Nodes at crossing points

[Pooya <Input Pooya de>]

Hi,

I am new to Dia and have a question:

Is it possible to create a node at crossing points? or at arbitrary position on a line?

I tried to realize this by changing the beginning of a line to a node symbol and then dragging it to the 
desired position. But the problem occuring then is, that the node is not centered on the line.

I would be glad of any help.
bye