My object, the planet Mercury, is moving in a circle back and forth. Its coordinate lies within 360 degrees. There is no problem in detecting its reversal if it is far from the 360 degree point (0 degrees).
an easy case:
13.08.2010 166.41245
14.08.2010 167.00584
15.08.2010 167.53165
16.08.2010 167.98625
17.08.2010 168.36589
18.08.2010 168.66672
19.08.2010 168.88494
20.08.2010 169.01682
21.08.2010 169.05885 This is where the backward movement begins
22.08.2010 169.00792 I detect it easily
23.08.2010 168.86147
24.08.2010 168.61771
25.08.2010 168.27591
26.08.2010 167.83665
I do this by searching for extremes.
from scipy.signal import argrelextrema
But if it goes from 359 degrees to 1 degree, I get constant crashes.
Here is an example where the system fails. It considers it is a reversal of Mercury, although it just goes from 359 degrees to the 0 degree. This is not the beginning of retrogression.
crash example
13.03.2010 350.60172
14.03.2010 352.53184
15.03.2010 354.47785
16.03.2010 356.43861
17.03.2010 358.41273 This is not the beginning of a backward movement (NOT MAXIMUM)
18.03.2010 0.39843 its just ingression from Pieces to Aries
19.03.2010 2.39354
20.03.2010 4.39545
21.03.2010 6.40106
22.03.2010 8.40673
23.03.2010 10.40828
24.03.2010 12.40098
25.03.2010 14.37956
26.03.2010 16.33824
So, I need desicion to find reversal points of a planet that moves on a circle 360 degrees.
IIUC, you can use a threshold to avoid false positive:
c = df['Coords']
m0 = c.diff().abs().le(1) # limit the gap, threshold=1
m1 = c.gt(c.shift(-1)) & c.gt(c.shift()) & m0 # upper peak ↗↘
m2 = c.lt(c.shift(-1)) & c.lt(c.shift()) & m0 # lower peak ↘↗
df['Reversal'] = m1|m2
Output:
>>> df
Date Coords Reversal
0 13.03.2010 350.60172 False
1 14.03.2010 352.53184 False
2 15.03.2010 354.47785 False
3 16.03.2010 356.43861 False
4 17.03.2010 358.41273 False
5 18.03.2010 0.39843 False # ignore this case
6 19.03.2010 2.39354 False
7 20.03.2010 4.39545 False
8 21.03.2010 6.40106 False
9 22.03.2010 8.40673 False
10 23.03.2010 10.40828 False
11 24.03.2010 12.40098 False
12 25.03.2010 14.37956 False
13 26.03.2010 16.33824 False
14 13.08.2010 166.41245 False
15 14.08.2010 167.00584 False
16 15.08.2010 167.53165 False
17 16.08.2010 167.98625 False
18 17.08.2010 168.36589 False
19 18.08.2010 168.66672 False
20 19.08.2010 168.88494 False
21 20.08.2010 169.01682 False
22 21.08.2010 169.05885 True # real case
23 22.08.2010 169.00792 False
24 23.08.2010 168.86147 False
25 24.08.2010 168.61771 False
26 25.08.2010 168.27591 False
27 26.08.2010 167.83665 False