I have a tileset with 64x64 pixel images and a map with 8x8 pixel tile size:
When i want to place a tileset item, the x/y position of tileset image is the bottom left of the tileset image. Is it possible to configure something to display de center of tileset image on the x/y position of tileset ?
Yes, you can do this by changing the “Drawing Offset” property of the tileset, which is an offset in pixels applied when drawing tiles from that tileset. If you want to center a 64x64 tile when placed on an 8x8 grid, a drawing offset of (-28, 28) should do the trick.
For changing any tileset property, you can click the small “Edit Tileset” button below the tileset view.
Currently Tiled has no support for layers with arbitrary data, like altitude in this case. Though if there is a limited set of valid altitudes, you could use a tile layer for this with a tileset where each tile represents a different altitude.
But of course, Tiled being open source you may want to try adding a special layer type for this with an appropriate editing tool.