diff --git a/modules/gmt/modgmt_strcomp.h b/modules/gmt/modgmt_strcomp.h
index 143822c..187d3a9 100644
--- a/modules/gmt/modgmt_strcomp.h
+++ b/modules/gmt/modgmt_strcomp.h
@@ -3,7 +3,9 @@
 #include <set>
 #include <string>
 #include <vector>
+#include "common.h"
 
+// Compare string with template
 class TemplateComparator
 {
  TemplateComparator() = delete;
@@ -65,3 +67,268 @@ class TemplateComparator
   InitCursors(root.get());
  }
 };
+
+
+// Common ancestor for all parameters
+template<bool Optional>
+class Parameter
+{
+ std::string name;
+ bool initialised;
+
+ protected:
+ Parameter() = default;
+ Parameter(const Parameter&) = delete;
+
+ Parameter(std::string&& str): name(std::move(str)), initialised(false) {}
+ Parameter(const std::string& str): name(str), initialised(false) {}
+
+ void SetState(bool newini) {initialised=newini;}
+
+ public:
+ bool Initialised() const {return initialised;}
+ const std::string& Name() {return name;}
+ constexpr bool isOptional() const {return Optional;}
+
+ static constexpr bool optional=Optional;
+};
+
+// Class for parameter which must be in named pair
+template <class Converter, bool O>
+class NamedParameter: public Converter, public Parameter<O>
+{
+ NamedParameter() = delete;
+ NamedParameter(const NamedParameter&) = delete;
+
+ using Parameter<O>::Initialised;
+
+ protected:
+ TemplateComparator compar;
+
+ public:
+ typedef Converter ConverterType;
+ // Constructor specifies template for comparison
+ template<class N, class T>
+ NamedParameter(N&& n, T&& t):compar(std::forward(t)) {Parameter<O>(std::forward(n));}
+
+ // Return error in case of repeated initialisation
+ bool Init(const ObjectBase* p, const std::string& str, std::string& err)
+ {
+  if(!compar.Compare(str)) return true;
+  if(Initialised()) return !Converter::Convert(p,err);
+  else SetState(Converter::Convert(p,err));
+  return true;
+ }
+};
+
+template<class Converter>
+using ONPar=NamedParameter<Converter,true>;
+template<class Converter>
+using RNPar=NamedParameter<Converter,false>;
+
+
+// Class for parameter which can be in named pair or not
+template <class Converter, bool O>
+class NamedFreeParameter: public NamedParameter<Converter,O>
+{
+ NamedFreeParameter() = delete;
+ NamedFreeParameter(const NamedFreeParameter&) = delete;
+
+ using NamedParameter<Converter,O>::compar;
+ using NamedParameter<Converter,O>::Initialised;
+
+ public:
+ typedef Converter ConverterType;
+ // Constructor specifies template for comparison
+ template<class N, class T>
+ NamedFreeParameter(N&& n, T&& t):NamedParameter<Converter,O>(std::forward(n),std::forward(t)) {}
+
+ // Return error in case of repeated initialisation
+ bool Init(const ObjectBase* p, const std::string& str)
+ {
+  if(!compar.Compare(str)) return true;
+  if(Initialised()) return !Converter::Convert(p);
+  else SetState(Converter::Convert(p));
+  return true;
+ }
+
+ bool Init(const ObjectBase* p)
+ {
+  if(Initialised()) return !Converter::Convert(p);
+  else SetState(Converter::Convert(p));
+  return true;
+ }
+};
+
+template<class Converter>
+using ONFPar=NamedFreeParameter<Converter,true>;
+template<class Converter>
+using RNFPar=NamedFreeParameter<Converter,false>;
+
+
+// Class for parameter which can be in some positions in list
+template <class Converter, bool O>
+class PositionalParameter: public Converter, public Parameter<O>
+{
+ using IType=ObjectList::IndexType;
+ PositionalParameter() = delete;
+ PositionalParameter(const PositionalParameter&) = delete;
+ std::set<IType> positions;
+ IType initpos;
+
+ using Parameter<O>::Initialised;
+ using Parameter<O>::SetState;
+
+ // Constructor specifies list of possible positions
+ PositionalParameter(IType i):initpos(0) {positions.insert(i);}
+ template<class... Args>
+ PositionalParameter(IType i, Args... args): PositionalParameter(args...) {positions.insert(i);}
+ public:
+ typedef Converter ConverterType;
+ template<class S>
+ PositionalParameter(S&& str, IType i):initpos(0) {Parameter<O>(std::forward(str)); positions.insert(i);}
+ template<class S, class... Args>
+ PositionalParameter(S&& str, IType i, Args... args): PositionalParameter(args...) {Parameter<O>(std::forward(str)); positions.insert(i);}
+
+ // Return error in case of repeated initialisation
