yes, this is what I mentioned. I think I won't have problem with tiles and this solution, because the line always vertical, and the plane never.
for terrain I do not need so exact values, I just store and use their middle pixel simply. maybe later if my code performance will be better... I just have to store additionally xy coords corresponding to the already stored maxz and minz values, and the middle coord is also already stored. but if the 3 points are producing a line, they do not determine a plane exactly, it could cause errors...
in case of buildings, more exactly mainly stairs and ladders, your code is required to replace the current c_tracings, but it will be also relatively easy to integrate it into my codes, by storing 3 tile corner values.