I tried to use the x2sys to calculate the crossover of global altimetry data. A weird problem emerged.
The crossover point will not be correctly calculated when the data cross the equator.
If I just select the data in the south hemisphere earth, it works. But if data was selected cross the equator, the problem emerged.
Here is the wrong result (cross equator and dateline):
or just the east but cross the equator:
Here is the reasonable result if data was selected over just one hemisphere:
Here is the code and data.download
The GMT is version 6.1.0 under MINGW64.