how to fuse two GPS into navsat_transform?

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Hi, dear:

I wonder to know how to fuse two GPS into navsat_transform if I have two imu(imu0 & imu1), two odometry sources(odom0 & odom1), two gps sources(gps0 & gps1)?

As my understanding:

1. for EKF_local_node, just fuse imu0 & imu1, odom0 & odom1.
2. for EKF_global_node, fuse imu0 & imu1, odom0 & odom1, and also feed the odom2 & odom3(generated by two gps sources gps0 & gps1, output of navsat_transform node ) into it.
3. launch navsat_transfor_node_0 node, feed into imu0 & gps0 & output of step 2.
4. launch navsat_transfor_node_1 node, feed into imu1 & gps1 & output of step 2.

Is this right? Please correct me if I'm wrong.

And another question:

a). In step3 and step4, how to verify which imu sources should feed in?

I mean in step3, can I change imu0->imu1 and in step4 change imu1->imu0 or other options? how to determine this? I don't think in navsat_transform node it can support multiple imu imput sources.

b). should I turn on each UTM's broadcast_utm_transform?

c). And any other place should I pay attention to?

Thank you very much for your help!