How can i retrived graph's coordinates of vertices?

I wanted to export those info into json but GraphML do not stores
coordinates info. As sigmajs can support coords and do not want to strain
browser side performance calculating layout.
I want to get already generated coordinates by sfdp_layout of the graph.

How can i do that?

Thanks

Phyo.

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Double posted , sorry.. Please use this one.

i wanted like this

{id: 1 , x : 10 , y : 20} for each nodes

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