I'm gathering all that information to try to build a full and complete guide to WvW that will help people to learn basic/advanced stuff about WvW.
Alright so this thread is only about offensive siege. Gathering information about siege placement for people to compile it in a video to make it simpler. So far I wrote down what I remember in the borderlands, sorry for my lack of knowledge in Eternal Battlegrounds.
Borderlands
Supply Camps
Siege isn't needed to assault a supply camp but can turn the fight around if you can build a ballista quickly a little in the back to support you.
Towers
Rams, cata and treb can be good at assaulting a gate. Cata or treb assaulting a wall can work great too.
North West Towers
You can place cata at the North wall on the cliff to be able to hit the wall, a treb can also hit the wall from further back. A cata under the lord room can also hit the South wall.
North Est Towers
You can treb the West wall if you put it on top of the supply depot at the North Est and is in a spot where it's harder to kill. Cata on the West wall is great too but if you put those on the lower cliff towards garrion you can still be in range to hit wall but also in a spot where defenders need to get out of the tower to defend their tower. (good tactic when you have a bigger zerg but they have lot of siege on the cliff/walls)
Briar Towers
You can cata the North wall from under the lord room, you can treb the walls from vale supply but only good if it's not the spawn of the bad guys owning the tower since there's a huge entrance in the back (Main entrance from the road is very small and easy to defend with ballista). You can also treb the main gate from the rock infront of the gate. Last good placement for siege is on the middle island at the Est of the tower, you can build treb and cata to hit the Est wall.
Lake Towers
You can build a treb in hills on the South West wall that will hit the walls and the gate of lake. You can also treb the main gate/wall from the small cliff located near the South Est spawn (only good if it's your spawn).
Keeps
A lot like towers, good specific spots though.
Garrison Keeps
You can treb the North West wall from the North West tower if you build it on top of the supply depot. You can treb the North Est wall from the North Est tower if you build a treb on the ramp (Would need a more specific description of where since there are a couple spots that works there).
Bay Keeps
You can treb the North Est wall from the high cliff at the South West of garrison. You can siege the South wall from the briar bridge behind the lord room. You can treb the inner walls from the cliff at the North Est of the bay and from just outside of the North West gate. You can also treb the South gate/walls from vale (only good if it's your spawn behind the supply). Yes, that is a lot of good treb location to siege that keep. You can also cata the water walls on the Est if you build the cata at the bottom of the North wall. You can also cata the inners from the South outer wall and cliff.
Hills Keeps
You can treb the North walls from the North Est supply if you build treb on the side of the cliff facing hills. You can cata the West walls or treb those from the mountain on the West of the wall.
Eternal Battleground
Supply Camps
Same as borderlands with good specific spots too.
Towers
Borderlands tactics works here too aswell as some good specific spots.
Keeps
A lot like towers, good specific spots though.
Stonemist
Don't know much about it, expand it please.