You have to prepare an ascii file with extension .xy (or .xyz) containing the geographical coordinates of the baseline. The file format is two (or three) space separated floats (real numbers) for the x- and y-coordinate on separate lines for each of the points (in case of three columns in the file x and y is derived from the first two columns).
You must also select the map projection in which you have specified the geographical coordinates.
NOTE: (.xy) or (.xyz) input files must be provided in metric unit [m]