When Superman uses his heat vision, can he measure exactly where he wants to hit someone? And how far can he expand his heat vision? Is his heat vision invisible to the human eye? I know we see it in the films for the audience to know that it is his heat vision is coming out.
Yes he can target it with very precise precision. No, there is no stated upper limit. Visibility depends on the medium and plot demands, it has been shown to be visible and invisible, as a line and as a point. Sometimes it is shown for the audience sake.
One example is Superman vs the Elite (movie). Sups uses his non-violent (infrared) heat vision to lobotomize Manchester Black through his pupils (real life biology aside). Pin point accuracy, no tissue damage.
A different example is Superman lobotomizing Doomsday in Justice League cartoon. We see the heat vision burning through Doomsday skull. Scars are left, smoke is seen as is the heat vision lasers.
Finally, again the Superman Batman Adventures had Superman shaving with his laser vision bouncing it off the mirror, it followed his eye balls.
How does it work- in Action Comics volume 1 (new 52) Superman says "my eyes don't just absorb radiation, they emit all kinds to" meaning that his eyes could manipulate the electromagnetic spectrum, beyond what humans perceive as visible color.
Can he direct it- yes, it would technically work the same way as someone focusing on something. But he could focus his sight in ways humans can't. He blanketed a large (a beach) area with heat vision in Superman/ Batman: Supergirl, and he focused his sight through retina to lobotomies someone in Superman vs the Elite.
Would a human be able to see this- it depends on the writer. Grant Morrison had him use invisible heat vision during a fight with the Ultra Marine Corpse . Man of Steel made it obvious.
And if a movie has invisible heat vision, they could use an object glowing with heat.
By saying heat vision you had given it away now we know it has something to do with infrared radiation which we perceived as heat and the visible wavelength which allows us to see. Honestly I don't know the answer to your question because superman usually do the interviewing not the other way around.