立つ and 立てる: standing up and setting objects upright
Compare where a person stands with where an object is placed upright, and examine 立てる for making a plan.
Where someone stands
入口の前に立たないでください。 asks someone not to stand in front of the entrance. 立つ, read たつ, has the negative form 立たない; 入口の前に gives the position.
席を立って、窓を開けました。 says that someone rose from their seat and opened the window. を in 席を marks the place left, not an object being set upright.
Set an object upright
机の上に写真立てを立てました。 says that someone stood a photo frame on the desk. 立てる, read たてる, marks the object placed upright with を.
倒れないように、看板をしっかり立ててください。 asks someone to set a sign up firmly so it will not fall. 立てて refers to establishing the upright state, not just its location.
Plans and the spelling for buildings
旅行の計画を立てています。 means that someone is making travel plans. 立てる applies even though no physical object is being raised upright.
家を建てる means building a house and is also read たてる, but uses 建. Distinguish planning with 立てる from construction with 建てる by the noun involved.
Does を in 席を立つ mean that the seat is being set upright?
Show the answer and why
No. A person rises from or leaves a seat, and 席を identifies that place. Setting an object upright uses 立てる.