In a series of posts, I would like to introduce using the City Energy Analyst (CEA) with Grasshopper. The linkage between the two tools is named as GTC, short for Grasshopper-to-CEA. GTC enables the users to conduct automated iterations with CEA and the parametric model in Grasshopper, serving purposes like optimization or sensitivity analysis. GTC has two main functions. One is that it functions as a parser, which converts the format of the geometries generated in Grasshopper to the CEA format. The other one is that it calls CEA to perform the simulations off the platform of Grasshopper. As the introductory post, this post introduces the installation of GTC and demonstrates creating input files in .dbf format with GTC.