Extract Part of a Single PDF Page from Bash

In order to extract a part of a PDF page on a Gnu/Linux machine I use the following command: gs -sDEVICE=pdfwrite -o out.pdf -g2300x2300 input.pdf The -g...x... option lets me choose coordinates on the input PDF. So, here is my question: 1. How do I shift the coordinates so that any rectangle on the input PDF might be chosen? and extending that question: 2. Is there any graphical interface that allows choosing the coordinates I want? (so far it's trial and error.) ---- I do not want to extract whole pages from the input PDF. The output format should again be PDF. I am not looking for extraction of text or images. A similar question had been asked on askubuntu.org , but the answers only deal with extracting whole pages or page ranges. I know I can do that with pdftk. A yet more specific question similar to this on was asked here before , but remained unanswered. On a Mac this whole affair is absolutely simple: The program preview has a function for exactly that. How do I snapshot a part of a single PDF page to output format PDF?