Formula for calculating "true" isometric tile row/number?

programming flash
1

Hi, I’m trying to do a isometric game, diamond shaped stage. And want to know how the formula for translating the mouse position over a tile into the correct row/column of it.

I position them with something like this:

for (var i=0; i<=rows-1; i++) {
    for (var j=0; j<=columns-1; j++) {
        var tileName = "t_"+i+"_"+j;
        var tile:Tile = new Tile();
        tile.name=tileName;
        // logic to display the right frame of tiles and such, blablabla...
        
        tile.x=(j-i)*tileHeight;
        tile.y = (j+i)*tileHeight/2;

        gameArr.push(gameGrid.addChild(tile));
    }
}

Usually the tiles are half as high as their width. A classic 2:1 ratio. Then I could use the following formula for transforming mouse position to a tiles row/column:

var column:int = mapSize-(((mouseY/ tileHeight) + (mouseX - (mapSize * tileHeight)) / tileWidth) - mapSize) *-1;

var row:int = mapSize-(((mouseY/ tileHeight) - (mouseX - (mapSize * tileHeight)) / tileWidth) -mapSize) *-1;

If the grid is 50 x 50, then mapSize is 50.

But I’m trying to do what I think is called “true” isometric. Where the angles are 60 120 60… eh, anywho, the height is slightly higher. My tiles for instance, are 15 x 8.3.

…So, any ideas on how the formula would look like? How do I translate the mouse position to the current tiles row and column it is over.

Just to be clear, my “north” is upper right side.
Like this:
[[0, 1, 2],
[3, 4, 5],
[6, 7, 8]]
And then rotates clockwise 45 degrees.