is the longest, with distance 14.142135623730951

When I try with different number like:

X = [0,0]
Y = [10,-10]
Z = [4,-3]

longest_distance(X,Y,Z)

The result should be The distance between PointX and PointY is the longest, with distance 14.142135623730951, but nothing happened and there is no error so I don't really know how to correct it

CodePudding user response：

Nothing happens because None of the conditions you set are being met. When using your input:

X = [0,0]
Y = [10,-10]
Z = [4,-3]

What happend is:

distance_XY = 14.14213...

distance_XZ = 5.0

distance_YZ = 9.219544...

We can clearly see that 'distance_XY' is the biggest, but all three conditions are False since: 14.14213... > 5.0 < 9.219544

Because of that you do not get any print. It is good practice to put else: and then write a general note stating that none of the conditions were met.

Nevertheless, I would try checking the maximum by doing the following:

max_val = max(distance_XY, distance_XZ, distance_YZ)
if distance_XY == max_val:
    print(f'The distance between PointX and PointY is the longest, with distance {distance_XY}')
elif distance_XZ == max_val:
    print(f'The distance between PointX and PointZ is the longest, with distance {distance_XZ}')
elif distance_YZ == max_val:
    print(f'The distance between PointY and PointZ is the longest, with distance {distance_YZ}')
else:
    print('None of the conditions were met, something went wrong')

CodePudding user response：

You are looking for the max of three values, but what are you checking for is order. In your second example:

distance_XY, distance_XZ, distance_YZ = 14.142135623730951 5.0 9.219544457292887.

This means that your first condition should be true. But it is not, since distance_XY > distance_XZ -> True (that's ok), but distance_XZ > distance_YZ -> False. So the second > causes the whole condition to become False, even though that's not relevant, since distance_XY is max.

Try to define your conditions differently to get the max of distances. Or use another max approach.

In general, to debug problems like that, try to add some print statement to look at intermediate values. Then try to think what could go wrong given these values.

For a concise approach using the max value, you could do something like the following:

def longest_distance(X, Y, Z):
    (a, b), (c, d), (e, f) = X, Y, Z

    distances = {("X", "Y"): (((a-c)**2)   ((b-d)**2)) ** (1/2),
                 ("X", "Z"): (((a-e)**2)   ((b-f)**2)) ** (1/2),
                 ("Y", "Z"): (((c-e)**2)   ((d-f)**2)) ** (1/2)}

    (max_name_x, max_name_y), max_value = max(distances.items(),
                                              key=lambda x: x[1])
    
    print(f'The distance between Point{max_name_x} and Point{max_name_y} '
          f'is the longest, with distance {max_value}')

CodePudding user response：

Try to get difference between two points and Store the value in variable.