ENH: Adding a sampling strategy to set the total number of samples to be used...

ENH: Adding a sampling strategy to set the total number of samples to be used for all classes, using class proportions

Modules/Applications/AppClassification/app/otbSampleSelection.cxx

@@ -174,6 +174,14 @@ private:
     SetMinimumParameterFloatValue("strategy.percent.p",0);
     SetMaximumParameterFloatValue("strategy.percent.p",1);
     SetDefaultParameterFloat("strategy.percent.p",0.5);
+
+    AddChoice("strategy.total","Set the total number of samples to generate, and use class proportions.");
+    SetParameterDescription("strategy.total","Set the total number of samples to generate, and use class proportions.");
+
+    AddParameter(ParameterType_Int,"strategy.total.v","The number of samples to generate");
+    SetParameterDescription("strategy.total.v","The number of samples to generate");
+    SetMinimumParameterIntValue("strategy.total.v",1);
+    SetDefaultParameterInt("strategy.total.v",1000);
     
     AddChoice("strategy.smallest","Set same number of samples for all classes, with the smallest class fully sampled");
     SetParameterDescription("strategy.smallest","Set same number of samples for all classes, with the smallest class fully sampled");
@@ -246,19 +254,27 @@ private:
       // percent
       case 2:
       {
-      otbAppLogINFO("Sampluing strategy: set a percentage of samples for each class.");
+      otbAppLogINFO("Sampling strategy: set a percentage of samples for each class.");
       m_RateCalculator->SetPercentageOfSamples(this->GetParameterFloat("strategy.percent.p"));
       }
       break;
-      // smallest class
+      // total
       case 3:
+      {
+      otbAppLogINFO("Sampling strategy: set the total number of samples to generate, use classes proportions.");
+      m_RateCalculator->SetTotalNumberOfSamples(this->GetParameterInt("strategy.total.v"));
+      }
+      break;
+
+      // smallest class
+      case 4:
         {
         otbAppLogINFO("Sampling strategy : fit the number of samples based on the smallest class");
         m_RateCalculator->SetMinimumNbOfSamplesByClass();
         }
       break;
       // all samples
-      case 4:
+      case 5:
         {
         otbAppLogINFO("Sampling strategy : take all samples");
         m_RateCalculator->SetAllSamples();

Modules/Learning/Sampling/include/otbSamplingRateCalculator.h

@@ -70,6 +70,9 @@ public:
 
   /** Method to set a percentage of samples for each class */
   void SetPercentageOfSamples(double percent);
+
+  /** Method to set the total number of samples to generate */
+  void SetTotalNumberOfSamples(unsigned long value);  
   
   /** Method to choose a sampling strategy based on the smallest class.
    * The number of samples in each class is set to this minimum size*/

Modules/Learning/Sampling/src/otbSamplingRateCalculator.cxx

@@ -120,7 +120,28 @@ void SamplingRateCalculator
     it->second.Required = static_cast<unsigned long>(vcl_floor(0.5+percent * it->second.Tot));
     it->second.Rate = percent;
     }
+}
+
+void SamplingRateCalculator
+::SetTotalNumberOfSamples(unsigned long value)
+{
+  // First, get total number of samples
+  unsigned long totalNumberOfSamplesAvailable = 0;
 
+  MapRateType::iterator it = m_RatesByClass.begin();
+  for (; it != m_RatesByClass.end() ; ++it)
+    {
+    totalNumberOfSamplesAvailable+=it->second.Tot;
+    }
+
+  // Then compute number of samples for each class
+  for (it = m_RatesByClass.begin(); it != m_RatesByClass.end() ; ++it)
+    {
+    double ratio = it->second.Tot / static_cast<double>(totalNumberOfSamplesAvailable);
+
+    it->second.Required = static_cast<unsigned long>(0.5+ratio*value);
+    this->UpdateRate(it->first);
+    }
 }
 
 void