How to select a line in an image using ImageJ/Fiji by setting its start and end points? As in not drawing it over the image, but inputting the coordinates directly somewhere.
open script editor, select IJ1 macro and then type the code below and then run.
makeLine(1, 1, 100, 100);
This will create a line ROI between (1,1) and (100, 100).
See https://imagej.nih.gov/ij/developer/macro/functions.html#makeLine