Garfield is gaseous detector simulation package developed recently to be used with root interface (C++/C coding).
Garfield++ is used to simulate GEM detector. 
Garfield++ has an input file (.result) that has all the information about the detector geometry and the electric field simulation. Steps to obtain the input file is summarized by the follow chart:
build the geometry -> build a mesh -> ElmerSolver(output .result file)
An open source for building the desired geometry is Gmsh which produce (.msh) file to be as an input file to Elmer which is responsible for the solving the electric field using the finite element method (FEM) and recording all the data in a (.ep and .result) files.
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