I am aware of the nature of isometric view games. I think you misinterpreted the question I had. the top portion of the image is not how my game looks at all. its simply an example of the type of operation I wish to perform - which is returning a tile(x,y) for any given pixel point. This type of operation is especially useful when determining perfect player-to-tile collisions. It's just much harder to do on an isometric grid.
in order to mathematically determine which tile a pixel point would reside on an isometric grid, my first guess would be to convert the isometric map to a traditional grid (in *memory*, not actual display).
I've finally got a working function. You plug in a pixel point, it multiplies it's y-height by 2 to be in sync with perfect diamond tiles (much like the ultima online tiles), then rotates the point 45 degrees counter clockwise from the map's origin to be aligned to a theoretical straight grid. This grid doesn't really exist, but it's how I can calculate what tile a pixel resides. from this point I perform my original equation as demonstrated in the upper portion of the image. tile = int(pixel_position/tilesize)+1. Tilesize is determined by measuring the hypotenuse of one quarter of the isometric tile.
here is the function for those who are interested...
function gettilex(x,y,tilesize#)
`stretch the iso grid vertically x2 to create
`perfectly square tiles
y=y*2
`find the angle to rotate to
`(current angle -45 degrees)
theta#=atan(x/y)-45
if theta#<0
theta#=theta#+360
endif
`perform rotation. grid should now be straight
newx = cos(theta#)*x - sin(theta#)*y
newy = sin(theta#)*x + cos(theta#)*y
`get tile ordered pair from pixel position
tilex = int(newx/tilesize#)+1
tiley = int(newy/tilesize#)+1
`return tile
endfunction tilex
