Re: Attiude with quaternions--

Supplement to my first reply to Steffen Loringer's question
=====================================


procedure EAToQuat ({i/o} var EA: EAType; {o} var q: quaternion);
{PURPOSE: Converts Euler angles representation to quaternion representation}
{POST: psiplusphi = psi + phi, SIndet = FALSE,
     psiminusphi = psi - phi, DIndet = FALSE}
{Remark: NB: The computation itself refers to psi, theta, phi only}
var htheta, hpsiplusphi, hpsiminusphi: real;
var hpsi, coshpsi, sinhpsi, hphi, coshphi, sinhphi: real;
var coshtheta, sinhtheta,
   coshpsiplusphi, sinhpsiplusphi,
   coshpsiminusphi, sinhpsiminusphi: real;
begin
 with EA do
 begin
   psiplusphi := psi + phi; SIndet := false;
   psiminusphi := psi - phi; DIndet := false;
   htheta := theta / 2;
 end; {with EA}
 coshtheta := cos (htheta); sinhtheta := sin (htheta);
 case EA.EAMode of

{============== Theoretical mechanics convention ===============}
'p', 'P':
begin
with EA do
begin
hpsiplusphi := (psiplusphi) / 2;
hpsiminusphi := (psiminusphi) / 2;
coshpsiplusphi := cos (hpsiplusphi); sinhpsiplusphi := sin (hpsiplusphi);
coshpsiminusphi := cos (hpsiminusphi); sinhpsiminusphi := sin (hpsiminusphi);
end;
with q do
begin
rc := coshtheta * coshpsiplusphi;
ic := sinhtheta * coshpsiminusphi;
jc := sinhtheta * sinhpsiminusphi;
kc := coshtheta * sinhpsiplusphi;
end; {with q}
end;

 {===========  Aerospace convention ==============}
 'a', 'A':
 begin
   with EA do
   begin
     hpsi := psi / 2;
     hphi := phi / 2;
   end;
   coshpsi := cos (hpsi); sinhpsi := sin (hpsi);
   coshphi := cos (hphi); sinhphi := sin (hphi);
   with q do
   begin
     rc := coshpsi * coshtheta * coshphi + sinhpsi * sinhtheta * sinhphi;
     ic := coshpsi * coshtheta * sinhphi - sinhpsi * sinhtheta * coshphi;
     jc := coshpsi * sinhtheta * coshphi + sinhpsi * coshtheta * sinhphi;
     kc := sinhpsi * coshtheta * coshphi - coshpsi * sinhtheta * sinhphi;
   end; {with q}
 end; {EA.EAMode = 'a', 'A'}

 end; {case EA.EAMode}
end; {EAToQuat}



Steffen Loringer wrote:

Hi,

I have the following quaternions:
q1: -0.552710
q2: -0.441034
q3: -0.604951
q4:  0.366106

and the attitude with YPR
yaw:     -97.406°
pitch:      20.230°
roll:      -90.000°

but I can't figure out how to get the YPR values from the Quaternions.

Can someone explain it the easy was?

Thanks a lot
Steve

.

Relevant Pages

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