Fix mixup between acquired PRF and processed PRF (#702)

* Add grid spacing to swath object.

* Fix acquired/processed PRF mixup in RadarGridParameters ctor.

* Fix acquired/processed PRF mixup in ResampSlc.

* pybind11 Swath time spacing property.

Author: bhawkins

cxx/isce3/image/ResampSlc.icc

@@ -100,7 +100,7 @@ inline void ResampSlc::_setDataFromSwath(const isce3::product::Swath& swath)
     _startingRange = swath.slantRange()[0];
     _rangePixelSpacing = swath.rangePixelSpacing();
     _sensingStart = swath.zeroDopplerTime()[0];
-    _prf = swath.nominalAcquisitionPRF();
+    _prf = 1.0 / swath.zeroDopplerTimeSpacing();
     _wavelength = swath.processedWavelength();
 }
 

cxx/isce3/product/RadarGridParameters.cpp

@@ -14,7 +14,7 @@ RadarGridParameters(const Swath & swath, isce3::core::LookSide lookSide) :
     _lookSide(lookSide),
     _sensingStart(swath.zeroDopplerTime()[0]),
     _wavelength(swath.processedWavelength()),
-    _prf(swath.nominalAcquisitionPRF()),
+    _prf(1.0 / swath.zeroDopplerTimeSpacing()),
     _startingRange(swath.slantRange()[0]),
     _rangePixelSpacing(swath.rangePixelSpacing()),
     _rlength(swath.lines()),

cxx/isce3/product/Serialization.h

@@ -113,6 +113,9 @@ namespace isce3 {
             isce3::io::loadFromH5(fgroup, "nominalAcquisitionPRF", value);
             swath.nominalAcquisitionPRF(value);
 
+            isce3::io::loadFromH5(group, "zeroDopplerTimeSpacing", value);
+            swath.zeroDopplerTimeSpacing(value);
+
             isce3::io::loadFromH5(fgroup, "sceneCenterGroundRangeSpacing", value);
             swath.sceneCenterGroundRangeSpacing(value);
 

cxx/isce3/product/Swath.h

@@ -77,6 +77,11 @@ class isce3::product::Swath {
         /** Set nominal acquisition PRF */
         inline void nominalAcquisitionPRF(double f) { _nominalAcquisitionPRF = f; }
 
+        /** Get time spacing of raster grid */
+        inline double zeroDopplerTimeSpacing() const { return _zeroDopplerTimeSpacing; }
+        /** Set time spacing of raster grid */
+        inline void zeroDopplerTimeSpacing(double dt) { _zeroDopplerTimeSpacing = dt; }
+
         /** Get scene center along track spacing */
         inline double sceneCenterAlongTrackSpacing() const {
             return _sceneCenterAlongTrackSpacing;
@@ -123,7 +128,8 @@ class isce3::product::Swath {
         double _processedCenterFrequency;
         double _acquiredRangeBandwidth;
         double _processedRangeBandwidth;
-        double _nominalAcquisitionPRF;
+        double _nominalAcquisitionPRF;      // acquired
+        double _zeroDopplerTimeSpacing;     // processed
         double _sceneCenterAlongTrackSpacing;
         double _sceneCenterGroundRangeSpacing;
         double _processedAzimuthBandwidth;

python/extensions/pybind_isce3/product/Swath.cpp

@@ -54,6 +54,9 @@ void addbinding(pybind11::class_<Swath> & pySwath)
         .def_property("nominal_acquisition_prf",
                 py::overload_cast<>(&Swath::nominalAcquisitionPRF, py::const_),
                 py::overload_cast<double>(&Swath::nominalAcquisitionPRF))
+        .def_property("zero_doppler_time_spacing",
+                py::overload_cast<>(&Swath::zeroDopplerTimeSpacing, py::const_),
+                py::overload_cast<double>(&Swath::zeroDopplerTimeSpacing))
         .def_property("scene_center_along_track_spacing",
                 py::overload_cast<>(&Swath::sceneCenterAlongTrackSpacing, py::const_),
                 py::overload_cast<double>(&Swath::sceneCenterAlongTrackSpacing))