How to change the pivot of each tile in isometric 45?

[ankisme]

Here is my picture, and the pivot of the tree png is wrong.

And the tree is 1x1.

Then the house is 3x2.

Now(I don’t want this):
the root of tree is not placed at the center of the tile.
the house use 4x3 tiles

What I want:
the root of tree is placed at the center of the tile.
the house use 3x2 tiles

And how to change the pivot of tree and house ?

Could I add the feature only by extension, or I have to add the feature only by edit the source code?

[ankisme]

I don’t know why my question not have someone to answer.

Maybe my english word is not properly.

But I really think it’s a fundamental feature.