ENH: rainfall time series interpolator (spatial) can be nn/lin

app/otbTimeSeriesIndexTrend.cxx

@@ -40,6 +40,7 @@
 // Resample
 #include "otbStreamingResampleImageFilter.h"
 #include "itkLinearInterpolateImageFunction.h"
+#include "itkNearestNeighborInterpolateImageFunction.h"
 
 // Dates
 #include "otbDates.h"
@@ -103,6 +104,7 @@ public:
   typedef otb::StreamingResampleImageFilter<FloatVectorImageType,
       FloatVectorImageType>                                                            ResampleImageFilterType;
   typedef itk::LinearInterpolateImageFunction<FloatVectorImageType>                    LinearInterpolatorType;
+  typedef itk::NearestNeighborInterpolateImageFunction<FloatVectorImageType>           NNInterpolatorType;
 
   /* typedefs for residues processing */
   typedef otb::functor::RainfallEstimatedNDVIResiduesFunctor<FloatVectorImageType::PixelType,
@@ -232,6 +234,12 @@ private:
     SetDefaultParameterInt         ("rain.reduce.cumul.nbdays", 150); // 150 days ~ 5 months
     MandatoryOff                   ("rain.reduce.cumul.nbdays");
 
+    // Method to resample rainfall time series
+    AddParameter(ParameterType_Choice, "rain.interpolator", "Interpolation");
+    MandatoryOff("rain.interpolator");
+    AddChoice("rain.interpolator.linear", "Linear interpolation");
+    AddChoice("rain.interpolator.nn",     "Nearest Neighbor interpolation");
+
     // Output residues
     AddParameter(ParameterType_OutputImage,  "residues",   "Output image for NDVI residues");
     SetDefaultOutputPixelType("residues", ImagePixelType_float);
@@ -474,12 +482,24 @@ private:
 
         // Resample rainfall
         LinearInterpolatorType::Pointer linInterpolator = LinearInterpolatorType::New();
+        NNInterpolatorType::Pointer nnInterpolator = NNInterpolatorType::New();
         m_ResampleFilter = ResampleImageFilterType::New();
         m_ResampleFilter->SetInput(m_RFCumulReduceFilter->GetOutput());
         m_ResampleFilter->SetOutputOrigin(m_NDVIConcatener->GetOutput()->GetOrigin());
         m_ResampleFilter->SetOutputSpacing(m_NDVIConcatener->GetOutput()->GetSignedSpacing());
         m_ResampleFilter->SetOutputSize(m_NDVIConcatener->GetOutput()->GetLargestPossibleRegion().GetSize());
-        m_ResampleFilter->SetInterpolator(linInterpolator);
+        if (HasValue("rain.interpolator") == 0)
+          {
+          m_ResampleFilter->SetInterpolator(linInterpolator);
+          }
+        else if (HasValue("rain.interpolator") == 1)
+          {
+          m_ResampleFilter->SetInterpolator(nnInterpolator);
+          }
+        else
+          {
+          otbAppLogFATAL("Unknown interpolator type!");
+          }
 
         // Write reduced rainfall
         if (HasValue("rainfcumul"))