Those things exist, and they work pretty good. I don't know if they have a single receiver or a separate receiver for each antenna. Examples: http://www.jrc.co

Those things exist, and they work pretty good. I don't know if they have a single receiver or a separate receiver for each antenna. Examples: http://www.jrc.co.jp/eng/product/lineup/jlr21_31/pdf/JLR-21.pdf http://www.jrc.co.jp/eng/product/lineup/jlr21_31/pdf/JLR-21.... https://comnav.com/wp-content/uploads/2018/10/WEB_GNSS-G2G2B.pdf https://comnav.com/wp-content/uploads/2018/10/WEB_GNSS-G2G2B... A traditional gyrocompass is the more common option though, I think.