Coordinate precision problem

[LemonLiTree]

hi，all
I found some precision issues
I get S2point first：S2Point point = S2LatLng::FromDegrees(1, 2).ToPoint();
Then I want to get the x coordinate of this point：S2LatLng(*point).lng().degrees();
The result I get is 0.99999999999999978
If I enter a longitude of 56.7, I get 56.699999999999996
I think this is the loss of precision when doing double calculations,
is there any way to solve this？

[jmr]

This is because S2LatLng and S2Point have different representations and the conversion is lossy.

Print it with a precision of 6 (like S2LatLng::ToStringInDegrees does) or 7. 7 decimal places is accurate to ~1cm.

[smcallis]

Without using double doubles or something this is unavoidable. That's an error of 2.22e-16 == 1 epsilon, which is basically as good as you can possibly do with IEEE double.