Sign of the matrix DCMbn_n in ins_gps.m

Question

Sign of the matrix DCMbn_n in ins_gps.m

ufengger opened this issue 7 years ago · 2 comments

Dear Rodrigo,

thank you for the useful toolbox!

Maybe my question is very stupid. I am confused about the sign of the matrix DCMbn_n in ins_gps.m from the line 307 to 308. In the matlab code ins_gps.m, the sign of DCMbn_n is negative, however, in your paper

(Gonzalez et al., 2015a) R. Gonzalez, J.I. Giribet, and H.D. Patiño. An approach to benchmarking of loosely coupled low-cost navigation systems. Mathematical and Computer Modelling of Dynamical Systems, vol. 21, issue 3, pp. 272-287, 2015.

the sign of DCMbn_n is positive, cf. eq (21e). I am a beginner in this area, so I am not sure whether I missed something or not.

Thanks again and best regards,

Haifeng Wu

Answer 1 · 2018-03-14T20:10:05.000Z

2018-03-13 5:39 GMT-03:00 ufengger <notifications@github.com>:

Dear Rodrigo, thank you for the useful toolbox! Maybe my question is very stupid. I am confused about the sign of the matrix DCMbn_n in ins_gps.m from the line 307 to 308. In the matlab code ins_gps.m, the sign of DCMbn_n is negative, however, in your paper (Gonzalez et al., 2015a) R. Gonzalez, J.I. Giribet, and H.D. Patiño. An approach to benchmarking of loosely coupled low-cost navigation systems. Mathematical and Computer Modelling of Dynamical Systems, vol. 21, issue 3, pp. 272-287, 2015. the sign of DCMbn_n is positive, cf. eq (21e). I am a beginner in this area, so I am not sure whether I missed something or not. Thanks again and best regards, Haifeng Wu

Dear Haifeng, Thank you very much for your comments. Your question is a valid one! NaveGo equation (21e) is based on (Groves, 2008) Eq. 12.80. The sign of the (DCMbn_n * gps.larm) term depends on how you consider the direction of the lever arm, from GNSS antenna to IMU (negative) or from IMU to GNSS antenna (positive). Since NaveGo considers the lever arm from the GNSS antenna to IMU, I think the sign in Eq. (21e) is wrong. It should be negative. Nevertheless, I think it is more common to define the lever arm as the distance from the IMU to GNSS antenna (positive). Therefore, I think I will change the sign of (DCMbn_n * gps.larm) for a positive sign and make very clear that the lever arm should be set from IMU to GNSS antenna. Please, check if this last approach provides better results in your experiments. Regards. -- Rodrigo Gonzalez

Answer 2 · 2018-03-15T02:01:44.000Z

Dear Rodrigo,

The sign of the (DCMbn_n * gps.larm) term depends on how you consider the direction of the lever arm, from GNSS antenna to IMU (negative) or from IMU to GNSS antenna (positive).

Since NaveGo considers the lever arm from the GNSS antenna to IMU, I think the sign in Eq. (21e) is wrong. It should be negative.

many thanks for your nice explanation!

Please, check if this last approach provides better results in your experiments.

Yes, it does improve the results!

Best regards,

Haifeng Wu