+ bool Init(IType i, const ObjectBase* p, std::string& err)
+ {
+  std::string cerr;
+  if(positions.cend()==positions.find(i)) return true;
+  if(Initialised()) return !Converter::Convert(p,cerr);
+  else
+  {
+   bool res=Converter::Convert(p,cerr);
+   if(res) initpos=i;
+   else
+   {
+    if(1==positions.size() && !O) // Only one position for required parameter. Error message must describe reason of failed conversion
+    {
+     err=std::move(cerr);
+     return false;
+    }
+   }
+   SetState(res);
+  }
+  return true;
+ }
+
+ IType InitialisedFromPosition() const {return initpos;}
+};
+
+template<class Converter>
+using OPosPar=PositionalParameter<Converter,true>;
+template<class Converter>
+using RPosPar=PositionalParameter<Converter,false>;
+
+// Parsing positional parameters
+// Generic template
+template<class... Args>
+class ParsePositionalParameters;
+
+// Recursive template
+template<class Arg, class... Args>
+class ParsePositionalParameters<Arg, Args...>: ParsePositionalParameters<Args...>
+{
+ typedef PositionalParameter<typename Arg::ConverterType, Arg::optional> PType;
+ static_assert(std::is_same<PType,Arg>::value,"ParsePositionalParameters template argument(s) must be PositionalParameter");
+ PType& par;
+
+ ParsePositionalParameters() = delete;
+ ParsePositionalParameters(const ParsePositionalParameters&) = delete;
+ ParsePositionalParameters(ParsePositionalParameters&&) = delete;
+
+ protected:
+ template<class Str>
+ void SetError(Str&& str) {ParsePositionalParameters<Args...>::SetError(std::forward(str));}
+ bool TryInit(ObjectList::IndexType i, const ObjectBase* ob)
+ {
+  std::string err;
+  bool res=par.Init(i,ob,err);
+  if(!res) SetError(err.empty()?("Ambiguous definition of parameter "+par.Name()):("Parameter "+par.Name()+" in position "+ToString(i)+": "+err));
+  return res && ParsePositionalParameters<Args...>::TryInit(i,ob);
+ }
+ bool Check()
+ {
+  if(!(par.Initialised() || par.isOptional()))
+  {
+   SetError("Parameter "+par.Name()+" required, but not set");
+   return false;
+  }
+  return ParsePositionalParameters<Args...>::Check();
+ }
+
+ // Return value: number of parameters initialised from position i (count only first two)
+ size_t isUsed(ObjectList::IndexType i, bool used=false) const
+ {
+  if(!par.Initialised() || (par.InitialisedFromPosition()!=i)) return ParsePositionalParameters<Args...>::isUsed(i,used);
+
+  if(used) // Error, two parameters initialised from one position
+  {
+   SetError(par.Name());
+   return 1;
+  }
+
+  auto res=ParsePositionalParameters<Args...>::isUsed(i,true);
+  if(res==1) // Two parameters initialised from one position, name of second parameter in error string
+  {
+   SetError("Parameters "+Error()+" and "+par.Name()+" are initialised from object in position "+ToString(i));
+   return 2;
+  }
+  else return 1; // All ok
+ }
+
+ public:
+ ParsePositionalParameters(PType& p, Args... args):par(p) {ParsePositionalParameters<Args...>(args...);}
+
+ std::string Error() const {return ParsePositionalParameters<Args...>::Error();}
+
+ bool Parse(const ObjectList* list)
+ {
+  std::string err;
+  for(ObjectList::IndexType i=0; i<list->Size(); i++)
+  {
+   if(!TryInit(i,list->At(i),err))
+   {
+    SetError("Error parsing argument "+ToString(i)+": "+err);
+    return false;
+   }
+  }
+  if(!Check()) return false;
+
+  for(ObjectList::IndexType i=0; i<list->Size(); i++)
+  {
+   auto n=isUsed(i);
+   if(n>1) return false; // Error message already set
+   if(0==n)
+   {
+    SetError("Unused object in position "+ToString(i));
+    return false;
+   }
+  }
+  return true;
+ }
+};
+
+
+// Bottom of recursion
+template<>
+class ParsePositionalParameters<>
+{
+ std::string err;
+
+ ParsePositionalParameters(const ParsePositionalParameters&) = delete;
+ ParsePositionalParameters(ParsePositionalParameters&&) = delete;
+
+ protected:
+ ParsePositionalParameters() = default;
+
+ bool TryInit(ObjectList::IndexType i, const ObjectBase* ob) const {return true;}
+ size_t isUsed(ObjectList::IndexType i, bool used=false) const {return 0;}
+ bool Check() const {return true;}
+
+ template<class Str>
+ void SetError(Str&& str) {err=std::forward(str);}
+
+ std::string Error() const {return err;}
+};