I'm trying to translate mouse coords to precise isometric coords (I can already find the tile the mouse is over, but I want it to be more precise). I've tried several different methods but I seem to keep falling short.

For drawing I use:

batch.draw(
    texture,
    (y * tileWidth / 2) + (x  * tileWidth / 2),
    (x  * tileHeight / 2) - (y * tileHeight / 2))

This is what I currently use for figuring out a tile position:

 float xt = x +  camPosition.x - (ScreenWidth/2) ;
 float yt = (ScreenHeight) - y + camPosition.y - (ScreenHeight/2);

 int tileY = Math.round((((xt) / tileWidth) - ((yt) / tileHeight)));
 int tileX = Math.round((((xt) / tileWidth) + ((yt) / tileHeight))- 1);

I'm just wondering how I could update these to allow for more precise coordinates, instead of tile only. EDIT: Following what ccxvii said below, and removing the -1 from tileX, the object follows my mouse just like I had wanted. Just going to re-examine the math and figure out if that change will result in other messes =o