3D Sun Loop Tracer: A Tool for Stereoscopy of Coronal Loops for NASA's STEREO Mission

Stereoscopy and triangulation can be used to determine the three-dimensional geometry of coronal loops seen in simultaneous images from the two STEREO spacecraft. Here we demonstrate a new tool 3D Sun Loop Tracer (SLT) that uses stereoscopy to determine the 3D structure of a loop that can be identified in both images. SLT proceeds in several stages. First, the user "seeds" the tool by selecting the same loop in two simultaneous images. The user identifies any point on the same loop in the first image and any point on the same loop in the second image. The selected points can be anywhere on the loop. Next, separately for each image, the loop segment is traced automatically using an algorithm which follows edges. Last, the two traces are fed to a triangulation program that matches the two segments to find corresponding "tiepoints" and performs the inversion to obtain the (x,y,z) coordinates of points on the loop. The tool has been developed and tested using a physics-based synthetic 3D coronal (K. Schrijver, private communication). We show that the method produces accurate results for loop reconstruction over a wide range of stereo angles.