DRCSIM: Where on the feet are the BDI feet frames located (poses reported in the AtlasSimInterfaceState message)? [closed]

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In the atlas_msgs/AtlasSimInterfaceState message, poses for both feet are reported. The frames used are obviously not the same as those used in the URDF model for the feet frames. Is there any documentation where on the feet both frames are located? There are various ways that can be used to estimate the location, but documentation would be preferred. Thanks for any pointers.