The 3D coordinates of a star sytem X can be calculated by a process called Trilateration. As input, the distances from system X to other (good reference) star systems are used. EDSC allows you to just that. The actual calculation of 3D coordinates is done by another tool from the same author: TGC, which is an acronym for The Great Collector.
Note: The author already had a domain for EDSC. For various reason he decided to reuse the domain for TGC. Hence confusion. The tool is mostly called TGC in the 3D coordinates thread. Outside of it its often incorrectly referred to as EDSC.