An anchor's position (that line projected from itself to the base of the planet) should be displayed when it's firing, so a defender knows where it can build anchors. Otherwise it's a stupid game of luck where you have to guess where you can put your fabbers so they don't get sniped by the anchor. If it's firing on your base, its position should be known.
We can't see artillery just because it is firing on our base, or Leviathans, catapults, shellers etc. If you're having trouble positioning fabbers for umbrellas, throw up an orbital radar somewhere safe first and problem solved. As long as you aren't tanking your energy at least Other options for taking out the anchor include the bluehawk T2 bot, catapults, and the missile ship I believe. tl, dr: radar and don't tank energy
Even if you can see the anchor itself, because of the way the orbital plane works, it's hard to see the horizontal distance between it and anything else unless that position beam is hitting the ground. The position beam should show up if the anchor is showing up on the map.