Reject unpaired coordinates before fitting a circle

Mapping/circle_fitting/circle_fitting.py

@@ -45,6 +45,9 @@ def circle_fitting(x, y):
         - The fitting error as a deviation metric (float).
     """
 
+    if len(x) != len(y):
+        raise ValueError("x and y must contain the same number of points")
+
     sumx = sum(x)
     sumy = sum(y)
     sumx2 = sum([ix ** 2 for ix in x])

docs/modules/3_mapping/circle_fitting/circle_fitting_main.rst

@@ -3,6 +3,9 @@ Object shape recognition using circle fitting
 
 This is an object shape recognition using circle fitting.
 
+Each range observation supplies a pair of coordinates. The two input lists
+must have equal lengths so each point contributes once to the fit.
+
 .. image:: https://github.com/AtsushiSakai/PythonRoboticsGifs/raw/master/Mapping/circle_fitting/animation.gif
 
 The blue circle is the true object shape.

tests/test_circle_fitting.py

@@ -1,3 +1,4 @@
+import pytest
 import conftest
 from Mapping.circle_fitting import circle_fitting as m
 
@@ -7,5 +8,12 @@ def test_1():
     m.main()
 
 
+@pytest.mark.parametrize("x, y", [([0, 2, 0, 1], [0, 0, 2]),
+                                   ([0, 0, 2], [0, 2, 0, 1])])
+def test_requires_paired_coordinates(x, y):
+    with pytest.raises(ValueError, match="same number"):
+        m.circle_fitting(x, y)
+
+
 if __name__ == '__main__':
     conftest.run_this_test(__file__)