Loosen DateTime::isClose() tolerance (#1029)

Author: gmgunter

cxx/isce3/core/DateTime.h

@@ -162,7 +162,7 @@ static const int DAYSPER400 = 146097;
 static const int DAYSPER4 = 1461;
 static const int MAXORDINAL = 3652059;
 
-static const double TOL_SECONDS = 1e-10;
+inline constexpr double TOL_SECONDS = 1e-9;
 
 // time section and fractional seconds are optional
 // to support trailing  white space, add ( )* to the

python/extensions/pybind_isce3/core/DateTime.cpp

@@ -99,7 +99,7 @@ void addbinding(py::class_<DateTime> & pyDateTime)
         .def("is_close",
                 (bool (DateTime::*)(const DateTime &, const TimeDelta &) const)&DateTime::isClose,
                 py::arg("other"),
-                py::arg("tol") = TimeDelta(1e-10))
+                py::arg("tol") = TimeDelta(isce3::core::TOL_SECONDS))
 //        .def("day_of_year", &DateTime::dayOfYear)  // XXX not implemented
         .def("seconds_of_day", &DateTime::secondsOfDay)
 //        .def("day_of_week", &DateTime::dayOfWeek)  // XXX not implemented

tests/python/extensions/pybind/core/datetime_.py

@@ -187,3 +187,24 @@ def test_isoformat():
     s = "2017-05-12T01:12:30.141592000"
     t = isce.core.DateTime(s)
     assert( t.isoformat() == s )
+
+def test_isoformat_roundtrip():
+    # DateTime.isoformat() only writes 9 digits, so choose eps < 1e-9
+    eps = 5e-10
+
+    # Construct a sequence of DateTimes separated by fixed intervals. The
+    # temporal spacing is not an integer number of nanoseconds.
+    n = 5
+    t0 = isce.core.DateTime(2022, 5, 4, 10, 3, 0.0)
+    dt = isce.core.TimeDelta(1.0 + eps)
+    times = [t0 + i * dt for i in range(n)]
+
+    # Converts DateTime -> str -> DateTime.
+    def roundtrip(t):
+        s = t.isoformat()
+        return isce.core.DateTime(s)
+
+    # Check that the tolerance of `is_close()` is loose enough to accommodate
+    # truncation of DateTimes due to serialization to text.
+    for t in times:
+        assert t.is_close(roundtrip(t))