drain, apron, flanges - not symmetrical
if there is an apron, or skirt, (visible front part of tub in an alcove and in some podiums), then it's crucial to know whether the drain is on the far left or far right. Also crucial is how many sides to add the tiling flange to. You can have tiling flange anywhere, and although you can add it yourself on site it is usually factory-installed if you know what you need when you order the tub.
Faucets (supply plumbing) are usually right above the drain.