This is what I've done -- just checked still works(some maps are tacky to work with like furious heights btw, could fix it with photoshop with multiple screen captures and resizing -- but that's lots of work.
/devmap bloodrun
/sv_cheats 1
/noclip 1
-- press forward and look up for few seconds
-- look down
-- reposition to get the entire map or make it centered
-- printscreen/screenshot
-- look in the screenshot folder