Left:WISPR-I running differenced image at 03:56 UT with the feature used in tracking (bright spot at the back of the cavity) circled in red. Center: nearly simultaneous STA/COR2 running differenced image (03:54 UT) with the common feature use for triangulation labeled v1/yellow arrow. Also shown are three predicted locations (red +’s) of the WISPR feature projected onto the COR2 image for three possible distances of the feature from PSP. The middle red + falls on the feature and thus determines the 3D location of the common feature (see text). Right: COR2 image at an earlier time (01:39 UT) when the full CME cavity structure was visible, allowing identification of the feature (marked v1/yellow arrow). The COR2 image is projected in the Helioprojective Cartesian (HPC) system (red and blue grid lines) with the Sun (yellow globe) drawn to scale.