ENH: Adding a missing const getter on GCPs

Code/IO/otbImage.h

@@ -145,6 +145,7 @@ public:
   virtual unsigned int GetGCPCount(void) const;
 
   virtual OTB_GCP& GetGCPs(unsigned int GCPnum);
+  virtual const OTB_GCP& GetGCPs(unsigned int GCPnum) const;
 
   virtual std::string GetGCPId(unsigned int GCPnum) const;
   virtual std::string GetGCPInfo(unsigned int GCPnum) const;

Code/IO/otbImage.txx

@@ -56,6 +56,12 @@ OTB_GCP& Image<TPixel, VImageDimension>::GetGCPs(unsigned int GCPnum)
   return (this->GetMetaDataInterface()->GetGCPs(GCPnum));
 }
 
+template <class TPixel, unsigned int VImageDimension>
+const OTB_GCP& Image<TPixel, VImageDimension>::GetGCPs(unsigned int GCPnum) const
+{
+  return (this->GetMetaDataInterface()->GetGCPs(GCPnum));
+}
+
 template <class TPixel, unsigned int VImageDimension>
 std::string Image<TPixel, VImageDimension>::GetGCPId(unsigned int GCPnum) const
 {