Discussion of Depth

[AltiusBimm]

A rather challenging subject in the design of isometric RPGs is the proper use of the order-of-drawing; otherwise know as depth.
I could use some help in this area as well, though I would also enjoy seeing a discussion of general depth philosophy.
So, getting to the point, let’s start with my dilemma:
(Skip reading this block of code unless you context for what comes after it.)

 my_rim =
  tile_add(global.bkg,
           global.rimtilex,
           global.rimtiley,
           75,
           37,
           x-6,
           y-(16*(my_span+my_altitude))-3,
           -(y-16*my_span-16)+150);
 my_base =
  tile_add(global.bkg,
           global.x,
           global.y,
           64,32,
           x,y,
           -y);
 my_top =
  tile_add(global.bkg,
           global.x,
           global.y,
           64,
           32,
           x,
           y-16*my_span-16*my_altitude,
           -(y-16*my_span-16));
Here is the important part:
Depth of base = -y
Depth of top = -(y-16*my_span-16)
Depth of rim = -(y-16*my_span-16)+150

SO:
(Slashing right to the core of what I am getting at)
Does anyone else have any depth equations which might help?
Those which I am using (specifically “-(y-16*my_span-16)+150”) do not work properly…the ‘my_top’ tile of a “pillar” which has lower y value is often place shallower than the rim of a pillar with a higher y value and a higher my_span value
(Note:
‘altitude’ is the distance from “0 altitude” [flatness] to the beginning of the bottom of the “pillar”
‘span’ refers to the distance from the beginning of the bottom of the ‘pillar’ to the end of the top)
This sounds right up IsmAvatar's alley

IA: The font tags you have chosen are not friendly to a web browser, so I have removed them. I suggest you don't use them again.

[IsmAvatar]

Actually, this isn't quite up my alley yet. I haven't got a clue what your talking about, sorry.

As for a discussion, feel free to start a discussion, as long as you pick the right forum for it (Probably the general forum)

[Noadi]

Same with me, I'm not quite sure what you mean. Could you explain a little more? Or maybe give us a diagram of what you're trying to do? I'm a very visual person maybe that will help.

[AltiusBimm]

Regarding the tags:
Okay, I won’t use those anymore, but can you tell me a way to make an indented first line of a paragraph without using them ?

Regarding the incomprehensibleness of my post:
I should have explained better, the type of my isometric system. As Noadi politely requested, here is an illustration of the problem.
www.geocities.com/yadra_voat/Isometrics.html
(You may need to manually paste the URL into an address bar, if Geocities gives an error message.)

On the left you can see the placement of the instance-tiles in the isometric plane.
(Represented by a single flat-looking tile.) This view shows the absolute positions of the instance-tiles, as well as their collision masks.
On the right you can see the “pillar” parts as well. All instance-tiles shown are at altitude zero, with a span of 3 or 4.

The problem is that the thin rim around the top of each pillar is not shown correctly.
It’s obvious to me that it’s caused by not having a good formula for setting the depth of the tiles that form the rims. (Each rim is made out of only one tile.)
I hope that helps ;D