Authors: Eleni Nikou (George Mason University), Jie Zhang (George Mason University), Matthew Dupertuis (George Mason University), Suman Dhakal (George Mason University)

This study introduces a fitting technique to obtain the 3-D geometric parameters of a CME along with their uncertainties. CMEs are large-scale eruptions that carry plasma and magnetic field from the Sun to the interplanetary space and usually show a two-front structure that consists of the ejecta and the shock. The graduated cylindrical shell model (GCS model) has been broadly used to reconstruct the geometry of the ejecta and depends on six free parameters which are the longitude, latitude, tilt angle, aspect ratio, half angle and height. The suggested fitting technique uses the MPFIT minimization IDL routine and combines multi-viewpoint white light observations from the STEREO, SOHO and PSP spacecraft with the GCS point cloud in order to obtain the best values of the geometric parameters along with their uncertainties. This method relies only on two input parameters, which are a set of observations and a set of initial guesses in order to minimize the chi-square between the observations and the model. A robust, fast and easy to use technique to estimate the CME geometric parameters along with their uncertainties will be of great help to space weather predictions. The difference of uncertainties of CME geometric parameters, when observed by one, two and three viewpoints, will be presented.