  We have studied two Coronal Mass Ejections (CMEs) that occurred on September
25 and 28, 2012 and interacted near the Earth. By fitting the Graduated
Cylindrical Shell (GCS) model on the SECCHI/COR2 images and applying the
Stereoscopic Self-Similar Expansion (SSSE) method on the SECCHI/HI images, the
initial direction of both the CMEs is estimated to be west of the Sun-Earth
line. Further, the three-dimensional (3D) heliospheric kinematics of these CMEs
have been estimated using Self-Similar Expansion (SSE) reconstruction method.
We show that use of SSE method with different values of angular extent of the
CMEs, leads to significantly different kinematics estimates for the CMEs
propagating away from the observer. Using the estimated kinematics and true
masses of the CMEs, we have derived the coefficient of restitution for the
collision which is found to be close to elastic. The in situ measurements at 1
AU show two distinct structures of interplanetary CMEs, heating of the
following CME, as well as ongoing interaction between the preceding and the
following CME. We highlight the signatures of interaction in remote and in situ
observations of these CMEs and the role of interaction in producing a major
geomagnetic storm.
